Add m-esr52 at 52.6.0

1 files changed, 4307 insertions, 0 deletions

diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
new file mode 100644
index 000000000..2e02aa63d
--- /dev/null
+++ b/js/src/jsscript.cpp
@@ -0,0 +1,4307 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * JS script operations.
+ */
+
+#include "jsscriptinlines.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/Unused.h"
+#include "mozilla/Vector.h"
+
+#include <algorithm>
+#include <string.h>
+
+#include "jsapi.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jsfun.h"
+#include "jsgc.h"
+#include "jsobj.h"
+#include "jsopcode.h"
+#include "jsprf.h"
+#include "jstypes.h"
+#include "jsutil.h"
+#include "jswrapper.h"
+
+#include "frontend/BytecodeCompiler.h"
+#include "frontend/BytecodeEmitter.h"
+#include "frontend/SharedContext.h"
+#include "gc/Marking.h"
+#include "jit/BaselineJIT.h"
+#include "jit/Ion.h"
+#include "jit/IonCode.h"
+#include "js/MemoryMetrics.h"
+#include "js/Utility.h"
+#include "vm/ArgumentsObject.h"
+#include "vm/Compression.h"
+#include "vm/Debugger.h"
+#include "vm/Opcodes.h"
+#include "vm/SelfHosting.h"
+#include "vm/Shape.h"
+#include "vm/SharedImmutableStringsCache.h"
+#include "vm/Xdr.h"
+
+#include "jsfuninlines.h"
+#include "jsobjinlines.h"
+
+#include "vm/EnvironmentObject-inl.h"
+#include "vm/NativeObject-inl.h"
+#include "vm/SharedImmutableStringsCache-inl.h"
+#include "vm/Stack-inl.h"
+
+using namespace js;
+using namespace js::gc;
+using namespace js::frontend;
+
+using mozilla::AsVariant;
+using mozilla::PodCopy;
+using mozilla::PodZero;
+using mozilla::RotateLeft;
+
+template<XDRMode mode>
+bool
+js::XDRScriptConst(XDRState<mode>* xdr, MutableHandleValue vp)
+{
+    JSContext* cx = xdr->cx();
+
+    /*
+     * A script constant can be an arbitrary primitive value as they are used
+     * to implement JSOP_LOOKUPSWITCH. But they cannot be objects, see
+     * bug 407186.
+     */
+    enum ConstTag {
+        SCRIPT_INT     = 0,
+        SCRIPT_DOUBLE  = 1,
+        SCRIPT_ATOM    = 2,
+        SCRIPT_TRUE    = 3,
+        SCRIPT_FALSE   = 4,
+        SCRIPT_NULL    = 5,
+        SCRIPT_OBJECT  = 6,
+        SCRIPT_VOID    = 7,
+        SCRIPT_HOLE    = 8
+    };
+
+    uint32_t tag;
+    if (mode == XDR_ENCODE) {
+        if (vp.isInt32()) {
+            tag = SCRIPT_INT;
+        } else if (vp.isDouble()) {
+            tag = SCRIPT_DOUBLE;
+        } else if (vp.isString()) {
+            tag = SCRIPT_ATOM;
+        } else if (vp.isTrue()) {
+            tag = SCRIPT_TRUE;
+        } else if (vp.isFalse()) {
+            tag = SCRIPT_FALSE;
+        } else if (vp.isNull()) {
+            tag = SCRIPT_NULL;
+        } else if (vp.isObject()) {
+            tag = SCRIPT_OBJECT;
+        } else if (vp.isMagic(JS_ELEMENTS_HOLE)) {
+            tag = SCRIPT_HOLE;
+        } else {
+            MOZ_ASSERT(vp.isUndefined());
+            tag = SCRIPT_VOID;
+        }
+    }
+
+    if (!xdr->codeUint32(&tag))
+        return false;
+
+    switch (tag) {
+      case SCRIPT_INT: {
+        uint32_t i;
+        if (mode == XDR_ENCODE)
+            i = uint32_t(vp.toInt32());
+        if (!xdr->codeUint32(&i))
+            return false;
+        if (mode == XDR_DECODE)
+            vp.set(Int32Value(int32_t(i)));
+        break;
+      }
+      case SCRIPT_DOUBLE: {
+        double d;
+        if (mode == XDR_ENCODE)
+            d = vp.toDouble();
+        if (!xdr->codeDouble(&d))
+            return false;
+        if (mode == XDR_DECODE)
+            vp.set(DoubleValue(d));
+        break;
+      }
+      case SCRIPT_ATOM: {
+        RootedAtom atom(cx);
+        if (mode == XDR_ENCODE)
+            atom = &vp.toString()->asAtom();
+        if (!XDRAtom(xdr, &atom))
+            return false;
+        if (mode == XDR_DECODE)
+            vp.set(StringValue(atom));
+        break;
+      }
+      case SCRIPT_TRUE:
+        if (mode == XDR_DECODE)
+            vp.set(BooleanValue(true));
+        break;
+      case SCRIPT_FALSE:
+        if (mode == XDR_DECODE)
+            vp.set(BooleanValue(false));
+        break;
+      case SCRIPT_NULL:
+        if (mode == XDR_DECODE)
+            vp.set(NullValue());
+        break;
+      case SCRIPT_OBJECT: {
+        RootedObject obj(cx);
+        if (mode == XDR_ENCODE)
+            obj = &vp.toObject();
+
+        if (!XDRObjectLiteral(xdr, &obj))
+            return false;
+
+        if (mode == XDR_DECODE)
+            vp.setObject(*obj);
+        break;
+      }
+      case SCRIPT_VOID:
+        if (mode == XDR_DECODE)
+            vp.set(UndefinedValue());
+        break;
+      case SCRIPT_HOLE:
+        if (mode == XDR_DECODE)
+            vp.setMagic(JS_ELEMENTS_HOLE);
+        break;
+    }
+    return true;
+}
+
+template bool
+js::XDRScriptConst(XDRState<XDR_ENCODE>*, MutableHandleValue);
+
+template bool
+js::XDRScriptConst(XDRState<XDR_DECODE>*, MutableHandleValue);
+
+// Code LazyScript's closed over bindings.
+template<XDRMode mode>
+static bool
+XDRLazyClosedOverBindings(XDRState<mode>* xdr, MutableHandle<LazyScript*> lazy)
+{
+    JSContext* cx = xdr->cx();
+    RootedAtom atom(cx);
+    for (size_t i = 0; i < lazy->numClosedOverBindings(); i++) {
+        uint8_t endOfScopeSentinel;
+        if (mode == XDR_ENCODE) {
+            atom = lazy->closedOverBindings()[i];
+            endOfScopeSentinel = !atom;
+        }
+
+        if (!xdr->codeUint8(&endOfScopeSentinel))
+            return false;
+
+        if (endOfScopeSentinel)
+            atom = nullptr;
+        else if (!XDRAtom(xdr, &atom))
+            return false;
+
+        if (mode == XDR_DECODE)
+            lazy->closedOverBindings()[i] = atom;
+    }
+
+    return true;
+}
+
+// Code the missing part needed to re-create a LazyScript from a JSScript.
+template<XDRMode mode>
+static bool
+XDRRelazificationInfo(XDRState<mode>* xdr, HandleFunction fun, HandleScript script,
+                      HandleScope enclosingScope, MutableHandle<LazyScript*> lazy)
+{
+    MOZ_ASSERT_IF(mode == XDR_ENCODE, script->isRelazifiable() && script->maybeLazyScript());
+    MOZ_ASSERT_IF(mode == XDR_ENCODE, !lazy->numInnerFunctions());
+
+    JSContext* cx = xdr->cx();
+
+    uint64_t packedFields;
+    {
+        uint32_t begin = script->sourceStart();
+        uint32_t end = script->sourceEnd();
+        uint32_t lineno = script->lineno();
+        uint32_t column = script->column();
+
+        if (mode == XDR_ENCODE) {
+            packedFields = lazy->packedFields();
+            MOZ_ASSERT(begin == lazy->begin());
+            MOZ_ASSERT(end == lazy->end());
+            MOZ_ASSERT(lineno == lazy->lineno());
+            MOZ_ASSERT(column == lazy->column());
+            // We can assert we have no inner functions because we don't
+            // relazify scripts with inner functions.  See
+            // JSFunction::createScriptForLazilyInterpretedFunction.
+            MOZ_ASSERT(lazy->numInnerFunctions() == 0);
+        }
+
+        if (!xdr->codeUint64(&packedFields))
+            return false;
+
+        if (mode == XDR_DECODE) {
+            lazy.set(LazyScript::Create(cx, fun, script, enclosingScope, script,
+                                        packedFields, begin, end, lineno, column));
+
+            // As opposed to XDRLazyScript, we need to restore the runtime bits
+            // of the script, as we are trying to match the fact this function
+            // has already been parsed and that it would need to be re-lazified.
+            lazy->initRuntimeFields(packedFields);
+        }
+    }
+
+    // Code binding names.
+    if (!XDRLazyClosedOverBindings(xdr, lazy))
+        return false;
+
+    // No need to do anything with inner functions, since we asserted we don't
+    // have any.
+
+    return true;
+}
+
+static inline uint32_t
+FindScopeIndex(JSScript* script, Scope& scope)
+{
+    ScopeArray* scopes = script->scopes();
+    GCPtrScope* vector = scopes->vector;
+    unsigned length = scopes->length;
+    for (uint32_t i = 0; i < length; ++i) {
+        if (vector[i] == &scope)
+            return i;
+    }
+
+    MOZ_CRASH("Scope not found");
+}
+
+enum XDRClassKind {
+    CK_RegexpObject,
+    CK_JSFunction,
+    CK_JSObject
+};
+
+template<XDRMode mode>
+bool
+js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScript enclosingScript,
+              HandleFunction fun, MutableHandleScript scriptp)
+{
+    /* NB: Keep this in sync with CopyScript. */
+
+    enum ScriptBits {
+        NoScriptRval,
+        Strict,
+        ContainsDynamicNameAccess,
+        FunHasExtensibleScope,
+        FunHasAnyAliasedFormal,
+        ArgumentsHasVarBinding,
+        NeedsArgsObj,
+        HasMappedArgsObj,
+        FunctionHasThisBinding,
+        FunctionHasExtraBodyVarScope,
+        IsGeneratorExp,
+        IsLegacyGenerator,
+        IsStarGenerator,
+        IsAsync,
+        OwnSource,
+        ExplicitUseStrict,
+        SelfHosted,
+        HasSingleton,
+        TreatAsRunOnce,
+        HasLazyScript,
+        HasNonSyntacticScope,
+        HasInnerFunctions,
+        NeedsHomeObject,
+        IsDerivedClassConstructor,
+        IsDefaultClassConstructor,
+    };
+
+    uint32_t length, lineno, column, nfixed, nslots;
+    uint32_t natoms, nsrcnotes, i;
+    uint32_t nconsts, nobjects, nscopes, nregexps, ntrynotes, nscopenotes, nyieldoffsets;
+    uint32_t prologueLength, version;
+    uint32_t funLength = 0;
+    uint32_t nTypeSets = 0;
+    uint32_t scriptBits = 0;
+    uint32_t bodyScopeIndex = 0;
+
+    JSContext* cx = xdr->cx();
+    RootedScript script(cx);
+    natoms = nsrcnotes = 0;
+    nconsts = nobjects = nscopes = nregexps = ntrynotes = nscopenotes = nyieldoffsets = 0;
+
+    if (mode == XDR_ENCODE) {
+        script = scriptp.get();
+        MOZ_ASSERT_IF(enclosingScript, enclosingScript->compartment() == script->compartment());
+        MOZ_ASSERT(script->functionNonDelazifying() == fun);
+
+        if (!fun && script->treatAsRunOnce()) {
+            // This is a toplevel or eval script that's runOnce.  We want to
+            // make sure that we're not XDR-saving an object we emitted for
+            // JSOP_OBJECT that then got modified.  So throw if we're not
+            // cloning in JSOP_OBJECT or if we ever didn't clone in it in the
+            // past.
+            JSCompartment* comp = cx->compartment();
+            if (!comp->creationOptions().cloneSingletons() ||
+                !comp->behaviors().getSingletonsAsTemplates())
+            {
+                return xdr->fail(JS::TranscodeResult_Failure_RunOnceNotSupported);
+            }
+        }
+    }
+
+    if (mode == XDR_ENCODE)
+        length = script->length();
+    if (!xdr->codeUint32(&length))
+        return false;
+
+    if (mode == XDR_ENCODE) {
+        prologueLength = script->mainOffset();
+        MOZ_ASSERT(script->getVersion() != JSVERSION_UNKNOWN);
+        version = script->getVersion();
+        lineno = script->lineno();
+        column = script->column();
+        nfixed = script->nfixed();
+        nslots = script->nslots();
+
+        bodyScopeIndex = script->bodyScopeIndex();
+        natoms = script->natoms();
+
+        nsrcnotes = script->numNotes();
+
+        if (script->hasConsts())
+            nconsts = script->consts()->length;
+        if (script->hasObjects())
+            nobjects = script->objects()->length;
+        nscopes = script->scopes()->length;
+        if (script->hasTrynotes())
+            ntrynotes = script->trynotes()->length;
+        if (script->hasScopeNotes())
+            nscopenotes = script->scopeNotes()->length;
+        if (script->hasYieldOffsets())
+            nyieldoffsets = script->yieldOffsets().length();
+
+        nTypeSets = script->nTypeSets();
+        funLength = script->funLength();
+
+        if (script->noScriptRval())
+            scriptBits |= (1 << NoScriptRval);
+        if (script->strict())
+            scriptBits |= (1 << Strict);
+        if (script->explicitUseStrict())
+            scriptBits |= (1 << ExplicitUseStrict);
+        if (script->selfHosted())
+            scriptBits |= (1 << SelfHosted);
+        if (script->bindingsAccessedDynamically())
+            scriptBits |= (1 << ContainsDynamicNameAccess);
+        if (script->funHasExtensibleScope())
+            scriptBits |= (1 << FunHasExtensibleScope);
+        if (script->funHasAnyAliasedFormal())
+            scriptBits |= (1 << FunHasAnyAliasedFormal);
+        if (script->argumentsHasVarBinding())
+            scriptBits |= (1 << ArgumentsHasVarBinding);
+        if (script->analyzedArgsUsage() && script->needsArgsObj())
+            scriptBits |= (1 << NeedsArgsObj);
+        if (script->hasMappedArgsObj())
+            scriptBits |= (1 << HasMappedArgsObj);
+        if (script->functionHasThisBinding())
+            scriptBits |= (1 << FunctionHasThisBinding);
+        if (script->functionHasExtraBodyVarScope())
+            scriptBits |= (1 << FunctionHasExtraBodyVarScope);
+        if (!enclosingScript || enclosingScript->scriptSource() != script->scriptSource())
+            scriptBits |= (1 << OwnSource);
+        if (script->isGeneratorExp())
+            scriptBits |= (1 << IsGeneratorExp);
+        if (script->isLegacyGenerator())
+            scriptBits |= (1 << IsLegacyGenerator);
+        if (script->isStarGenerator())
+            scriptBits |= (1 << IsStarGenerator);
+        if (script->asyncKind() == AsyncFunction)
+            scriptBits |= (1 << IsAsync);
+        if (script->hasSingletons())
+            scriptBits |= (1 << HasSingleton);
+        if (script->treatAsRunOnce())
+            scriptBits |= (1 << TreatAsRunOnce);
+        if (script->isRelazifiable())
+            scriptBits |= (1 << HasLazyScript);
+        if (script->hasNonSyntacticScope())
+            scriptBits |= (1 << HasNonSyntacticScope);
+        if (script->hasInnerFunctions())
+            scriptBits |= (1 << HasInnerFunctions);
+        if (script->needsHomeObject())
+            scriptBits |= (1 << NeedsHomeObject);
+        if (script->isDerivedClassConstructor())
+            scriptBits |= (1 << IsDerivedClassConstructor);
+        if (script->isDefaultClassConstructor())
+            scriptBits |= (1 << IsDefaultClassConstructor);
+    }
+
+    if (!xdr->codeUint32(&prologueLength))
+        return false;
+    if (!xdr->codeUint32(&version))
+        return false;
+
+    // To fuse allocations, we need lengths of all embedded arrays early.
+    if (!xdr->codeUint32(&natoms))
+        return false;
+    if (!xdr->codeUint32(&nsrcnotes))
+        return false;
+    if (!xdr->codeUint32(&nconsts))
+        return false;
+    if (!xdr->codeUint32(&nobjects))
+        return false;
+    if (!xdr->codeUint32(&nscopes))
+        return false;
+    if (!xdr->codeUint32(&ntrynotes))
+        return false;
+    if (!xdr->codeUint32(&nscopenotes))
+        return false;
+    if (!xdr->codeUint32(&nyieldoffsets))
+        return false;
+    if (!xdr->codeUint32(&nTypeSets))
+        return false;
+    if (!xdr->codeUint32(&funLength))
+        return false;
+    if (!xdr->codeUint32(&scriptBits))
+        return false;
+
+    if (mode == XDR_DECODE) {
+        JSVersion version_ = JSVersion(version);
+        MOZ_ASSERT((version_ & VersionFlags::MASK) == unsigned(version_));
+
+        CompileOptions options(cx);
+        options.setVersion(version_)
+               .setNoScriptRval(!!(scriptBits & (1 << NoScriptRval)))
+               .setSelfHostingMode(!!(scriptBits & (1 << SelfHosted)));
+        RootedScriptSource sourceObject(cx);
+        if (scriptBits & (1 << OwnSource)) {
+            ScriptSource* ss = cx->new_<ScriptSource>();
+            if (!ss)
+                return false;
+            ScriptSourceHolder ssHolder(ss);
+
+            /*
+             * We use this CompileOptions only to initialize the
+             * ScriptSourceObject. Most CompileOptions fields aren't used by
+             * ScriptSourceObject, and those that are (element; elementAttributeName)
+             * aren't preserved by XDR. So this can be simple.
+             */
+            CompileOptions options(cx);
+            ss->initFromOptions(cx, options);
+            sourceObject = ScriptSourceObject::create(cx, ss);
+            if (!sourceObject ||
+                !ScriptSourceObject::initFromOptions(cx, sourceObject, options))
+                return false;
+        } else {
+            MOZ_ASSERT(enclosingScript);
+            // When decoding, all the scripts and the script source object
+            // are in the same compartment, so the script's source object
+            // should never be a cross-compartment wrapper.
+            MOZ_ASSERT(enclosingScript->sourceObject()->is<ScriptSourceObject>());
+            sourceObject = &enclosingScript->sourceObject()->as<ScriptSourceObject>();
+        }
+
+        script = JSScript::Create(cx, options, sourceObject, 0, 0);
+        if (!script)
+            return false;
+
+        // Set the script in its function now so that inner scripts to be
+        // decoded may iterate the static scope chain.
+        if (fun)
+            fun->initScript(script);
+    }
+
+    if (mode == XDR_DECODE) {
+        if (!JSScript::partiallyInit(cx, script, nscopes, nconsts, nobjects, ntrynotes,
+                                     nscopenotes, nyieldoffsets, nTypeSets))
+        {
+            return false;
+        }
+
+        MOZ_ASSERT(!script->mainOffset());
+        script->mainOffset_ = prologueLength;
+        script->funLength_ = funLength;
+
+        scriptp.set(script);
+
+        if (scriptBits & (1 << Strict))
+            script->strict_ = true;
+        if (scriptBits & (1 << ExplicitUseStrict))
+            script->explicitUseStrict_ = true;
+        if (scriptBits & (1 << ContainsDynamicNameAccess))
+            script->bindingsAccessedDynamically_ = true;
+        if (scriptBits & (1 << FunHasExtensibleScope))
+            script->funHasExtensibleScope_ = true;
+        if (scriptBits & (1 << FunHasAnyAliasedFormal))
+            script->funHasAnyAliasedFormal_ = true;
+        if (scriptBits & (1 << ArgumentsHasVarBinding))
+            script->setArgumentsHasVarBinding();
+        if (scriptBits & (1 << NeedsArgsObj))
+            script->setNeedsArgsObj(true);
+        if (scriptBits & (1 << HasMappedArgsObj))
+            script->hasMappedArgsObj_ = true;
+        if (scriptBits & (1 << FunctionHasThisBinding))
+            script->functionHasThisBinding_ = true;
+        if (scriptBits & (1 << FunctionHasExtraBodyVarScope))
+            script->functionHasExtraBodyVarScope_ = true;
+        if (scriptBits & (1 << IsGeneratorExp))
+            script->isGeneratorExp_ = true;
+        if (scriptBits & (1 << HasSingleton))
+            script->hasSingletons_ = true;
+        if (scriptBits & (1 << TreatAsRunOnce))
+            script->treatAsRunOnce_ = true;
+        if (scriptBits & (1 << HasNonSyntacticScope))
+            script->hasNonSyntacticScope_ = true;
+        if (scriptBits & (1 << HasInnerFunctions))
+            script->hasInnerFunctions_ = true;
+        if (scriptBits & (1 << NeedsHomeObject))
+            script->needsHomeObject_ = true;
+        if (scriptBits & (1 << IsDerivedClassConstructor))
+            script->isDerivedClassConstructor_ = true;
+        if (scriptBits & (1 << IsDefaultClassConstructor))
+            script->isDefaultClassConstructor_ = true;
+
+        if (scriptBits & (1 << IsLegacyGenerator)) {
+            MOZ_ASSERT(!(scriptBits & (1 << IsStarGenerator)));
+            script->setGeneratorKind(LegacyGenerator);
+        } else if (scriptBits & (1 << IsStarGenerator))
+            script->setGeneratorKind(StarGenerator);
+
+        if (scriptBits & (1 << IsAsync))
+            script->setAsyncKind(AsyncFunction);
+    }
+
+    JS_STATIC_ASSERT(sizeof(jsbytecode) == 1);
+    JS_STATIC_ASSERT(sizeof(jssrcnote) == 1);
+
+    if (scriptBits & (1 << OwnSource)) {
+        if (!script->scriptSource()->performXDR<mode>(xdr))
+            return false;
+    }
+    if (!xdr->codeUint32(&script->sourceStart_))
+        return false;
+    if (!xdr->codeUint32(&script->sourceEnd_))
+        return false;
+
+    if (!xdr->codeUint32(&lineno) ||
+        !xdr->codeUint32(&column) ||
+        !xdr->codeUint32(&nfixed) ||
+        !xdr->codeUint32(&nslots))
+    {
+        return false;
+    }
+
+    if (!xdr->codeUint32(&bodyScopeIndex))
+        return false;
+
+    if (mode == XDR_DECODE) {
+        script->lineno_ = lineno;
+        script->column_ = column;
+        script->nfixed_ = nfixed;
+        script->nslots_ = nslots;
+        script->bodyScopeIndex_ = bodyScopeIndex;
+    }
+
+    auto scriptDataGuard = mozilla::MakeScopeExit([&] {
+        if (mode == XDR_DECODE)
+            script->freeScriptData();
+    });
+
+    if (mode == XDR_DECODE) {
+        if (!script->createScriptData(cx, length, nsrcnotes, natoms))
+            return false;
+    }
+
+    jsbytecode* code = script->code();
+    if (!xdr->codeBytes(code, length) || !xdr->codeBytes(code + length, nsrcnotes)) {
+        return false;
+    }
+
+    for (i = 0; i != natoms; ++i) {
+        if (mode == XDR_DECODE) {
+            RootedAtom tmp(cx);
+            if (!XDRAtom(xdr, &tmp))
+                return false;
+            script->atoms()[i].init(tmp);
+        } else {
+            RootedAtom tmp(cx, script->atoms()[i]);
+            if (!XDRAtom(xdr, &tmp))
+                return false;
+        }
+    }
+
+    scriptDataGuard.release();
+    if (mode == XDR_DECODE) {
+        if (!script->shareScriptData(cx))
+            return false;
+    }
+
+    if (nconsts) {
+        GCPtrValue* vector = script->consts()->vector;
+        RootedValue val(cx);
+        for (i = 0; i != nconsts; ++i) {
+            if (mode == XDR_ENCODE)
+                val = vector[i];
+            if (!XDRScriptConst(xdr, &val))
+                return false;
+            if (mode == XDR_DECODE)
+                vector[i].init(val);
+        }
+    }
+
+    {
+        MOZ_ASSERT(nscopes != 0);
+        GCPtrScope* vector = script->scopes()->vector;
+        RootedScope scope(cx);
+        RootedScope enclosing(cx);
+        ScopeKind scopeKind;
+        uint32_t enclosingScopeIndex = 0;
+        for (i = 0; i != nscopes; ++i) {
+            if (mode == XDR_ENCODE) {
+                scope = vector[i];
+                scopeKind = scope->kind();
+            } else {
+                scope = nullptr;
+            }
+
+            if (!xdr->codeEnum32(&scopeKind))
+                return false;
+
+            if (mode == XDR_ENCODE) {
+                if (i == 0) {
+                    enclosingScopeIndex = UINT32_MAX;
+                } else {
+                    MOZ_ASSERT(scope->enclosing());
+                    enclosingScopeIndex = FindScopeIndex(script, *scope->enclosing());
+                }
+            }
+
+            if (!xdr->codeUint32(&enclosingScopeIndex))
+                return false;
+
+            if (mode == XDR_DECODE) {
+                if (i == 0) {
+                    MOZ_ASSERT(enclosingScopeIndex == UINT32_MAX);
+                    enclosing = scriptEnclosingScope;
+                } else {
+                    MOZ_ASSERT(enclosingScopeIndex < i);
+                    enclosing = vector[enclosingScopeIndex];
+                }
+            }
+
+            switch (scopeKind) {
+              case ScopeKind::Function:
+                MOZ_ASSERT(i == script->bodyScopeIndex());
+                if (!FunctionScope::XDR(xdr, fun, enclosing, &scope))
+                    return false;
+                break;
+              case ScopeKind::FunctionBodyVar:
+              case ScopeKind::ParameterExpressionVar:
+                if (!VarScope::XDR(xdr, scopeKind, enclosing, &scope))
+                    return false;
+                break;
+              case ScopeKind::Lexical:
+              case ScopeKind::SimpleCatch:
+              case ScopeKind::Catch:
+              case ScopeKind::NamedLambda:
+              case ScopeKind::StrictNamedLambda:
+                if (!LexicalScope::XDR(xdr, scopeKind, enclosing, &scope))
+                    return false;
+                break;
+              case ScopeKind::With:
+                if (mode == XDR_DECODE) {
+                    scope = WithScope::create(cx, enclosing);
+                    if (!scope)
+                        return false;
+                }
+                break;
+              case ScopeKind::Eval:
+              case ScopeKind::StrictEval:
+                if (!EvalScope::XDR(xdr, scopeKind, enclosing, &scope))
+                    return false;
+                break;
+              case ScopeKind::Global:
+              case ScopeKind::NonSyntactic:
+                if (!GlobalScope::XDR(xdr, scopeKind, &scope))
+                    return false;
+                break;
+              case ScopeKind::Module:
+                MOZ_CRASH("NYI");
+                break;
+            }
+
+            if (mode == XDR_DECODE)
+                vector[i].init(scope);
+        }
+    }
+
+    /*
+     * Here looping from 0-to-length to xdr objects is essential to ensure that
+     * all references to enclosing blocks (via FindScopeIndex below) happen
+     * after the enclosing block has been XDR'd.
+     */
+    for (i = 0; i != nobjects; ++i) {
+        GCPtrObject* objp = &script->objects()->vector[i];
+        XDRClassKind classk;
+
+        if (mode == XDR_ENCODE) {
+            JSObject* obj = *objp;
+            if (obj->is<RegExpObject>())
+                classk = CK_RegexpObject;
+            else if (obj->is<JSFunction>())
+                classk = CK_JSFunction;
+            else if (obj->is<PlainObject>() || obj->is<ArrayObject>())
+                classk = CK_JSObject;
+            else
+                MOZ_CRASH("Cannot encode this class of object.");
+        }
+
+        if (!xdr->codeEnum32(&classk))
+            return false;
+
+        switch (classk) {
+          case CK_RegexpObject: {
+            Rooted<RegExpObject*> regexp(cx);
+            if (mode == XDR_ENCODE)
+                regexp = &(*objp)->as<RegExpObject>();
+            if (!XDRScriptRegExpObject(xdr, &regexp))
+                return false;
+            if (mode == XDR_DECODE)
+                *objp = regexp;
+            break;
+          }
+
+          case CK_JSFunction: {
+            /* Code the nested function's enclosing scope. */
+            uint32_t funEnclosingScopeIndex = 0;
+            RootedScope funEnclosingScope(cx);
+            if (mode == XDR_ENCODE) {
+                RootedFunction function(cx, &(*objp)->as<JSFunction>());
+
+                if (function->isInterpretedLazy()) {
+                    funEnclosingScope = function->lazyScript()->enclosingScope();
+                } else if (function->isInterpreted()) {
+                    funEnclosingScope = function->nonLazyScript()->enclosingScope();
+                } else {
+                    MOZ_ASSERT(function->isAsmJSNative());
+                    return xdr->fail(JS::TranscodeResult_Failure_AsmJSNotSupported);
+                }
+
+                funEnclosingScopeIndex = FindScopeIndex(script, *funEnclosingScope);
+            }
+
+            if (!xdr->codeUint32(&funEnclosingScopeIndex))
+                return false;
+
+            if (mode == XDR_DECODE) {
+                MOZ_ASSERT(funEnclosingScopeIndex < script->scopes()->length);
+                funEnclosingScope = script->scopes()->vector[funEnclosingScopeIndex];
+            }
+
+            // Code nested function and script.
+            RootedFunction tmp(cx);
+            if (mode == XDR_ENCODE)
+                tmp = &(*objp)->as<JSFunction>();
+            if (!XDRInterpretedFunction(xdr, funEnclosingScope, script, &tmp))
+                return false;
+            *objp = tmp;
+            break;
+          }
+
+          case CK_JSObject: {
+            /* Code object literal. */
+            RootedObject tmp(cx, *objp);
+            if (!XDRObjectLiteral(xdr, &tmp))
+                return false;
+            *objp = tmp;
+            break;
+          }
+
+          default: {
+            MOZ_ASSERT(false, "Unknown class kind.");
+            return xdr->fail(JS::TranscodeResult_Failure_UnknownClassKind);
+          }
+        }
+    }
+
+    if (ntrynotes != 0) {
+        JSTryNote* tnfirst = script->trynotes()->vector;
+        MOZ_ASSERT(script->trynotes()->length == ntrynotes);
+        JSTryNote* tn = tnfirst + ntrynotes;
+        do {
+            --tn;
+            if (!xdr->codeUint8(&tn->kind) ||
+                !xdr->codeUint32(&tn->stackDepth) ||
+                !xdr->codeUint32(&tn->start) ||
+                !xdr->codeUint32(&tn->length)) {
+                return false;
+            }
+        } while (tn != tnfirst);
+    }
+
+    for (i = 0; i < nscopenotes; ++i) {
+        ScopeNote* note = &script->scopeNotes()->vector[i];
+        if (!xdr->codeUint32(&note->index) ||
+            !xdr->codeUint32(&note->start) ||
+            !xdr->codeUint32(&note->length) ||
+            !xdr->codeUint32(&note->parent))
+        {
+            return false;
+        }
+    }
+
+    for (i = 0; i < nyieldoffsets; ++i) {
+        uint32_t* offset = &script->yieldOffsets()[i];
+        if (!xdr->codeUint32(offset))
+            return false;
+    }
+
+    if (scriptBits & (1 << HasLazyScript)) {
+        Rooted<LazyScript*> lazy(cx);
+        if (mode == XDR_ENCODE)
+            lazy = script->maybeLazyScript();
+
+        if (!XDRRelazificationInfo(xdr, fun, script, scriptEnclosingScope, &lazy))
+            return false;
+
+        if (mode == XDR_DECODE)
+            script->setLazyScript(lazy);
+    }
+
+    if (mode == XDR_DECODE) {
+        scriptp.set(script);
+
+        /* see BytecodeEmitter::tellDebuggerAboutCompiledScript */
+        if (!fun)
+            Debugger::onNewScript(cx, script);
+    }
+
+    return true;
+}
+
+template bool
+js::XDRScript(XDRState<XDR_ENCODE>*, HandleScope, HandleScript, HandleFunction,
+              MutableHandleScript);
+
+template bool
+js::XDRScript(XDRState<XDR_DECODE>*, HandleScope, HandleScript, HandleFunction,
+              MutableHandleScript);
+
+template<XDRMode mode>
+bool
+js::XDRLazyScript(XDRState<mode>* xdr, HandleScope enclosingScope, HandleScript enclosingScript,
+                  HandleFunction fun, MutableHandle<LazyScript*> lazy)
+{
+    JSContext* cx = xdr->cx();
+
+    {
+        uint32_t begin;
+        uint32_t end;
+        uint32_t lineno;
+        uint32_t column;
+        uint64_t packedFields;
+
+        if (mode == XDR_ENCODE) {
+            // Note: it's possible the LazyScript has a non-null script_ pointer
+            // to a JSScript. We don't encode it: we can just delazify the
+            // lazy script.
+
+            MOZ_ASSERT(fun == lazy->functionNonDelazifying());
+
+            begin = lazy->begin();
+            end = lazy->end();
+            lineno = lazy->lineno();
+            column = lazy->column();
+            packedFields = lazy->packedFields();
+        }
+
+        if (!xdr->codeUint32(&begin) || !xdr->codeUint32(&end) ||
+            !xdr->codeUint32(&lineno) || !xdr->codeUint32(&column) ||
+            !xdr->codeUint64(&packedFields))
+        {
+            return false;
+        }
+
+        if (mode == XDR_DECODE) {
+            lazy.set(LazyScript::Create(cx, fun, nullptr, enclosingScope, enclosingScript,
+                                        packedFields, begin, end, lineno, column));
+            if (!lazy)
+                return false;
+            fun->initLazyScript(lazy);
+        }
+    }
+
+    // Code closed-over bindings.
+    if (!XDRLazyClosedOverBindings(xdr, lazy))
+        return false;
+
+    // Code inner functions.
+    {
+        RootedFunction func(cx);
+        GCPtrFunction* innerFunctions = lazy->innerFunctions();
+        size_t numInnerFunctions = lazy->numInnerFunctions();
+        for (size_t i = 0; i < numInnerFunctions; i++) {
+            if (mode == XDR_ENCODE)
+                func = innerFunctions[i];
+
+            if (!XDRInterpretedFunction(xdr, nullptr, nullptr, &func))
+                return false;
+
+            if (mode == XDR_DECODE)
+                innerFunctions[i] = func;
+        }
+    }
+
+    return true;
+}
+
+template bool
+js::XDRLazyScript(XDRState<XDR_ENCODE>*, HandleScope, HandleScript,
+                  HandleFunction, MutableHandle<LazyScript*>);
+
+template bool
+js::XDRLazyScript(XDRState<XDR_DECODE>*, HandleScope, HandleScript,
+                  HandleFunction, MutableHandle<LazyScript*>);
+
+void
+JSScript::setSourceObject(JSObject* object)
+{
+    MOZ_ASSERT(compartment() == object->compartment());
+    sourceObject_ = object;
+}
+
+js::ScriptSourceObject&
+JSScript::scriptSourceUnwrap() const {
+    return UncheckedUnwrap(sourceObject())->as<ScriptSourceObject>();
+}
+
+js::ScriptSource*
+JSScript::scriptSource() const {
+    return scriptSourceUnwrap().source();
+}
+
+js::ScriptSource*
+JSScript::maybeForwardedScriptSource() const {
+    return UncheckedUnwrap(MaybeForwarded(sourceObject()))->as<ScriptSourceObject>().source();
+}
+
+bool
+JSScript::initScriptCounts(JSContext* cx)
+{
+    MOZ_ASSERT(!hasScriptCounts());
+
+    // Record all pc which are the first instruction of a basic block.
+    mozilla::Vector<jsbytecode*, 16, SystemAllocPolicy> jumpTargets;
+    jsbytecode* mainPc = main();
+    jsbytecode* end = codeEnd();
+    for (jsbytecode* pc = code(); pc != end; pc = GetNextPc(pc)) {
+        if (BytecodeIsJumpTarget(JSOp(*pc)) || pc == mainPc) {
+            if (!jumpTargets.append(pc)) {
+                ReportOutOfMemory(cx);
+                return false;
+            }
+        }
+    }
+
+    // Initialize all PCCounts counters to 0.
+    ScriptCounts::PCCountsVector base;
+    if (!base.reserve(jumpTargets.length())) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+
+    for (size_t i = 0; i < jumpTargets.length(); i++)
+        base.infallibleEmplaceBack(pcToOffset(jumpTargets[i]));
+
+    // Create compartment's scriptCountsMap if necessary.
+    ScriptCountsMap* map = compartment()->scriptCountsMap;
+    if (!map) {
+        map = cx->new_<ScriptCountsMap>();
+        if (!map) {
+            ReportOutOfMemory(cx);
+            return false;
+        }
+
+        if (!map->init()) {
+            js_delete(map);
+            ReportOutOfMemory(cx);
+            return false;
+        }
+
+        compartment()->scriptCountsMap = map;
+    }
+
+    // Allocate the ScriptCounts.
+    ScriptCounts* sc = cx->new_<ScriptCounts>(Move(base));
+    if (!sc) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    auto guardScriptCounts = mozilla::MakeScopeExit([&] () {
+        js_delete(sc);
+    });
+
+    // Register the current ScriptCounts in the compartment's map.
+    if (!map->putNew(this, sc)) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+
+    // safe to set this;  we can't fail after this point.
+    hasScriptCounts_ = true;
+    guardScriptCounts.release();
+
+    // Enable interrupts in any interpreter frames running on this script. This
+    // is used to let the interpreter increment the PCCounts, if present.
+    for (ActivationIterator iter(cx->runtime()); !iter.done(); ++iter) {
+        if (iter->isInterpreter())
+            iter->asInterpreter()->enableInterruptsIfRunning(this);
+    }
+
+    return true;
+}
+
+static inline ScriptCountsMap::Ptr GetScriptCountsMapEntry(JSScript* script)
+{
+    MOZ_ASSERT(script->hasScriptCounts());
+    ScriptCountsMap* map = script->compartment()->scriptCountsMap;
+    ScriptCountsMap::Ptr p = map->lookup(script);
+    MOZ_ASSERT(p);
+    return p;
+}
+
+ScriptCounts&
+JSScript::getScriptCounts()
+{
+    ScriptCountsMap::Ptr p = GetScriptCountsMapEntry(this);
+    return *p->value();
+}
+
+js::PCCounts*
+ScriptCounts::maybeGetPCCounts(size_t offset) {
+    PCCounts searched = PCCounts(offset);
+    PCCounts* elem = std::lower_bound(pcCounts_.begin(), pcCounts_.end(), searched);
+    if (elem == pcCounts_.end() || elem->pcOffset() != offset)
+        return nullptr;
+    return elem;
+}
+
+const js::PCCounts*
+ScriptCounts::maybeGetPCCounts(size_t offset) const {
+    PCCounts searched = PCCounts(offset);
+    const PCCounts* elem = std::lower_bound(pcCounts_.begin(), pcCounts_.end(), searched);
+    if (elem == pcCounts_.end() || elem->pcOffset() != offset)
+        return nullptr;
+    return elem;
+}
+
+js::PCCounts*
+ScriptCounts::getImmediatePrecedingPCCounts(size_t offset)
+{
+    PCCounts searched = PCCounts(offset);
+    PCCounts* elem = std::lower_bound(pcCounts_.begin(), pcCounts_.end(), searched);
+    if (elem == pcCounts_.end())
+        return &pcCounts_.back();
+    if (elem->pcOffset() == offset)
+        return elem;
+    if (elem != pcCounts_.begin())
+        return elem - 1;
+    return nullptr;
+}
+
+const js::PCCounts*
+ScriptCounts::maybeGetThrowCounts(size_t offset) const {
+    PCCounts searched = PCCounts(offset);
+    const PCCounts* elem = std::lower_bound(throwCounts_.begin(), throwCounts_.end(), searched);
+    if (elem == throwCounts_.end() || elem->pcOffset() != offset)
+        return nullptr;
+    return elem;
+}
+
+const js::PCCounts*
+ScriptCounts::getImmediatePrecedingThrowCounts(size_t offset) const
+{
+    PCCounts searched = PCCounts(offset);
+    const PCCounts* elem = std::lower_bound(throwCounts_.begin(), throwCounts_.end(), searched);
+    if (elem == throwCounts_.end()) {
+        if (throwCounts_.begin() == throwCounts_.end())
+            return nullptr;
+        return &throwCounts_.back();
+    }
+    if (elem->pcOffset() == offset)
+        return elem;
+    if (elem != throwCounts_.begin())
+        return elem - 1;
+    return nullptr;
+}
+
+js::PCCounts*
+ScriptCounts::getThrowCounts(size_t offset) {
+    PCCounts searched = PCCounts(offset);
+    PCCounts* elem = std::lower_bound(throwCounts_.begin(), throwCounts_.end(), searched);
+    if (elem == throwCounts_.end() || elem->pcOffset() != offset)
+        elem = throwCounts_.insert(elem, searched);
+    return elem;
+}
+
+void
+JSScript::setIonScript(JSRuntime* maybeRuntime, js::jit::IonScript* ionScript)
+{
+    MOZ_ASSERT_IF(ionScript != ION_DISABLED_SCRIPT, !baselineScript()->hasPendingIonBuilder());
+    if (hasIonScript())
+        js::jit::IonScript::writeBarrierPre(zone(), ion);
+    ion = ionScript;
+    MOZ_ASSERT_IF(hasIonScript(), hasBaselineScript());
+    updateBaselineOrIonRaw(maybeRuntime);
+}
+
+js::PCCounts*
+JSScript::maybeGetPCCounts(jsbytecode* pc) {
+    MOZ_ASSERT(containsPC(pc));
+    return getScriptCounts().maybeGetPCCounts(pcToOffset(pc));
+}
+
+const js::PCCounts*
+JSScript::maybeGetThrowCounts(jsbytecode* pc) {
+    MOZ_ASSERT(containsPC(pc));
+    return getScriptCounts().maybeGetThrowCounts(pcToOffset(pc));
+}
+
+js::PCCounts*
+JSScript::getThrowCounts(jsbytecode* pc) {
+    MOZ_ASSERT(containsPC(pc));
+    return getScriptCounts().getThrowCounts(pcToOffset(pc));
+}
+
+uint64_t
+JSScript::getHitCount(jsbytecode* pc)
+{
+    MOZ_ASSERT(containsPC(pc));
+    if (pc < main())
+        pc = main();
+
+    ScriptCounts& sc = getScriptCounts();
+    size_t targetOffset = pcToOffset(pc);
+    const js::PCCounts* baseCount = sc.getImmediatePrecedingPCCounts(targetOffset);
+    if (!baseCount)
+        return 0;
+    if (baseCount->pcOffset() == targetOffset)
+        return baseCount->numExec();
+    MOZ_ASSERT(baseCount->pcOffset() < targetOffset);
+    uint64_t count = baseCount->numExec();
+    do {
+        const js::PCCounts* throwCount = sc.getImmediatePrecedingThrowCounts(targetOffset);
+        if (!throwCount)
+            return count;
+        if (throwCount->pcOffset() <= baseCount->pcOffset())
+            return count;
+        count -= throwCount->numExec();
+        targetOffset = throwCount->pcOffset() - 1;
+    } while (true);
+}
+
+void
+JSScript::incHitCount(jsbytecode* pc)
+{
+    MOZ_ASSERT(containsPC(pc));
+    if (pc < main())
+        pc = main();
+
+    ScriptCounts& sc = getScriptCounts();
+    js::PCCounts* baseCount = sc.getImmediatePrecedingPCCounts(pcToOffset(pc));
+    if (!baseCount)
+        return;
+    baseCount->numExec()++;
+}
+
+void
+JSScript::addIonCounts(jit::IonScriptCounts* ionCounts)
+{
+    ScriptCounts& sc = getScriptCounts();
+    if (sc.ionCounts_)
+        ionCounts->setPrevious(sc.ionCounts_);
+    sc.ionCounts_ = ionCounts;
+}
+
+jit::IonScriptCounts*
+JSScript::getIonCounts()
+{
+    return getScriptCounts().ionCounts_;
+}
+
+void
+JSScript::takeOverScriptCountsMapEntry(ScriptCounts* entryValue)
+{
+#ifdef DEBUG
+    ScriptCountsMap::Ptr p = GetScriptCountsMapEntry(this);
+    MOZ_ASSERT(entryValue == p->value());
+#endif
+    hasScriptCounts_ = false;
+}
+
+void
+JSScript::releaseScriptCounts(ScriptCounts* counts)
+{
+    ScriptCountsMap::Ptr p = GetScriptCountsMapEntry(this);
+    *counts = Move(*p->value());
+    js_delete(p->value());
+    compartment()->scriptCountsMap->remove(p);
+    hasScriptCounts_ = false;
+}
+
+void
+JSScript::destroyScriptCounts(FreeOp* fop)
+{
+    if (hasScriptCounts()) {
+        ScriptCounts scriptCounts;
+        releaseScriptCounts(&scriptCounts);
+    }
+}
+
+void
+ScriptSourceObject::trace(JSTracer* trc, JSObject* obj)
+{
+    ScriptSourceObject* sso = static_cast<ScriptSourceObject*>(obj);
+
+    // Don't trip over the poison 'not yet initialized' values.
+    if (!sso->getReservedSlot(INTRODUCTION_SCRIPT_SLOT).isMagic(JS_GENERIC_MAGIC)) {
+        JSScript* script = sso->introductionScript();
+        if (script) {
+            TraceManuallyBarrieredEdge(trc, &script, "ScriptSourceObject introductionScript");
+            sso->setReservedSlot(INTRODUCTION_SCRIPT_SLOT, PrivateValue(script));
+        }
+    }
+}
+
+void
+ScriptSourceObject::finalize(FreeOp* fop, JSObject* obj)
+{
+    MOZ_ASSERT(fop->onMainThread());
+    ScriptSourceObject* sso = &obj->as<ScriptSourceObject>();
+
+    // If code coverage is enabled, record the filename associated with this
+    // source object.
+    if (fop->runtime()->lcovOutput.isEnabled())
+        sso->compartment()->lcovOutput.collectSourceFile(sso->compartment(), sso);
+
+    sso->source()->decref();
+    sso->setReservedSlot(SOURCE_SLOT, PrivateValue(nullptr));
+}
+
+static const ClassOps ScriptSourceObjectClassOps = {
+    nullptr, /* addProperty */
+    nullptr, /* delProperty */
+    nullptr, /* getProperty */
+    nullptr, /* setProperty */
+    nullptr, /* enumerate */
+    nullptr, /* resolve */
+    nullptr, /* mayResolve */
+    ScriptSourceObject::finalize,
+    nullptr, /* call */
+    nullptr, /* hasInstance */
+    nullptr, /* construct */
+    ScriptSourceObject::trace
+};
+
+const Class ScriptSourceObject::class_ = {
+    "ScriptSource",
+    JSCLASS_HAS_RESERVED_SLOTS(RESERVED_SLOTS) |
+    JSCLASS_IS_ANONYMOUS |
+    JSCLASS_FOREGROUND_FINALIZE,
+    &ScriptSourceObjectClassOps
+};
+
+ScriptSourceObject*
+ScriptSourceObject::create(ExclusiveContext* cx, ScriptSource* source)
+{
+    RootedObject object(cx, NewObjectWithGivenProto(cx, &class_, nullptr));
+    if (!object)
+        return nullptr;
+    RootedScriptSource sourceObject(cx, &object->as<ScriptSourceObject>());
+
+    source->incref();    // The matching decref is in ScriptSourceObject::finalize.
+    sourceObject->initReservedSlot(SOURCE_SLOT, PrivateValue(source));
+
+    // The remaining slots should eventually be populated by a call to
+    // initFromOptions. Poison them until that point.
+    sourceObject->initReservedSlot(ELEMENT_SLOT, MagicValue(JS_GENERIC_MAGIC));
+    sourceObject->initReservedSlot(ELEMENT_PROPERTY_SLOT, MagicValue(JS_GENERIC_MAGIC));
+    sourceObject->initReservedSlot(INTRODUCTION_SCRIPT_SLOT, MagicValue(JS_GENERIC_MAGIC));
+
+    return sourceObject;
+}
+
+/* static */ bool
+ScriptSourceObject::initFromOptions(JSContext* cx, HandleScriptSource source,
+                                    const ReadOnlyCompileOptions& options)
+{
+    releaseAssertSameCompartment(cx, source);
+    MOZ_ASSERT(source->getReservedSlot(ELEMENT_SLOT).isMagic(JS_GENERIC_MAGIC));
+    MOZ_ASSERT(source->getReservedSlot(ELEMENT_PROPERTY_SLOT).isMagic(JS_GENERIC_MAGIC));
+    MOZ_ASSERT(source->getReservedSlot(INTRODUCTION_SCRIPT_SLOT).isMagic(JS_GENERIC_MAGIC));
+
+    RootedValue element(cx, ObjectOrNullValue(options.element()));
+    if (!cx->compartment()->wrap(cx, &element))
+        return false;
+    source->setReservedSlot(ELEMENT_SLOT, element);
+
+    RootedValue elementAttributeName(cx);
+    if (options.elementAttributeName())
+        elementAttributeName = StringValue(options.elementAttributeName());
+    else
+        elementAttributeName = UndefinedValue();
+    if (!cx->compartment()->wrap(cx, &elementAttributeName))
+        return false;
+    source->setReservedSlot(ELEMENT_PROPERTY_SLOT, elementAttributeName);
+
+    // There is no equivalent of cross-compartment wrappers for scripts. If the
+    // introduction script and ScriptSourceObject are in different compartments,
+    // we would be creating a cross-compartment script reference, which is
+    // forbidden. In that case, simply don't bother to retain the introduction
+    // script.
+    if (options.introductionScript() &&
+        options.introductionScript()->compartment() == cx->compartment())
+    {
+        source->setReservedSlot(INTRODUCTION_SCRIPT_SLOT, PrivateValue(options.introductionScript()));
+    } else {
+        source->setReservedSlot(INTRODUCTION_SCRIPT_SLOT, UndefinedValue());
+    }
+
+    return true;
+}
+
+/* static */ bool
+JSScript::loadSource(JSContext* cx, ScriptSource* ss, bool* worked)
+{
+    MOZ_ASSERT(!ss->hasSourceData());
+    *worked = false;
+    if (!cx->runtime()->sourceHook || !ss->sourceRetrievable())
+        return true;
+    char16_t* src = nullptr;
+    size_t length;
+    if (!cx->runtime()->sourceHook->load(cx, ss->filename(), &src, &length))
+        return false;
+    if (!src)
+        return true;
+    if (!ss->setSource(cx, mozilla::UniquePtr<char16_t[], JS::FreePolicy>(src), length))
+        return false;
+
+    *worked = true;
+    return true;
+}
+
+JSFlatString*
+JSScript::sourceData(JSContext* cx)
+{
+    MOZ_ASSERT(scriptSource()->hasSourceData());
+    return scriptSource()->substring(cx, sourceStart(), sourceEnd());
+}
+
+UncompressedSourceCache::AutoHoldEntry::AutoHoldEntry()
+  : cache_(nullptr), sourceChunk_()
+{
+}
+
+void
+UncompressedSourceCache::AutoHoldEntry::holdEntry(UncompressedSourceCache* cache,
+                                                  const ScriptSourceChunk& sourceChunk)
+{
+    // Initialise the holder for a specific cache and script source. This will
+    // hold on to the cached source chars in the event that the cache is purged.
+    MOZ_ASSERT(!cache_ && !sourceChunk_.valid() && !charsToFree_);
+    cache_ = cache;
+    sourceChunk_ = sourceChunk;
+}
+
+void
+UncompressedSourceCache::AutoHoldEntry::holdChars(UniqueTwoByteChars chars)
+{
+    MOZ_ASSERT(!cache_ && !sourceChunk_.valid() && !charsToFree_);
+    charsToFree_ = Move(chars);
+}
+
+void
+UncompressedSourceCache::AutoHoldEntry::deferDelete(UniqueTwoByteChars chars)
+{
+    // Take ownership of source chars now the cache is being purged. Remove our
+    // reference to the ScriptSource which might soon be destroyed.
+    MOZ_ASSERT(cache_ && sourceChunk_.valid() && !charsToFree_);
+    cache_ = nullptr;
+    sourceChunk_ = ScriptSourceChunk();
+    charsToFree_ = Move(chars);
+}
+
+UncompressedSourceCache::AutoHoldEntry::~AutoHoldEntry()
+{
+    if (cache_) {
+        MOZ_ASSERT(sourceChunk_.valid());
+        cache_->releaseEntry(*this);
+    }
+}
+
+void
+UncompressedSourceCache::holdEntry(AutoHoldEntry& holder, const ScriptSourceChunk& ssc)
+{
+    MOZ_ASSERT(!holder_);
+    holder.holdEntry(this, ssc);
+    holder_ = &holder;
+}
+
+void
+UncompressedSourceCache::releaseEntry(AutoHoldEntry& holder)
+{
+    MOZ_ASSERT(holder_ == &holder);
+    holder_ = nullptr;
+}
+
+const char16_t*
+UncompressedSourceCache::lookup(const ScriptSourceChunk& ssc, AutoHoldEntry& holder)
+{
+    MOZ_ASSERT(!holder_);
+    if (!map_)
+        return nullptr;
+    if (Map::Ptr p = map_->lookup(ssc)) {
+        holdEntry(holder, ssc);
+        return p->value().get();
+    }
+    return nullptr;
+}
+
+bool
+UncompressedSourceCache::put(const ScriptSourceChunk& ssc, UniqueTwoByteChars str,
+                             AutoHoldEntry& holder)
+{
+    MOZ_ASSERT(!holder_);
+
+    if (!map_) {
+        UniquePtr<Map> map = MakeUnique<Map>();
+        if (!map || !map->init())
+            return false;
+
+        map_ = Move(map);
+    }
+
+    if (!map_->put(ssc, Move(str)))
+        return false;
+
+    holdEntry(holder, ssc);
+    return true;
+}
+
+void
+UncompressedSourceCache::purge()
+{
+    if (!map_)
+        return;
+
+    for (Map::Range r = map_->all(); !r.empty(); r.popFront()) {
+        if (holder_ && r.front().key() == holder_->sourceChunk()) {
+            holder_->deferDelete(Move(r.front().value()));
+            holder_ = nullptr;
+        }
+    }
+
+    map_.reset();
+}
+
+size_t
+UncompressedSourceCache::sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf)
+{
+    size_t n = 0;
+    if (map_ && !map_->empty()) {
+        n += map_->sizeOfIncludingThis(mallocSizeOf);
+        for (Map::Range r = map_->all(); !r.empty(); r.popFront())
+            n += mallocSizeOf(r.front().value().get());
+    }
+    return n;
+}
+
+const char16_t*
+ScriptSource::chunkChars(JSContext* cx, UncompressedSourceCache::AutoHoldEntry& holder,
+                         size_t chunk)
+{
+    const Compressed& c = data.as<Compressed>();
+
+    ScriptSourceChunk ssc(this, chunk);
+    if (const char16_t* decompressed = cx->caches.uncompressedSourceCache.lookup(ssc, holder))
+        return decompressed;
+
+    size_t totalLengthInBytes = length() * sizeof(char16_t);
+    size_t chunkBytes = Compressor::chunkSize(totalLengthInBytes, chunk);
+
+    MOZ_ASSERT((chunkBytes % sizeof(char16_t)) == 0);
+    const size_t lengthWithNull = (chunkBytes / sizeof(char16_t)) + 1;
+    UniqueTwoByteChars decompressed(js_pod_malloc<char16_t>(lengthWithNull));
+    if (!decompressed) {
+        JS_ReportOutOfMemory(cx);
+        return nullptr;
+    }
+
+    if (!DecompressStringChunk((const unsigned char*) c.raw.chars(),
+                               chunk,
+                               reinterpret_cast<unsigned char*>(decompressed.get()),
+                               chunkBytes))
+    {
+        JS_ReportOutOfMemory(cx);
+        return nullptr;
+    }
+
+    decompressed[lengthWithNull - 1] = '\0';
+
+    const char16_t* ret = decompressed.get();
+    if (!cx->caches.uncompressedSourceCache.put(ssc, Move(decompressed), holder)) {
+        JS_ReportOutOfMemory(cx);
+        return nullptr;
+    }
+    return ret;
+}
+
+const char16_t*
+ScriptSource::chars(JSContext* cx, UncompressedSourceCache::AutoHoldEntry& holder,
+                    size_t begin, size_t len)
+{
+    MOZ_ASSERT(begin + len <= length());
+
+    if (data.is<Uncompressed>()) {
+        const char16_t* chars = data.as<Uncompressed>().string.chars();
+        if (!chars)
+            return nullptr;
+        return chars + begin;
+    }
+
+    if (data.is<Missing>())
+        MOZ_CRASH("ScriptSource::chars() on ScriptSource with SourceType = Missing");
+
+    MOZ_ASSERT(data.is<Compressed>());
+
+    // Determine which chunk(s) we are interested in, and the offsets within
+    // these chunks.
+    size_t firstChunk, lastChunk;
+    size_t firstChunkOffset, lastChunkOffset;
+    MOZ_ASSERT(len > 0);
+    Compressor::toChunkOffset(begin * sizeof(char16_t), &firstChunk, &firstChunkOffset);
+    Compressor::toChunkOffset((begin + len - 1) * sizeof(char16_t), &lastChunk, &lastChunkOffset);
+
+    MOZ_ASSERT(firstChunkOffset % sizeof(char16_t) == 0);
+    size_t firstChar = firstChunkOffset / sizeof(char16_t);
+
+    if (firstChunk == lastChunk) {
+        const char16_t* chars = chunkChars(cx, holder, firstChunk);
+        if (!chars)
+            return nullptr;
+        return chars + firstChar;
+    }
+
+    // We need multiple chunks. Allocate a (null-terminated) buffer to hold
+    // |len| chars and copy uncompressed chars from the chunks into it. We use
+    // chunkChars() so we benefit from chunk caching by UncompressedSourceCache.
+
+    MOZ_ASSERT(firstChunk < lastChunk);
+
+    size_t lengthWithNull = len + 1;
+    UniqueTwoByteChars decompressed(js_pod_malloc<char16_t>(lengthWithNull));
+    if (!decompressed) {
+        JS_ReportOutOfMemory(cx);
+        return nullptr;
+    }
+
+    size_t totalLengthInBytes = length() * sizeof(char16_t);
+    char16_t* cursor = decompressed.get();
+
+    for (size_t i = firstChunk; i <= lastChunk; i++) {
+        UncompressedSourceCache::AutoHoldEntry chunkHolder;
+        const char16_t* chars = chunkChars(cx, chunkHolder, i);
+        if (!chars)
+            return nullptr;
+
+        size_t numChars = Compressor::chunkSize(totalLengthInBytes, i) / sizeof(char16_t);
+        if (i == firstChunk) {
+            MOZ_ASSERT(firstChar < numChars);
+            chars += firstChar;
+            numChars -= firstChar;
+        } else if (i == lastChunk) {
+            size_t numCharsNew = lastChunkOffset / sizeof(char16_t) + 1;
+            MOZ_ASSERT(numCharsNew <= numChars);
+            numChars = numCharsNew;
+        }
+        mozilla::PodCopy(cursor, chars, numChars);
+        cursor += numChars;
+    }
+
+    *cursor++ = '\0';
+    MOZ_ASSERT(size_t(cursor - decompressed.get()) == lengthWithNull);
+
+    // Transfer ownership to |holder|.
+    const char16_t* ret = decompressed.get();
+    holder.holdChars(Move(decompressed));
+    return ret;
+}
+
+JSFlatString*
+ScriptSource::substring(JSContext* cx, size_t start, size_t stop)
+{
+    MOZ_ASSERT(start <= stop);
+    size_t len = stop - start;
+    UncompressedSourceCache::AutoHoldEntry holder;
+    const char16_t* chars = this->chars(cx, holder, start, len);
+    if (!chars)
+        return nullptr;
+    return NewStringCopyN<CanGC>(cx, chars, len);
+}
+
+JSFlatString*
+ScriptSource::substringDontDeflate(JSContext* cx, size_t start, size_t stop)
+{
+    MOZ_ASSERT(start <= stop);
+    size_t len = stop - start;
+    UncompressedSourceCache::AutoHoldEntry holder;
+    const char16_t* chars = this->chars(cx, holder, start, len);
+    if (!chars)
+        return nullptr;
+    return NewStringCopyNDontDeflate<CanGC>(cx, chars, len);
+}
+
+MOZ_MUST_USE bool
+ScriptSource::setSource(ExclusiveContext* cx,
+                        mozilla::UniquePtr<char16_t[], JS::FreePolicy>&& source,
+                        size_t length)
+{
+    auto& cache = cx->zone()->runtimeFromAnyThread()->sharedImmutableStrings();
+    auto deduped = cache.getOrCreate(mozilla::Move(source), length);
+    if (!deduped) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    setSource(mozilla::Move(*deduped));
+    return true;
+}
+
+void
+ScriptSource::setSource(SharedImmutableTwoByteString&& string)
+{
+    MOZ_ASSERT(data.is<Missing>());
+    data = SourceType(Uncompressed(mozilla::Move(string)));
+}
+
+MOZ_MUST_USE bool
+ScriptSource::setCompressedSource(ExclusiveContext* cx,
+                                  mozilla::UniquePtr<char[], JS::FreePolicy>&& raw,
+                                  size_t rawLength,
+                                  size_t sourceLength)
+{
+    MOZ_ASSERT(raw);
+    auto& cache = cx->zone()->runtimeFromAnyThread()->sharedImmutableStrings();
+    auto deduped = cache.getOrCreate(mozilla::Move(raw), rawLength);
+    if (!deduped) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    setCompressedSource(mozilla::Move(*deduped), sourceLength);
+    return true;
+}
+
+void
+ScriptSource::setCompressedSource(SharedImmutableString&& raw, size_t uncompressedLength)
+{
+    MOZ_ASSERT(data.is<Missing>() || data.is<Uncompressed>());
+    MOZ_ASSERT_IF(data.is<Uncompressed>(),
+                  data.as<Uncompressed>().string.length() == uncompressedLength);
+
+    data = SourceType(Compressed(mozilla::Move(raw), uncompressedLength));
+}
+
+bool
+ScriptSource::setSourceCopy(ExclusiveContext* cx, SourceBufferHolder& srcBuf,
+                            bool argumentsNotIncluded, SourceCompressionTask* task)
+{
+    MOZ_ASSERT(!hasSourceData());
+    argumentsNotIncluded_ = argumentsNotIncluded;
+
+    auto& cache = cx->zone()->runtimeFromAnyThread()->sharedImmutableStrings();
+    auto deduped = cache.getOrCreate(srcBuf.get(), srcBuf.length(), [&]() {
+        return srcBuf.ownsChars()
+            ? mozilla::UniquePtr<char16_t[], JS::FreePolicy>(srcBuf.take())
+            : DuplicateString(srcBuf.get(), srcBuf.length());
+    });
+    if (!deduped) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    setSource(mozilla::Move(*deduped));
+
+    // There are several cases where source compression is not a good idea:
+    //  - If the script is tiny, then compression will save little or no space.
+    //  - If there is only one core, then compression will contend with JS
+    //    execution (which hurts benchmarketing).
+    //  - If the source contains a giant string, then parsing will finish much
+    //    faster than compression which increases latency (this case is handled
+    //    in Parser::stringLiteral).
+    //
+    // Lastly, since the parsing thread will eventually perform a blocking wait
+    // on the compression task's thread, require that there are at least 2
+    // helper threads:
+    //  - If we are on a helper thread, there must be another helper thread to
+    //    execute our compression task.
+    //  - If we are on the main thread, there must be at least two helper
+    //    threads since at most one helper thread can be blocking on the main
+    //    thread (see HelperThreadState::canStartParseTask) which would cause a
+    //    deadlock if there wasn't a second helper thread that could make
+    //    progress on our compression task.
+    bool canCompressOffThread =
+        HelperThreadState().cpuCount > 1 &&
+        HelperThreadState().threadCount >= 2 &&
+        CanUseExtraThreads();
+    const size_t TINY_SCRIPT = 256;
+    if (TINY_SCRIPT <= srcBuf.length() && canCompressOffThread) {
+        task->ss = this;
+        if (!StartOffThreadCompression(cx, task))
+            return false;
+    }
+
+    return true;
+}
+
+static MOZ_MUST_USE bool
+reallocUniquePtr(UniquePtr<char[], JS::FreePolicy>& unique, size_t size)
+{
+    auto newPtr = static_cast<char*>(js_realloc(unique.get(), size));
+    if (!newPtr)
+        return false;
+
+    // Since the realloc succeeded, unique is now holding a freed pointer.
+    mozilla::Unused << unique.release();
+    unique.reset(newPtr);
+    return true;
+}
+
+SourceCompressionTask::ResultType
+SourceCompressionTask::work()
+{
+    MOZ_ASSERT(ss->data.is<ScriptSource::Uncompressed>());
+
+    // Try to keep the maximum memory usage down by only allocating half the
+    // size of the string, first.
+    size_t inputBytes = ss->length() * sizeof(char16_t);
+    size_t firstSize = inputBytes / 2;
+    mozilla::UniquePtr<char[], JS::FreePolicy> compressed(js_pod_malloc<char>(firstSize));
+    if (!compressed)
+        return OOM;
+
+    const char16_t* chars = ss->data.as<ScriptSource::Uncompressed>().string.chars();
+    Compressor comp(reinterpret_cast<const unsigned char*>(chars),
+                    inputBytes);
+    if (!comp.init())
+        return OOM;
+
+    comp.setOutput(reinterpret_cast<unsigned char*>(compressed.get()), firstSize);
+    bool cont = true;
+    bool reallocated = false;
+    while (cont) {
+        if (abort_)
+            return Aborted;
+
+        switch (comp.compressMore()) {
+          case Compressor::CONTINUE:
+            break;
+          case Compressor::MOREOUTPUT: {
+            if (reallocated) {
+                // The compressed string is longer than the original string.
+                return Aborted;
+            }
+
+            // The compressed output is greater than half the size of the
+            // original string. Reallocate to the full size.
+            if (!reallocUniquePtr(compressed, inputBytes))
+                return OOM;
+
+            comp.setOutput(reinterpret_cast<unsigned char*>(compressed.get()), inputBytes);
+            reallocated = true;
+            break;
+          }
+          case Compressor::DONE:
+            cont = false;
+            break;
+          case Compressor::OOM:
+            return OOM;
+        }
+    }
+
+    size_t totalBytes = comp.totalBytesNeeded();
+
+    // Shrink the buffer to the size of the compressed data.
+    if (!reallocUniquePtr(compressed, totalBytes))
+        return OOM;
+
+    comp.finish(compressed.get(), totalBytes);
+
+    auto& strings = cx->sharedImmutableStrings();
+    resultString = strings.getOrCreate(mozilla::Move(compressed), totalBytes);
+    if (!resultString)
+        return OOM;
+
+    return Success;
+}
+
+void
+ScriptSource::addSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf,
+                                     JS::ScriptSourceInfo* info) const
+{
+    info->misc += mallocSizeOf(this) +
+                  mallocSizeOf(filename_.get()) +
+                  mallocSizeOf(introducerFilename_.get());
+    info->numScripts++;
+}
+
+template<XDRMode mode>
+bool
+ScriptSource::performXDR(XDRState<mode>* xdr)
+{
+    struct CompressedLengthMatcher
+    {
+        size_t match(Uncompressed&) {
+            return 0;
+        }
+
+        size_t match(Compressed& c) {
+            return c.raw.length();
+        }
+
+        size_t match(Missing&) {
+            MOZ_CRASH("Missing source data in ScriptSource::performXDR");
+            return 0;
+        }
+    };
+
+    struct RawDataMatcher
+    {
+        void* match(Uncompressed& u) {
+            return (void*) u.string.chars();
+        }
+
+        void* match(Compressed& c) {
+            return (void*) c.raw.chars();
+        }
+
+        void* match(Missing&) {
+            MOZ_CRASH("Missing source data in ScriptSource::performXDR");
+            return nullptr;
+        }
+    };
+
+    uint8_t hasSource = hasSourceData();
+    if (!xdr->codeUint8(&hasSource))
+        return false;
+
+    uint8_t retrievable = sourceRetrievable_;
+    if (!xdr->codeUint8(&retrievable))
+        return false;
+    sourceRetrievable_ = retrievable;
+
+    if (hasSource && !sourceRetrievable_) {
+        uint32_t len = 0;
+        if (mode == XDR_ENCODE)
+            len = length();
+        if (!xdr->codeUint32(&len))
+            return false;
+
+        uint32_t compressedLength;
+        if (mode == XDR_ENCODE) {
+            CompressedLengthMatcher m;
+            compressedLength = data.match(m);
+        }
+        if (!xdr->codeUint32(&compressedLength))
+            return false;
+
+        {
+            uint8_t argumentsNotIncluded;
+            if (mode == XDR_ENCODE)
+                argumentsNotIncluded = argumentsNotIncluded_;
+            if (!xdr->codeUint8(&argumentsNotIncluded))
+                return false;
+            if (mode == XDR_DECODE)
+                argumentsNotIncluded_ = argumentsNotIncluded;
+        }
+
+        size_t byteLen = compressedLength ? compressedLength : (len * sizeof(char16_t));
+        if (mode == XDR_DECODE) {
+            uint8_t* p = xdr->cx()->template pod_malloc<uint8_t>(Max<size_t>(byteLen, 1));
+            if (!p || !xdr->codeBytes(p, byteLen)) {
+                js_free(p);
+                return false;
+            }
+
+            if (compressedLength) {
+                mozilla::UniquePtr<char[], JS::FreePolicy> compressedSource(
+                    reinterpret_cast<char*>(p));
+                if (!setCompressedSource(xdr->cx(), mozilla::Move(compressedSource), byteLen, len))
+                    return false;
+            } else {
+                mozilla::UniquePtr<char16_t[], JS::FreePolicy> source(
+                    reinterpret_cast<char16_t*>(p));
+                if (!setSource(xdr->cx(), mozilla::Move(source), len))
+                    return false;
+            }
+        } else {
+            RawDataMatcher rdm;
+            void* p = data.match(rdm);
+            if (!xdr->codeBytes(p, byteLen))
+                return false;
+        }
+    }
+
+    uint8_t haveSourceMap = hasSourceMapURL();
+    if (!xdr->codeUint8(&haveSourceMap))
+        return false;
+
+    if (haveSourceMap) {
+        uint32_t sourceMapURLLen = (mode == XDR_DECODE) ? 0 : js_strlen(sourceMapURL_.get());
+        if (!xdr->codeUint32(&sourceMapURLLen))
+            return false;
+
+        if (mode == XDR_DECODE) {
+            sourceMapURL_ = xdr->cx()->template make_pod_array<char16_t>(sourceMapURLLen + 1);
+            if (!sourceMapURL_)
+                return false;
+        }
+        if (!xdr->codeChars(sourceMapURL_.get(), sourceMapURLLen)) {
+            if (mode == XDR_DECODE)
+                sourceMapURL_ = nullptr;
+            return false;
+        }
+        sourceMapURL_[sourceMapURLLen] = '\0';
+    }
+
+    uint8_t haveDisplayURL = hasDisplayURL();
+    if (!xdr->codeUint8(&haveDisplayURL))
+        return false;
+
+    if (haveDisplayURL) {
+        uint32_t displayURLLen = (mode == XDR_DECODE) ? 0 : js_strlen(displayURL_.get());
+        if (!xdr->codeUint32(&displayURLLen))
+            return false;
+
+        if (mode == XDR_DECODE) {
+            displayURL_ = xdr->cx()->template make_pod_array<char16_t>(displayURLLen + 1);
+            if (!displayURL_)
+                return false;
+        }
+        if (!xdr->codeChars(displayURL_.get(), displayURLLen)) {
+            if (mode == XDR_DECODE)
+                displayURL_ = nullptr;
+            return false;
+        }
+        displayURL_[displayURLLen] = '\0';
+    }
+
+    uint8_t haveFilename = !!filename_;
+    if (!xdr->codeUint8(&haveFilename))
+        return false;
+
+    if (haveFilename) {
+        const char* fn = filename();
+        if (!xdr->codeCString(&fn))
+            return false;
+        if (mode == XDR_DECODE && !setFilename(xdr->cx(), fn))
+            return false;
+    }
+
+    return true;
+}
+
+// Format and return a cx->zone()->pod_malloc'ed URL for a generated script like:
+//   {filename} line {lineno} > {introducer}
+// For example:
+//   foo.js line 7 > eval
+// indicating code compiled by the call to 'eval' on line 7 of foo.js.
+static char*
+FormatIntroducedFilename(ExclusiveContext* cx, const char* filename, unsigned lineno,
+                         const char* introducer)
+{
+    // Compute the length of the string in advance, so we can allocate a
+    // buffer of the right size on the first shot.
+    //
+    // (JS_smprintf would be perfect, as that allocates the result
+    // dynamically as it formats the string, but it won't allocate from cx,
+    // and wants us to use a special free function.)
+    char linenoBuf[15];
+    size_t filenameLen = strlen(filename);
+    size_t linenoLen = SprintfLiteral(linenoBuf, "%u", lineno);
+    size_t introducerLen = strlen(introducer);
+    size_t len = filenameLen                    +
+                 6 /* == strlen(" line ") */    +
+                 linenoLen                      +
+                 3 /* == strlen(" > ") */       +
+                 introducerLen                  +
+                 1 /* \0 */;
+    char* formatted = cx->zone()->pod_malloc<char>(len);
+    if (!formatted) {
+        ReportOutOfMemory(cx);
+        return nullptr;
+    }
+    mozilla::DebugOnly<size_t> checkLen = snprintf(formatted, len, "%s line %s > %s",
+                                                   filename, linenoBuf, introducer);
+    MOZ_ASSERT(checkLen == len - 1);
+
+    return formatted;
+}
+
+bool
+ScriptSource::initFromOptions(ExclusiveContext* cx, const ReadOnlyCompileOptions& options)
+{
+    MOZ_ASSERT(!filename_);
+    MOZ_ASSERT(!introducerFilename_);
+
+    mutedErrors_ = options.mutedErrors();
+
+    introductionType_ = options.introductionType;
+    setIntroductionOffset(options.introductionOffset);
+
+    if (options.hasIntroductionInfo) {
+        MOZ_ASSERT(options.introductionType != nullptr);
+        const char* filename = options.filename() ? options.filename() : "<unknown>";
+        char* formatted = FormatIntroducedFilename(cx, filename, options.introductionLineno,
+                                                   options.introductionType);
+        if (!formatted)
+            return false;
+        filename_.reset(formatted);
+    } else if (options.filename()) {
+        if (!setFilename(cx, options.filename()))
+            return false;
+    }
+
+    if (options.introducerFilename()) {
+        introducerFilename_ = DuplicateString(cx, options.introducerFilename());
+        if (!introducerFilename_)
+            return false;
+    }
+
+    return true;
+}
+
+bool
+ScriptSource::setFilename(ExclusiveContext* cx, const char* filename)
+{
+    MOZ_ASSERT(!filename_);
+    filename_ = DuplicateString(cx, filename);
+    return filename_ != nullptr;
+}
+
+bool
+ScriptSource::setDisplayURL(ExclusiveContext* cx, const char16_t* displayURL)
+{
+    MOZ_ASSERT(displayURL);
+    if (hasDisplayURL()) {
+        // FIXME: filename_.get() should be UTF-8 (bug 987069).
+        if (cx->isJSContext() &&
+            !JS_ReportErrorFlagsAndNumberLatin1(cx->asJSContext(), JSREPORT_WARNING,
+                                                GetErrorMessage, nullptr,
+                                                JSMSG_ALREADY_HAS_PRAGMA, filename_.get(),
+                                                "//# sourceURL"))
+        {
+            return false;
+        }
+    }
+    size_t len = js_strlen(displayURL) + 1;
+    if (len == 1)
+        return true;
+
+    displayURL_ = DuplicateString(cx, displayURL);
+    return displayURL_ != nullptr;
+}
+
+bool
+ScriptSource::setSourceMapURL(ExclusiveContext* cx, const char16_t* sourceMapURL)
+{
+    MOZ_ASSERT(sourceMapURL);
+
+    size_t len = js_strlen(sourceMapURL) + 1;
+    if (len == 1)
+        return true;
+
+    sourceMapURL_ = DuplicateString(cx, sourceMapURL);
+    return sourceMapURL_ != nullptr;
+}
+
+/*
+ * Shared script data management.
+ */
+
+SharedScriptData*
+js::SharedScriptData::new_(ExclusiveContext* cx, uint32_t codeLength,
+                           uint32_t srcnotesLength, uint32_t natoms)
+{
+    uint32_t dataLength = natoms * sizeof(GCPtrAtom) + codeLength + srcnotesLength;
+    uint32_t allocLength = offsetof(SharedScriptData, data_) + dataLength;
+    auto entry = reinterpret_cast<SharedScriptData*>(cx->zone()->pod_malloc<uint8_t>(allocLength));
+    if (!entry) {
+        ReportOutOfMemory(cx);
+        return nullptr;
+    }
+
+    entry->refCount_ = 0;
+    entry->dataLength_ = dataLength;
+    entry->natoms_ = natoms;
+    entry->codeLength_ = codeLength;
+
+    /*
+     * Call constructors to initialize the storage that will be accessed as a
+     * GCPtrAtom array via atoms().
+     */
+    GCPtrAtom* atoms = entry->atoms();
+    MOZ_ASSERT(reinterpret_cast<uintptr_t>(atoms) % sizeof(GCPtrAtom*) == 0);
+    for (unsigned i = 0; i < natoms; ++i)
+        new (&atoms[i]) GCPtrAtom();
+
+    return entry;
+}
+
+bool
+JSScript::createScriptData(ExclusiveContext* cx, uint32_t codeLength, uint32_t srcnotesLength,
+                           uint32_t natoms)
+{
+    MOZ_ASSERT(!scriptData());
+    SharedScriptData* ssd = SharedScriptData::new_(cx, codeLength, srcnotesLength, natoms);
+    if (!ssd)
+        return false;
+
+    setScriptData(ssd);
+    return true;
+}
+
+void
+JSScript::freeScriptData()
+{
+    MOZ_ASSERT(scriptData_->refCount() == 1);
+    scriptData_->decRefCount();
+    scriptData_ = nullptr;
+}
+
+void
+JSScript::setScriptData(js::SharedScriptData* data)
+{
+    MOZ_ASSERT(!scriptData_);
+    scriptData_ = data;
+    scriptData_->incRefCount();
+}
+
+/*
+ * Takes ownership of its *ssd parameter and either adds it into the runtime's
+ * ScriptDataTable or frees it if a matching entry already exists.
+ *
+ * Sets the |code| and |atoms| fields on the given JSScript.
+ */
+bool
+JSScript::shareScriptData(ExclusiveContext* cx)
+{
+    SharedScriptData* ssd = scriptData();
+    MOZ_ASSERT(ssd);
+    MOZ_ASSERT(ssd->refCount() == 1);
+
+    AutoLockForExclusiveAccess lock(cx);
+
+    ScriptBytecodeHasher::Lookup l(ssd);
+
+    ScriptDataTable::AddPtr p = cx->scriptDataTable(lock).lookupForAdd(l);
+    if (p) {
+        MOZ_ASSERT(ssd != *p);
+        freeScriptData();
+        setScriptData(*p);
+    } else {
+        if (!cx->scriptDataTable(lock).add(p, ssd)) {
+            freeScriptData();
+            ReportOutOfMemory(cx);
+            return false;
+        }
+
+        // Being in the table counts as a reference on the script data.
+        scriptData()->incRefCount();
+    }
+
+    MOZ_ASSERT(scriptData()->refCount() >= 2);
+    return true;
+}
+
+void
+js::SweepScriptData(JSRuntime* rt, AutoLockForExclusiveAccess& lock)
+{
+    // Entries are removed from the table when their reference count is one,
+    // i.e. when the only reference to them is from the table entry.
+
+    ScriptDataTable& table = rt->scriptDataTable(lock);
+
+    for (ScriptDataTable::Enum e(table); !e.empty(); e.popFront()) {
+        SharedScriptData* scriptData = e.front();
+        if (scriptData->refCount() == 1) {
+            scriptData->decRefCount();
+            e.removeFront();
+        }
+    }
+}
+
+void
+js::FreeScriptData(JSRuntime* rt, AutoLockForExclusiveAccess& lock)
+{
+    ScriptDataTable& table = rt->scriptDataTable(lock);
+    if (!table.initialized())
+        return;
+
+    // The table should be empty unless the embedding leaked GC things.
+    MOZ_ASSERT_IF(rt->gc.shutdownCollectedEverything(), table.empty());
+
+    for (ScriptDataTable::Enum e(table); !e.empty(); e.popFront()) {
+#ifdef DEBUG
+        SharedScriptData* scriptData = e.front();
+        fprintf(stderr, "ERROR: GC found live SharedScriptData %p with ref count %d at shutdown\n",
+                scriptData, scriptData->refCount());
+#endif
+        js_free(e.front());
+    }
+
+    table.clear();
+}
+
+/*
+ * JSScript::data and SharedScriptData::data have complex,
+ * manually-controlled, memory layouts.
+ *
+ * JSScript::data begins with some optional array headers. They are optional
+ * because they often aren't needed, i.e. the corresponding arrays often have
+ * zero elements. Each header has a bit in JSScript::hasArrayBits that
+ * indicates if it's present within |data|; from this the offset of each
+ * present array header can be computed. Each header has an accessor function
+ * in JSScript that encapsulates this offset computation.
+ *
+ * Array type      Array elements  Accessor
+ * ----------      --------------  --------
+ * ConstArray      Consts          consts()
+ * ObjectArray     Objects         objects()
+ * ObjectArray     Regexps         regexps()
+ * TryNoteArray    Try notes       trynotes()
+ * ScopeNoteArray  Scope notes     scopeNotes()
+ *
+ * Then are the elements of several arrays.
+ * - Most of these arrays have headers listed above (if present). For each of
+ *   these, the array pointer and the array length is stored in the header.
+ * - The remaining arrays have pointers and lengths that are stored directly in
+ *   JSScript. This is because, unlike the others, they are nearly always
+ *   non-zero length and so the optional-header space optimization isn't
+ *   worthwhile.
+ *
+ * Array elements   Pointed to by         Length
+ * --------------   -------------         ------
+ * Consts           consts()->vector      consts()->length
+ * Objects          objects()->vector     objects()->length
+ * Regexps          regexps()->vector     regexps()->length
+ * Try notes        trynotes()->vector    trynotes()->length
+ * Scope notes      scopeNotes()->vector  scopeNotes()->length
+ *
+ * IMPORTANT: This layout has two key properties.
+ * - It ensures that everything has sufficient alignment; in particular, the
+ *   consts() elements need Value alignment.
+ * - It ensures there are no gaps between elements, which saves space and makes
+ *   manual layout easy. In particular, in the second part, arrays with larger
+ *   elements precede arrays with smaller elements.
+ *
+ * SharedScriptData::data contains data that can be shared within a
+ * runtime. These items' layout is manually controlled to make it easier to
+ * manage both during (temporary) allocation and during matching against
+ * existing entries in the runtime. As the jsbytecode has to come first to
+ * enable lookup by bytecode identity, SharedScriptData::data, the atoms part
+ * has to manually be aligned sufficiently by adding padding after the notes
+ * part.
+ *
+ * Array elements   Pointed to by         Length
+ * --------------   -------------         ------
+ * jsbytecode       code                  length
+ * jsscrnote        notes()               numNotes()
+ * Atoms            atoms                 natoms
+ *
+ * The following static assertions check JSScript::data's alignment properties.
+ */
+
+template<class T>
+constexpr bool
+KeepsValueAlignment() {
+    return alignof(JS::Value) % alignof(T) == 0 &&
+           sizeof(T) % sizeof(JS::Value) == 0;
+}
+
+template<class T>
+constexpr bool
+HasValueAlignment() {
+    return alignof(JS::Value) == alignof(T) &&
+           sizeof(T) == sizeof(JS::Value);
+}
+
+template<class T1, class T2>
+constexpr bool
+NoPaddingBetweenEntries() {
+    return alignof(T1) % alignof(T2) == 0;
+}
+
+/*
+ * These assertions ensure that there is no padding between the array headers,
+ * and also that the consts() elements (which follow immediately afterward) are
+ * Value-aligned.  (There is an assumption that |data| itself is Value-aligned;
+ * we check this below).
+ */
+JS_STATIC_ASSERT(KeepsValueAlignment<ConstArray>());
+JS_STATIC_ASSERT(KeepsValueAlignment<ObjectArray>());       /* there are two of these */
+JS_STATIC_ASSERT(KeepsValueAlignment<TryNoteArray>());
+JS_STATIC_ASSERT(KeepsValueAlignment<ScopeNoteArray>());
+
+/* These assertions ensure there is no padding required between array elements. */
+JS_STATIC_ASSERT(HasValueAlignment<GCPtrValue>());
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<GCPtrValue, GCPtrObject>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<GCPtrObject, GCPtrObject>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<GCPtrObject, JSTryNote>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<JSTryNote, uint32_t>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<uint32_t, uint32_t>()));
+
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<GCPtrValue, ScopeNote>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<ScopeNote, ScopeNote>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<JSTryNote, ScopeNote>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<GCPtrObject, ScopeNote>()));
+JS_STATIC_ASSERT((NoPaddingBetweenEntries<ScopeNote, uint32_t>()));
+
+static inline size_t
+ScriptDataSize(uint32_t nscopes, uint32_t nconsts, uint32_t nobjects,
+               uint32_t ntrynotes, uint32_t nscopenotes, uint32_t nyieldoffsets)
+{
+    size_t size = 0;
+
+    MOZ_ASSERT(nscopes != 0);
+    size += sizeof(ScopeArray) + nscopes * sizeof(Scope*);
+    if (nconsts != 0)
+        size += sizeof(ConstArray) + nconsts * sizeof(Value);
+    if (nobjects != 0)
+        size += sizeof(ObjectArray) + nobjects * sizeof(NativeObject*);
+    if (ntrynotes != 0)
+        size += sizeof(TryNoteArray) + ntrynotes * sizeof(JSTryNote);
+    if (nscopenotes != 0)
+        size += sizeof(ScopeNoteArray) + nscopenotes * sizeof(ScopeNote);
+    if (nyieldoffsets != 0)
+        size += sizeof(YieldOffsetArray) + nyieldoffsets * sizeof(uint32_t);
+
+     return size;
+}
+
+void
+JSScript::initCompartment(ExclusiveContext* cx)
+{
+    compartment_ = cx->compartment_;
+}
+
+/* static */ JSScript*
+JSScript::Create(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
+                 HandleObject sourceObject, uint32_t bufStart, uint32_t bufEnd)
+{
+    MOZ_ASSERT(bufStart <= bufEnd);
+
+    RootedScript script(cx, Allocate<JSScript>(cx));
+    if (!script)
+        return nullptr;
+
+    PodZero(script.get());
+
+    script->initCompartment(cx);
+
+    script->selfHosted_ = options.selfHostingMode;
+    script->noScriptRval_ = options.noScriptRval;
+    script->treatAsRunOnce_ = options.isRunOnce;
+
+    script->version = options.version;
+    MOZ_ASSERT(script->getVersion() == options.version);     // assert that no overflow occurred
+
+    script->setSourceObject(sourceObject);
+    script->sourceStart_ = bufStart;
+    script->sourceEnd_ = bufEnd;
+
+    return script;
+}
+
+static inline uint8_t*
+AllocScriptData(JS::Zone* zone, size_t size)
+{
+    if (!size)
+        return nullptr;
+
+    uint8_t* data = zone->pod_calloc<uint8_t>(JS_ROUNDUP(size, sizeof(Value)));
+    if (!data)
+        return nullptr;
+    MOZ_ASSERT(size_t(data) % sizeof(Value) == 0);
+    return data;
+}
+
+/* static */ bool
+JSScript::partiallyInit(ExclusiveContext* cx, HandleScript script, uint32_t nscopes,
+                        uint32_t nconsts, uint32_t nobjects, uint32_t ntrynotes,
+                        uint32_t nscopenotes, uint32_t nyieldoffsets, uint32_t nTypeSets)
+{
+    size_t size = ScriptDataSize(nscopes, nconsts, nobjects, ntrynotes,
+                                 nscopenotes, nyieldoffsets);
+    script->data = AllocScriptData(script->zone(), size);
+    if (size && !script->data) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    script->dataSize_ = size;
+
+    MOZ_ASSERT(nTypeSets <= UINT16_MAX);
+    script->nTypeSets_ = uint16_t(nTypeSets);
+
+    uint8_t* cursor = script->data;
+
+    // There must always be at least 1 scope, the body scope.
+    MOZ_ASSERT(nscopes != 0);
+    cursor += sizeof(ScopeArray);
+
+    if (nconsts != 0) {
+        script->setHasArray(CONSTS);
+        cursor += sizeof(ConstArray);
+    }
+    if (nobjects != 0) {
+        script->setHasArray(OBJECTS);
+        cursor += sizeof(ObjectArray);
+    }
+
+    if (ntrynotes != 0) {
+        script->setHasArray(TRYNOTES);
+        cursor += sizeof(TryNoteArray);
+    }
+    if (nscopenotes != 0) {
+        script->setHasArray(SCOPENOTES);
+        cursor += sizeof(ScopeNoteArray);
+    }
+
+    YieldOffsetArray* yieldOffsets = nullptr;
+    if (nyieldoffsets != 0) {
+        yieldOffsets = reinterpret_cast<YieldOffsetArray*>(cursor);
+        cursor += sizeof(YieldOffsetArray);
+    }
+
+    if (nconsts != 0) {
+        MOZ_ASSERT(reinterpret_cast<uintptr_t>(cursor) % sizeof(JS::Value) == 0);
+        script->consts()->length = nconsts;
+        script->consts()->vector = (GCPtrValue*)cursor;
+        cursor += nconsts * sizeof(script->consts()->vector[0]);
+    }
+
+    script->scopes()->length = nscopes;
+    script->scopes()->vector = (GCPtrScope*)cursor;
+    cursor += nscopes * sizeof(script->scopes()->vector[0]);
+
+    if (nobjects != 0) {
+        script->objects()->length = nobjects;
+        script->objects()->vector = (GCPtrObject*)cursor;
+        cursor += nobjects * sizeof(script->objects()->vector[0]);
+    }
+
+    if (ntrynotes != 0) {
+        script->trynotes()->length = ntrynotes;
+        script->trynotes()->vector = reinterpret_cast<JSTryNote*>(cursor);
+        size_t vectorSize = ntrynotes * sizeof(script->trynotes()->vector[0]);
+#ifdef DEBUG
+        memset(cursor, 0, vectorSize);
+#endif
+        cursor += vectorSize;
+    }
+
+    if (nscopenotes != 0) {
+        script->scopeNotes()->length = nscopenotes;
+        script->scopeNotes()->vector = reinterpret_cast<ScopeNote*>(cursor);
+        size_t vectorSize = nscopenotes * sizeof(script->scopeNotes()->vector[0]);
+#ifdef DEBUG
+        memset(cursor, 0, vectorSize);
+#endif
+        cursor += vectorSize;
+    }
+
+    if (nyieldoffsets != 0) {
+        yieldOffsets->init(reinterpret_cast<uint32_t*>(cursor), nyieldoffsets);
+        size_t vectorSize = nyieldoffsets * sizeof(script->yieldOffsets()[0]);
+#ifdef DEBUG
+        memset(cursor, 0, vectorSize);
+#endif
+        cursor += vectorSize;
+    }
+
+    MOZ_ASSERT(cursor == script->data + size);
+    return true;
+}
+
+/* static */ bool
+JSScript::initFunctionPrototype(ExclusiveContext* cx, Handle<JSScript*> script,
+                                HandleFunction functionProto)
+{
+    uint32_t numScopes = 1;
+    uint32_t numConsts = 0;
+    uint32_t numObjects = 0;
+    uint32_t numTryNotes = 0;
+    uint32_t numScopeNotes = 0;
+    uint32_t numYieldOffsets = 0;
+    uint32_t numTypeSets = 0;
+    if (!partiallyInit(cx, script, numScopes, numConsts, numObjects, numTryNotes,
+                       numScopeNotes, numYieldOffsets, numTypeSets))
+    {
+        return false;
+    }
+
+    RootedScope enclosing(cx, &cx->global()->emptyGlobalScope());
+    Scope* functionProtoScope = FunctionScope::create(cx, nullptr, false, false, functionProto,
+                                                      enclosing);
+    if (!functionProtoScope)
+        return false;
+    script->scopes()->vector[0].init(functionProtoScope);
+
+    uint32_t codeLength = 1;
+    uint32_t srcNotesLength = 1;
+    uint32_t numAtoms = 0;
+    if (!script->createScriptData(cx, codeLength, srcNotesLength, numAtoms))
+        return false;
+
+    jsbytecode* code = script->code();
+    code[0] = JSOP_RETRVAL;
+    code[1] = SRC_NULL;
+    return script->shareScriptData(cx);
+}
+
+static void
+InitAtomMap(frontend::AtomIndexMap& indices, GCPtrAtom* atoms)
+{
+    for (AtomIndexMap::Range r = indices.all(); !r.empty(); r.popFront()) {
+        JSAtom* atom = r.front().key();
+        uint32_t index = r.front().value();
+        MOZ_ASSERT(index < indices.count());
+        atoms[index].init(atom);
+    }
+}
+
+/* static */ void
+JSScript::initFromFunctionBox(ExclusiveContext* cx, HandleScript script,
+                              frontend::FunctionBox* funbox)
+{
+    JSFunction* fun = funbox->function();
+    if (fun->isInterpretedLazy())
+        fun->setUnlazifiedScript(script);
+    else
+        fun->setScript(script);
+
+    script->funHasExtensibleScope_ = funbox->hasExtensibleScope();
+    script->needsHomeObject_       = funbox->needsHomeObject();
+    script->isDerivedClassConstructor_ = funbox->isDerivedClassConstructor();
+
+    if (funbox->argumentsHasLocalBinding()) {
+        script->setArgumentsHasVarBinding();
+        if (funbox->definitelyNeedsArgsObj())
+            script->setNeedsArgsObj(true);
+    } else {
+        MOZ_ASSERT(!funbox->definitelyNeedsArgsObj());
+    }
+    script->hasMappedArgsObj_ = funbox->hasMappedArgsObj();
+
+    script->functionHasThisBinding_ = funbox->hasThisBinding();
+    script->functionHasExtraBodyVarScope_ = funbox->hasExtraBodyVarScope();
+
+    script->funLength_ = funbox->length;
+
+    script->isGeneratorExp_ = funbox->isGenexpLambda;
+    script->setGeneratorKind(funbox->generatorKind());
+    script->setAsyncKind(funbox->asyncKind());
+
+    PositionalFormalParameterIter fi(script);
+    while (fi && !fi.closedOver())
+        fi++;
+    script->funHasAnyAliasedFormal_ = !!fi;
+
+    script->setHasInnerFunctions(funbox->hasInnerFunctions());
+}
+
+/* static */ void
+JSScript::initFromModuleContext(ExclusiveContext* cx, HandleScript script,
+                                frontend::ModuleSharedContext* modulesc)
+{
+    script->funHasExtensibleScope_ = false;
+    script->needsHomeObject_ = false;
+    script->isDerivedClassConstructor_ = false;
+    script->funLength_ = 0;
+
+    script->isGeneratorExp_ = false;
+    script->setGeneratorKind(NotGenerator);
+
+    // Since modules are only run once, mark the script so that initializers
+    // created within it may be given more precise types.
+    script->setTreatAsRunOnce();
+    MOZ_ASSERT(!script->hasRunOnce());
+}
+
+/* static */ bool
+JSScript::fullyInitFromEmitter(ExclusiveContext* cx, HandleScript script, BytecodeEmitter* bce)
+{
+    /* The counts of indexed things must be checked during code generation. */
+    MOZ_ASSERT(bce->atomIndices->count() <= INDEX_LIMIT);
+    MOZ_ASSERT(bce->objectList.length <= INDEX_LIMIT);
+
+    uint32_t mainLength = bce->offset();
+    uint32_t prologueLength = bce->prologueOffset();
+    uint32_t nsrcnotes;
+    if (!bce->finishTakingSrcNotes(&nsrcnotes))
+        return false;
+    uint32_t natoms = bce->atomIndices->count();
+    if (!partiallyInit(cx, script,
+                       bce->scopeList.length(), bce->constList.length(), bce->objectList.length,
+                       bce->tryNoteList.length(), bce->scopeNoteList.length(),
+                       bce->yieldOffsetList.length(), bce->typesetCount))
+    {
+        return false;
+    }
+
+    MOZ_ASSERT(script->mainOffset() == 0);
+    script->mainOffset_ = prologueLength;
+
+    script->lineno_ = bce->firstLine;
+
+    if (!script->createScriptData(cx, prologueLength + mainLength, nsrcnotes, natoms))
+        return false;
+
+    jsbytecode* code = script->code();
+    PodCopy<jsbytecode>(code, bce->prologue.code.begin(), prologueLength);
+    PodCopy<jsbytecode>(code + prologueLength, bce->main.code.begin(), mainLength);
+    bce->copySrcNotes((jssrcnote*)(code + script->length()), nsrcnotes);
+    InitAtomMap(*bce->atomIndices, script->atoms());
+
+    if (!script->shareScriptData(cx))
+        return false;
+
+    if (bce->constList.length() != 0)
+        bce->constList.finish(script->consts());
+    if (bce->objectList.length != 0)
+        bce->objectList.finish(script->objects());
+    if (bce->scopeList.length() != 0)
+        bce->scopeList.finish(script->scopes());
+    if (bce->tryNoteList.length() != 0)
+        bce->tryNoteList.finish(script->trynotes());
+    if (bce->scopeNoteList.length() != 0)
+        bce->scopeNoteList.finish(script->scopeNotes(), prologueLength);
+    script->strict_ = bce->sc->strict();
+    script->explicitUseStrict_ = bce->sc->hasExplicitUseStrict();
+    script->bindingsAccessedDynamically_ = bce->sc->bindingsAccessedDynamically();
+    script->hasSingletons_ = bce->hasSingletons;
+
+    uint64_t nslots = bce->maxFixedSlots + static_cast<uint64_t>(bce->maxStackDepth);
+    if (nslots > UINT32_MAX) {
+        bce->reportError(nullptr, JSMSG_NEED_DIET, js_script_str);
+        return false;
+    }
+
+    script->nfixed_ = bce->maxFixedSlots;
+    script->nslots_ = nslots;
+    script->bodyScopeIndex_ = bce->bodyScopeIndex;
+    script->hasNonSyntacticScope_ = bce->outermostScope()->hasOnChain(ScopeKind::NonSyntactic);
+
+    if (bce->sc->isFunctionBox())
+        initFromFunctionBox(cx, script, bce->sc->asFunctionBox());
+    else if (bce->sc->isModuleContext())
+        initFromModuleContext(cx, script, bce->sc->asModuleContext());
+
+    // Copy yield offsets last, as the generator kind is set in
+    // initFromFunctionBox.
+    if (bce->yieldOffsetList.length() != 0)
+        bce->yieldOffsetList.finish(script->yieldOffsets(), prologueLength);
+
+#ifdef DEBUG
+    script->assertValidJumpTargets();
+#endif
+
+    return true;
+}
+
+#ifdef DEBUG
+void
+JSScript::assertValidJumpTargets() const
+{
+    jsbytecode* end = codeEnd();
+    jsbytecode* mainEntry = main();
+    for (jsbytecode* pc = code(); pc != end; pc = GetNextPc(pc)) {
+        // Check jump instructions' target.
+        if (IsJumpOpcode(JSOp(*pc))) {
+            jsbytecode* target = pc + GET_JUMP_OFFSET(pc);
+            MOZ_ASSERT(mainEntry <= target && target < end);
+            MOZ_ASSERT(BytecodeIsJumpTarget(JSOp(*target)));
+
+            // Check fallthrough of conditional jump instructions.
+            if (BytecodeFallsThrough(JSOp(*pc))) {
+                jsbytecode* fallthrough = GetNextPc(pc);
+                MOZ_ASSERT(mainEntry <= fallthrough && fallthrough < end);
+                MOZ_ASSERT(BytecodeIsJumpTarget(JSOp(*fallthrough)));
+            }
+        }
+
+        // Check table switch case labels.
+        if (JSOp(*pc) == JSOP_TABLESWITCH) {
+            jsbytecode* pc2 = pc;
+            int32_t len = GET_JUMP_OFFSET(pc2);
+
+            // Default target.
+            MOZ_ASSERT(mainEntry <= pc + len && pc + len < end);
+            MOZ_ASSERT(BytecodeIsJumpTarget(JSOp(*(pc + len))));
+
+            pc2 += JUMP_OFFSET_LEN;
+            int32_t low = GET_JUMP_OFFSET(pc2);
+            pc2 += JUMP_OFFSET_LEN;
+            int32_t high = GET_JUMP_OFFSET(pc2);
+
+            for (int i = 0; i < high - low + 1; i++) {
+                pc2 += JUMP_OFFSET_LEN;
+                int32_t off = (int32_t) GET_JUMP_OFFSET(pc2);
+                // Case (i + low)
+                MOZ_ASSERT_IF(off, mainEntry <= pc + off && pc + off < end);
+                MOZ_ASSERT_IF(off, BytecodeIsJumpTarget(JSOp(*(pc + off))));
+            }
+        }
+    }
+
+    // Check catch/finally blocks as jump targets.
+    if (hasTrynotes()) {
+        JSTryNote* tn = trynotes()->vector;
+        JSTryNote* tnlimit = tn + trynotes()->length;
+        for (; tn < tnlimit; tn++) {
+            jsbytecode* tryStart = mainEntry + tn->start;
+            jsbytecode* tryPc = tryStart - 1;
+            if (JSOp(*tryPc) != JSOP_TRY)
+                continue;
+
+            jsbytecode* tryTarget = tryStart + tn->length;
+            MOZ_ASSERT(mainEntry <= tryTarget && tryTarget < end);
+            MOZ_ASSERT(BytecodeIsJumpTarget(JSOp(*tryTarget)));
+        }
+    }
+}
+#endif
+
+size_t
+JSScript::computedSizeOfData() const
+{
+    return dataSize();
+}
+
+size_t
+JSScript::sizeOfData(mozilla::MallocSizeOf mallocSizeOf) const
+{
+    return mallocSizeOf(data);
+}
+
+size_t
+JSScript::sizeOfTypeScript(mozilla::MallocSizeOf mallocSizeOf) const
+{
+    return types_->sizeOfIncludingThis(mallocSizeOf);
+}
+
+/*
+ * Nb: srcnotes are variable-length.  This function computes the number of
+ * srcnote *slots*, which may be greater than the number of srcnotes.
+ */
+uint32_t
+JSScript::numNotes()
+{
+    jssrcnote* sn;
+    jssrcnote* notes_ = notes();
+    for (sn = notes_; !SN_IS_TERMINATOR(sn); sn = SN_NEXT(sn))
+        continue;
+    return sn - notes_ + 1;    /* +1 for the terminator */
+}
+
+js::GlobalObject&
+JSScript::uninlinedGlobal() const
+{
+    return global();
+}
+
+void
+JSScript::finalize(FreeOp* fop)
+{
+    // NOTE: this JSScript may be partially initialized at this point.  E.g. we
+    // may have created it and partially initialized it with
+    // JSScript::Create(), but not yet finished initializing it with
+    // fullyInitFromEmitter() or fullyInitTrivial().
+
+    // Collect code coverage information for this script and all its inner
+    // scripts, and store the aggregated information on the compartment.
+    if (fop->runtime()->lcovOutput.isEnabled())
+        compartment()->lcovOutput.collectCodeCoverageInfo(compartment(), sourceObject(), this);
+
+    fop->runtime()->spsProfiler.onScriptFinalized(this);
+
+    if (types_)
+        types_->destroy();
+
+    jit::DestroyJitScripts(fop, this);
+
+    destroyScriptCounts(fop);
+    destroyDebugScript(fop);
+
+    if (data) {
+        JS_POISON(data, 0xdb, computedSizeOfData());
+        fop->free_(data);
+    }
+
+    if (scriptData_)
+        scriptData_->decRefCount();
+
+    fop->runtime()->contextFromMainThread()->caches.lazyScriptCache.remove(this);
+
+    // In most cases, our LazyScript's script pointer will reference this
+    // script, and thus be nulled out by normal weakref processing. However, if
+    // we unlazified the LazyScript during incremental sweeping, it will have a
+    // completely different JSScript.
+    MOZ_ASSERT_IF(lazyScript && !IsAboutToBeFinalizedUnbarriered(&lazyScript),
+                  !lazyScript->hasScript() || lazyScript->maybeScriptUnbarriered() != this);
+}
+
+static const uint32_t GSN_CACHE_THRESHOLD = 100;
+
+void
+GSNCache::purge()
+{
+    code = nullptr;
+    if (map.initialized())
+        map.finish();
+}
+
+jssrcnote*
+js::GetSrcNote(GSNCache& cache, JSScript* script, jsbytecode* pc)
+{
+    size_t target = pc - script->code();
+    if (target >= script->length())
+        return nullptr;
+
+    if (cache.code == script->code()) {
+        MOZ_ASSERT(cache.map.initialized());
+        GSNCache::Map::Ptr p = cache.map.lookup(pc);
+        return p ? p->value() : nullptr;
+    }
+
+    size_t offset = 0;
+    jssrcnote* result;
+    for (jssrcnote* sn = script->notes(); ; sn = SN_NEXT(sn)) {
+        if (SN_IS_TERMINATOR(sn)) {
+            result = nullptr;
+            break;
+        }
+        offset += SN_DELTA(sn);
+        if (offset == target && SN_IS_GETTABLE(sn)) {
+            result = sn;
+            break;
+        }
+    }
+
+    if (cache.code != script->code() && script->length() >= GSN_CACHE_THRESHOLD) {
+        unsigned nsrcnotes = 0;
+        for (jssrcnote* sn = script->notes(); !SN_IS_TERMINATOR(sn);
+             sn = SN_NEXT(sn))
+        {
+            if (SN_IS_GETTABLE(sn))
+                ++nsrcnotes;
+        }
+        if (cache.code) {
+            MOZ_ASSERT(cache.map.initialized());
+            cache.map.finish();
+            cache.code = nullptr;
+        }
+        if (cache.map.init(nsrcnotes)) {
+            pc = script->code();
+            for (jssrcnote* sn = script->notes(); !SN_IS_TERMINATOR(sn);
+                 sn = SN_NEXT(sn))
+            {
+                pc += SN_DELTA(sn);
+                if (SN_IS_GETTABLE(sn))
+                    cache.map.putNewInfallible(pc, sn);
+            }
+            cache.code = script->code();
+        }
+    }
+
+    return result;
+}
+
+jssrcnote*
+js::GetSrcNote(JSContext* cx, JSScript* script, jsbytecode* pc)
+{
+    return GetSrcNote(cx->caches.gsnCache, script, pc);
+}
+
+unsigned
+js::PCToLineNumber(unsigned startLine, jssrcnote* notes, jsbytecode* code, jsbytecode* pc,
+                   unsigned* columnp)
+{
+    unsigned lineno = startLine;
+    unsigned column = 0;
+
+    /*
+     * Walk through source notes accumulating their deltas, keeping track of
+     * line-number notes, until we pass the note for pc's offset within
+     * script->code.
+     */
+    ptrdiff_t offset = 0;
+    ptrdiff_t target = pc - code;
+    for (jssrcnote* sn = notes; !SN_IS_TERMINATOR(sn); sn = SN_NEXT(sn)) {
+        offset += SN_DELTA(sn);
+        if (offset > target)
+            break;
+
+        SrcNoteType type = (SrcNoteType) SN_TYPE(sn);
+        if (type == SRC_SETLINE) {
+            lineno = unsigned(GetSrcNoteOffset(sn, 0));
+            column = 0;
+        } else if (type == SRC_NEWLINE) {
+            lineno++;
+            column = 0;
+        } else if (type == SRC_COLSPAN) {
+            ptrdiff_t colspan = SN_OFFSET_TO_COLSPAN(GetSrcNoteOffset(sn, 0));
+            MOZ_ASSERT(ptrdiff_t(column) + colspan >= 0);
+            column += colspan;
+        }
+    }
+
+    if (columnp)
+        *columnp = column;
+
+    return lineno;
+}
+
+unsigned
+js::PCToLineNumber(JSScript* script, jsbytecode* pc, unsigned* columnp)
+{
+    /* Cope with InterpreterFrame.pc value prior to entering Interpret. */
+    if (!pc)
+        return 0;
+
+    return PCToLineNumber(script->lineno(), script->notes(), script->code(), pc, columnp);
+}
+
+jsbytecode*
+js::LineNumberToPC(JSScript* script, unsigned target)
+{
+    ptrdiff_t offset = 0;
+    ptrdiff_t best = -1;
+    unsigned lineno = script->lineno();
+    unsigned bestdiff = SN_MAX_OFFSET;
+    for (jssrcnote* sn = script->notes(); !SN_IS_TERMINATOR(sn); sn = SN_NEXT(sn)) {
+        /*
+         * Exact-match only if offset is not in the prologue; otherwise use
+         * nearest greater-or-equal line number match.
+         */
+        if (lineno == target && offset >= ptrdiff_t(script->mainOffset()))
+            goto out;
+        if (lineno >= target) {
+            unsigned diff = lineno - target;
+            if (diff < bestdiff) {
+                bestdiff = diff;
+                best = offset;
+            }
+        }
+        offset += SN_DELTA(sn);
+        SrcNoteType type = (SrcNoteType) SN_TYPE(sn);
+        if (type == SRC_SETLINE) {
+            lineno = unsigned(GetSrcNoteOffset(sn, 0));
+        } else if (type == SRC_NEWLINE) {
+            lineno++;
+        }
+    }
+    if (best >= 0)
+        offset = best;
+out:
+    return script->offsetToPC(offset);
+}
+
+JS_FRIEND_API(unsigned)
+js::GetScriptLineExtent(JSScript* script)
+{
+    unsigned lineno = script->lineno();
+    unsigned maxLineNo = lineno;
+    for (jssrcnote* sn = script->notes(); !SN_IS_TERMINATOR(sn); sn = SN_NEXT(sn)) {
+        SrcNoteType type = (SrcNoteType) SN_TYPE(sn);
+        if (type == SRC_SETLINE)
+            lineno = unsigned(GetSrcNoteOffset(sn, 0));
+        else if (type == SRC_NEWLINE)
+            lineno++;
+
+        if (maxLineNo < lineno)
+            maxLineNo = lineno;
+    }
+
+    return 1 + maxLineNo - script->lineno();
+}
+
+void
+js::DescribeScriptedCallerForCompilation(JSContext* cx, MutableHandleScript maybeScript,
+                                         const char** file, unsigned* linenop,
+                                         uint32_t* pcOffset, bool* mutedErrors,
+                                         LineOption opt)
+{
+    if (opt == CALLED_FROM_JSOP_EVAL) {
+        jsbytecode* pc = nullptr;
+        maybeScript.set(cx->currentScript(&pc));
+        static_assert(JSOP_SPREADEVAL_LENGTH == JSOP_STRICTSPREADEVAL_LENGTH,
+                    "next op after a spread must be at consistent offset");
+        static_assert(JSOP_EVAL_LENGTH == JSOP_STRICTEVAL_LENGTH,
+                    "next op after a direct eval must be at consistent offset");
+        MOZ_ASSERT(JSOp(*pc) == JSOP_EVAL || JSOp(*pc) == JSOP_STRICTEVAL ||
+                   JSOp(*pc) == JSOP_SPREADEVAL || JSOp(*pc) == JSOP_STRICTSPREADEVAL);
+
+        bool isSpread = JSOp(*pc) == JSOP_SPREADEVAL || JSOp(*pc) == JSOP_STRICTSPREADEVAL;
+        jsbytecode* nextpc = pc + (isSpread ? JSOP_SPREADEVAL_LENGTH : JSOP_EVAL_LENGTH);
+        MOZ_ASSERT(*nextpc == JSOP_LINENO);
+
+        *file = maybeScript->filename();
+        *linenop = GET_UINT32(nextpc);
+        *pcOffset = pc - maybeScript->code();
+        *mutedErrors = maybeScript->mutedErrors();
+        return;
+    }
+
+    NonBuiltinFrameIter iter(cx, cx->compartment()->principals());
+
+    if (iter.done()) {
+        maybeScript.set(nullptr);
+        *file = nullptr;
+        *linenop = 0;
+        *pcOffset = 0;
+        *mutedErrors = false;
+        return;
+    }
+
+    *file = iter.filename();
+    *linenop = iter.computeLine();
+    *mutedErrors = iter.mutedErrors();
+
+    // These values are only used for introducer fields which are debugging
+    // information and can be safely left null for wasm frames.
+    if (iter.hasScript()) {
+        maybeScript.set(iter.script());
+        *pcOffset = iter.pc() - maybeScript->code();
+    } else {
+        maybeScript.set(nullptr);
+        *pcOffset = 0;
+    }
+}
+
+template <class T>
+static inline T*
+Rebase(JSScript* dst, JSScript* src, T* srcp)
+{
+    size_t off = reinterpret_cast<uint8_t*>(srcp) - src->data;
+    return reinterpret_cast<T*>(dst->data + off);
+}
+
+static JSObject*
+CloneInnerInterpretedFunction(JSContext* cx, HandleScope enclosingScope, HandleFunction srcFun)
+{
+    /* NB: Keep this in sync with XDRInterpretedFunction. */
+    RootedObject cloneProto(cx);
+    if (srcFun->isStarGenerator()) {
+        cloneProto = GlobalObject::getOrCreateStarGeneratorFunctionPrototype(cx, cx->global());
+        if (!cloneProto)
+            return nullptr;
+    }
+
+    gc::AllocKind allocKind = srcFun->getAllocKind();
+    uint16_t flags = srcFun->flags();
+    if (srcFun->isSelfHostedBuiltin()) {
+        // Functions in the self-hosting compartment are only extended in
+        // debug mode. For top-level functions, FUNCTION_EXTENDED gets used by
+        // the cloning algorithm. Do the same for inner functions here.
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        flags |= JSFunction::Flags::EXTENDED;
+    }
+    RootedAtom atom(cx, srcFun->displayAtom());
+    RootedFunction clone(cx, NewFunctionWithProto(cx, nullptr, srcFun->nargs(),
+                                                  JSFunction::Flags(flags), nullptr, atom,
+                                                  cloneProto, allocKind, TenuredObject));
+    if (!clone)
+        return nullptr;
+
+    JSScript::AutoDelazify srcScript(cx, srcFun);
+    if (!srcScript)
+        return nullptr;
+    JSScript* cloneScript = CloneScriptIntoFunction(cx, enclosingScope, clone, srcScript);
+    if (!cloneScript)
+        return nullptr;
+
+    if (!JSFunction::setTypeForScriptedFunction(cx, clone))
+        return nullptr;
+
+    return clone;
+}
+
+bool
+js::detail::CopyScript(JSContext* cx, HandleScript src, HandleScript dst,
+                       MutableHandle<GCVector<Scope*>> scopes)
+{
+    if (src->treatAsRunOnce() && !src->functionNonDelazifying()) {
+        JS_ReportErrorASCII(cx, "No cloning toplevel run-once scripts");
+        return false;
+    }
+
+    /* NB: Keep this in sync with XDRScript. */
+
+    /* Some embeddings are not careful to use ExposeObjectToActiveJS as needed. */
+    MOZ_ASSERT(!src->sourceObject()->asTenured().isMarked(gc::GRAY));
+
+    uint32_t nconsts   = src->hasConsts()   ? src->consts()->length   : 0;
+    uint32_t nobjects  = src->hasObjects()  ? src->objects()->length  : 0;
+    uint32_t nscopes   = src->scopes()->length;
+    uint32_t ntrynotes = src->hasTrynotes() ? src->trynotes()->length : 0;
+    uint32_t nscopenotes = src->hasScopeNotes() ? src->scopeNotes()->length : 0;
+    uint32_t nyieldoffsets = src->hasYieldOffsets() ? src->yieldOffsets().length() : 0;
+
+    /* Script data */
+
+    size_t size = src->dataSize();
+    ScopedJSFreePtr<uint8_t> data(AllocScriptData(cx->zone(), size));
+    if (size && !data) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+
+    /* Scopes */
+
+    // The passed in scopes vector contains body scopes that needed to be
+    // cloned especially, depending on whether the script is a function or
+    // global scope. Starting at scopes.length() means we only deal with
+    // intra-body scopes.
+    {
+        MOZ_ASSERT(nscopes != 0);
+        MOZ_ASSERT(src->bodyScopeIndex() + 1 == scopes.length());
+        GCPtrScope* vector = src->scopes()->vector;
+        RootedScope original(cx);
+        RootedScope clone(cx);
+        for (uint32_t i = scopes.length(); i < nscopes; i++) {
+            original = vector[i];
+            clone = Scope::clone(cx, original, scopes[FindScopeIndex(src, *original->enclosing())]);
+            if (!clone || !scopes.append(clone))
+                return false;
+        }
+    }
+
+    /* Objects */
+
+    AutoObjectVector objects(cx);
+    if (nobjects != 0) {
+        GCPtrObject* vector = src->objects()->vector;
+        RootedObject obj(cx);
+        RootedObject clone(cx);
+        for (unsigned i = 0; i < nobjects; i++) {
+            obj = vector[i];
+            clone = nullptr;
+            if (obj->is<RegExpObject>()) {
+                clone = CloneScriptRegExpObject(cx, obj->as<RegExpObject>());
+            } else if (obj->is<JSFunction>()) {
+                RootedFunction innerFun(cx, &obj->as<JSFunction>());
+                if (innerFun->isNative()) {
+                    if (cx->compartment() != innerFun->compartment()) {
+                        MOZ_ASSERT(innerFun->isAsmJSNative());
+                        JS_ReportErrorASCII(cx, "AsmJS modules do not yet support cloning.");
+                        return false;
+                    }
+                    clone = innerFun;
+                } else {
+                    if (innerFun->isInterpretedLazy()) {
+                        AutoCompartment ac(cx, innerFun);
+                        if (!innerFun->getOrCreateScript(cx))
+                            return false;
+                    }
+
+                    Scope* enclosing = innerFun->nonLazyScript()->enclosingScope();
+                    RootedScope enclosingClone(cx, scopes[FindScopeIndex(src, *enclosing)]);
+                    clone = CloneInnerInterpretedFunction(cx, enclosingClone, innerFun);
+                }
+            } else {
+                clone = DeepCloneObjectLiteral(cx, obj, TenuredObject);
+            }
+
+            if (!clone || !objects.append(clone))
+                return false;
+        }
+    }
+
+    /* This assignment must occur before all the Rebase calls. */
+    dst->data = data.forget();
+    dst->dataSize_ = size;
+    MOZ_ASSERT(bool(dst->data) == bool(src->data));
+    if (dst->data)
+        memcpy(dst->data, src->data, size);
+
+    /* Script filenames, bytecodes and atoms are runtime-wide. */
+    dst->setScriptData(src->scriptData());
+
+    dst->lineno_ = src->lineno();
+    dst->mainOffset_ = src->mainOffset();
+    dst->nfixed_ = src->nfixed();
+    dst->nslots_ = src->nslots();
+    dst->bodyScopeIndex_ = src->bodyScopeIndex_;
+    dst->funLength_ = src->funLength();
+    dst->nTypeSets_ = src->nTypeSets();
+    if (src->argumentsHasVarBinding()) {
+        dst->setArgumentsHasVarBinding();
+        if (src->analyzedArgsUsage())
+            dst->setNeedsArgsObj(src->needsArgsObj());
+    }
+    dst->hasMappedArgsObj_ = src->hasMappedArgsObj();
+    dst->functionHasThisBinding_ = src->functionHasThisBinding();
+    dst->functionHasExtraBodyVarScope_ = src->functionHasExtraBodyVarScope();
+    dst->cloneHasArray(src);
+    dst->strict_ = src->strict();
+    dst->explicitUseStrict_ = src->explicitUseStrict();
+    dst->hasNonSyntacticScope_ = scopes[0]->hasOnChain(ScopeKind::NonSyntactic);
+    dst->bindingsAccessedDynamically_ = src->bindingsAccessedDynamically();
+    dst->funHasExtensibleScope_ = src->funHasExtensibleScope();
+    dst->funHasAnyAliasedFormal_ = src->funHasAnyAliasedFormal();
+    dst->hasSingletons_ = src->hasSingletons();
+    dst->treatAsRunOnce_ = src->treatAsRunOnce();
+    dst->hasInnerFunctions_ = src->hasInnerFunctions();
+    dst->isGeneratorExp_ = src->isGeneratorExp();
+    dst->setGeneratorKind(src->generatorKind());
+    dst->isDerivedClassConstructor_ = src->isDerivedClassConstructor();
+    dst->needsHomeObject_ = src->needsHomeObject();
+    dst->isDefaultClassConstructor_ = src->isDefaultClassConstructor();
+    dst->isAsync_ = src->asyncKind() == AsyncFunction;
+
+    if (nconsts != 0) {
+        GCPtrValue* vector = Rebase<GCPtrValue>(dst, src, src->consts()->vector);
+        dst->consts()->vector = vector;
+        for (unsigned i = 0; i < nconsts; ++i)
+            MOZ_ASSERT_IF(vector[i].isMarkable(), vector[i].toString()->isAtom());
+    }
+    if (nobjects != 0) {
+        GCPtrObject* vector = Rebase<GCPtrObject>(dst, src, src->objects()->vector);
+        dst->objects()->vector = vector;
+        for (unsigned i = 0; i < nobjects; ++i)
+            vector[i].init(&objects[i]->as<NativeObject>());
+    }
+    {
+        GCPtrScope* vector = Rebase<GCPtrScope>(dst, src, src->scopes()->vector);
+        dst->scopes()->vector = vector;
+        for (uint32_t i = 0; i < nscopes; ++i)
+            vector[i].init(scopes[i]);
+    }
+    if (ntrynotes != 0)
+        dst->trynotes()->vector = Rebase<JSTryNote>(dst, src, src->trynotes()->vector);
+    if (nscopenotes != 0)
+        dst->scopeNotes()->vector = Rebase<ScopeNote>(dst, src, src->scopeNotes()->vector);
+    if (nyieldoffsets != 0)
+        dst->yieldOffsets().vector_ = Rebase<uint32_t>(dst, src, src->yieldOffsets().vector_);
+
+    /*
+     * Function delazification assumes that their script does not have a
+     * non-syntactic global scope.  We ensure that as follows:
+     *
+     * 1) Initial parsing only creates lazy functions if
+     *    !hasNonSyntacticScope.
+     * 2) Cloning a lazy function into a non-global scope will always require
+     *    that its script be cloned.  See comments in
+     *    CloneFunctionObjectUseSameScript.
+     * 3) Cloning a script never sets a lazyScript on the clone, so the function
+     *    cannot be relazified.
+     *
+     * If you decide that lazy functions should be supported with a
+     * non-syntactic global scope, make sure delazification can deal.
+     */
+    MOZ_ASSERT_IF(dst->hasNonSyntacticScope(), !dst->maybeLazyScript());
+    MOZ_ASSERT_IF(dst->hasNonSyntacticScope(), !dst->isRelazifiable());
+    return true;
+}
+
+static JSScript*
+CreateEmptyScriptForClone(JSContext* cx, HandleScript src)
+{
+    /*
+     * Wrap the script source object as needed. Self-hosted scripts may be
+     * in another runtime, so lazily create a new script source object to
+     * use for them.
+     */
+    RootedObject sourceObject(cx);
+    if (cx->runtime()->isSelfHostingCompartment(src->compartment())) {
+        if (!cx->compartment()->selfHostingScriptSource) {
+            CompileOptions options(cx);
+            FillSelfHostingCompileOptions(options);
+
+            ScriptSourceObject* obj = frontend::CreateScriptSourceObject(cx, options);
+            if (!obj)
+                return nullptr;
+            cx->compartment()->selfHostingScriptSource.set(obj);
+        }
+        sourceObject = cx->compartment()->selfHostingScriptSource;
+    } else {
+        sourceObject = src->sourceObject();
+        if (!cx->compartment()->wrap(cx, &sourceObject))
+            return nullptr;
+    }
+
+    CompileOptions options(cx);
+    options.setMutedErrors(src->mutedErrors())
+           .setSelfHostingMode(src->selfHosted())
+           .setNoScriptRval(src->noScriptRval())
+           .setVersion(src->getVersion());
+
+    return JSScript::Create(cx, options, sourceObject, src->sourceStart(), src->sourceEnd());
+}
+
+JSScript*
+js::CloneGlobalScript(JSContext* cx, ScopeKind scopeKind, HandleScript src)
+{
+    MOZ_ASSERT(scopeKind == ScopeKind::Global || scopeKind == ScopeKind::NonSyntactic);
+
+    RootedScript dst(cx, CreateEmptyScriptForClone(cx, src));
+    if (!dst)
+        return nullptr;
+
+    MOZ_ASSERT(src->bodyScopeIndex() == 0);
+    Rooted<GCVector<Scope*>> scopes(cx, GCVector<Scope*>(cx));
+    Rooted<GlobalScope*> original(cx, &src->bodyScope()->as<GlobalScope>());
+    GlobalScope* clone = GlobalScope::clone(cx, original, scopeKind);
+    if (!clone || !scopes.append(clone))
+        return nullptr;
+
+    if (!detail::CopyScript(cx, src, dst, &scopes))
+        return nullptr;
+
+    return dst;
+}
+
+JSScript*
+js::CloneScriptIntoFunction(JSContext* cx, HandleScope enclosingScope, HandleFunction fun,
+                            HandleScript src)
+{
+    MOZ_ASSERT(fun->isInterpreted());
+    MOZ_ASSERT(!fun->hasScript() || fun->hasUncompiledScript());
+
+    RootedScript dst(cx, CreateEmptyScriptForClone(cx, src));
+    if (!dst)
+        return nullptr;
+
+    // Clone the non-intra-body scopes.
+    Rooted<GCVector<Scope*>> scopes(cx, GCVector<Scope*>(cx));
+    RootedScope original(cx);
+    RootedScope enclosingClone(cx);
+    for (uint32_t i = 0; i <= src->bodyScopeIndex(); i++) {
+        original = src->getScope(i);
+
+        if (i == 0) {
+            enclosingClone = enclosingScope;
+        } else {
+            MOZ_ASSERT(src->getScope(i - 1) == original->enclosing());
+            enclosingClone = scopes[i - 1];
+        }
+
+        Scope* clone;
+        if (original->is<FunctionScope>())
+            clone = FunctionScope::clone(cx, original.as<FunctionScope>(), fun, enclosingClone);
+        else
+            clone = Scope::clone(cx, original, enclosingClone);
+
+        if (!clone || !scopes.append(clone))
+            return nullptr;
+    }
+
+    // Save flags in case we need to undo the early mutations.
+    const int preservedFlags = fun->flags();
+    if (!detail::CopyScript(cx, src, dst, &scopes)) {
+        fun->setFlags(preservedFlags);
+        return nullptr;
+    }
+
+    // Finally set the script after all the fallible operations.
+    if (fun->isInterpretedLazy())
+        fun->setUnlazifiedScript(dst);
+    else
+        fun->initScript(dst);
+
+    return dst;
+}
+
+DebugScript*
+JSScript::debugScript()
+{
+    MOZ_ASSERT(hasDebugScript_);
+    DebugScriptMap* map = compartment()->debugScriptMap;
+    MOZ_ASSERT(map);
+    DebugScriptMap::Ptr p = map->lookup(this);
+    MOZ_ASSERT(p);
+    return p->value();
+}
+
+DebugScript*
+JSScript::releaseDebugScript()
+{
+    MOZ_ASSERT(hasDebugScript_);
+    DebugScriptMap* map = compartment()->debugScriptMap;
+    MOZ_ASSERT(map);
+    DebugScriptMap::Ptr p = map->lookup(this);
+    MOZ_ASSERT(p);
+    DebugScript* debug = p->value();
+    map->remove(p);
+    hasDebugScript_ = false;
+    return debug;
+}
+
+void
+JSScript::destroyDebugScript(FreeOp* fop)
+{
+    if (hasDebugScript_) {
+#ifdef DEBUG
+        for (jsbytecode* pc = code(); pc < codeEnd(); pc++) {
+            if (BreakpointSite* site = getBreakpointSite(pc)) {
+                /* Breakpoints are swept before finalization. */
+                MOZ_ASSERT(site->firstBreakpoint() == nullptr);
+                MOZ_ASSERT(getBreakpointSite(pc) == nullptr);
+            }
+        }
+#endif
+        fop->free_(releaseDebugScript());
+    }
+}
+
+bool
+JSScript::ensureHasDebugScript(JSContext* cx)
+{
+    if (hasDebugScript_)
+        return true;
+
+    size_t nbytes = offsetof(DebugScript, breakpoints) + length() * sizeof(BreakpointSite*);
+    DebugScript* debug = (DebugScript*) zone()->pod_calloc<uint8_t>(nbytes);
+    if (!debug)
+        return false;
+
+    /* Create compartment's debugScriptMap if necessary. */
+    DebugScriptMap* map = compartment()->debugScriptMap;
+    if (!map) {
+        map = cx->new_<DebugScriptMap>();
+        if (!map || !map->init()) {
+            js_free(debug);
+            js_delete(map);
+            return false;
+        }
+        compartment()->debugScriptMap = map;
+    }
+
+    if (!map->putNew(this, debug)) {
+        js_free(debug);
+        return false;
+    }
+    hasDebugScript_ = true; // safe to set this;  we can't fail after this point
+
+    /*
+     * Ensure that any Interpret() instances running on this script have
+     * interrupts enabled. The interrupts must stay enabled until the
+     * debug state is destroyed.
+     */
+    for (ActivationIterator iter(cx->runtime()); !iter.done(); ++iter) {
+        if (iter->isInterpreter())
+            iter->asInterpreter()->enableInterruptsIfRunning(this);
+    }
+
+    return true;
+}
+
+void
+JSScript::setNewStepMode(FreeOp* fop, uint32_t newValue)
+{
+    DebugScript* debug = debugScript();
+    uint32_t prior = debug->stepMode;
+    debug->stepMode = newValue;
+
+    if (!prior != !newValue) {
+        if (hasBaselineScript())
+            baseline->toggleDebugTraps(this, nullptr);
+
+        if (!stepModeEnabled() && !debug->numSites)
+            fop->free_(releaseDebugScript());
+    }
+}
+
+bool
+JSScript::incrementStepModeCount(JSContext* cx)
+{
+    assertSameCompartment(cx, this);
+    MOZ_ASSERT(cx->compartment()->isDebuggee());
+
+    if (!ensureHasDebugScript(cx))
+        return false;
+
+    DebugScript* debug = debugScript();
+    uint32_t count = debug->stepMode;
+    setNewStepMode(cx->runtime()->defaultFreeOp(), count + 1);
+    return true;
+}
+
+void
+JSScript::decrementStepModeCount(FreeOp* fop)
+{
+    DebugScript* debug = debugScript();
+    uint32_t count = debug->stepMode;
+    MOZ_ASSERT(count > 0);
+    setNewStepMode(fop, count - 1);
+}
+
+BreakpointSite*
+JSScript::getOrCreateBreakpointSite(JSContext* cx, jsbytecode* pc)
+{
+    if (!ensureHasDebugScript(cx))
+        return nullptr;
+
+    DebugScript* debug = debugScript();
+    BreakpointSite*& site = debug->breakpoints[pcToOffset(pc)];
+
+    if (!site) {
+        site = cx->runtime()->new_<BreakpointSite>(this, pc);
+        if (!site) {
+            ReportOutOfMemory(cx);
+            return nullptr;
+        }
+        debug->numSites++;
+    }
+
+    return site;
+}
+
+void
+JSScript::destroyBreakpointSite(FreeOp* fop, jsbytecode* pc)
+{
+    DebugScript* debug = debugScript();
+    BreakpointSite*& site = debug->breakpoints[pcToOffset(pc)];
+    MOZ_ASSERT(site);
+
+    fop->delete_(site);
+    site = nullptr;
+
+    if (--debug->numSites == 0 && !stepModeEnabled())
+        fop->free_(releaseDebugScript());
+}
+
+void
+JSScript::clearBreakpointsIn(FreeOp* fop, js::Debugger* dbg, JSObject* handler)
+{
+    if (!hasAnyBreakpointsOrStepMode())
+        return;
+
+    for (jsbytecode* pc = code(); pc < codeEnd(); pc++) {
+        BreakpointSite* site = getBreakpointSite(pc);
+        if (site) {
+            Breakpoint* nextbp;
+            for (Breakpoint* bp = site->firstBreakpoint(); bp; bp = nextbp) {
+                nextbp = bp->nextInSite();
+                if ((!dbg || bp->debugger == dbg) && (!handler || bp->getHandler() == handler))
+                    bp->destroy(fop);
+            }
+        }
+    }
+}
+
+bool
+JSScript::hasBreakpointsAt(jsbytecode* pc)
+{
+    BreakpointSite* site = getBreakpointSite(pc);
+    if (!site)
+        return false;
+
+    return site->enabledCount > 0;
+}
+
+void
+SharedScriptData::traceChildren(JSTracer* trc)
+{
+    MOZ_ASSERT(refCount() != 0);
+    for (uint32_t i = 0; i < natoms(); ++i)
+        TraceNullableEdge(trc, &atoms()[i], "atom");
+}
+
+void
+JSScript::traceChildren(JSTracer* trc)
+{
+    // NOTE: this JSScript may be partially initialized at this point.  E.g. we
+    // may have created it and partially initialized it with
+    // JSScript::Create(), but not yet finished initializing it with
+    // fullyInitFromEmitter() or fullyInitTrivial().
+
+    MOZ_ASSERT_IF(trc->isMarkingTracer() &&
+                  static_cast<GCMarker*>(trc)->shouldCheckCompartments(),
+                  zone()->isCollecting());
+
+    if (scriptData())
+        scriptData()->traceChildren(trc);
+
+    if (ScopeArray* scopearray = scopes())
+        TraceRange(trc, scopearray->length, scopearray->vector, "scopes");
+
+    if (hasConsts()) {
+        ConstArray* constarray = consts();
+        TraceRange(trc, constarray->length, constarray->vector, "consts");
+    }
+
+    if (hasObjects()) {
+        ObjectArray* objarray = objects();
+        TraceRange(trc, objarray->length, objarray->vector, "objects");
+    }
+
+    MOZ_ASSERT_IF(sourceObject(), MaybeForwarded(sourceObject())->compartment() == compartment());
+    TraceNullableEdge(trc, &sourceObject_, "sourceObject");
+
+    if (maybeLazyScript())
+        TraceManuallyBarrieredEdge(trc, &lazyScript, "lazyScript");
+
+    if (trc->isMarkingTracer())
+        compartment()->mark();
+
+    jit::TraceJitScripts(trc, this);
+}
+
+void
+LazyScript::finalize(FreeOp* fop)
+{
+    fop->free_(table_);
+}
+
+size_t
+JSScript::calculateLiveFixed(jsbytecode* pc)
+{
+    size_t nlivefixed = numAlwaysLiveFixedSlots();
+
+    if (nfixed() != nlivefixed) {
+        Scope* scope = lookupScope(pc);
+        if (scope)
+            scope = MaybeForwarded(scope);
+
+        // Find the nearest LexicalScope in the same script.
+        while (scope && scope->is<WithScope>()) {
+            scope = scope->enclosing();
+            if (scope)
+                scope = MaybeForwarded(scope);
+        }
+
+        if (scope) {
+            if (scope->is<LexicalScope>())
+                nlivefixed = scope->as<LexicalScope>().nextFrameSlot();
+            else if (scope->is<VarScope>())
+                nlivefixed = scope->as<VarScope>().nextFrameSlot();
+        }
+    }
+
+    MOZ_ASSERT(nlivefixed <= nfixed());
+    MOZ_ASSERT(nlivefixed >= numAlwaysLiveFixedSlots());
+
+    return nlivefixed;
+}
+
+Scope*
+JSScript::lookupScope(jsbytecode* pc)
+{
+    MOZ_ASSERT(containsPC(pc));
+
+    if (!hasScopeNotes())
+        return nullptr;
+
+    size_t offset = pc - code();
+
+    ScopeNoteArray* notes = scopeNotes();
+    Scope* scope = nullptr;
+
+    // Find the innermost block chain using a binary search.
+    size_t bottom = 0;
+    size_t top = notes->length;
+
+    while (bottom < top) {
+        size_t mid = bottom + (top - bottom) / 2;
+        const ScopeNote* note = &notes->vector[mid];
+        if (note->start <= offset) {
+            // Block scopes are ordered in the list by their starting offset, and since
+            // blocks form a tree ones earlier in the list may cover the pc even if
+            // later blocks end before the pc. This only happens when the earlier block
+            // is a parent of the later block, so we need to check parents of |mid| in
+            // the searched range for coverage.
+            size_t check = mid;
+            while (check >= bottom) {
+                const ScopeNote* checkNote = &notes->vector[check];
+                MOZ_ASSERT(checkNote->start <= offset);
+                if (offset < checkNote->start + checkNote->length) {
+                    // We found a matching block chain but there may be inner ones
+                    // at a higher block chain index than mid. Continue the binary search.
+                    if (checkNote->index == ScopeNote::NoScopeIndex)
+                        scope = nullptr;
+                    else
+                        scope = getScope(checkNote->index);
+                    break;
+                }
+                if (checkNote->parent == UINT32_MAX)
+                    break;
+                check = checkNote->parent;
+            }
+            bottom = mid + 1;
+        } else {
+            top = mid;
+        }
+    }
+
+    return scope;
+}
+
+Scope*
+JSScript::innermostScope(jsbytecode* pc)
+{
+    if (Scope* scope = lookupScope(pc))
+        return scope;
+    return bodyScope();
+}
+
+void
+JSScript::setArgumentsHasVarBinding()
+{
+    argsHasVarBinding_ = true;
+    needsArgsAnalysis_ = true;
+}
+
+void
+JSScript::setNeedsArgsObj(bool needsArgsObj)
+{
+    MOZ_ASSERT_IF(needsArgsObj, argumentsHasVarBinding());
+    needsArgsAnalysis_ = false;
+    needsArgsObj_ = needsArgsObj;
+}
+
+void
+js::SetFrameArgumentsObject(JSContext* cx, AbstractFramePtr frame,
+                            HandleScript script, JSObject* argsobj)
+{
+    /*
+     * Replace any optimized arguments in the frame with an explicit arguments
+     * object. Note that 'arguments' may have already been overwritten.
+     */
+
+    Rooted<BindingIter> bi(cx, BindingIter(script));
+    while (bi && bi.name() != cx->names().arguments)
+        bi++;
+    if (!bi)
+        return;
+
+    if (bi.location().kind() == BindingLocation::Kind::Environment) {
+        /*
+         * Scan the script to find the slot in the call object that 'arguments'
+         * is assigned to.
+         */
+        jsbytecode* pc = script->code();
+        while (*pc != JSOP_ARGUMENTS)
+            pc += GetBytecodeLength(pc);
+        pc += JSOP_ARGUMENTS_LENGTH;
+        MOZ_ASSERT(*pc == JSOP_SETALIASEDVAR);
+
+        // Note that here and below, it is insufficient to only check for
+        // JS_OPTIMIZED_ARGUMENTS, as Ion could have optimized out the
+        // arguments slot.
+        EnvironmentObject& env = frame.callObj().as<EnvironmentObject>();
+        if (IsOptimizedPlaceholderMagicValue(env.aliasedBinding(bi)))
+            env.setAliasedBinding(cx, bi, ObjectValue(*argsobj));
+    } else {
+        MOZ_ASSERT(bi.location().kind() == BindingLocation::Kind::Frame);
+        uint32_t frameSlot = bi.location().slot();
+        if (IsOptimizedPlaceholderMagicValue(frame.unaliasedLocal(frameSlot)))
+            frame.unaliasedLocal(frameSlot) = ObjectValue(*argsobj);
+    }
+}
+
+/* static */ bool
+JSScript::argumentsOptimizationFailed(JSContext* cx, HandleScript script)
+{
+    MOZ_ASSERT(script->functionNonDelazifying());
+    MOZ_ASSERT(script->analyzedArgsUsage());
+    MOZ_ASSERT(script->argumentsHasVarBinding());
+
+    /*
+     * It is possible that the arguments optimization has already failed,
+     * everything has been fixed up, but there was an outstanding magic value
+     * on the stack that has just now flowed into an apply. In this case, there
+     * is nothing to do; GuardFunApplySpeculation will patch in the real
+     * argsobj.
+     */
+    if (script->needsArgsObj())
+        return true;
+
+    MOZ_ASSERT(!script->isGenerator());
+
+    script->needsArgsObj_ = true;
+
+    /*
+     * Since we can't invalidate baseline scripts, set a flag that's checked from
+     * JIT code to indicate the arguments optimization failed and JSOP_ARGUMENTS
+     * should create an arguments object next time.
+     */
+    if (script->hasBaselineScript())
+        script->baselineScript()->setNeedsArgsObj();
+
+    /*
+     * By design, the arguments optimization is only made when there are no
+     * outstanding cases of MagicValue(JS_OPTIMIZED_ARGUMENTS) at any points
+     * where the optimization could fail, other than an active invocation of
+     * 'f.apply(x, arguments)'. Thus, there are no outstanding values of
+     * MagicValue(JS_OPTIMIZED_ARGUMENTS) on the stack. However, there are
+     * three things that need fixup:
+     *  - there may be any number of activations of this script that don't have
+     *    an argsObj that now need one.
+     *  - jit code compiled (and possible active on the stack) with the static
+     *    assumption of !script->needsArgsObj();
+     *  - type inference data for the script assuming script->needsArgsObj
+     */
+    for (AllScriptFramesIter i(cx); !i.done(); ++i) {
+        /*
+         * We cannot reliably create an arguments object for Ion activations of
+         * this script.  To maintain the invariant that "script->needsArgsObj
+         * implies fp->hasArgsObj", the Ion bail mechanism will create an
+         * arguments object right after restoring the BaselineFrame and before
+         * entering Baseline code (in jit::FinishBailoutToBaseline).
+         */
+        if (i.isIon())
+            continue;
+        AbstractFramePtr frame = i.abstractFramePtr();
+        if (frame.isFunctionFrame() && frame.script() == script) {
+            /* We crash on OOM since cleaning up here would be complicated. */
+            AutoEnterOOMUnsafeRegion oomUnsafe;
+            ArgumentsObject* argsobj = ArgumentsObject::createExpected(cx, frame);
+            if (!argsobj)
+                oomUnsafe.crash("JSScript::argumentsOptimizationFailed");
+            SetFrameArgumentsObject(cx, frame, script, argsobj);
+        }
+    }
+
+    return true;
+}
+
+bool
+JSScript::formalIsAliased(unsigned argSlot)
+{
+    if (functionHasParameterExprs())
+        return false;
+
+    for (PositionalFormalParameterIter fi(this); fi; fi++) {
+        if (fi.argumentSlot() == argSlot)
+            return fi.closedOver();
+    }
+    MOZ_CRASH("Argument slot not found");
+}
+
+bool
+JSScript::formalLivesInArgumentsObject(unsigned argSlot)
+{
+    return argsObjAliasesFormals() && !formalIsAliased(argSlot);
+}
+
+LazyScript::LazyScript(JSFunction* fun, void* table, uint64_t packedFields,
+                       uint32_t begin, uint32_t end, uint32_t lineno, uint32_t column)
+  : script_(nullptr),
+    function_(fun),
+    enclosingScope_(nullptr),
+    sourceObject_(nullptr),
+    table_(table),
+    packedFields_(packedFields),
+    begin_(begin),
+    end_(end),
+    lineno_(lineno),
+    column_(column)
+{
+    MOZ_ASSERT(begin <= end);
+}
+
+void
+LazyScript::initScript(JSScript* script)
+{
+    MOZ_ASSERT(script);
+    MOZ_ASSERT(!script_.unbarrieredGet());
+    script_.set(script);
+}
+
+void
+LazyScript::resetScript()
+{
+    MOZ_ASSERT(script_.unbarrieredGet());
+    script_.set(nullptr);
+}
+
+void
+LazyScript::setEnclosingScopeAndSource(Scope* enclosingScope, ScriptSourceObject* sourceObject)
+{
+    MOZ_ASSERT(function_->compartment() == sourceObject->compartment());
+    // This method may be called to update the enclosing scope. See comment
+    // above the callsite in BytecodeEmitter::emitFunction.
+    MOZ_ASSERT_IF(sourceObject_, sourceObject_ == sourceObject && enclosingScope_);
+    MOZ_ASSERT_IF(!sourceObject_, !enclosingScope_);
+
+    enclosingScope_ = enclosingScope;
+    sourceObject_ = sourceObject;
+}
+
+ScriptSourceObject*
+LazyScript::sourceObject() const
+{
+    return sourceObject_ ? &sourceObject_->as<ScriptSourceObject>() : nullptr;
+}
+
+ScriptSource*
+LazyScript::maybeForwardedScriptSource() const
+{
+    return UncheckedUnwrap(MaybeForwarded(sourceObject()))->as<ScriptSourceObject>().source();
+}
+
+/* static */ LazyScript*
+LazyScript::CreateRaw(ExclusiveContext* cx, HandleFunction fun,
+                      uint64_t packedFields, uint32_t begin, uint32_t end,
+                      uint32_t lineno, uint32_t column)
+{
+    union {
+        PackedView p;
+        uint64_t packed;
+    };
+
+    packed = packedFields;
+
+    // Reset runtime flags to obtain a fresh LazyScript.
+    p.hasBeenCloned = false;
+    p.treatAsRunOnce = false;
+
+    size_t bytes = (p.numClosedOverBindings * sizeof(JSAtom*))
+                 + (p.numInnerFunctions * sizeof(GCPtrFunction));
+
+    ScopedJSFreePtr<uint8_t> table(bytes ? fun->zone()->pod_malloc<uint8_t>(bytes) : nullptr);
+    if (bytes && !table) {
+        ReportOutOfMemory(cx);
+        return nullptr;
+    }
+
+    LazyScript* res = Allocate<LazyScript>(cx);
+    if (!res)
+        return nullptr;
+
+    cx->compartment()->scheduleDelazificationForDebugger();
+
+    return new (res) LazyScript(fun, table.forget(), packed, begin, end, lineno, column);
+}
+
+/* static */ LazyScript*
+LazyScript::Create(ExclusiveContext* cx, HandleFunction fun,
+                   const frontend::AtomVector& closedOverBindings,
+                   Handle<GCVector<JSFunction*, 8>> innerFunctions,
+                   JSVersion version,
+                   uint32_t begin, uint32_t end, uint32_t lineno, uint32_t column)
+{
+    union {
+        PackedView p;
+        uint64_t packedFields;
+    };
+
+    p.version = version;
+    p.shouldDeclareArguments = false;
+    p.hasThisBinding = false;
+    p.isAsync = false;
+    p.numClosedOverBindings = closedOverBindings.length();
+    p.numInnerFunctions = innerFunctions.length();
+    p.generatorKindBits = GeneratorKindAsBits(NotGenerator);
+    p.strict = false;
+    p.bindingsAccessedDynamically = false;
+    p.hasDebuggerStatement = false;
+    p.hasDirectEval = false;
+    p.isLikelyConstructorWrapper = false;
+    p.isDerivedClassConstructor = false;
+    p.needsHomeObject = false;
+
+    LazyScript* res = LazyScript::CreateRaw(cx, fun, packedFields, begin, end, lineno, column);
+    if (!res)
+        return nullptr;
+
+    JSAtom** resClosedOverBindings = res->closedOverBindings();
+    for (size_t i = 0; i < res->numClosedOverBindings(); i++)
+        resClosedOverBindings[i] = closedOverBindings[i];
+
+    GCPtrFunction* resInnerFunctions = res->innerFunctions();
+    for (size_t i = 0; i < res->numInnerFunctions(); i++)
+        resInnerFunctions[i].init(innerFunctions[i]);
+
+    MOZ_ASSERT_IF(res, res->version() == version);
+    return res;
+}
+
+/* static */ LazyScript*
+LazyScript::Create(ExclusiveContext* cx, HandleFunction fun,
+                   HandleScript script, HandleScope enclosingScope,
+                   HandleScript enclosingScript,
+                   uint64_t packedFields, uint32_t begin, uint32_t end,
+                   uint32_t lineno, uint32_t column)
+{
+    // Dummy atom which is not a valid property name.
+    RootedAtom dummyAtom(cx, cx->names().comma);
+
+    // Dummy function which is not a valid function as this is the one which is
+    // holding this lazy script.
+    HandleFunction dummyFun = fun;
+
+    LazyScript* res = LazyScript::CreateRaw(cx, fun, packedFields, begin, end, lineno, column);
+    if (!res)
+        return nullptr;
+
+    // Fill with dummies, to be GC-safe after the initialization of the free
+    // variables and inner functions.
+    size_t i, num;
+    JSAtom** closedOverBindings = res->closedOverBindings();
+    for (i = 0, num = res->numClosedOverBindings(); i < num; i++)
+        closedOverBindings[i] = dummyAtom;
+
+    GCPtrFunction* functions = res->innerFunctions();
+    for (i = 0, num = res->numInnerFunctions(); i < num; i++)
+        functions[i].init(dummyFun);
+
+    // Set the enclosing scope and source object of the lazy function. These
+    // values should only be non-null if we have a non-lazy enclosing script.
+    // AddLazyFunctionsForCompartment relies on the source object being null
+    // if we're nested inside another lazy function.
+    MOZ_ASSERT(!!enclosingScript == !!enclosingScope);
+    MOZ_ASSERT(!res->sourceObject());
+    MOZ_ASSERT(!res->enclosingScope());
+    if (enclosingScript)
+        res->setEnclosingScopeAndSource(enclosingScope, &enclosingScript->scriptSourceUnwrap());
+
+    MOZ_ASSERT(!res->hasScript());
+    if (script)
+        res->initScript(script);
+
+    return res;
+}
+
+void
+LazyScript::initRuntimeFields(uint64_t packedFields)
+{
+    union {
+        PackedView p;
+        uint64_t packed;
+    };
+
+    packed = packedFields;
+    p_.hasBeenCloned = p.hasBeenCloned;
+    p_.treatAsRunOnce = p.treatAsRunOnce;
+}
+
+bool
+LazyScript::hasUncompiledEnclosingScript() const
+{
+    // It can happen that we created lazy scripts while compiling an enclosing
+    // script, but we errored out while compiling that script. When we iterate
+    // over lazy script in a compartment, we might see lazy scripts that never
+    // escaped to script and should be ignored.
+    //
+    // If the enclosing scope is a function with a null script or has a script
+    // without code, it was not successfully compiled.
+
+    if (!enclosingScope() || !enclosingScope()->is<FunctionScope>())
+        return false;
+
+    JSFunction* fun = enclosingScope()->as<FunctionScope>().canonicalFunction();
+    return !fun->hasScript() || fun->hasUncompiledScript() || !fun->nonLazyScript()->code();
+}
+
+void
+JSScript::updateBaselineOrIonRaw(JSRuntime* maybeRuntime)
+{
+    if (hasBaselineScript() && baseline->hasPendingIonBuilder()) {
+        MOZ_ASSERT(maybeRuntime);
+        MOZ_ASSERT(!isIonCompilingOffThread());
+        baselineOrIonRaw = maybeRuntime->jitRuntime()->lazyLinkStub()->raw();
+        baselineOrIonSkipArgCheck = maybeRuntime->jitRuntime()->lazyLinkStub()->raw();
+    } else if (hasIonScript()) {
+        baselineOrIonRaw = ion->method()->raw();
+        baselineOrIonSkipArgCheck = ion->method()->raw() + ion->getSkipArgCheckEntryOffset();
+    } else if (hasBaselineScript()) {
+        baselineOrIonRaw = baseline->method()->raw();
+        baselineOrIonSkipArgCheck = baseline->method()->raw();
+    } else {
+        baselineOrIonRaw = nullptr;
+        baselineOrIonSkipArgCheck = nullptr;
+    }
+}
+
+bool
+JSScript::hasLoops()
+{
+    if (!hasTrynotes())
+        return false;
+    JSTryNote* tn = trynotes()->vector;
+    JSTryNote* tnlimit = tn + trynotes()->length;
+    for (; tn < tnlimit; tn++) {
+        if (tn->kind == JSTRY_FOR_IN || tn->kind == JSTRY_LOOP)
+            return true;
+    }
+    return false;
+}
+
+bool
+JSScript::mayReadFrameArgsDirectly()
+{
+    return argumentsHasVarBinding() || (function() && function()->hasRest());
+}
+
+static inline void
+LazyScriptHash(uint32_t lineno, uint32_t column, uint32_t begin, uint32_t end,
+               HashNumber hashes[3])
+{
+    HashNumber hash = lineno;
+    hash = RotateLeft(hash, 4) ^ column;
+    hash = RotateLeft(hash, 4) ^ begin;
+    hash = RotateLeft(hash, 4) ^ end;
+
+    hashes[0] = hash;
+    hashes[1] = RotateLeft(hashes[0], 4) ^ begin;
+    hashes[2] = RotateLeft(hashes[1], 4) ^ end;
+}
+
+void
+LazyScriptHashPolicy::hash(const Lookup& lookup, HashNumber hashes[3])
+{
+    LazyScript* lazy = lookup.lazy;
+    LazyScriptHash(lazy->lineno(), lazy->column(), lazy->begin(), lazy->end(), hashes);
+}
+
+void
+LazyScriptHashPolicy::hash(JSScript* script, HashNumber hashes[3])
+{
+    LazyScriptHash(script->lineno(), script->column(), script->sourceStart(), script->sourceEnd(), hashes);
+}
+
+bool
+LazyScriptHashPolicy::match(JSScript* script, const Lookup& lookup)
+{
+    JSContext* cx = lookup.cx;
+    LazyScript* lazy = lookup.lazy;
+
+    // To be a match, the script and lazy script need to have the same line
+    // and column and to be at the same position within their respective
+    // source blobs, and to have the same source contents and version.
+    //
+    // While the surrounding code in the source may differ, this is
+    // sufficient to ensure that compiling the lazy script will yield an
+    // identical result to compiling the original script.
+    //
+    // Note that the filenames and origin principals of the lazy script and
+    // original script can differ. If there is a match, these will be fixed
+    // up in the resulting clone by the caller.
+
+    if (script->lineno() != lazy->lineno() ||
+        script->column() != lazy->column() ||
+        script->getVersion() != lazy->version() ||
+        script->sourceStart() != lazy->begin() ||
+        script->sourceEnd() != lazy->end())
+    {
+        return false;
+    }
+
+    UncompressedSourceCache::AutoHoldEntry holder;
+
+    size_t scriptBegin = script->sourceStart();
+    size_t length = script->sourceEnd() - scriptBegin;
+    const char16_t* scriptChars = script->scriptSource()->chars(cx, holder, scriptBegin, length);
+    if (!scriptChars)
+        return false;
+
+    MOZ_ASSERT(scriptBegin == lazy->begin());
+    const char16_t* lazyChars = lazy->scriptSource()->chars(cx, holder, scriptBegin, length);
+    if (!lazyChars)
+        return false;
+
+    return !memcmp(scriptChars, lazyChars, length);
+}
+
+void
+JSScript::AutoDelazify::holdScript(JS::HandleFunction fun)
+{
+    if (fun) {
+        if (fun->compartment()->isSelfHosting) {
+            // The self-hosting compartment is shared across runtimes, so we
+            // can't use JSAutoCompartment: it could cause races. Functions in
+            // the self-hosting compartment will never be lazy, so we can safely
+            // assume we don't have to delazify.
+            script_ = fun->nonLazyScript();
+        } else {
+            JSAutoCompartment ac(cx_, fun);
+            script_ = fun->getOrCreateScript(cx_);
+            if (script_) {
+                oldDoNotRelazify_ = script_->doNotRelazify_;
+                script_->setDoNotRelazify(true);
+            }
+        }
+    }
+}
+
+void
+JSScript::AutoDelazify::dropScript()
+{
+    // Don't touch script_ if it's in the self-hosting compartment, see the
+    // comment in holdScript.
+    if (script_ && !script_->compartment()->isSelfHosting)
+        script_->setDoNotRelazify(oldDoNotRelazify_);
+    script_ = nullptr;
+}
+
+JS::ubi::Node::Size
+JS::ubi::Concrete<JSScript>::size(mozilla::MallocSizeOf mallocSizeOf) const
+{
+    Size size = Arena::thingSize(get().asTenured().getAllocKind());
+
+    size += get().sizeOfData(mallocSizeOf);
+    size += get().sizeOfTypeScript(mallocSizeOf);
+
+    size_t baselineSize = 0;
+    size_t baselineStubsSize = 0;
+    jit::AddSizeOfBaselineData(&get(), mallocSizeOf, &baselineSize, &baselineStubsSize);
+    size += baselineSize;
+    size += baselineStubsSize;
+
+    size += jit::SizeOfIonData(&get(), mallocSizeOf);
+
+    MOZ_ASSERT(size > 0);
+    return size;
+}
+
+const char*
+JS::ubi::Concrete<JSScript>::scriptFilename() const
+{
+    return get().filename();
+}
+
+JS::ubi::Node::Size
+JS::ubi::Concrete<js::LazyScript>::size(mozilla::MallocSizeOf mallocSizeOf) const
+{
+    Size size = js::gc::Arena::thingSize(get().asTenured().getAllocKind());
+    size += get().sizeOfExcludingThis(mallocSizeOf);
+    return size;
+}
+
+const char*
+JS::ubi::Concrete<js::LazyScript>::scriptFilename() const
+{
+    auto sourceObject = get().sourceObject();
+    if (!sourceObject)
+        return nullptr;
+
+    auto source = sourceObject->source();
+    if (!source)
+        return nullptr;
+
+    return source->filename();
+}