Bug 1343481 - Part 3: Add JSOP_AWAIT and rename {yieldIndex,yieldOffset} to {yieldAndAwaitIndex,yieldAndAwaitOffset}.

Tag #1287

16 files changed, 142 insertions, 110 deletions

diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index b8a9bdf7e..6a6deed12 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -2046,7 +2046,7 @@ class ForOfLoopControl : public LoopControl
             return false;
 
         MOZ_ASSERT(numYieldsAtBeginCodeNeedingIterClose_ == UINT32_MAX);
-        numYieldsAtBeginCodeNeedingIterClose_ = bce->yieldOffsetList.numYields;
+        numYieldsAtBeginCodeNeedingIterClose_ = bce->yieldAndAwaitOffsetList.numYields;
 
         return true;
     }
@@ -2088,7 +2088,7 @@ class ForOfLoopControl : public LoopControl
         // If any yields were emitted, then this for-of loop is inside a star
         // generator and must handle the case of Generator.return. Like in
         // yield*, it is handled with a finally block.
-        uint32_t numYieldsEmitted = bce->yieldOffsetList.numYields;
+        uint32_t numYieldsEmitted = bce->yieldAndAwaitOffsetList.numYields;
         if (numYieldsEmitted > numYieldsAtBeginCodeNeedingIterClose_) {
             if (!tryCatch_->emitFinally())
                 return false;
@@ -2190,7 +2190,7 @@ BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
     scopeList(cx),
     tryNoteList(cx),
     scopeNoteList(cx),
-    yieldOffsetList(cx),
+    yieldAndAwaitOffsetList(cx),
     typesetCount(0),
     hasSingletons(false),
     hasTryFinally(false),
@@ -4798,26 +4798,26 @@ BytecodeEmitter::emitYieldOp(JSOp op)
     if (op == JSOP_FINALYIELDRVAL)
         return emit1(JSOP_FINALYIELDRVAL);
 
-    MOZ_ASSERT(op == JSOP_INITIALYIELD || op == JSOP_YIELD);
+    MOZ_ASSERT(op == JSOP_INITIALYIELD || op == JSOP_YIELD || op == JSOP_AWAIT);
 
     ptrdiff_t off;
     if (!emitN(op, 3, &off))
         return false;
 
-    uint32_t yieldIndex = yieldOffsetList.length();
-    if (yieldIndex >= JS_BIT(24)) {
+    uint32_t yieldAndAwaitIndex = yieldAndAwaitOffsetList.length();
+    if (yieldAndAwaitIndex >= JS_BIT(24)) {
         reportError(nullptr, JSMSG_TOO_MANY_YIELDS);
         return false;
     }
 
     if (op == JSOP_YIELD)
-        yieldOffsetList.numYields++;
+        yieldAndAwaitOffsetList.numYields++;
     else
-        yieldOffsetList.numAwaits++;
+        yieldAndAwaitOffsetList.numAwaits++;
 
-    SET_UINT24(code(off), yieldIndex);
+    SET_UINT24(code(off), yieldAndAwaitIndex);
 
-    if (!yieldOffsetList.append(offset()))
+    if (!yieldAndAwaitOffsetList.append(offset()))
         return false;
 
     return emit1(JSOP_DEBUGAFTERYIELD);
@@ -8530,7 +8530,7 @@ BytecodeEmitter::emitYield(ParseNode* pn)
 {
     MOZ_ASSERT(sc->isFunctionBox());
 
-    if (pn->getOp() == JSOP_YIELD) {
+    if (pn->getOp() == JSOP_YIELD || pn->getOp() == JSOP_AWAIT) {
         bool needsIteratorResult = sc->asFunctionBox()->needsIteratorResult();
         if (needsIteratorResult) {
             if (!emitPrepareIteratorResult())
@@ -11293,7 +11293,7 @@ CGScopeNoteList::finish(ScopeNoteArray* array, uint32_t prologueLength)
 }
 
 void
-CGYieldOffsetList::finish(YieldOffsetArray& array, uint32_t prologueLength)
+CGYieldAndAwaitOffsetList::finish(YieldAndAwaitOffsetArray& array, uint32_t prologueLength)
 {
     MOZ_ASSERT(length() == array.length());
 
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 595ee6405..7f2dddfed 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -98,15 +98,15 @@ struct CGScopeNoteList {
     void finish(ScopeNoteArray* array, uint32_t prologueLength);
 };
 
-struct CGYieldOffsetList {
+struct CGYieldAndAwaitOffsetList {
     Vector<uint32_t> list;
     uint32_t numYields;
     uint32_t numAwaits;
-    explicit CGYieldOffsetList(ExclusiveContext* cx) : list(cx), numYields(0), numAwaits(0) {}
+    explicit CGYieldAndAwaitOffsetList(ExclusiveContext* cx) : list(cx), numYields(0), numAwaits(0) {}
 
     MOZ_MUST_USE bool append(uint32_t offset) { return list.append(offset); }
     size_t length() const { return list.length(); }
-    void finish(YieldOffsetArray& array, uint32_t prologueLength);
+    void finish(YieldAndAwaitOffsetArray& array, uint32_t prologueLength);
 };
 
 static size_t MaxBytecodeLength = INT32_MAX;
@@ -237,10 +237,10 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     CGScopeNoteList  scopeNoteList;  /* list of emitted block scope notes */
 
     /*
-     * For each yield op, map the yield index (stored as bytecode operand) to
-     * the offset of the next op.
+     * For each yield or await op, map the yield and await index (stored as
+     * bytecode operand) to the offset of the next op.
      */
-    CGYieldOffsetList yieldOffsetList;
+    CGYieldAndAwaitOffsetList yieldAndAwaitOffsetList;
 
     uint16_t        typesetCount;   /* Number of JOF_TYPESET opcodes generated */
 
diff --git a/js/src/frontend/FullParseHandler.h b/js/src/frontend/FullParseHandler.h
index 2d7f57e1e..6ab93f3f9 100644
--- a/js/src/frontend/FullParseHandler.h
+++ b/js/src/frontend/FullParseHandler.h
@@ -453,7 +453,7 @@ class FullParseHandler
 
     ParseNode* newAwaitExpression(uint32_t begin, ParseNode* value, ParseNode* gen) {
         TokenPos pos(begin, value ? value->pn_pos.end : begin + 1);
-        return new_<BinaryNode>(PNK_AWAIT, JSOP_YIELD, pos, value, gen);
+        return new_<BinaryNode>(PNK_AWAIT, JSOP_AWAIT, pos, value, gen);
     }
 
     // Statements
diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index b2f9d3b23..52c3eccef 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -43,7 +43,7 @@ using mozilla::AssertedCast;
 
 BaselineCompiler::BaselineCompiler(JSContext* cx, TempAllocator& alloc, JSScript* script)
   : BaselineCompilerSpecific(cx, alloc, script),
-    yieldOffsets_(cx),
+    yieldAndAwaitOffsets_(cx),
     modifiesArguments_(false)
 {
 }
@@ -210,7 +210,7 @@ BaselineCompiler::compile()
                             pcMappingIndexEntries.length(),
                             pcEntries.length(),
                             bytecodeTypeMapEntries,
-                            yieldOffsets_.length(),
+                            yieldAndAwaitOffsets_.length(),
                             traceLoggerToggleOffsets_.length()),
         JS::DeletePolicy<BaselineScript>(cx->runtime()));
     if (!baselineScript) {
@@ -275,7 +275,7 @@ BaselineCompiler::compile()
     // searches for the sought entry when queries are in linear order.
     bytecodeMap[script->nTypeSets()] = 0;
 
-    baselineScript->copyYieldEntries(script, yieldOffsets_);
+    baselineScript->copyYieldAndAwaitEntries(script, yieldAndAwaitOffsets_);
 
     if (compileDebugInstrumentation_)
         baselineScript->setHasDebugInstrumentation();
@@ -4174,27 +4174,28 @@ BaselineCompiler::emit_JSOP_GENERATOR()
 }
 
 bool
-BaselineCompiler::addYieldOffset()
+BaselineCompiler::addYieldAndAwaitOffset()
 {
-    MOZ_ASSERT(*pc == JSOP_INITIALYIELD || *pc == JSOP_YIELD);
+    MOZ_ASSERT(*pc == JSOP_INITIALYIELD || *pc == JSOP_YIELD || *pc == JSOP_AWAIT);
 
-    uint32_t yieldIndex = GET_UINT24(pc);
+    uint32_t yieldAndAwaitIndex = GET_UINT24(pc);
 
-    while (yieldIndex >= yieldOffsets_.length()) {
-        if (!yieldOffsets_.append(0))
+    while (yieldAndAwaitIndex >= yieldAndAwaitOffsets_.length()) {
+        if (!yieldAndAwaitOffsets_.append(0))
             return false;
     }
 
-    static_assert(JSOP_INITIALYIELD_LENGTH == JSOP_YIELD_LENGTH,
-                  "code below assumes INITIALYIELD and YIELD have same length");
-    yieldOffsets_[yieldIndex] = script->pcToOffset(pc + JSOP_YIELD_LENGTH);
+    static_assert(JSOP_INITIALYIELD_LENGTH == JSOP_YIELD_LENGTH &&
+                  JSOP_INITIALYIELD_LENGTH == JSOP_AWAIT_LENGTH,
+                  "code below assumes INITIALYIELD and YIELD and AWAIT have same length");
+    yieldAndAwaitOffsets_[yieldAndAwaitIndex] = script->pcToOffset(pc + JSOP_YIELD_LENGTH);
     return true;
 }
 
 bool
 BaselineCompiler::emit_JSOP_INITIALYIELD()
 {
-    if (!addYieldOffset())
+    if (!addYieldAndAwaitOffset())
         return false;
 
     frame.syncStack(0);
@@ -4204,7 +4205,8 @@ BaselineCompiler::emit_JSOP_INITIALYIELD()
     masm.unboxObject(frame.addressOfStackValue(frame.peek(-1)), genObj);
 
     MOZ_ASSERT(GET_UINT24(pc) == 0);
-    masm.storeValue(Int32Value(0), Address(genObj, GeneratorObject::offsetOfYieldIndexSlot()));
+    masm.storeValue(Int32Value(0),
+                    Address(genObj, GeneratorObject::offsetOfYieldAndAwaitIndexSlot()));
 
     Register envObj = R0.scratchReg();
     Address envChainSlot(genObj, GeneratorObject::offsetOfEnvironmentChainSlot());
@@ -4233,7 +4235,7 @@ static const VMFunction NormalSuspendInfo =
 bool
 BaselineCompiler::emit_JSOP_YIELD()
 {
-    if (!addYieldOffset())
+    if (!addYieldAndAwaitOffset())
         return false;
 
     // Store generator in R0.
@@ -4250,7 +4252,7 @@ BaselineCompiler::emit_JSOP_YIELD()
         // generator is in the closing state, see GeneratorObject::suspend.
 
         masm.storeValue(Int32Value(GET_UINT24(pc)),
-                        Address(genObj, GeneratorObject::offsetOfYieldIndexSlot()));
+                        Address(genObj, GeneratorObject::offsetOfYieldAndAwaitIndexSlot()));
 
         Register envObj = R0.scratchReg();
         Address envChainSlot(genObj, GeneratorObject::offsetOfEnvironmentChainSlot());
@@ -4282,6 +4284,12 @@ BaselineCompiler::emit_JSOP_YIELD()
     return emitReturn();
 }
 
+bool
+BaselineCompiler::emit_JSOP_AWAIT()
+{
+    return emit_JSOP_YIELD();
+}
+
 typedef bool (*DebugAfterYieldFn)(JSContext*, BaselineFrame*);
 static const VMFunction DebugAfterYieldInfo =
     FunctionInfo<DebugAfterYieldFn>(jit::DebugAfterYield, "DebugAfterYield");
@@ -4501,16 +4509,17 @@ BaselineCompiler::emit_JSOP_RESUME()
     masm.pushValue(retVal);
 
     if (resumeKind == GeneratorObject::NEXT) {
-        // Determine the resume address based on the yieldIndex and the
-        // yieldIndex -> native table in the BaselineScript.
+        // Determine the resume address based on the yieldAndAwaitIndex and the
+        // yieldAndAwaitIndex -> native table in the BaselineScript.
         masm.load32(Address(scratch1, BaselineScript::offsetOfYieldEntriesOffset()), scratch2);
         masm.addPtr(scratch2, scratch1);
-        masm.unboxInt32(Address(genObj, GeneratorObject::offsetOfYieldIndexSlot()), scratch2);
+        masm.unboxInt32(Address(genObj, GeneratorObject::offsetOfYieldAndAwaitIndexSlot()),
+                        scratch2);
         masm.loadPtr(BaseIndex(scratch1, scratch2, ScaleFromElemWidth(sizeof(uintptr_t))), scratch1);
 
         // Mark as running and jump to the generator's JIT code.
-        masm.storeValue(Int32Value(GeneratorObject::YIELD_INDEX_RUNNING),
-                        Address(genObj, GeneratorObject::offsetOfYieldIndexSlot()));
+        masm.storeValue(Int32Value(GeneratorObject::YIELD_AND_AWAIT_INDEX_RUNNING),
+                        Address(genObj, GeneratorObject::offsetOfYieldAndAwaitIndexSlot()));
         masm.jump(scratch1);
     } else {
         MOZ_ASSERT(resumeKind == GeneratorObject::THROW || resumeKind == GeneratorObject::CLOSE);
diff --git a/js/src/jit/BaselineCompiler.h b/js/src/jit/BaselineCompiler.h
index 95e0c77ad..1f236ed82 100644
--- a/js/src/jit/BaselineCompiler.h
+++ b/js/src/jit/BaselineCompiler.h
@@ -207,6 +207,7 @@ namespace jit {
     _(JSOP_GENERATOR)          \
     _(JSOP_INITIALYIELD)       \
     _(JSOP_YIELD)              \
+    _(JSOP_AWAIT)              \
     _(JSOP_DEBUGAFTERYIELD)    \
     _(JSOP_FINALYIELDRVAL)     \
     _(JSOP_RESUME)             \
@@ -255,9 +256,9 @@ class BaselineCompiler : public BaselineCompilerSpecific
     // equivalent positions when debug mode is off.
     CodeOffset postDebugPrologueOffset_;
 
-    // For each INITIALYIELD or YIELD op, this Vector maps the yield index
-    // to the bytecode offset of the next op.
-    Vector<uint32_t>            yieldOffsets_;
+    // For each INITIALYIELD or YIELD or AWAIT op, this Vector maps the yield
+    // index to the bytecode offset of the next op.
+    Vector<uint32_t>            yieldAndAwaitOffsets_;
 
     // Whether any on stack arguments are modified.
     bool modifiesArguments_;
@@ -349,7 +350,7 @@ class BaselineCompiler : public BaselineCompilerSpecific
 
     MOZ_MUST_USE bool addPCMappingEntry(bool addIndexEntry);
 
-    MOZ_MUST_USE bool addYieldOffset();
+    MOZ_MUST_USE bool addYieldAndAwaitOffset();
 
     void getEnvironmentCoordinateObject(Register reg);
     Address getEnvironmentCoordinateAddressFromObject(Register objReg, Register reg);
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index 9530f65fa..e65f10aac 100644
--- a/js/src/jit/BaselineIC.cpp
+++ b/js/src/jit/BaselineIC.cpp
@@ -6600,12 +6600,13 @@ ICCall_IsSuspendedStarGenerator::Compiler::generateStubCode(MacroAssembler& masm
     masm.branchTestObjClass(Assembler::NotEqual, genObj, scratch, &StarGeneratorObject::class_,
                             &returnFalse);
 
-    // If the yield index slot holds an int32 value < YIELD_INDEX_CLOSING,
+    // If the yield index slot holds an int32 value < YIELD_AND_AWAIT_INDEX_CLOSING,
     // the generator is suspended.
-    masm.loadValue(Address(genObj, GeneratorObject::offsetOfYieldIndexSlot()), argVal);
+    masm.loadValue(Address(genObj, GeneratorObject::offsetOfYieldAndAwaitIndexSlot()), argVal);
     masm.branchTestInt32(Assembler::NotEqual, argVal, &returnFalse);
     masm.unboxInt32(argVal, scratch);
-    masm.branch32(Assembler::AboveOrEqual, scratch, Imm32(StarGeneratorObject::YIELD_INDEX_CLOSING),
+    masm.branch32(Assembler::AboveOrEqual, scratch,
+                  Imm32(StarGeneratorObject::YIELD_AND_AWAIT_INDEX_CLOSING),
                   &returnFalse);
 
     masm.moveValue(BooleanValue(true), R0);
diff --git a/js/src/jit/BaselineJIT.cpp b/js/src/jit/BaselineJIT.cpp
index 5c21926b5..94e018252 100644
--- a/js/src/jit/BaselineJIT.cpp
+++ b/js/src/jit/BaselineJIT.cpp
@@ -760,12 +760,12 @@ BaselineScript::icEntryFromReturnAddress(uint8_t* returnAddr)
 }
 
 void
-BaselineScript::copyYieldEntries(JSScript* script, Vector<uint32_t>& yieldOffsets)
+BaselineScript::copyYieldAndAwaitEntries(JSScript* script, Vector<uint32_t>& yieldAndAwaitOffsets)
 {
     uint8_t** entries = yieldEntryList();
 
-    for (size_t i = 0; i < yieldOffsets.length(); i++) {
-        uint32_t offset = yieldOffsets[i];
+    for (size_t i = 0; i < yieldAndAwaitOffsets.length(); i++) {
+        uint32_t offset = yieldAndAwaitOffsets[i];
         entries[i] = nativeCodeForPC(script, script->offsetToPC(offset));
     }
 }
diff --git a/js/src/jit/BaselineJIT.h b/js/src/jit/BaselineJIT.h
index 5e7775a61..b6ccd2ff9 100644
--- a/js/src/jit/BaselineJIT.h
+++ b/js/src/jit/BaselineJIT.h
@@ -397,7 +397,7 @@ struct BaselineScript
     void copyICEntries(JSScript* script, const BaselineICEntry* entries, MacroAssembler& masm);
     void adoptFallbackStubs(FallbackICStubSpace* stubSpace);
 
-    void copyYieldEntries(JSScript* script, Vector<uint32_t>& yieldOffsets);
+    void copyYieldAndAwaitEntries(JSScript* script, Vector<uint32_t>& yieldAndAwaitOffsets);
 
     PCMappingIndexEntry& pcMappingIndexEntry(size_t index);
     CompactBufferReader pcMappingReader(size_t indexEntry);
diff --git a/js/src/jit/VMFunctions.cpp b/js/src/jit/VMFunctions.cpp
index 1ff7adfd1..652c23bf1 100644
--- a/js/src/jit/VMFunctions.cpp
+++ b/js/src/jit/VMFunctions.cpp
@@ -735,7 +735,7 @@ bool
 NormalSuspend(JSContext* cx, HandleObject obj, BaselineFrame* frame, jsbytecode* pc,
               uint32_t stackDepth)
 {
-    MOZ_ASSERT(*pc == JSOP_YIELD);
+    MOZ_ASSERT(*pc == JSOP_YIELD || *pc == JSOP_AWAIT);
 
     // Return value is still on the stack.
     MOZ_ASSERT(stackDepth >= 1);
@@ -816,7 +816,7 @@ GeneratorThrowOrClose(JSContext* cx, BaselineFrame* frame, Handle<GeneratorObjec
     // work. This function always returns false, so we're guaranteed to enter
     // the exception handler where we will clear the pc.
     JSScript* script = frame->script();
-    uint32_t offset = script->yieldOffsets()[genObj->yieldIndex()];
+    uint32_t offset = script->yieldAndAwaitOffsets()[genObj->yieldAndAwaitIndex()];
     frame->setOverridePc(script->offsetToPC(offset));
 
     MOZ_ALWAYS_TRUE(DebugAfterYield(cx, frame));
diff --git a/js/src/jsopcode.h b/js/src/jsopcode.h
index e56eebb2d..e417e3a64 100644
--- a/js/src/jsopcode.h
+++ b/js/src/jsopcode.h
@@ -655,7 +655,8 @@ IsValidBytecodeOffset(JSContext* cx, JSScript* script, size_t offset);
 inline bool
 FlowsIntoNext(JSOp op)
 {
-    /* JSOP_YIELD is considered to flow into the next instruction, like JSOP_CALL. */
+    // JSOP_YIELD/JSOP_AWAIT is considered to flow into the next instruction,
+    // like JSOP_CALL.
     switch (op) {
       case JSOP_RETRVAL:
       case JSOP_RETURN:
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index eb74a1ec6..bdd411d04 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -402,8 +402,8 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
             ntrynotes = script->trynotes()->length;
         if (script->hasScopeNotes())
             nscopenotes = script->scopeNotes()->length;
-        if (script->hasYieldOffsets())
-            nyieldoffsets = script->yieldOffsets().length();
+        if (script->hasYieldAndAwaitOffsets())
+            nyieldoffsets = script->yieldAndAwaitOffsets().length();
 
         nTypeSets = script->nTypeSets();
         funLength = script->funLength();
@@ -902,7 +902,7 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
     }
 
     for (i = 0; i < nyieldoffsets; ++i) {
-        uint32_t* offset = &script->yieldOffsets()[i];
+        uint32_t* offset = &script->yieldAndAwaitOffsets()[i];
         if (!xdr->codeUint32(offset))
             return false;
     }
@@ -2456,7 +2456,7 @@ ScriptDataSize(uint32_t nscopes, uint32_t nconsts, uint32_t nobjects,
     if (nscopenotes != 0)
         size += sizeof(ScopeNoteArray) + nscopenotes * sizeof(ScopeNote);
     if (nyieldoffsets != 0)
-        size += sizeof(YieldOffsetArray) + nyieldoffsets * sizeof(uint32_t);
+        size += sizeof(YieldAndAwaitOffsetArray) + nyieldoffsets * sizeof(uint32_t);
 
      return size;
 }
@@ -2558,10 +2558,10 @@ JSScript::partiallyInit(ExclusiveContext* cx, HandleScript script, uint32_t nsco
         cursor += sizeof(ScopeNoteArray);
     }
 
-    YieldOffsetArray* yieldOffsets = nullptr;
+    YieldAndAwaitOffsetArray* yieldAndAwaitOffsets = nullptr;
     if (nyieldoffsets != 0) {
-        yieldOffsets = reinterpret_cast<YieldOffsetArray*>(cursor);
-        cursor += sizeof(YieldOffsetArray);
+        yieldAndAwaitOffsets = reinterpret_cast<YieldAndAwaitOffsetArray*>(cursor);
+        cursor += sizeof(YieldAndAwaitOffsetArray);
     }
 
     if (nconsts != 0) {
@@ -2602,8 +2602,8 @@ JSScript::partiallyInit(ExclusiveContext* cx, HandleScript script, uint32_t nsco
     }
 
     if (nyieldoffsets != 0) {
-        yieldOffsets->init(reinterpret_cast<uint32_t*>(cursor), nyieldoffsets);
-        size_t vectorSize = nyieldoffsets * sizeof(script->yieldOffsets()[0]);
+        yieldAndAwaitOffsets->init(reinterpret_cast<uint32_t*>(cursor), nyieldoffsets);
+        size_t vectorSize = nyieldoffsets * sizeof(script->yieldAndAwaitOffsets()[0]);
 #ifdef DEBUG
         memset(cursor, 0, vectorSize);
 #endif
@@ -2623,10 +2623,10 @@ JSScript::initFunctionPrototype(ExclusiveContext* cx, Handle<JSScript*> script,
     uint32_t numObjects = 0;
     uint32_t numTryNotes = 0;
     uint32_t numScopeNotes = 0;
-    uint32_t numYieldOffsets = 0;
+    uint32_t numYieldAndAwaitOffsets = 0;
     uint32_t numTypeSets = 0;
     if (!partiallyInit(cx, script, numScopes, numConsts, numObjects, numTryNotes,
-                       numScopeNotes, numYieldOffsets, numTypeSets))
+                       numScopeNotes, numYieldAndAwaitOffsets, numTypeSets))
     {
         return false;
     }
@@ -2739,7 +2739,7 @@ JSScript::fullyInitFromEmitter(ExclusiveContext* cx, HandleScript script, Byteco
     if (!partiallyInit(cx, script,
                        bce->scopeList.length(), bce->constList.length(), bce->objectList.length,
                        bce->tryNoteList.length(), bce->scopeNoteList.length(),
-                       bce->yieldOffsetList.length(), bce->typesetCount))
+                       bce->yieldAndAwaitOffsetList.length(), bce->typesetCount))
     {
         return false;
     }
@@ -2794,8 +2794,8 @@ JSScript::fullyInitFromEmitter(ExclusiveContext* cx, HandleScript script, Byteco
 
     // Copy yield offsets last, as the generator kind is set in
     // initFromFunctionBox.
-    if (bce->yieldOffsetList.length() != 0)
-        bce->yieldOffsetList.finish(script->yieldOffsets(), prologueLength);
+    if (bce->yieldAndAwaitOffsetList.length() != 0)
+        bce->yieldAndAwaitOffsetList.finish(script->yieldAndAwaitOffsets(), prologueLength);
 
 #ifdef DEBUG
     script->assertValidJumpTargets();
@@ -3242,7 +3242,7 @@ js::detail::CopyScript(JSContext* cx, HandleScript src, HandleScript dst,
     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;
+    uint32_t nyieldoffsets = src->hasYieldAndAwaitOffsets() ? src->yieldAndAwaitOffsets().length() : 0;
 
     /* Script data */
 
@@ -3380,8 +3380,10 @@ js::detail::CopyScript(JSContext* cx, HandleScript src, HandleScript dst,
         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_);
+    if (nyieldoffsets != 0) {
+        dst->yieldAndAwaitOffsets().vector_ =
+            Rebase<uint32_t>(dst, src, src->yieldAndAwaitOffsets().vector_);
+    }
 
     /*
      * Function delazification assumes that their script does not have a
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index 13eaeff34..c19fbfc71 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -156,7 +156,7 @@ struct ScopeNoteArray {
     uint32_t   length;          // Count of indexed try notes.
 };
 
-class YieldOffsetArray {
+class YieldAndAwaitOffsetArray {
     friend bool
     detail::CopyScript(JSContext* cx, HandleScript src, HandleScript dst,
                        MutableHandle<GCVector<Scope*>> scopes);
@@ -1699,7 +1699,9 @@ class JSScript : public js::gc::TenuredCell
     bool hasObjects() const      { return hasArray(OBJECTS); }
     bool hasTrynotes() const     { return hasArray(TRYNOTES); }
     bool hasScopeNotes() const   { return hasArray(SCOPENOTES); }
-    bool hasYieldOffsets() const { return isStarGenerator() || isLegacyGenerator() || isAsync(); }
+    bool hasYieldAndAwaitOffsets() const {
+        return isStarGenerator() || isLegacyGenerator() || isAsync();
+    }
 
 #define OFF(fooOff, hasFoo, t)   (fooOff() + (hasFoo() ? sizeof(t) : 0))
 
@@ -1708,7 +1710,9 @@ class JSScript : public js::gc::TenuredCell
     size_t objectsOffset() const      { return OFF(constsOffset,     hasConsts,     js::ConstArray); }
     size_t trynotesOffset() const     { return OFF(objectsOffset,    hasObjects,    js::ObjectArray); }
     size_t scopeNotesOffset() const   { return OFF(trynotesOffset,   hasTrynotes,   js::TryNoteArray); }
-    size_t yieldOffsetsOffset() const { return OFF(scopeNotesOffset, hasScopeNotes, js::ScopeNoteArray); }
+    size_t yieldAndAwaitOffsetsOffset() const {
+        return OFF(scopeNotesOffset, hasScopeNotes, js::ScopeNoteArray);
+    }
 
 #undef OFF
 
@@ -1738,9 +1742,10 @@ class JSScript : public js::gc::TenuredCell
         return reinterpret_cast<js::ScopeNoteArray*>(data + scopeNotesOffset());
     }
 
-    js::YieldOffsetArray& yieldOffsets() {
-        MOZ_ASSERT(hasYieldOffsets());
-        return *reinterpret_cast<js::YieldOffsetArray*>(data + yieldOffsetsOffset());
+    js::YieldAndAwaitOffsetArray& yieldAndAwaitOffsets() {
+        MOZ_ASSERT(hasYieldAndAwaitOffsets());
+        return *reinterpret_cast<js::YieldAndAwaitOffsetArray*>(data +
+                                                                yieldAndAwaitOffsetsOffset());
     }
 
     bool hasLoops();
diff --git a/js/src/vm/GeneratorObject.cpp b/js/src/vm/GeneratorObject.cpp
index c0dff8faa..a61d37132 100644
--- a/js/src/vm/GeneratorObject.cpp
+++ b/js/src/vm/GeneratorObject.cpp
@@ -64,10 +64,14 @@ bool
 GeneratorObject::suspend(JSContext* cx, HandleObject obj, AbstractFramePtr frame, jsbytecode* pc,
                          Value* vp, unsigned nvalues)
 {
-    MOZ_ASSERT(*pc == JSOP_INITIALYIELD || *pc == JSOP_YIELD);
+    MOZ_ASSERT(*pc == JSOP_INITIALYIELD || *pc == JSOP_YIELD || *pc == JSOP_AWAIT);
 
     Rooted<GeneratorObject*> genObj(cx, &obj->as<GeneratorObject>());
     MOZ_ASSERT(!genObj->hasExpressionStack());
+    MOZ_ASSERT_IF(*pc == JSOP_AWAIT, genObj->callee().isAsync());
+    MOZ_ASSERT_IF(*pc == JSOP_YIELD,
+                  genObj->callee().isStarGenerator() ||
+                  genObj->callee().isLegacyGenerator());
 
     if (*pc == JSOP_YIELD && genObj->isClosing() && genObj->is<LegacyGeneratorObject>()) {
         RootedValue val(cx, ObjectValue(*frame.callee()));
@@ -75,8 +79,8 @@ GeneratorObject::suspend(JSContext* cx, HandleObject obj, AbstractFramePtr frame
         return false;
     }
 
-    uint32_t yieldIndex = GET_UINT24(pc);
-    genObj->setYieldIndex(yieldIndex);
+    uint32_t yieldAndAwaitIndex = GET_UINT24(pc);
+    genObj->setYieldAndAwaitIndex(yieldAndAwaitIndex);
     genObj->setEnvironmentChain(*frame.environmentChain());
 
     if (nvalues) {
@@ -173,7 +177,7 @@ GeneratorObject::resume(JSContext* cx, InterpreterActivation& activation,
     }
 
     JSScript* script = callee->nonLazyScript();
-    uint32_t offset = script->yieldOffsets()[genObj->yieldIndex()];
+    uint32_t offset = script->yieldAndAwaitOffsets()[genObj->yieldAndAwaitIndex()];
     activation.regs().pc = script->offsetToPC(offset);
 
     // Always push on a value, even if we are raising an exception. In the
diff --git a/js/src/vm/GeneratorObject.h b/js/src/vm/GeneratorObject.h
index ca1452b34..beb15f790 100644
--- a/js/src/vm/GeneratorObject.h
+++ b/js/src/vm/GeneratorObject.h
@@ -21,15 +21,15 @@ class GeneratorObject : public NativeObject
   public:
     // Magic values stored in the yield index slot when the generator is
     // running or closing. See the yield index comment below.
-    static const int32_t YIELD_INDEX_RUNNING = INT32_MAX;
-    static const int32_t YIELD_INDEX_CLOSING = INT32_MAX - 1;
+    static const int32_t YIELD_AND_AWAIT_INDEX_RUNNING = INT32_MAX;
+    static const int32_t YIELD_AND_AWAIT_INDEX_CLOSING = INT32_MAX - 1;
 
     enum {
         CALLEE_SLOT = 0,
         ENV_CHAIN_SLOT,
         ARGS_OBJ_SLOT,
         EXPRESSION_STACK_SLOT,
-        YIELD_INDEX_SLOT,
+        YIELD_AND_AWAIT_INDEX_SLOT,
         NEWTARGET_SLOT,
         RESERVED_SLOTS
     };
@@ -124,47 +124,48 @@ class GeneratorObject : public NativeObject
     // The yield index slot is abused for a few purposes.  It's undefined if
     // it hasn't been set yet (before the initial yield), and null if the
     // generator is closed. If the generator is running, the yield index is
-    // YIELD_INDEX_RUNNING. If the generator is in that bizarre "closing"
-    // state, the yield index is YIELD_INDEX_CLOSING.
+    // YIELD_AND_AWAIT_INDEX_RUNNING. If the generator is in that bizarre
+    // "closing" state, the yield index is YIELD_AND_AWAIT_INDEX_CLOSING.
     //
     // If the generator is suspended, it's the yield index (stored as
-    // JSOP_INITIALYIELD/JSOP_YIELD operand) of the yield instruction that
-    // suspended the generator. The yield index can be mapped to the bytecode
-    // offset (interpreter) or to the native code offset (JIT).
+    // JSOP_INITIALYIELD/JSOP_YIELD/JSOP_AWAIT operand) of the yield
+    // instruction that suspended the generator. The yield index can be mapped
+    // to the bytecode offset (interpreter) or to the native code offset (JIT).
 
     bool isRunning() const {
         MOZ_ASSERT(!isClosed());
-        return getFixedSlot(YIELD_INDEX_SLOT).toInt32() == YIELD_INDEX_RUNNING;
+        return getFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT).toInt32() == YIELD_AND_AWAIT_INDEX_RUNNING;
     }
     bool isClosing() const {
-        return getFixedSlot(YIELD_INDEX_SLOT).toInt32() == YIELD_INDEX_CLOSING;
+        return getFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT).toInt32() == YIELD_AND_AWAIT_INDEX_CLOSING;
     }
     bool isSuspended() const {
         // Note: also update Baseline's IsSuspendedStarGenerator code if this
         // changes.
         MOZ_ASSERT(!isClosed());
-        static_assert(YIELD_INDEX_CLOSING < YIELD_INDEX_RUNNING,
-                      "test below should return false for YIELD_INDEX_RUNNING");
-        return getFixedSlot(YIELD_INDEX_SLOT).toInt32() < YIELD_INDEX_CLOSING;
+        static_assert(YIELD_AND_AWAIT_INDEX_CLOSING < YIELD_AND_AWAIT_INDEX_RUNNING,
+                      "test below should return false for YIELD_AND_AWAIT_INDEX_RUNNING");
+        return getFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT).toInt32() < YIELD_AND_AWAIT_INDEX_CLOSING;
     }
     void setRunning() {
         MOZ_ASSERT(isSuspended());
-        setFixedSlot(YIELD_INDEX_SLOT, Int32Value(YIELD_INDEX_RUNNING));
+        setFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT, Int32Value(YIELD_AND_AWAIT_INDEX_RUNNING));
     }
     void setClosing() {
         MOZ_ASSERT(isSuspended());
-        setFixedSlot(YIELD_INDEX_SLOT, Int32Value(YIELD_INDEX_CLOSING));
-    }
-    void setYieldIndex(uint32_t yieldIndex) {
-        MOZ_ASSERT_IF(yieldIndex == 0, getFixedSlot(YIELD_INDEX_SLOT).isUndefined());
-        MOZ_ASSERT_IF(yieldIndex != 0, isRunning() || isClosing());
-        MOZ_ASSERT(yieldIndex < uint32_t(YIELD_INDEX_CLOSING));
-        setFixedSlot(YIELD_INDEX_SLOT, Int32Value(yieldIndex));
+        setFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT, Int32Value(YIELD_AND_AWAIT_INDEX_CLOSING));
+    }
+    void setYieldAndAwaitIndex(uint32_t yieldAndAwaitIndex) {
+        MOZ_ASSERT_IF(yieldAndAwaitIndex == 0,
+                      getFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT).isUndefined());
+        MOZ_ASSERT_IF(yieldAndAwaitIndex != 0, isRunning() || isClosing());
+        MOZ_ASSERT(yieldAndAwaitIndex < uint32_t(YIELD_AND_AWAIT_INDEX_CLOSING));
+        setFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT, Int32Value(yieldAndAwaitIndex));
         MOZ_ASSERT(isSuspended());
     }
-    uint32_t yieldIndex() const {
+    uint32_t yieldAndAwaitIndex() const {
         MOZ_ASSERT(isSuspended());
-        return getFixedSlot(YIELD_INDEX_SLOT).toInt32();
+        return getFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT).toInt32();
     }
     bool isClosed() const {
         return getFixedSlot(CALLEE_SLOT).isNull();
@@ -174,7 +175,7 @@ class GeneratorObject : public NativeObject
         setFixedSlot(ENV_CHAIN_SLOT, NullValue());
         setFixedSlot(ARGS_OBJ_SLOT, NullValue());
         setFixedSlot(EXPRESSION_STACK_SLOT, NullValue());
-        setFixedSlot(YIELD_INDEX_SLOT, NullValue());
+        setFixedSlot(YIELD_AND_AWAIT_INDEX_SLOT, NullValue());
         setFixedSlot(NEWTARGET_SLOT, NullValue());
     }
 
@@ -187,8 +188,8 @@ class GeneratorObject : public NativeObject
     static size_t offsetOfArgsObjSlot() {
         return getFixedSlotOffset(ARGS_OBJ_SLOT);
     }
-    static size_t offsetOfYieldIndexSlot() {
-        return getFixedSlotOffset(YIELD_INDEX_SLOT);
+    static size_t offsetOfYieldAndAwaitIndexSlot() {
+        return getFixedSlotOffset(YIELD_AND_AWAIT_INDEX_SLOT);
     }
     static size_t offsetOfExpressionStackSlot() {
         return getFixedSlotOffset(EXPRESSION_STACK_SLOT);
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 030f0f3b6..92bb18b36 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -1940,7 +1940,6 @@ CASE(JSOP_NOP)
 CASE(JSOP_NOP_DESTRUCTURING)
 CASE(JSOP_UNUSED126)
 CASE(JSOP_UNUSED192)
-CASE(JSOP_UNUSED209)
 CASE(JSOP_UNUSED210)
 CASE(JSOP_UNUSED211)
 CASE(JSOP_TRY_DESTRUCTURING_ITERCLOSE)
@@ -3994,6 +3993,7 @@ CASE(JSOP_INITIALYIELD)
 }
 
 CASE(JSOP_YIELD)
+CASE(JSOP_AWAIT)
 {
     MOZ_ASSERT(!cx->isExceptionPending());
     MOZ_ASSERT(REGS.fp()->isFunctionFrame());
diff --git a/js/src/vm/Opcodes.h b/js/src/vm/Opcodes.h
index 3c4d61a67..b44628080 100644
--- a/js/src/vm/Opcodes.h
+++ b/js/src/vm/Opcodes.h
@@ -2055,7 +2055,7 @@
      * interpretation.
      *   Category: Statements
      *   Type: Generator
-     *   Operands: uint24_t yieldIndex
+     *   Operands: uint24_t yieldAndAwaitIndex
      *   Stack: generator =>
      */ \
     macro(JSOP_INITIALYIELD,  202,"initialyield", NULL,   4,  1,  1,  JOF_UINT24) \
@@ -2064,7 +2064,7 @@
      * returns 'rval1'. Pushes sent value from 'send()' onto the stack.
      *   Category: Statements
      *   Type: Generator
-     *   Operands: uint24_t yieldIndex
+     *   Operands: uint24_t yieldAndAwaitIndex
      *   Stack: rval1, gen => rval2
      */ \
     macro(JSOP_YIELD,         203,"yield",       NULL,    4,  2,  1,  JOF_UINT24) \
@@ -2119,7 +2119,15 @@
      *   Stack: =>
      */ \
     macro(JSOP_DEBUGAFTERYIELD,  208, "debugafteryield",  NULL,  1,  0,  0,  JOF_BYTE) \
-    macro(JSOP_UNUSED209,     209, "unused209",    NULL,  1,  0,  0,  JOF_BYTE) \
+    /*
+     * Pops the generator and the return value 'result', stops interpretation
+     * and returns 'result'. Pushes resolved value onto the stack.
+     *   Category: Statements
+     *   Type: Generator
+     *   Operands: uint24_t yieldAndAwaitIndex
+     *   Stack: result, gen => resolved
+     */ \
+    macro(JSOP_AWAIT,         209, "await",        NULL,  4,  2,  1,  JOF_UINT24) \
     macro(JSOP_UNUSED210,     210, "unused210",    NULL,  1,  0,  0,  JOF_BYTE) \
     macro(JSOP_UNUSED211,     211, "unused211",    NULL,  1,  0,  0,  JOF_BYTE) \
     /*