1344477 - Part 1: Add JSOP_CALL_IGNORES_RV for function call that ignores return value.

13 files changed, 125 insertions, 51 deletions

diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index 6b64bfb44..b2f9d3b23 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -3292,6 +3292,12 @@ BaselineCompiler::emit_JSOP_CALL()
 }
 
 bool
+BaselineCompiler::emit_JSOP_CALL_IGNORES_RV()
+{
+    return emitCall();
+}
+
+bool
 BaselineCompiler::emit_JSOP_CALLITER()
 {
     return emitCall();
diff --git a/js/src/jit/BaselineCompiler.h b/js/src/jit/BaselineCompiler.h
index 910a52980..95e0c77ad 100644
--- a/js/src/jit/BaselineCompiler.h
+++ b/js/src/jit/BaselineCompiler.h
@@ -159,6 +159,7 @@ namespace jit {
     _(JSOP_INITALIASEDLEXICAL) \
     _(JSOP_UNINITIALIZED)      \
     _(JSOP_CALL)               \
+    _(JSOP_CALL_IGNORES_RV)    \
     _(JSOP_CALLITER)           \
     _(JSOP_FUNCALL)            \
     _(JSOP_FUNAPPLY)           \
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index 506cbf1d2..8a7c68e59 100644
--- a/js/src/jit/BaselineIC.cpp
+++ b/js/src/jit/BaselineIC.cpp
@@ -10,6 +10,8 @@
 #include "mozilla/SizePrintfMacros.h"
 #include "mozilla/TemplateLib.h"
 
+#include "jsfriendapi.h"
+#include "jsfun.h"
 #include "jslibmath.h"
 #include "jstypes.h"
 
@@ -5494,11 +5496,17 @@ TryAttachCallStub(JSContext* cx, ICCall_Fallback* stub, HandleScript script, jsb
             MOZ_ASSERT_IF(templateObject, !templateObject->group()->maybePreliminaryObjects());
         }
 
+        bool ignoresReturnValue = false;
+        if (op == JSOP_CALL_IGNORES_RV && fun->isNative()) {
+            const JSJitInfo* jitInfo = fun->jitInfo();
+            ignoresReturnValue = jitInfo && jitInfo->type() == JSJitInfo::IgnoresReturnValueNative;
+        }
+
         JitSpew(JitSpew_BaselineIC, "  Generating Call_Native stub (fun=%p, cons=%s, spread=%s)",
                 fun.get(), constructing ? "yes" : "no", isSpread ? "yes" : "no");
         ICCall_Native::Compiler compiler(cx, stub->fallbackMonitorStub()->firstMonitorStub(),
-                                         fun, templateObject, constructing, isSpread,
-                                         script->pcToOffset(pc));
+                                         fun, templateObject, constructing, ignoresReturnValue,
+                                         isSpread, script->pcToOffset(pc));
         ICStub* newStub = compiler.getStub(compiler.getStubSpace(script));
         if (!newStub)
             return false;
@@ -5601,12 +5609,14 @@ DoCallFallback(JSContext* cx, BaselineFrame* frame, ICCall_Fallback* stub_, uint
 
     MOZ_ASSERT(argc == GET_ARGC(pc));
     bool constructing = (op == JSOP_NEW);
+    bool ignoresReturnValue = (op == JSOP_CALL_IGNORES_RV);
 
     // Ensure vp array is rooted - we may GC in here.
     size_t numValues = argc + 2 + constructing;
     AutoArrayRooter vpRoot(cx, numValues, vp);
 
-    CallArgs callArgs = CallArgsFromSp(argc + constructing, vp + numValues, constructing);
+    CallArgs callArgs = CallArgsFromSp(argc + constructing, vp + numValues, constructing,
+                                       ignoresReturnValue);
     RootedValue callee(cx, vp[0]);
 
     // Handle funapply with JSOP_ARGUMENTS
@@ -5636,6 +5646,7 @@ DoCallFallback(JSContext* cx, BaselineFrame* frame, ICCall_Fallback* stub_, uint
             return false;
     } else {
         MOZ_ASSERT(op == JSOP_CALL ||
+                   op == JSOP_CALL_IGNORES_RV ||
                    op == JSOP_CALLITER ||
                    op == JSOP_FUNCALL ||
                    op == JSOP_FUNAPPLY ||
@@ -6686,7 +6697,12 @@ ICCall_Native::Compiler::generateStubCode(MacroAssembler& masm)
     // stub and use that instead of the original one.
     masm.callWithABI(Address(ICStubReg, ICCall_Native::offsetOfNative()));
 #else
-    masm.callWithABI(Address(callee, JSFunction::offsetOfNativeOrScript()));
+    if (ignoresReturnValue_) {
+        masm.loadPtr(Address(callee, JSFunction::offsetOfJitInfo()), callee);
+        masm.callWithABI(Address(callee, JSJitInfo::offsetOfIgnoresReturnValueNative()));
+    } else {
+        masm.callWithABI(Address(callee, JSFunction::offsetOfNativeOrScript()));
+    }
 #endif
 
     // Test for failure.
diff --git a/js/src/jit/BaselineIC.h b/js/src/jit/BaselineIC.h
index 9941cc93d..e1ad12559 100644
--- a/js/src/jit/BaselineIC.h
+++ b/js/src/jit/BaselineIC.h
@@ -2277,6 +2277,7 @@ class ICSetProp_CallNative : public ICSetPropCallSetter
 
 // Call
 //      JSOP_CALL
+//      JSOP_CALL_IGNORES_RV
 //      JSOP_FUNAPPLY
 //      JSOP_FUNCALL
 //      JSOP_NEW
@@ -2547,6 +2548,7 @@ class ICCall_Native : public ICMonitoredStub
       protected:
         ICStub* firstMonitorStub_;
         bool isConstructing_;
+        bool ignoresReturnValue_;
         bool isSpread_;
         RootedFunction callee_;
         RootedObject templateObject_;
@@ -2556,17 +2558,19 @@ class ICCall_Native : public ICMonitoredStub
         virtual int32_t getKey() const {
             return static_cast<int32_t>(engine_) |
                   (static_cast<int32_t>(kind) << 1) |
-                  (static_cast<int32_t>(isConstructing_) << 17) |
-                  (static_cast<int32_t>(isSpread_) << 18);
+                  (static_cast<int32_t>(isSpread_) << 17) |
+                  (static_cast<int32_t>(isConstructing_) << 18) |
+                  (static_cast<int32_t>(ignoresReturnValue_) << 19);
         }
 
       public:
         Compiler(JSContext* cx, ICStub* firstMonitorStub,
                  HandleFunction callee, HandleObject templateObject,
-                 bool isConstructing, bool isSpread, uint32_t pcOffset)
+                 bool isConstructing, bool ignoresReturnValue, bool isSpread, uint32_t pcOffset)
           : ICCallStubCompiler(cx, ICStub::Call_Native),
             firstMonitorStub_(firstMonitorStub),
             isConstructing_(isConstructing),
+            ignoresReturnValue_(ignoresReturnValue),
             isSpread_(isSpread),
             callee_(cx, callee),
             templateObject_(cx, templateObject),
diff --git a/js/src/jit/CodeGenerator.cpp b/js/src/jit/CodeGenerator.cpp
index 573993d5e..114fc96b3 100644
--- a/js/src/jit/CodeGenerator.cpp
+++ b/js/src/jit/CodeGenerator.cpp
@@ -3688,7 +3688,13 @@ CodeGenerator::visitCallNative(LCallNative* call)
     masm.passABIArg(argContextReg);
     masm.passABIArg(argUintNReg);
     masm.passABIArg(argVpReg);
-    masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, target->native()));
+    JSNative native = target->native();
+    if (call->ignoresReturnValue()) {
+        const JSJitInfo* jitInfo = target->jitInfo();
+        if (jitInfo && jitInfo->type() == JSJitInfo::IgnoresReturnValueNative)
+            native = jitInfo->ignoresReturnValueMethod;
+    }
+    masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, native));
 
     emitTracelogStopEvent(TraceLogger_Call);
 
@@ -3845,13 +3851,15 @@ CodeGenerator::visitCallGetIntrinsicValue(LCallGetIntrinsicValue* lir)
     callVM(GetIntrinsicValueInfo, lir);
 }
 
-typedef bool (*InvokeFunctionFn)(JSContext*, HandleObject, bool, uint32_t, Value*, MutableHandleValue);
+typedef bool (*InvokeFunctionFn)(JSContext*, HandleObject, bool, bool, uint32_t, Value*,
+                                 MutableHandleValue);
 static const VMFunction InvokeFunctionInfo =
     FunctionInfo<InvokeFunctionFn>(InvokeFunction, "InvokeFunction");
 
 void
 CodeGenerator::emitCallInvokeFunction(LInstruction* call, Register calleereg,
-                                      bool constructing, uint32_t argc, uint32_t unusedStack)
+                                      bool constructing, bool ignoresReturnValue,
+                                      uint32_t argc, uint32_t unusedStack)
 {
     // Nestle %esp up to the argument vector.
     // Each path must account for framePushed_ separately, for callVM to be valid.
@@ -3859,6 +3867,7 @@ CodeGenerator::emitCallInvokeFunction(LInstruction* call, Register calleereg,
 
     pushArg(masm.getStackPointer()); // argv.
     pushArg(Imm32(argc));            // argc.
+    pushArg(Imm32(ignoresReturnValue));
     pushArg(Imm32(constructing));    // constructing.
     pushArg(calleereg);              // JSFunction*.
 
@@ -3945,8 +3954,8 @@ CodeGenerator::visitCallGeneric(LCallGeneric* call)
 
     // Handle uncompiled or native functions.
     masm.bind(&invoke);
-    emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->numActualArgs(),
-                           unusedStack);
+    emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->ignoresReturnValue(),
+                           call->numActualArgs(), unusedStack);
 
     masm.bind(&end);
 
@@ -4001,7 +4010,8 @@ CodeGenerator::visitCallKnown(LCallKnown* call)
     masm.checkStackAlignment();
 
     if (target->isClassConstructor() && !call->isConstructing()) {
-        emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->numActualArgs(), unusedStack);
+        emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->ignoresReturnValue(),
+                               call->numActualArgs(), unusedStack);
         return;
     }
 
@@ -4045,7 +4055,8 @@ CodeGenerator::visitCallKnown(LCallKnown* call)
     if (call->isConstructing() && target->nargs() > call->numActualArgs())
         emitCallInvokeFunctionShuffleNewTarget(call, calleereg, target->nargs(), unusedStack);
     else
-        emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->numActualArgs(), unusedStack);
+        emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->ignoresReturnValue(),
+                               call->numActualArgs(), unusedStack);
 
     masm.bind(&end);
 
@@ -4072,6 +4083,7 @@ CodeGenerator::emitCallInvokeFunction(T* apply, Register extraStackSize)
 
     pushArg(objreg);                           // argv.
     pushArg(ToRegister(apply->getArgc()));     // argc.
+    pushArg(Imm32(false));                     // ignoresReturnValue.
     pushArg(Imm32(false));                     // isConstrucing.
     pushArg(ToRegister(apply->getFunction())); // JSFunction*.
 
diff --git a/js/src/jit/CodeGenerator.h b/js/src/jit/CodeGenerator.h
index b5f170d84..1c9a7e89b 100644
--- a/js/src/jit/CodeGenerator.h
+++ b/js/src/jit/CodeGenerator.h
@@ -165,8 +165,8 @@ class CodeGenerator final : public CodeGeneratorSpecific
     void visitOutOfLineCallPostWriteElementBarrier(OutOfLineCallPostWriteElementBarrier* ool);
     void visitCallNative(LCallNative* call);
     void emitCallInvokeFunction(LInstruction* call, Register callereg,
-                                bool isConstructing, uint32_t argc,
-                                uint32_t unusedStack);
+                                bool isConstructing, bool ignoresReturnValue,
+                                uint32_t argc, uint32_t unusedStack);
     void visitCallGeneric(LCallGeneric* call);
     void emitCallInvokeFunctionShuffleNewTarget(LCallKnown *call,
                                                 Register calleeReg,
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index e98a4056e..2d053de5a 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -1939,6 +1939,7 @@ IonBuilder::inspectOpcode(JSOp op)
         return jsop_funapply(GET_ARGC(pc));
 
       case JSOP_CALL:
+      case JSOP_CALL_IGNORES_RV:
       case JSOP_CALLITER:
       case JSOP_NEW:
       case JSOP_SUPERCALL:
@@ -1946,7 +1947,8 @@ IonBuilder::inspectOpcode(JSOp op)
             if (!outermostBuilder()->iterators_.append(current->peek(-1)))
                 return false;
         }
-        return jsop_call(GET_ARGC(pc), (JSOp)*pc == JSOP_NEW || (JSOp)*pc == JSOP_SUPERCALL);
+        return jsop_call(GET_ARGC(pc), (JSOp)*pc == JSOP_NEW || (JSOp)*pc == JSOP_SUPERCALL,
+                         (JSOp)*pc == JSOP_CALL_IGNORES_RV);
 
       case JSOP_EVAL:
       case JSOP_STRICTEVAL:
@@ -5874,7 +5876,7 @@ IonBuilder::inlineGenericFallback(JSFunction* target, CallInfo& callInfo, MBasic
         return false;
 
     // Create a new CallInfo to track modified state within this block.
-    CallInfo fallbackInfo(alloc(), callInfo.constructing());
+    CallInfo fallbackInfo(alloc(), callInfo.constructing(), callInfo.ignoresReturnValue());
     if (!fallbackInfo.init(callInfo))
         return false;
     fallbackInfo.popFormals(fallbackBlock);
@@ -5913,7 +5915,7 @@ IonBuilder::inlineObjectGroupFallback(CallInfo& callInfo, MBasicBlock* dispatchB
     MOZ_ASSERT(cache->idempotent());
 
     // Create a new CallInfo to track modified state within the fallback path.
-    CallInfo fallbackInfo(alloc(), callInfo.constructing());
+    CallInfo fallbackInfo(alloc(), callInfo.constructing(), callInfo.ignoresReturnValue());
     if (!fallbackInfo.init(callInfo))
         return false;
 
@@ -6089,7 +6091,7 @@ IonBuilder::inlineCalls(CallInfo& callInfo, const ObjectVector& targets, BoolVec
         inlineBlock->rewriteSlot(funIndex, funcDef);
 
         // Create a new CallInfo to track modified state within the inline block.
-        CallInfo inlineInfo(alloc(), callInfo.constructing());
+        CallInfo inlineInfo(alloc(), callInfo.constructing(), callInfo.ignoresReturnValue());
         if (!inlineInfo.init(callInfo))
             return false;
         inlineInfo.popFormals(inlineBlock);
@@ -6538,7 +6540,8 @@ IonBuilder::jsop_funcall(uint32_t argc)
     TemporaryTypeSet* calleeTypes = current->peek(calleeDepth)->resultTypeSet();
     JSFunction* native = getSingleCallTarget(calleeTypes);
     if (!native || !native->isNative() || native->native() != &fun_call) {
-        CallInfo callInfo(alloc(), false);
+        CallInfo callInfo(alloc(), /* constructing = */ false,
+                          /* ignoresReturnValue = */ BytecodeIsPopped(pc));
         if (!callInfo.init(current, argc))
             return false;
         return makeCall(native, callInfo);
@@ -6563,7 +6566,8 @@ IonBuilder::jsop_funcall(uint32_t argc)
         argc -= 1;
     }
 
-    CallInfo callInfo(alloc(), false);
+    CallInfo callInfo(alloc(), /* constructing = */ false,
+                      /* ignoresReturnValue = */ BytecodeIsPopped(pc));
     if (!callInfo.init(current, argc))
         return false;
 
@@ -6600,7 +6604,8 @@ IonBuilder::jsop_funapply(uint32_t argc)
     TemporaryTypeSet* calleeTypes = current->peek(calleeDepth)->resultTypeSet();
     JSFunction* native = getSingleCallTarget(calleeTypes);
     if (argc != 2 || info().analysisMode() == Analysis_ArgumentsUsage) {
-        CallInfo callInfo(alloc(), false);
+        CallInfo callInfo(alloc(), /* constructing = */ false,
+                          /* ignoresReturnValue = */ BytecodeIsPopped(pc));
         if (!callInfo.init(current, argc))
             return false;
         return makeCall(native, callInfo);
@@ -6629,7 +6634,8 @@ IonBuilder::jsop_funapply(uint32_t argc)
             return jsop_funapplyarray(argc);
         }
 
-        CallInfo callInfo(alloc(), false);
+        CallInfo callInfo(alloc(), /* constructing = */ false,
+                          /* ignoresReturnValue = */ BytecodeIsPopped(pc));
         if (!callInfo.init(current, argc))
             return false;
         return makeCall(native, callInfo);
@@ -6738,7 +6744,8 @@ IonBuilder::jsop_funapplyarguments(uint32_t argc)
     // can inline the apply() target and don't care about the actual arguments
     // that were passed in.
 
-    CallInfo callInfo(alloc(), false);
+    CallInfo callInfo(alloc(), /* constructing = */ false,
+                      /* ignoresReturnValue = */ BytecodeIsPopped(pc));
 
     // Vp
     MDefinition* vp = current->pop();
@@ -6784,7 +6791,7 @@ IonBuilder::jsop_funapplyarguments(uint32_t argc)
 }
 
 bool
-IonBuilder::jsop_call(uint32_t argc, bool constructing)
+IonBuilder::jsop_call(uint32_t argc, bool constructing, bool ignoresReturnValue)
 {
     startTrackingOptimizations();
 
@@ -6810,7 +6817,7 @@ IonBuilder::jsop_call(uint32_t argc, bool constructing)
     if (calleeTypes && !getPolyCallTargets(calleeTypes, constructing, targets, 4))
         return false;
 
-    CallInfo callInfo(alloc(), constructing);
+    CallInfo callInfo(alloc(), constructing, ignoresReturnValue);
     if (!callInfo.init(current, argc))
         return false;
 
@@ -6946,7 +6953,8 @@ IonBuilder::makeCallHelper(JSFunction* target, CallInfo& callInfo)
     }
 
     MCall* call = MCall::New(alloc(), target, targetArgs + 1 + callInfo.constructing(),
-                             callInfo.argc(), callInfo.constructing(), isDOMCall);
+                             callInfo.argc(), callInfo.constructing(),
+                             callInfo.ignoresReturnValue(), isDOMCall);
     if (!call)
         return nullptr;
 
@@ -7047,7 +7055,7 @@ IonBuilder::jsop_eval(uint32_t argc)
     // Emit a normal call if the eval has never executed. This keeps us from
     // disabling compilation for the script when testing with --ion-eager.
     if (calleeTypes && calleeTypes->empty())
-        return jsop_call(argc, /* constructing = */ false);
+        return jsop_call(argc, /* constructing = */ false, false);
 
     JSFunction* singleton = getSingleCallTarget(calleeTypes);
     if (!singleton)
@@ -7063,7 +7071,8 @@ IonBuilder::jsop_eval(uint32_t argc)
         if (info().funMaybeLazy()->isArrow())
             return abort("Direct eval from arrow function");
 
-        CallInfo callInfo(alloc(), /* constructing = */ false);
+        CallInfo callInfo(alloc(), /* constructing = */ false,
+                          /* ignoresReturnValue = */ BytecodeIsPopped(pc));
         if (!callInfo.init(current, argc))
             return false;
         callInfo.setImplicitlyUsedUnchecked();
@@ -7102,7 +7111,8 @@ IonBuilder::jsop_eval(uint32_t argc)
                 current->push(dynamicName);
                 current->push(constant(UndefinedValue())); // thisv
 
-                CallInfo evalCallInfo(alloc(), /* constructing = */ false);
+                CallInfo evalCallInfo(alloc(), /* constructing = */ false,
+                                      /* ignoresReturnValue = */ BytecodeIsPopped(pc));
                 if (!evalCallInfo.init(current, /* argc = */ 0))
                     return false;
 
@@ -7119,7 +7129,7 @@ IonBuilder::jsop_eval(uint32_t argc)
         return resumeAfter(ins) && pushTypeBarrier(ins, types, BarrierKind::TypeSet);
     }
 
-    return jsop_call(argc, /* constructing = */ false);
+    return jsop_call(argc, /* constructing = */ false, false);
 }
 
 bool
@@ -12001,7 +12011,8 @@ IonBuilder::getPropTryCommonGetter(bool* emitted, MDefinition* obj, PropertyName
 
     current->push(obj);
 
-    CallInfo callInfo(alloc(), false);
+    CallInfo callInfo(alloc(), /* constructing = */ false,
+                      /* ignoresReturnValue = */ BytecodeIsPopped(pc));
     if (!callInfo.init(current, 0))
         return false;
 
@@ -12496,7 +12507,8 @@ IonBuilder::setPropTryCommonSetter(bool* emitted, MDefinition* obj,
 
     // Call the setter. Note that we have to push the original value, not
     // the setter's return value.
-    CallInfo callInfo(alloc(), false);
+    CallInfo callInfo(alloc(), /* constructing = */ false,
+                      /* ignoresReturnValue = */ BytecodeIsPopped(pc));
     if (!callInfo.init(current, 1))
         return false;
 
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index dd40b4bd6..9e40b3959 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -699,6 +699,7 @@ class IonBuilder
     MOZ_MUST_USE bool jsop_funapplyarguments(uint32_t argc);
     MOZ_MUST_USE bool jsop_funapplyarray(uint32_t argc);
     MOZ_MUST_USE bool jsop_call(uint32_t argc, bool constructing);
+    MOZ_MUST_USE bool jsop_call(uint32_t argc, bool constructing, bool ignoresReturnValue);
     MOZ_MUST_USE bool jsop_eval(uint32_t argc);
     MOZ_MUST_USE bool jsop_ifeq(JSOp op);
     MOZ_MUST_USE bool jsop_try();
@@ -1352,16 +1353,21 @@ class CallInfo
     MDefinition* newTargetArg_;
     MDefinitionVector args_;
 
-    bool constructing_;
-    bool setter_;
+    bool constructing_:1;
+
+    // True if the caller does not use the return value.
+    bool ignoresReturnValue_:1;
+
+    bool setter_:1;
 
   public:
-    CallInfo(TempAllocator& alloc, bool constructing)
+    CallInfo(TempAllocator& alloc, bool constructing, bool ignoresReturnValue)
       : fun_(nullptr),
         thisArg_(nullptr),
         newTargetArg_(nullptr),
         args_(alloc),
         constructing_(constructing),
+        ignoresReturnValue_(ignoresReturnValue),
         setter_(false)
     { }
 
@@ -1370,6 +1376,7 @@ class CallInfo
 
         fun_ = callInfo.fun();
         thisArg_ = callInfo.thisArg();
+        ignoresReturnValue_ = callInfo.ignoresReturnValue();
 
         if (constructing())
             newTargetArg_ = callInfo.getNewTarget();
@@ -1466,6 +1473,10 @@ class CallInfo
         return constructing_;
     }
 
+    bool ignoresReturnValue() const {
+        return ignoresReturnValue_;
+    }
+
     void setNewTarget(MDefinition* newTarget) {
         MOZ_ASSERT(constructing());
         newTargetArg_ = newTarget;
diff --git a/js/src/jit/MIR.cpp b/js/src/jit/MIR.cpp
index fa9cc3019..10671cfda 100644
--- a/js/src/jit/MIR.cpp
+++ b/js/src/jit/MIR.cpp
@@ -1970,7 +1970,7 @@ WrappedFunction::WrappedFunction(JSFunction* fun)
 
 MCall*
 MCall::New(TempAllocator& alloc, JSFunction* target, size_t maxArgc, size_t numActualArgs,
-           bool construct, bool isDOMCall)
+           bool construct, bool ignoresReturnValue, bool isDOMCall)
 {
     WrappedFunction* wrappedTarget = target ? new(alloc) WrappedFunction(target) : nullptr;
     MOZ_ASSERT(maxArgc >= numActualArgs);
@@ -1979,7 +1979,7 @@ MCall::New(TempAllocator& alloc, JSFunction* target, size_t maxArgc, size_t numA
         MOZ_ASSERT(!construct);
         ins = new(alloc) MCallDOMNative(wrappedTarget, numActualArgs);
     } else {
-        ins = new(alloc) MCall(wrappedTarget, numActualArgs, construct);
+        ins = new(alloc) MCall(wrappedTarget, numActualArgs, construct, ignoresReturnValue);
     }
     if (!ins->init(alloc, maxArgc + NumNonArgumentOperands))
         return nullptr;
diff --git a/js/src/jit/MIR.h b/js/src/jit/MIR.h
index 9076339f1..ac55b1150 100644
--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -4043,14 +4043,18 @@ class MCall
     uint32_t numActualArgs_;
 
     // True if the call is for JSOP_NEW.
-    bool construct_;
+    bool construct_:1;
 
-    bool needsArgCheck_;
+    // True if the caller does not use the return value.
+    bool ignoresReturnValue_:1;
 
-    MCall(WrappedFunction* target, uint32_t numActualArgs, bool construct)
+    bool needsArgCheck_:1;
+
+    MCall(WrappedFunction* target, uint32_t numActualArgs, bool construct, bool ignoresReturnValue)
       : target_(target),
         numActualArgs_(numActualArgs),
         construct_(construct),
+        ignoresReturnValue_(ignoresReturnValue),
         needsArgCheck_(true)
     {
         setResultType(MIRType::Value);
@@ -4059,7 +4063,7 @@ class MCall
   public:
     INSTRUCTION_HEADER(Call)
     static MCall* New(TempAllocator& alloc, JSFunction* target, size_t maxArgc, size_t numActualArgs,
-                      bool construct, bool isDOMCall);
+                      bool construct, bool ignoresReturnValue, bool isDOMCall);
 
     void initFunction(MDefinition* func) {
         initOperand(FunctionOperandIndex, func);
@@ -4104,6 +4108,10 @@ class MCall
         return construct_;
     }
 
+    bool ignoresReturnValue() const {
+        return ignoresReturnValue_;
+    }
+
     // The number of stack arguments is the max between the number of formal
     // arguments and the number of actual arguments. The number of stack
     // argument includes the |undefined| padding added in case of underflow.
@@ -4147,7 +4155,7 @@ class MCallDOMNative : public MCall
     // virtual things from MCall.
   protected:
     MCallDOMNative(WrappedFunction* target, uint32_t numActualArgs)
-        : MCall(target, numActualArgs, false)
+        : MCall(target, numActualArgs, false, false)
     {
         MOZ_ASSERT(getJitInfo()->type() != JSJitInfo::InlinableNative);
 
@@ -4162,7 +4170,8 @@ class MCallDOMNative : public MCall
     }
 
     friend MCall* MCall::New(TempAllocator& alloc, JSFunction* target, size_t maxArgc,
-                             size_t numActualArgs, bool construct, bool isDOMCall);
+                             size_t numActualArgs, bool construct, bool ignoresReturnValue,
+                             bool isDOMCall);
 
     const JSJitInfo* getJitInfo() const;
   public:
diff --git a/js/src/jit/VMFunctions.cpp b/js/src/jit/VMFunctions.cpp
index 5bcd36ba0..e58c3f570 100644
--- a/js/src/jit/VMFunctions.cpp
+++ b/js/src/jit/VMFunctions.cpp
@@ -54,8 +54,8 @@ VMFunction::addToFunctions()
 }
 
 bool
-InvokeFunction(JSContext* cx, HandleObject obj, bool constructing, uint32_t argc, Value* argv,
-               MutableHandleValue rval)
+InvokeFunction(JSContext* cx, HandleObject obj, bool constructing, bool ignoresReturnValue,
+               uint32_t argc, Value* argv, MutableHandleValue rval)
 {
     TraceLoggerThread* logger = TraceLoggerForMainThread(cx->runtime());
     TraceLogStartEvent(logger, TraceLogger_Call);
@@ -104,7 +104,7 @@ InvokeFunction(JSContext* cx, HandleObject obj, bool constructing, uint32_t argc
         return InternalConstructWithProvidedThis(cx, fval, thisv, cargs, newTarget, rval);
     }
 
-    InvokeArgs args(cx);
+    InvokeArgsMaybeIgnoresReturnValue args(cx, ignoresReturnValue);
     if (!args.init(cx, argc))
         return false;
 
@@ -120,7 +120,7 @@ InvokeFunctionShuffleNewTarget(JSContext* cx, HandleObject obj, uint32_t numActu
 {
     MOZ_ASSERT(numFormalArgs > numActualArgs);
     argv[1 + numActualArgs] = argv[1 + numFormalArgs];
-    return InvokeFunction(cx, obj, true, numActualArgs, argv, rval);
+    return InvokeFunction(cx, obj, true, false, numActualArgs, argv, rval);
 }
 
 bool
diff --git a/js/src/jit/VMFunctions.h b/js/src/jit/VMFunctions.h
index 9a2edd0f3..bd65df134 100644
--- a/js/src/jit/VMFunctions.h
+++ b/js/src/jit/VMFunctions.h
@@ -584,8 +584,8 @@ class AutoDetectInvalidation
 };
 
 MOZ_MUST_USE bool
-InvokeFunction(JSContext* cx, HandleObject obj0, bool constructing, uint32_t argc, Value* argv,
-               MutableHandleValue rval);
+InvokeFunction(JSContext* cx, HandleObject obj0, bool constructing, bool ignoresReturnValue,
+               uint32_t argc, Value* argv, MutableHandleValue rval);
 MOZ_MUST_USE bool
 InvokeFunctionShuffleNewTarget(JSContext* cx, HandleObject obj, uint32_t numActualArgs,
                                uint32_t numFormalArgs, Value* argv, MutableHandleValue rval);
diff --git a/js/src/jit/shared/LIR-shared.h b/js/src/jit/shared/LIR-shared.h
index ffa4d8367..2b242d2e4 100644
--- a/js/src/jit/shared/LIR-shared.h
+++ b/js/src/jit/shared/LIR-shared.h
@@ -1898,6 +1898,9 @@ class LJSCallInstructionHelper : public LCallInstructionHelper<Defs, Operands, T
     bool isConstructing() const {
         return mir()->isConstructing();
     }
+    bool ignoresReturnValue() const {
+        return mir()->ignoresReturnValue();
+    }
 };
 
 // Generates a polymorphic callsite, wherein the function being called is