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

js/public/CallArgs.h

@@ -128,7 +128,10 @@ class MOZ_STACK_CLASS CallArgsBase : public WantUsedRval
   protected:
     Value* argv_;
     unsigned argc_;
-    bool constructing_;
+    bool constructing_:1;
+
+    // True if the caller does not use the return value.
+    bool ignoresReturnValue_:1;
 
   public:
     // CALLEE ACCESS
@@ -164,6 +167,10 @@ class MOZ_STACK_CLASS CallArgsBase : public WantUsedRval
         return true;
     }
 
+    bool ignoresReturnValue() const {
+        return ignoresReturnValue_;
+    }
+
     MutableHandleValue newTarget() const {
         MOZ_ASSERT(constructing_);
         return MutableHandleValue::fromMarkedLocation(&this->argv_[argc_]);
@@ -280,14 +287,17 @@ class MOZ_STACK_CLASS CallArgs : public detail::CallArgsBase<detail::IncludeUsed
 {
   private:
     friend CallArgs CallArgsFromVp(unsigned argc, Value* vp);
-    friend CallArgs CallArgsFromSp(unsigned stackSlots, Value* sp, bool constructing);
+    friend CallArgs CallArgsFromSp(unsigned stackSlots, Value* sp, bool constructing,
+                                   bool ignoresReturnValue);
 
-    static CallArgs create(unsigned argc, Value* argv, bool constructing) {
+    static CallArgs create(unsigned argc, Value* argv, bool constructing,
+                           bool ignoresReturnValue = false) {
         CallArgs args;
         args.clearUsedRval();
         args.argv_ = argv;
         args.argc_ = argc;
         args.constructing_ = constructing;
+        args.ignoresReturnValue_ = ignoresReturnValue;
 #ifdef DEBUG
         for (unsigned i = 0; i < argc; ++i)
             MOZ_ASSERT_IF(argv[i].isGCThing(), !GCThingIsMarkedGray(GCCellPtr(argv[i])));
@@ -314,9 +324,11 @@ CallArgsFromVp(unsigned argc, Value* vp)
 // eventually move it to an internal header.  Embedders should use
 // JS::CallArgsFromVp!
 MOZ_ALWAYS_INLINE CallArgs
-CallArgsFromSp(unsigned stackSlots, Value* sp, bool constructing = false)
+CallArgsFromSp(unsigned stackSlots, Value* sp, bool constructing = false,
+               bool ignoresReturnValue = false)
 {
-    return CallArgs::create(stackSlots - constructing, sp - stackSlots, constructing);
+    return CallArgs::create(stackSlots - constructing, sp - stackSlots, constructing,
+                            ignoresReturnValue);
 }
 
 } // namespace JS

js/src/frontend/BytecodeEmitter.cpp

@@ -4603,7 +4603,7 @@ BytecodeEmitter::emitSwitch(ParseNode* pn)
             // If the expression is a literal, suppress line number emission so
             // that debugging works more naturally.
             if (caseValue) {
-                if (!emitTree(caseValue,
+                if (!emitTree(caseValue, ValueUsage::WantValue,
                               caseValue->isLiteral() ? SUPPRESS_LINENOTE : EMIT_LINENOTE))
                 {
                     return false;
@@ -6652,7 +6652,7 @@ BytecodeEmitter::emitLexicalScopeBody(ParseNode* body, EmitLineNumberNote emitLi
     }
 
     // Line notes were updated by emitLexicalScope.
-    return emitTree(body, emitLineNote);
+    return emitTree(body, ValueUsage::WantValue, emitLineNote);
 }
 
 // Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See
@@ -6754,9 +6754,9 @@ BytecodeEmitter::emitRequireObjectCoercible()
         return false;
     if (!emit2(JSOP_PICK, 2))              // VAL REQUIREOBJECTCOERCIBLE UNDEFINED VAL
         return false;
-    if (!emitCall(JSOP_CALL, 1))           // VAL IGNORED
+    if (!emitCall(JSOP_CALL_IGNORES_RV, 1))// VAL IGNORED
         return false;
-    checkTypeSet(JSOP_CALL);
+    checkTypeSet(JSOP_CALL_IGNORES_RV);
 
     if (!emit1(JSOP_POP))                  // VAL
         return false;
@@ -7276,12 +7276,14 @@ BytecodeEmitter::emitCStyleFor(ParseNode* pn, EmitterScope* headLexicalEmitterSc
         // scope, but we still need to emit code for the initializers.)
         if (!updateSourceCoordNotes(init->pn_pos.begin))
             return false;
+        if (init->isForLoopDeclaration()) {
             if (!emitTree(init))
                 return false;
-
+        } else {
-        if (!init->isForLoopDeclaration()) {
             // 'init' is an expression, not a declaration. emitTree left its
             // value on the stack.
+            if (!emitTree(init, ValueUsage::IgnoreValue))
+                return false;
             if (!emit1(JSOP_POP))
                 return false;
         }
@@ -7363,7 +7365,7 @@ BytecodeEmitter::emitCStyleFor(ParseNode* pn, EmitterScope* headLexicalEmitterSc
 
         if (!updateSourceCoordNotes(update->pn_pos.begin))
             return false;
-        if (!emitTree(update))
+        if (!emitTree(update, ValueUsage::IgnoreValue))
             return false;
         if (!emit1(JSOP_POP))
             return false;
@@ -8690,8 +8692,9 @@ BytecodeEmitter::emitStatement(ParseNode* pn)
 
     if (useful) {
         JSOp op = wantval ? JSOP_SETRVAL : JSOP_POP;
+        ValueUsage valueUsage = wantval ? ValueUsage::WantValue : ValueUsage::IgnoreValue;
         MOZ_ASSERT_IF(pn2->isKind(PNK_ASSIGN), pn2->isOp(JSOP_NOP));
-        if (!emitTree(pn2))
+        if (!emitTree(pn2, valueUsage))
             return false;
         if (!emit1(op))
             return false;
@@ -9041,7 +9044,7 @@ BytecodeEmitter::emitOptimizeSpread(ParseNode* arg0, JumpList* jmp, bool* emitte
 }
 
 bool
-BytecodeEmitter::emitCallOrNew(ParseNode* pn)
+BytecodeEmitter::emitCallOrNew(ParseNode* pn, ValueUsage valueUsage /* = ValueUsage::WantValue */)
 {
     bool callop = pn->isKind(PNK_CALL) || pn->isKind(PNK_TAGGED_TEMPLATE);
     /*
@@ -9220,13 +9223,20 @@ BytecodeEmitter::emitCallOrNew(ParseNode* pn)
     }
 
     if (!spread) {
+        if (pn->getOp() == JSOP_CALL && valueUsage == ValueUsage::IgnoreValue) {
+            if (!emitCall(JSOP_CALL_IGNORES_RV, argc, pn))
+                return false;
+            checkTypeSet(JSOP_CALL_IGNORES_RV);
+        } else {
             if (!emitCall(pn->getOp(), argc, pn))
                 return false;
+            checkTypeSet(pn->getOp());
+        }
     } else {
         if (!emit1(pn->getOp()))
             return false;
-    }
         checkTypeSet(pn->getOp());
+    }
     if (pn->isOp(JSOP_EVAL) ||
         pn->isOp(JSOP_STRICTEVAL) ||
         pn->isOp(JSOP_SPREADEVAL) ||
@@ -9324,12 +9334,13 @@ BytecodeEmitter::emitLogical(ParseNode* pn)
 }
 
 bool
-BytecodeEmitter::emitSequenceExpr(ParseNode* pn)
+BytecodeEmitter::emitSequenceExpr(ParseNode* pn,
+                                  ValueUsage valueUsage /* = ValueUsage::WantValue */)
 {
     for (ParseNode* child = pn->pn_head; ; child = child->pn_next) {
         if (!updateSourceCoordNotes(child->pn_pos.begin))
             return false;
-        if (!emitTree(child))
+        if (!emitTree(child, child->pn_next ? ValueUsage::IgnoreValue : valueUsage))
             return false;
         if (!child->pn_next)
             break;
@@ -9392,7 +9403,8 @@ BytecodeEmitter::emitLabeledStatement(const LabeledStatement* pn)
 }
 
 bool
-BytecodeEmitter::emitConditionalExpression(ConditionalExpression& conditional)
+BytecodeEmitter::emitConditionalExpression(ConditionalExpression& conditional,
+                                           ValueUsage valueUsage /* = ValueUsage::WantValue */)
 {
     /* Emit the condition, then branch if false to the else part. */
     if (!emitTree(&conditional.condition()))
@@ -9402,13 +9414,13 @@ BytecodeEmitter::emitConditionalExpression(ConditionalExpression& conditional)
     if (!ifThenElse.emitCond())
         return false;
 
-    if (!emitTreeInBranch(&conditional.thenExpression()))
+    if (!emitTreeInBranch(&conditional.thenExpression(), valueUsage))
         return false;
 
     if (!ifThenElse.emitElse())
         return false;
 
-    if (!emitTreeInBranch(&conditional.elseExpression()))
+    if (!emitTreeInBranch(&conditional.elseExpression(), valueUsage))
         return false;
 
     if (!ifThenElse.emitEnd())
@@ -10289,7 +10301,8 @@ BytecodeEmitter::emitClass(ParseNode* pn)
 }
 
 bool
-BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
+BytecodeEmitter::emitTree(ParseNode* pn, ValueUsage valueUsage /* = ValueUsage::WantValue */,
+                          EmitLineNumberNote emitLineNote /* = EMIT_LINENOTE */)
 {
     JS_CHECK_RECURSION(cx, return false);
 
@@ -10411,7 +10424,7 @@ BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
         break;
 
       case PNK_COMMA:
-        if (!emitSequenceExpr(pn))
+        if (!emitSequenceExpr(pn, valueUsage))
             return false;
         break;
 
@@ -10433,7 +10446,7 @@ BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
         break;
 
       case PNK_CONDITIONAL:
-        if (!emitConditionalExpression(pn->as<ConditionalExpression>()))
+        if (!emitConditionalExpression(pn->as<ConditionalExpression>(), valueUsage))
             return false;
         break;
 
@@ -10546,7 +10559,7 @@ BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
       case PNK_CALL:
       case PNK_GENEXP:
       case PNK_SUPERCALL:
-        if (!emitCallOrNew(pn))
+        if (!emitCallOrNew(pn, valueUsage))
             return false;
         break;
 
@@ -10704,12 +10717,13 @@ BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
 }
 
 bool
-BytecodeEmitter::emitTreeInBranch(ParseNode* pn)
+BytecodeEmitter::emitTreeInBranch(ParseNode* pn,
+                                  ValueUsage valueUsage /* = ValueUsage::WantValue */)
 {
     // Code that may be conditionally executed always need their own TDZ
     // cache.
     TDZCheckCache tdzCache(this);
-    return emitTree(pn);
+    return emitTree(pn, valueUsage);
 }
 
 static bool

js/src/frontend/BytecodeEmitter.h

@@ -171,6 +171,11 @@ struct JumpList {
     void patchAll(jsbytecode* code, JumpTarget target);
 };
 
+enum class ValueUsage {
+    WantValue,
+    IgnoreValue
+};
+
 struct MOZ_STACK_CLASS BytecodeEmitter
 {
     class TDZCheckCache;
@@ -434,10 +439,12 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     };
 
     // Emit code for the tree rooted at pn.
-    MOZ_MUST_USE bool emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote = EMIT_LINENOTE);
+    MOZ_MUST_USE bool emitTree(ParseNode* pn, ValueUsage valueUsage = ValueUsage::WantValue,
+                               EmitLineNumberNote emitLineNote = EMIT_LINENOTE);
 
     // Emit code for the tree rooted at pn with its own TDZ cache.
-    MOZ_MUST_USE bool emitTreeInBranch(ParseNode* pn);
+    MOZ_MUST_USE bool emitTreeInBranch(ParseNode* pn,
+                                       ValueUsage valueUsage = ValueUsage::WantValue);
 
     // Emit global, eval, or module code for tree rooted at body. Always
     // encompasses the entire source.
@@ -724,16 +731,18 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     MOZ_MUST_USE bool emitRightAssociative(ParseNode* pn);
     MOZ_MUST_USE bool emitLeftAssociative(ParseNode* pn);
     MOZ_MUST_USE bool emitLogical(ParseNode* pn);
-    MOZ_MUST_USE bool emitSequenceExpr(ParseNode* pn);
+    MOZ_MUST_USE bool emitSequenceExpr(ParseNode* pn,
+                                       ValueUsage valueUsage = ValueUsage::WantValue);
 
     MOZ_NEVER_INLINE MOZ_MUST_USE bool emitIncOrDec(ParseNode* pn);
 
-    MOZ_MUST_USE bool emitConditionalExpression(ConditionalExpression& conditional);
+    MOZ_MUST_USE bool emitConditionalExpression(ConditionalExpression& conditional,
+                                                ValueUsage valueUsage = ValueUsage::WantValue);
 
     MOZ_MUST_USE bool isRestParameter(ParseNode* pn, bool* result);
     MOZ_MUST_USE bool emitOptimizeSpread(ParseNode* arg0, JumpList* jmp, bool* emitted);
 
-    MOZ_MUST_USE bool emitCallOrNew(ParseNode* pn);
+    MOZ_MUST_USE bool emitCallOrNew(ParseNode* pn, ValueUsage valueUsage = ValueUsage::WantValue);
     MOZ_MUST_USE bool emitSelfHostedCallFunction(ParseNode* pn);
     MOZ_MUST_USE bool emitSelfHostedResumeGenerator(ParseNode* pn);
     MOZ_MUST_USE bool emitSelfHostedForceInterpreter(ParseNode* pn);

js/src/jit/BaselineCompiler.cpp

@@ -3297,6 +3297,12 @@ BaselineCompiler::emit_JSOP_CALL()
     return emitCall();
 }
 
+bool
+BaselineCompiler::emit_JSOP_CALL_IGNORES_RV()
+{
+    return emitCall();
+}
+
 bool
 BaselineCompiler::emit_JSOP_CALLITER()
 {

js/src/jit/BaselineCompiler.h

@@ -160,6 +160,7 @@ namespace jit {
     _(JSOP_INITALIASEDLEXICAL) \
     _(JSOP_UNINITIALIZED)      \
     _(JSOP_CALL)               \
+    _(JSOP_CALL_IGNORES_RV)    \
     _(JSOP_CALLITER)           \
     _(JSOP_FUNCALL)            \
     _(JSOP_FUNAPPLY)           \

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,
+                                         fun, templateObject, constructing, ignoresReturnValue,
-                                         script->pcToOffset(pc));
+                                         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
+    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.

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_) << 17) |
-                  (static_cast<int32_t>(isSpread_) << 18);
+                  (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),

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(),
+    emitCallInvokeFunction(call, calleereg, call->isConstructing(), call->ignoresReturnValue(),
-                           unusedStack);
+                           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*.
 

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,
+                                bool isConstructing, bool ignoresReturnValue,
-                                uint32_t unusedStack);
+                                uint32_t argc, uint32_t unusedStack);
     void visitCallGeneric(LCallGeneric* call);
     void emitCallInvokeFunctionShuffleNewTarget(LCallKnown *call,
                                                 Register calleeReg,

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:
@@ -5872,7 +5874,7 @@ 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);
@@ -5911,7 +5913,7 @@ 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;
 
@@ -6087,7 +6089,7 @@ 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);
@@ -6536,7 +6538,8 @@ 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);
@@ -6561,7 +6564,8 @@ 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;
 
@@ -6598,7 +6602,8 @@ 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);
@@ -6627,7 +6632,8 @@ 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);
@@ -6736,7 +6742,8 @@ 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();
@@ -6782,7 +6789,7 @@ 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();
 
@@ -6808,7 +6815,7 @@ 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;
 
@@ -6944,7 +6951,8 @@ 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;
 
@@ -7045,7 +7053,7 @@ 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)
@@ -7061,7 +7069,8 @@ 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();
@@ -7100,7 +7109,8 @@ 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;
 
@@ -7117,7 +7127,7 @@ 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
@@ -11999,7 +12009,8 @@ 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;
 
@@ -12494,7 +12505,8 @@ 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;
 

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 constructing_:1;
-    bool setter_;
+
+    // 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;

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;

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:

js/src/jit/VMFunctions.cpp

@@ -54,8 +54,8 @@ VMFunction::addToFunctions()
 }
 
 bool
-InvokeFunction(JSContext* cx, HandleObject obj, bool constructing, uint32_t argc, Value* argv,
+InvokeFunction(JSContext* cx, HandleObject obj, bool constructing, bool ignoresReturnValue,
-               MutableHandleValue rval)
+               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

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,
+InvokeFunction(JSContext* cx, HandleObject obj0, bool constructing, bool ignoresReturnValue,
-               MutableHandleValue rval);
+               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);

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

js/src/jsfriendapi.h

@@ -2254,6 +2254,7 @@ struct JSJitInfo {
         Method,
         StaticMethod,
         InlinableNative,
+        IgnoresReturnValueNative,
         // Must be last
         OpTypeCount
     };
@@ -2345,8 +2346,13 @@ struct JSJitInfo {
         JSJitMethodOp method;
         /** A DOM static method, used for Promise wrappers */
         JSNative staticMethod;
+        JSNative ignoresReturnValueMethod;
     };
 
+    static unsigned offsetOfIgnoresReturnValueNative() {
+        return offsetof(JSJitInfo, ignoresReturnValueMethod);
+    }
+
     union {
         uint16_t protoID;
         js::jit::InlinableNative inlinableNative;

js/src/jsfun.h

@@ -585,6 +585,10 @@ class JSFunction : public js::NativeObject
         return offsetof(JSFunction, u.nativeOrScript);
     }
 
+    static unsigned offsetOfJitInfo() {
+        return offsetof(JSFunction, u.n.jitinfo);
+    }
+
     inline void trace(JSTracer* trc);
 
     /* Bound function accessors. */

js/src/jsopcode.cpp

@@ -132,7 +132,8 @@ js::StackUses(JSScript* script, jsbytecode* pc)
         return 2 + GET_ARGC(pc) + 1;
       default:
         /* stack: fun, this, [argc arguments] */
-        MOZ_ASSERT(op == JSOP_CALL || op == JSOP_EVAL || op == JSOP_CALLITER ||
+        MOZ_ASSERT(op == JSOP_CALL || op == JSOP_CALL_IGNORES_RV || op == JSOP_EVAL ||
+                   op == JSOP_CALLITER ||
                    op == JSOP_STRICTEVAL || op == JSOP_FUNCALL || op == JSOP_FUNAPPLY);
         return 2 + GET_ARGC(pc);
     }
@@ -1363,6 +1364,7 @@ ExpressionDecompiler::decompilePC(jsbytecode* pc)
       case JSOP_NEWTARGET:
         return write("new.target");
       case JSOP_CALL:
+      case JSOP_CALL_IGNORES_RV:
       case JSOP_CALLITER:
       case JSOP_FUNCALL:
         return decompilePCForStackOperand(pc, -int32_t(GET_ARGC(pc) + 2)) &&
@@ -1662,7 +1664,7 @@ DecompileArgumentFromStack(JSContext* cx, int formalIndex, char** res)
 
     /* Don't handle getters, setters or calls from fun.call/fun.apply. */
     JSOp op = JSOp(*current);
-    if (op != JSOP_CALL && op != JSOP_NEW)
+    if (op != JSOP_CALL && op != JSOP_CALL_IGNORES_RV && op != JSOP_NEW)
         return true;
 
     if (static_cast<unsigned>(formalIndex) >= GET_ARGC(current))
@@ -1725,6 +1727,8 @@ js::CallResultEscapes(jsbytecode* pc)
 
     if (*pc == JSOP_CALL)
         pc += JSOP_CALL_LENGTH;
+    else if (*pc == JSOP_CALL_IGNORES_RV)
+        pc += JSOP_CALL_IGNORES_RV_LENGTH;
     else if (*pc == JSOP_SPREADCALL)
         pc += JSOP_SPREADCALL_LENGTH;
     else

js/src/vm/Interpreter.cpp

@@ -470,7 +470,13 @@ js::InternalCallOrConstruct(JSContext* cx, const CallArgs& args, MaybeConstruct
 
     if (fun->isNative()) {
         MOZ_ASSERT_IF(construct, !fun->isConstructor());
-        return CallJSNative(cx, fun->native(), args);
+        JSNative native = fun->native();
+        if (!construct && args.ignoresReturnValue()) {
+            const JSJitInfo* jitInfo = fun->jitInfo();
+            if (jitInfo && jitInfo->type() == JSJitInfo::IgnoresReturnValueNative)
+                native = jitInfo->ignoresReturnValueMethod;
+        }
+        return CallJSNative(cx, native, args);
     }
 
     if (!JSFunction::getOrCreateScript(cx, fun))
@@ -2974,6 +2980,7 @@ CASE(JSOP_FUNAPPLY)
 
 CASE(JSOP_NEW)
 CASE(JSOP_CALL)
+CASE(JSOP_CALL_IGNORES_RV)
 CASE(JSOP_CALLITER)
 CASE(JSOP_SUPERCALL)
 CASE(JSOP_FUNCALL)
@@ -2982,10 +2989,11 @@ CASE(JSOP_FUNCALL)
         cx->runtime()->spsProfiler.updatePC(script, REGS.pc);
 
     MaybeConstruct construct = MaybeConstruct(*REGS.pc == JSOP_NEW || *REGS.pc == JSOP_SUPERCALL);
+    bool ignoresReturnValue = *REGS.pc == JSOP_CALL_IGNORES_RV;
     unsigned argStackSlots = GET_ARGC(REGS.pc) + construct;
 
     MOZ_ASSERT(REGS.stackDepth() >= 2u + GET_ARGC(REGS.pc));
-    CallArgs args = CallArgsFromSp(argStackSlots, REGS.sp, construct);
+    CallArgs args = CallArgsFromSp(argStackSlots, REGS.sp, construct, ignoresReturnValue);
 
     JSFunction* maybeFun;
     bool isFunction = IsFunctionObject(args.calleev(), &maybeFun);

js/src/vm/Opcodes.h

@@ -2292,14 +2292,23 @@
      *   Operands:
      *   Stack: =>
      */ \
-    macro(JSOP_JUMPTARGET,  230, "jumptarget",     NULL,  1,  0,  0,  JOF_BYTE)
+    macro(JSOP_JUMPTARGET,  230, "jumptarget",     NULL,  1,  0,  0,  JOF_BYTE)\
+    /*
+     * Like JSOP_CALL, but tells the function that the return value is ignored.
+     * stack.
+     *   Category: Statements
+     *   Type: Function
+     *   Operands: uint16_t argc
+     *   Stack: callee, this, args[0], ..., args[argc-1] => rval
+     *   nuses: (argc+2)
+     */ \
+    macro(JSOP_CALL_IGNORES_RV, 231, "call-ignores-rv", NULL, 3, -1, 1, JOF_UINT16|JOF_INVOKE|JOF_TYPESET)
 
 /*
  * In certain circumstances it may be useful to "pad out" the opcode space to
  * a power of two.  Use this macro to do so.
  */
 #define FOR_EACH_TRAILING_UNUSED_OPCODE(macro) \
-    macro(231) \
     macro(232) \
     macro(233) \
     macro(234) \

js/src/vm/Stack.h

@@ -1006,6 +1006,17 @@ class InvokeArgs : public detail::GenericArgsBase<NO_CONSTRUCT>
     explicit InvokeArgs(JSContext* cx) : Base(cx) {}
 };
 
+/** Function call args of statically-unknown count. */
+class InvokeArgsMaybeIgnoresReturnValue : public detail::GenericArgsBase<NO_CONSTRUCT>
+{
+    using Base = detail::GenericArgsBase<NO_CONSTRUCT>;
+
+  public:
+    explicit InvokeArgsMaybeIgnoresReturnValue(JSContext* cx, bool ignoresReturnValue) : Base(cx) {
+        this->ignoresReturnValue_ = ignoresReturnValue;
+    }
+};
+
 /** Function call args of statically-known count. */
 template <size_t N>
 class FixedInvokeArgs : public detail::FixedArgsBase<NO_CONSTRUCT, N>