Use a WeakCell in the CallIC type vector.

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index ae2d92158dd75cfc89366a37afd9f57c750725aa..a1bef5176d49f07534e3294ca9a459eb09ac0ac0 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -2115,10 +2115,30 @@ void CallICStub::Generate(MacroAssembler* masm) {
 
   // The checks. First, does rdi match the recorded monomorphic target?
   __ SmiToInteger32(rdx, rdx);
-  __ cmpp(rdi, FieldOperand(rbx, rdx, times_pointer_size,
-                            FixedArray::kHeaderSize));
+  __ movp(rcx,
+          FieldOperand(rbx, rdx, times_pointer_size, FixedArray::kHeaderSize));
+
+  // We don't know that we have a weak cell. We might have a private symbol
+  // or an AllocationSite, but the memory is safe to examine.
+  // AllocationSite::kTransitionInfoOffset - contains a Smi or pointer to
+  // FixedArray.
+  // WeakCell::kValueOffset - contains a JSFunction or Smi(0)
+  // Symbol::kHashFieldSlot - if the low bit is 1, then the hash is not
+  // computed, meaning that it can't appear to be a pointer. If the low bit is
+  // 0, then hash is computed, but the 0 bit prevents the field from appearing
+  // to be a pointer.
+  STATIC_ASSERT(WeakCell::kSize >= kPointerSize);
+  STATIC_ASSERT(AllocationSite::kTransitionInfoOffset ==
+                    WeakCell::kValueOffset &&
+                WeakCell::kValueOffset == Symbol::kHashFieldSlot);
+
+  __ cmpp(rdi, FieldOperand(rcx, WeakCell::kValueOffset));
   __ j(not_equal, &extra_checks_or_miss);
 
+  // The compare above could have been a SMI/SMI comparison. Guard against this
+  // convincing us that we have a monomorphic JSFunction.
+  __ JumpIfSmi(rdi, &extra_checks_or_miss);
+
   __ bind(&have_js_function);
   if (CallAsMethod()) {
     EmitContinueIfStrictOrNative(masm, &cont);
@@ -2147,8 +2167,6 @@ void CallICStub::Generate(MacroAssembler* masm) {
   __ bind(&extra_checks_or_miss);
   Label uninitialized, miss;
 
-  __ movp(rcx, FieldOperand(rbx, rdx, times_pointer_size,
-                            FixedArray::kHeaderSize));
   __ Cmp(rcx, TypeFeedbackVector::MegamorphicSentinel(isolate));
   __ j(equal, &slow_start);
 
@@ -2191,14 +2209,20 @@ void CallICStub::Generate(MacroAssembler* masm) {
   // Update stats.
   __ SmiAddConstant(FieldOperand(rbx, with_types_offset), Smi::FromInt(1));
 
-  // Store the function.
-  __ movp(FieldOperand(rbx, rdx, times_pointer_size, FixedArray::kHeaderSize),
-          rdi);
+  // Store the function. Use a stub since we need a frame for allocation.
+  // rbx - vector
+  // rdx - slot (needs to be in smi form)
+  // rdi - function
+  {
+    FrameScope scope(masm, StackFrame::INTERNAL);
+    CreateWeakCellStub create_stub(isolate);
+
+    __ Integer32ToSmi(rdx, rdx);
+    __ Push(rdi);
+    __ CallStub(&create_stub);
+    __ Pop(rdi);
+  }
 
-  // Update the write barrier.
-  __ movp(rax, rdi);
-  __ RecordWriteArray(rbx, rax, rdx, kDontSaveFPRegs, EMIT_REMEMBERED_SET,
-                      OMIT_SMI_CHECK);
   __ jmp(&have_js_function);
 
   // We are here because tracing is on or we encountered a MISS case we can't
@@ -2260,6 +2284,7 @@ void CodeStub::GenerateStubsAheadOfTime(Isolate* isolate) {
   // It is important that the store buffer overflow stubs are generated first.
   ArrayConstructorStubBase::GenerateStubsAheadOfTime(isolate);
   CreateAllocationSiteStub::GenerateAheadOfTime(isolate);
+  CreateWeakCellStub::GenerateAheadOfTime(isolate);
   BinaryOpICStub::GenerateAheadOfTime(isolate);
   BinaryOpICWithAllocationSiteStub::GenerateAheadOfTime(isolate);
 }