Code cleanup in GenerateRecordCallTarget.

src/x64/code-stubs-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 1767 matching lines @@
 }
 
 
 static void CallStubInRecordCallTarget(MacroAssembler* masm, CodeStub* stub) {
   // eax : number of arguments to the construct function
   // ebx : Feedback vector
   // edx : slot in feedback vector (Smi)
   // edi : the function to call
   FrameScope scope(masm, StackFrame::INTERNAL);
 
-  // Arguments register must be smi-tagged to call out.
+  // Number-of-arguments register must be smi-tagged to call out.
   __ Integer32ToSmi(rax, rax);
   __ Push(rax);
   __ Push(rdi);
   __ Integer32ToSmi(rdx, rdx);
   __ Push(rdx);
   __ Push(rbx);
 
   __ CallStub(stub);
 
   __ Pop(rbx);
@@ skipping 16 matching lines @@
   Label initialize, done, miss, megamorphic, not_array_function,
       done_no_smi_convert;
 
   // Load the cache state into rcx.
   __ SmiToInteger32(rdx, rdx);
   __ movp(rcx, FieldOperand(rbx, rdx, times_pointer_size,
                             FixedArray::kHeaderSize));
 
   // A monomorphic cache hit or an already megamorphic state: invoke the
   // function without changing the state.
+  // We don't know if rcx is a WeakCell or a Symbol, but it's harmless to read
+  // at this position in a symbol (see static asserts in
+  // type-feedback-vector.h).
   Label check_allocation_site;
   __ cmpp(rdi, FieldOperand(rcx, WeakCell::kValueOffset));
   __ j(equal, &done, Label::kFar);
   __ CompareRoot(rcx, Heap::kmegamorphic_symbolRootIndex);
   __ j(equal, &done, Label::kFar);
-  __ CompareRoot(FieldOperand(rcx, 0), Heap::kWeakCellMapRootIndex);
+  __ CompareRoot(FieldOperand(rcx, HeapObject::kMapOffset),
+                 Heap::kWeakCellMapRootIndex);
   __ j(not_equal, FLAG_pretenuring_call_new ? &miss : &check_allocation_site);
 
-  // If edi is not equal to the weak cell value, and the weak cell value is
-  // cleared, we have a new chance to become monomorphic. Otherwise, we
-  // need to go megamorphic.
+  // If the weak cell is cleared, we have a new chance to become monomorphic.
   __ CheckSmi(FieldOperand(rcx, WeakCell::kValueOffset));
   __ j(equal, &initialize);
   __ jmp(&megamorphic);
 
   if (!FLAG_pretenuring_call_new) {
     __ bind(&check_allocation_site);
     // If we came here, we need to see if we are the array function.
     // If we didn't have a matching function, and we didn't find the megamorph
     // sentinel, then we have in the slot either some other function or an
-    // AllocationSite. Do a map check on the object in rcx.
+    // AllocationSite.
     __ CompareRoot(FieldOperand(rcx, 0), Heap::kAllocationSiteMapRootIndex);
     __ j(not_equal, &miss);
 
     // Make sure the function is the Array() function
     __ LoadGlobalFunction(Context::ARRAY_FUNCTION_INDEX, rcx);
     __ cmpp(rdi, rcx);
     __ j(not_equal, &megamorphic);
     __ jmp(&done);
   }
 
@@ skipping 3510 matching lines @@
   CallApiFunctionAndReturn(masm, api_function_address, thunk_ref, getter_arg,
                            kStackSpace, nullptr, return_value_operand, NULL);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64