Make x64 to use the RecordWrite stub. This is a step towards getting

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
===================================================================
--- src/x64/code-stubs-x64.cc	(revision 8207)
+++ src/x64/code-stubs-x64.cc	(working copy)
@@ -2427,16 +2427,18 @@
   // Store last subject and last input.
   __ movq(rax, Operand(rsp, kSubjectOffset));
   __ movq(FieldOperand(rbx, RegExpImpl::kLastSubjectOffset), rax);
-  __ movq(rcx, rbx);
-  __ RecordWrite(rcx,
-                 RegExpImpl::kLastSubjectOffset,
-                 rax,
-                 rdi,
-                 kDontSaveFPRegs);
+  __ RecordWriteField(rbx,
+                      RegExpImpl::kLastSubjectOffset,
+                      rax,
+                      rdi,
+                      kDontSaveFPRegs);
   __ movq(rax, Operand(rsp, kSubjectOffset));
   __ movq(FieldOperand(rbx, RegExpImpl::kLastInputOffset), rax);
-  __ movq(rcx, rbx);
-  __ RecordWrite(rcx, RegExpImpl::kLastInputOffset, rax, rdi, kDontSaveFPRegs);
+  __ RecordWriteField(rbx,
+                      RegExpImpl::kLastInputOffset,
+                      rax,
+                      rdi,
+                      kDontSaveFPRegs);
 
   // Get the static offsets vector filled by the native regexp code.
   __ LoadAddress(rcx,
@@ -5178,6 +5180,30 @@
 }
 
 
+// Takes the input in 3 registers: address_ value_ and object_.  A pointer to
+// the value has just been written into the object, now this stub makes sure
+// we keep the GC informed.  The word in the object where the value has been
+// written is in the address register.
+void RecordWriteStub::Generate(MacroAssembler* masm) {
+  Label skip_non_incremental_part;
+  __ jmp(&skip_non_incremental_part, Label::kNear);

[Lasse Reichstein, 2011/06/07 14:02:53]

But why overwrite?
Why not just:
  if (!HEAP->incremental_marking()->IsMarking()) {
    __ nop(2);
  } else {
    __ jmp(&....);
  }
And is this even safe? The label is unbound, so won't we be overwriting this
later?

[Erik Corry, 2011/06/08 10:38:55]

We will be ovewriting the opcode every time we start and end an incremental
mark-sweep collection.  The overwrite is only of the offset, not the opcode.

+  if (!HEAP->incremental_marking()->IsMarking()) {

[Lasse Reichstein, 2011/06/07 14:02:53]

HEAP should be replaced by something faster. Maybe you can get the isolate from
the MacroAssembler.

[Erik Corry, 2011/06/08 10:38:55]

Done.

+    ASSERT(masm->get_opcode(-2) == kSkipNonIncrementalPartInstruction);
+    masm->set_opcode(-2, kTwoByteNopInstruction);
+  }
+
+  if (remembered_set_action_ == EMIT_REMEMBERED_SET) {
+    __ RememberedSetHelper(
+        address_, value_, save_fp_regs_mode_, MacroAssembler::kReturnAtEnd);
+  } else {
+    __ ret(0);
+  }
+
+  __ bind(&skip_non_incremental_part);
+  __ int3();
+}
+
+
 #undef __
 
 } }  // namespace v8::internal