X64: implement DoHasCachedArrayIndex in lithium compiler.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
===================================================================
--- src/x64/lithium-codegen-x64.cc	(revision 7013)
+++ src/x64/lithium-codegen-x64.cc	(working copy)
@@ -1632,7 +1632,17 @@
 
 
 void LCodeGen::DoHasCachedArrayIndex(LHasCachedArrayIndex* instr) {
-  Abort("Unimplemented: %s", "DoHasCachedArrayIndex");
+  Register input = ToRegister(instr->InputAt(0));
+  Register result = ToRegister(instr->result());
+
+  ASSERT(instr->hydrogen()->value()->representation().IsTagged());
+  __ LoadRoot(result, Heap::kTrueValueRootIndex);
+  __ testl(FieldOperand(input, String::kHashFieldOffset),
+          Immediate(String::kContainsCachedArrayIndexMask));

[Lasse Reichstein, 2011/03/02 09:59:07]

Indentation.

[Rico, 2011/03/02 10:12:15]

Done.

+  NearLabel done;
+  __ j(not_zero, &done);
+  __ LoadRoot(result, Heap::kFalseValueRootIndex);

[Lasse Reichstein, 2011/03/02 09:59:07]

Could we do just one computed load from the root array here?
E.g.
  ASSERT(Heap::kTrueValueRootIndex + 1 == Heap::kFalseValueRootIndex);
  __ setcc(zero, result);
  __ movzxbl(result, result);
  __ LoadRoot(result, result, Heap::kTrueValueRootIndex);

(adding a 
  void LoadRoot(Register dst, Register dynIdx, int idx) {
    __ movq(dst, Operand(kRootRegister, dynIdx, times_pointer_size, idx *
kPointerSize);
  }
if it's not there already).

I think we use similar code elsewhere.

[Rico, 2011/03/02 10:12:15]

As discussed offline this will not really have any effect here, leaving it as is
to be consistent with the remainder of the lithium instructions.

+  __ bind(&done);
 }