Optimize the equality check case of ICCompare stubs.

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
===================================================================
--- src/ia32/code-stubs-ia32.cc	(revision 9957)
+++ src/ia32/code-stubs-ia32.cc	(working copy)
@@ -6502,6 +6502,55 @@
 }
 
 
+void ICCompareStub::GenerateKnownObjects(MacroAssembler* masm, Map* map) {
+  Label miss;
+  __ mov(ecx, edx);
+  __ and_(ecx, eax);
+  __ JumpIfSmi(ecx, &miss, Label::kNear);
+
+  __ mov(ecx, FieldOperand(eax, HeapObject::kMapOffset));
+  __ mov(ebx, FieldOperand(edx, HeapObject::kMapOffset));
+  __ cmp(ecx, Handle<Map>(map));
+  __ j(not_equal, &miss, Label::kNear);
+  __ cmp(ebx, Handle<Map>(map));
+  __ j(not_equal, &miss, Label::kNear);
+
+  __ sub(eax, edx);
+  __ ret(0);
+
+  __ bind(&miss);

[Kevin Millikin (Chromium), 2011/11/10 19:08:42]

All the code from here and below looks like it could be generated by a call to
GenerateMiss(masm) (if this function were non-static).

[Rico, 2011/11/11 08:49:11]

Done.

+
+  // Save the registers.
+  __ pop(ecx);

[Kevin Millikin (Chromium), 2011/11/10 19:08:42]

And come to think of it, I don't know why we preserve the incoming arguments
under the return address in the existing code.  Instead, it would be a bit more
straightforward to save them above and save a pair of push/pops to do:

{ FrameScope scope(masm, StackFrame::INTERNAL);
  __ push(edx);  // Preserve edx and eax.
  __ push(eax);
  __ push(edx);  // And also use them as the arguments.
  __ push(eax);
  __ push(Immediate(Smi::FromInt(Token::EQ)));
  __ CallExternalReference(runtime, 3);
  __ pop(eax);
  __ pop(edx);
}
// Compute the entry point of the rewritten stub.
__ lea(edi, FieldOperand(eax, Code::kHeaderSize));
// Do a tail call to the rewritten stub.
__ jmp(edi);

[Kevin Millikin (Chromium), 2011/11/10 19:11:18]

Actually, that code has a bug.  You need lea before popping to restore eax.

+  __ push(edx);
+  __ push(eax);
+  __ push(ecx);
+
+  // Call the runtime system in a fresh internal frame.
+  ExternalReference runtime = ExternalReference(IC_Utility(IC::kCompareIC_Miss),
+                                                masm->isolate());
+  {
+    FrameScope scope(masm, StackFrame::INTERNAL);
+    __ push(edx);
+    __ push(eax);
+    __ push(Immediate(Smi::FromInt(Token::EQ)));
+    __ CallExternalReference(runtime, 3);
+  }
+
+  // Compute the entry point of the rewritten stub.
+  __ lea(edi, FieldOperand(eax, Code::kHeaderSize));
+
+  // Restore registers.
+  __ pop(ecx);
+  __ pop(eax);
+  __ pop(edx);
+  __ push(ecx);
+
+  // Do a tail call to the rewritten stub.
+  __ jmp(edi);
+}
+
+
 void ICCompareStub::GenerateMiss(MacroAssembler* masm) {
   // Save the registers.
   __ pop(ecx);