Better sequences for class id loading on ia32.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
===================================================================
--- runtime/vm/intermediate_language_ia32.cc	(revision 38158)
+++ runtime/vm/intermediate_language_ia32.cc	(working copy)
@@ -945,17 +945,15 @@
 void LoadClassIdInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   const Register object = locs()->in(0).reg();
   const Register result = locs()->out(0).reg();
-  Label not_smi, done;
+  Label done;
 
   // We don't use Assembler::LoadTaggedClassIdMayBeSmi() here---which uses
   // a conditional move instead, and requires an additional register---because
   // it is slower, probably due to branch prediction usually working just fine
   // in this case.
+  __ movl(result, Immediate(kSmiCid << 1));

[srdjan, 2014/07/11 18:23:30]

ASSERT result != object

[zra, 2014/07/11 18:28:41]

Done.

   __ testl(object, Immediate(kSmiTagMask));
-  __ j(NOT_ZERO, &not_smi, Assembler::kNearJump);
-  __ movl(result, Immediate(Smi::RawValue(kSmiCid)));
-  __ jmp(&done, Assembler::kNearJump);
-  __ Bind(&not_smi);
+  __ j(EQUAL, &done, Assembler::kNearJump);
   __ LoadClassId(result, object);
   __ SmiTag(result);
   __ Bind(&done);