Optimizations to IC stub for unoptimized code performance on x64.

runtime/vm/assembler_ia32.cc

Index: runtime/vm/assembler_ia32.cc
diff --git a/runtime/vm/assembler_ia32.cc b/runtime/vm/assembler_ia32.cc
index 713365db6367d1067a1442869329a423cb0f3bee..ad379a21437f4aa62af268ba8b665d15516a578b 100644
--- a/runtime/vm/assembler_ia32.cc
+++ b/runtime/vm/assembler_ia32.cc
@@ -2903,26 +2903,33 @@ void Assembler::SmiUntagOrCheckClass(Register object,
 
 
 void Assembler::LoadClassIdMayBeSmi(Register result, Register object) {
-  ASSERT(result != object);
-  static const intptr_t kSmiCidSource = kSmiCid << RawObject::kClassIdTagPos;
+  Label smi, join;
 
-  // Make a dummy "Object" whose cid is kSmiCid.
-  movl(result, Immediate(reinterpret_cast<int32_t>(&kSmiCidSource) + 1));
-
-  // Check if object (in tmp) is a Smi.
   testl(object, Immediate(kSmiTagMask));
+  j(EQUAL, &smi, Assembler::kNearJump);
+  LoadClassId(result, object);
+  jmp(&join, Assembler::kNearJump);
+
+  Bind(&smi);
+  movl(result, Immediate(kSmiCid));
 
-  // If the object is not a Smi, use the original object to load the cid.
-  // Otherwise, the dummy object is used, and the result is kSmiCid.
-  cmovne(result, object);
-  LoadClassId(result, result);
+  Bind(&join);
 }
 
 
 void Assembler::LoadTaggedClassIdMayBeSmi(Register result, Register object) {
-  LoadClassIdMayBeSmi(result, object);
-  // Tag the result.
+  Label smi, join;
+
+  testl(object, Immediate(kSmiTagMask));
+  j(EQUAL, &smi, Assembler::kNearJump);
+  LoadClassId(result, object);
   SmiTag(result);
+  jmp(&join, Assembler::kNearJump);
+
+  Bind(&smi);
+  movl(result, Immediate(Smi::RawValue(kSmiCid)));
+
+  Bind(&join);
 }