Improve polymorphic loads on single slots.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 6ddc024258940f2776c0b400105a6dd9b56dddfe..34a9bb7aff9cba102a494000976326fe984a9458 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -4128,6 +4128,24 @@ void LCodeGen::DoCheckMap(LCheckMap* instr) {
 }
 
 
+void LCodeGen::DoCheckMapSet(LCheckMapSet* instr) {
+  LOperand* input = instr->InputAt(0);
+  ASSERT(input->IsRegister());
+  Register reg = ToRegister(input);
+
+  Label success;
+  SmallMapList* map_set = instr->hydrogen()->map_set();
+  for (int i = 0; i < map_set->length() - 1; i++) {
+    Handle<Map> map = map_set->at(i);
+    __ CompareMap(reg, map, &success, REQUIRE_EXACT_MAP);
+    __ j(equal, &success);
+  }
+  Handle<Map> map = map_set->last();
+  DoCheckMapCommon(reg, map, REQUIRE_EXACT_MAP, instr->environment());
+  __ bind(&success);
+}
+
+
 void LCodeGen::DoClampDToUint8(LClampDToUint8* instr) {
   XMMRegister value_reg = ToDoubleRegister(instr->unclamped());
   Register result_reg = ToRegister(instr->result());