Improve polymorphic loads on single slots.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index fcbc90da5f8ed39fe30dee540a5c0e08542579a5..1d1af3a73d932818c57b4fef2ee57721bd4dd65f 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -4238,14 +4238,22 @@ void LCodeGen::DoCheckMapCommon(Register reg,
 }
 
 
-void LCodeGen::DoCheckMap(LCheckMap* instr) {
+void LCodeGen::DoCheckMaps(LCheckMaps* instr) {
   Register scratch = scratch0();
   LOperand* input = instr->InputAt(0);
   ASSERT(input->IsRegister());
   Register reg = ToRegister(input);
-  Handle<Map> map = instr->hydrogen()->map();
-  DoCheckMapCommon(reg, scratch, map, instr->hydrogen()->mode(),
-                   instr->environment());
+
+  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, scratch, map, &success, REQUIRE_EXACT_MAP);
+    __ b(eq, &success);
+  }
+  Handle<Map> map = map_set->last();
+  DoCheckMapCommon(reg, scratch, map, REQUIRE_EXACT_MAP, instr->environment());
+  __ bind(&success);
 }