MIPS: Improve polymorphic loads on single slots.

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 1b36d5b5c25ff386d80e2a9ab7ec3a495cd48bce..e9023fa6eaff77ff664e5cf3cf87313018f11f67 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -4242,9 +4242,16 @@ void LCodeGen::DoCheckMaps(LCheckMaps* instr) {
   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);
+    __ CompareMapAndBranch(
+        reg, scratch, map, &success, eq, &success, REQUIRE_EXACT_MAP);
+  }
+  Handle<Map> map = map_set->last();
+  DoCheckMapCommon(reg, scratch, map, REQUIRE_EXACT_MAP, instr->environment());
+  __ bind(&success);
 }