Improve ==/=== comparison in Hydrogen for monomorphic maps

src/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 9175 matching lines @@
     int left_position,
     int right_position,
     BailoutId bailout_id) {
   Representation left_rep = Representation::FromType(left_type);
   Representation right_rep = Representation::FromType(right_type);
   Representation combined_rep = Representation::FromType(combined_type);
 
   if (combined_type->Is(Type::Receiver())) {
     if (Token::IsEqualityOp(op)) {
       // Can we get away with map check and not instance type check?
+      HValue* operand_to_check =
+          left->block()->block_id() < right->block()->block_id() ? left : right;
       if (combined_type->IsClass()) {
         Handle<Map> map = combined_type->AsClass();
-        AddCheckMap(left, map);
-        AddCheckMap(right, map);
+        AddCheckMap(operand_to_check, map);
         HCompareObjectEqAndBranch* result =
             New<HCompareObjectEqAndBranch>(left, right);
         if (FLAG_emit_opt_code_positions) {
           result->set_operand_position(zone(), 0, left_position);
           result->set_operand_position(zone(), 1, right_position);
         }
         return result;
       } else {
-        BuildCheckHeapObject(left);
-        Add<HCheckInstanceType>(left, HCheckInstanceType::IS_SPEC_OBJECT);
-        BuildCheckHeapObject(right);
-        Add<HCheckInstanceType>(right, HCheckInstanceType::IS_SPEC_OBJECT);
+        BuildCheckHeapObject(operand_to_check);
+        Add<HCheckInstanceType>(operand_to_check,
+                                HCheckInstanceType::IS_SPEC_OBJECT);
         HCompareObjectEqAndBranch* result =
             New<HCompareObjectEqAndBranch>(left, right);
         return result;
       }
     } else {
       Bailout(kUnsupportedNonPrimitiveCompare);
       return NULL;
     }
   } else if (combined_type->Is(Type::InternalizedString()) &&
              Token::IsEqualityOp(op)) {
@@ skipping 1555 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal