Optimize the equality check case of ICCompare stubs.

src/hydrogen.cc

Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc	(revision 9957)
+++ src/hydrogen.cc	(working copy)
@@ -5998,14 +5998,27 @@
     switch (op) {
       case Token::EQ:
       case Token::EQ_STRICT: {
-        AddInstruction(new(zone()) HCheckNonSmi(left));
-        AddInstruction(HCheckInstanceType::NewIsSpecObject(left));
-        AddInstruction(new(zone()) HCheckNonSmi(right));
-        AddInstruction(HCheckInstanceType::NewIsSpecObject(right));
-        HCompareObjectEqAndBranch* result =
-            new(zone()) HCompareObjectEqAndBranch(left, right);
-        result->set_position(expr->position());
-        return ast_context()->ReturnControl(result, expr->id());
+        // Can we get away with map check and not instance type check?
+        Handle<Map> map = oracle()->GetCompareMap(expr);
+        if (!map.is_null()) {
+          AddInstruction(new(zone()) HCheckNonSmi(left));
+          AddInstruction(new(zone()) HCheckMap(left, map));
+          AddInstruction(new(zone()) HCheckNonSmi(right));
+          AddInstruction(new(zone()) HCheckMap(right, map));
+          HCompareObjectEqAndBranch* result =
+              new(zone()) HCompareObjectEqAndBranch(left, right);
+          result->set_position(expr->position());
+          return ast_context()->ReturnControl(result, expr->id());
+        } else {
+          AddInstruction(new(zone()) HCheckNonSmi(left));
+          AddInstruction(HCheckInstanceType::NewIsSpecObject(left));
+          AddInstruction(new(zone()) HCheckNonSmi(right));
+          AddInstruction(HCheckInstanceType::NewIsSpecObject(right));
+          HCompareObjectEqAndBranch* result =
+              new(zone()) HCompareObjectEqAndBranch(left, right);
+          result->set_position(expr->position());
+          return ast_context()->ReturnControl(result, expr->id());
+        }
       }
       default:
         return Bailout("Unsupported non-primitive compare");