Reland "Allocation site support for monomorphic StringAdds in BinaryOps".

src/ic.h

Index: src/ic.h
diff --git a/src/ic.h b/src/ic.h
index d1d2b6139d06c09e526a130bf8e2d7dc8e3467a0..308ab9530898caf8e00ea7f74216d5113c9e1703 100644
--- a/src/ic.h
+++ b/src/ic.h
@@ -861,10 +861,27 @@ class BinaryOpIC: public IC {
             right_kind_ > SMI && right_kind_ <= NUMBER));
     }
 
+    // Returns true if the IC _could_ create allocation mementos.
+    bool CouldCreateAllocationMementos() const {
+      if (left_kind_ == STRING || right_kind_ == STRING) {
+        ASSERT_EQ(Token::ADD, op_);
+        return true;
+      }
+      return false;
+    }
+
+    // Returns true if the IC _should_ create allocation mementos.
+    bool ShouldCreateAllocationMementos() const {
+      return FLAG_allocation_site_pretenuring &&
+          CouldCreateAllocationMementos();
+    }
+
     bool HasSideEffects() const {
       return Max(left_kind_, right_kind_) == GENERIC;
     }
 
+    // Returns true if the IC should enable the inline smi code (i.e. if either
+    // parameter may be a smi).
     bool UseInlinedSmiCode() const {
       return KindMaybeSmi(left_kind_) || KindMaybeSmi(right_kind_);
     }
@@ -926,8 +943,9 @@ class BinaryOpIC: public IC {
 
   static Builtins::JavaScript TokenToJSBuiltin(Token::Value op);
 
-  MUST_USE_RESULT MaybeObject* Transition(Handle<Object> left,
-                                          Handle<Object> right);
+  MaybeObject* Transition(Handle<AllocationSite> allocation_site,
+                          Handle<Object> left,
+                          Handle<Object> right) V8_WARN_UNUSED_RESULT;
 };
 
 
@@ -1036,6 +1054,7 @@ DECLARE_RUNTIME_FUNCTION(MaybeObject*, StoreIC_MissFromStubFailure);
 DECLARE_RUNTIME_FUNCTION(MaybeObject*, KeyedCallIC_MissFromStubFailure);
 DECLARE_RUNTIME_FUNCTION(MaybeObject*, ElementsTransitionAndStoreIC_Miss);
 DECLARE_RUNTIME_FUNCTION(MaybeObject*, BinaryOpIC_Miss);
+DECLARE_RUNTIME_FUNCTION(MaybeObject*, BinaryOpIC_MissWithAllocationSite);
 DECLARE_RUNTIME_FUNCTION(MaybeObject*, CompareNilIC_Miss);
 DECLARE_RUNTIME_FUNCTION(MaybeObject*, ToBooleanIC_Miss);