[crankshaft] Re-add fast-case for string add left/right.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include <cstring>
 #include <iosfwd>
 
@@ skipping 7330 matching lines @@
   Unique<Map> original_map_;
   Unique<Map> transitioned_map_;
   uint32_t bit_field_;
 };
 
 
 class HStringAdd final : public HBinaryOperation {
  public:
   static HInstruction* New(
       Isolate* isolate, Zone* zone, HValue* context, HValue* left,
-      HValue* right, Strength strength = Strength::WEAK,
-      PretenureFlag pretenure_flag = NOT_TENURED,
+      HValue* right, PretenureFlag pretenure_flag = NOT_TENURED,
       StringAddFlags flags = STRING_ADD_CHECK_BOTH,
       Handle<AllocationSite> allocation_site = Handle<AllocationSite>::null());
 
   StringAddFlags flags() const { return flags_; }
   PretenureFlag pretenure_flag() const { return pretenure_flag_; }
 
   Representation RequiredInputRepresentation(int index) override {
     return Representation::Tagged();
   }
 
   std::ostream& PrintDataTo(std::ostream& os) const override;  // NOLINT
 
   DECLARE_CONCRETE_INSTRUCTION(StringAdd)
 
  protected:
   bool DataEquals(HValue* other) override {
     return flags_ == HStringAdd::cast(other)->flags_ &&
         pretenure_flag_ == HStringAdd::cast(other)->pretenure_flag_;
   }
 
  private:
-  HStringAdd(HValue* context, HValue* left, HValue* right, Strength strength,
+  HStringAdd(HValue* context, HValue* left, HValue* right,
              PretenureFlag pretenure_flag, StringAddFlags flags,
              Handle<AllocationSite> allocation_site)
-      : HBinaryOperation(context, left, right, strength, HType::String()),
+      : HBinaryOperation(context, left, right, Strength::WEAK, HType::String()),
         flags_(flags),
         pretenure_flag_(pretenure_flag) {
     set_representation(Representation::Tagged());
-    SetFlag(kUseGVN);
+    if ((flags & STRING_ADD_CONVERT) == STRING_ADD_CONVERT) {
+      SetAllSideEffects();
+      ClearFlag(kUseGVN);
+    } else {
+      SetChangesFlag(kNewSpacePromotion);
+      SetFlag(kUseGVN);
+    }
     SetDependsOnFlag(kMaps);
-    SetChangesFlag(kNewSpacePromotion);
     if (FLAG_trace_pretenuring) {
       PrintF("HStringAdd with AllocationSite %p %s\n",
              allocation_site.is_null()
                  ? static_cast<void*>(NULL)
                  : static_cast<void*>(*allocation_site),
              pretenure_flag == TENURED ? "tenured" : "not tenured");
     }
   }
 
-  // No side-effects except possible allocation:
-  bool IsDeletable() const override { return true; }
+  bool IsDeletable() const final {
+    return (flags_ & STRING_ADD_CONVERT) != STRING_ADD_CONVERT;
+  }
 
   const StringAddFlags flags_;
   const PretenureFlag pretenure_flag_;
 };
 
 
 class HStringCharCodeAt final : public HTemplateInstruction<3> {
  public:
   DECLARE_INSTRUCTION_WITH_CONTEXT_FACTORY_P2(HStringCharCodeAt,
                                               HValue*,
@@ skipping 564 matching lines @@
 };
 
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_