Constant-fold strings in HGraphBuilder::BuildBinaryOperation.

src/hydrogen.cc

 // Copyright 2013 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.
 
 #include "src/hydrogen.h"
 
 #include <sstream>
 
 #include "src/v8.h"
 
@@ skipping 10470 matching lines @@
     if (right_type->Is(Type::Number())) {
       DCHECK(left_type->Is(Type::String()));
       right = BuildNumberToString(right, right_type);
     } else if (!right_type->Is(Type::String())) {
       DCHECK(left_type->Is(Type::String()));
       HValue* function = AddLoadJSBuiltin(Builtins::STRING_ADD_LEFT);
       Add<HPushArguments>(left, right);
       return AddUncasted<HInvokeFunction>(function, 2);
     }
 
-    // Fast path for empty constant strings.
-    if (left->IsConstant() &&
-        HConstant::cast(left)->HasStringValue() &&
-        HConstant::cast(left)->StringValue()->length() == 0) {
-      return right;
-    }
-    if (right->IsConstant() &&
-        HConstant::cast(right)->HasStringValue() &&
-        HConstant::cast(right)->StringValue()->length() == 0) {
-      return left;
+    // Fast paths for empty constant strings.
+    Handle<String> left_string =
+        left->IsConstant() && HConstant::cast(left)->HasStringValue()
+            ? HConstant::cast(left)->StringValue()
+            : Handle<String>();
+    Handle<String> right_string =
+        right->IsConstant() && HConstant::cast(right)->HasStringValue()
+            ? HConstant::cast(right)->StringValue()
+            : Handle<String>();
+    if (!left_string.is_null() && left_string->length() == 0) return right;
+    if (!right_string.is_null() && right_string->length() == 0) return left;
+    if (!left_string.is_null() && !right_string.is_null()) {
+      return AddUncasted<HStringAdd>(
+          left, right, allocation_mode.GetPretenureMode(),
+          STRING_ADD_CHECK_NONE, allocation_mode.feedback_site());
     }
 
     // Register the dependent code with the allocation site.
     if (!allocation_mode.feedback_site().is_null()) {
       DCHECK(!graph()->info()->IsStub());
       Handle<AllocationSite> site(allocation_mode.feedback_site());
       AllocationSite::RegisterForDeoptOnTenureChange(site, top_info());
     }
 
     // Inline the string addition into the stub when creating allocation
@@ skipping 2923 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal