Turn a Dart String + String into a JavaScript String + String.

sdk/lib/_internal/compiler/implementation/ssa/optimize.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 abstract class OptimizationPhase {
   String get name;
   void visitGraph(HGraph graph);
 }
@@ skipping 267 matching lines @@
     }
 
     // Try converting the instruction to a builtin instruction.
     HInstruction instruction =
         node.specializer.tryConvertToBuiltin(node, compiler);
     if (instruction != null) return instruction;
 
     Selector selector = node.selector;
     HInstruction input = node.inputs[1];
 
-    if (selector.isCall()) {
+    if (selector.isCall() || selector.isOperator()) {
       Element target;
       if (input.isExtendableArray(compiler)) {
         if (selector.applies(backend.jsArrayRemoveLast, compiler)) {
           target = backend.jsArrayRemoveLast;
         } else if (selector.applies(backend.jsArrayAdd, compiler)) {
           // The codegen special cases array calls, but does not
           // inline argument type checks.
           if (!compiler.enableTypeAssertions) {
             target = backend.jsArrayAdd;
           }
         }
       } else if (input.isString(compiler)) {
         if (selector.applies(backend.jsStringSplit, compiler)) {
           if (node.inputs[2].isString(compiler)) {
             target = backend.jsStringSplit;
           }
-        } else if (selector.applies(backend.jsStringConcat, compiler)) {
-          // `concat` is turned into a JavaScript '+' so we need to
+        } else if (selector.applies(backend.jsStringOperatorAdd, compiler)) {
+          // `operator+` is turned into a JavaScript '+' so we need to
           // make sure the receiver is not null.
           if (node.inputs[2].isString(compiler) && !input.canBeNull()) {
-            target = backend.jsStringConcat;
+            target = backend.jsStringOperatorAdd;
           }
         } else if (selector.applies(backend.jsStringToString, compiler)
                    && !input.canBeNull()) {
           return input;
         }
       }
       if (target != null) {
         // TODO(ngeoffray): There is a strong dependency between codegen
         // and this optimization that the dynamic invoke does not need an
         // interceptor. We currently need to keep a
@@ skipping 1184 matching lines @@
       // that knows it is not of a specific Type.
     }
 
     for (HIf ifUser in notIfUsers) {
       changeUsesDominatedBy(ifUser.elseBlock, input, convertedType);
       // TODO(ngeoffray): Also change uses for the then block on a HType
       // that knows it is not of a specific Type.
     }
   }
 }