Fix for interpolation codegen bug

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 245 matching lines @@
       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)) {
+      } else if (input.isStringOrNull(compiler)) {
         if (selector.applies(backend.jsStringSplit, compiler)) {
           HInstruction argument = node.inputs[2];
-          if (argument.isString(compiler) && !argument.canBeNull()) {
+          if (argument.isString(compiler)) {
             target = backend.jsStringSplit;
           }
         } else if (selector.applies(backend.jsStringOperatorAdd, compiler)) {
           // `operator+` is turned into a JavaScript '+' so we need to
           // make sure the receiver and the argument are not null.
           HInstruction argument = node.inputs[2];
           if (argument.isString(compiler)
-              && !argument.canBeNull()
               && !input.canBeNull()) {
             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
@@ skipping 497 matching lines @@
     HInstruction folded = graph.addConstant(
         constantSystem.createString(
             new DartString.concat(leftString.value, rightString.value)),
         compiler);
     if (prefix == null) return folded;
     return new HStringConcat(prefix, folded, node.node, backend.stringType);
   }
 
   HInstruction visitStringify(HStringify node) {
     HInstruction input = node.inputs[0];
-    if (input.isString(compiler) && !input.canBeNull()) return input;
+    if (input.isString(compiler)) return input;
     if (input.isConstant()) {
       HConstant constant = input;
       if (!constant.constant.isPrimitive()) return node;
       PrimitiveConstant primitive = constant.constant;
       return graph.addConstant(constantSystem.createString(
           primitive.toDartString()), compiler);
     }
     return node;
   }
 
@@ skipping 1160 matching lines @@
 
     keyedValues.forEach((receiver, values) {
       result.keyedValues[receiver] =
           new Map<HInstruction, HInstruction>.from(values);
     });
 
     result.nonEscapingReceivers.addAll(nonEscapingReceivers);
     return result;
   }
 }