Fix Leg test failures.

frog/leg/ssa/optimize.dart

 // Copyright (c) 2011, 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.
 
 class SsaOptimizerTask extends CompilerTask {
   SsaOptimizerTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA optimizer';
 
   void optimize(HGraph graph) {
     measure(() {
@@ skipping 81 matching lines @@
     if (node.left.isLiteralString() && node.right is HLiteral) {
       // TODO(lrn): Perform concatenation in Dart.
     }
     return visitInvokeBinary(node);
   }
 
   HInstruction visitEquals(HEquals node) {
     if (node.left is HLiteral && node.right is HLiteral) {
       HLiteral op1 = node.left;
       HLiteral op2 = node.right;
-      return new HLiteral(op1.value == op2.value, HType.BOOLEAN);
+      if (op1.isLiteralString()) {
+        if (op2.isLiteralString() && op1.value.definitlyEquals(op2.value)) {
+          return new HLiteral(true, HType.BOOLEAN);
+        }
+      } else {
+        return new HLiteral(op1.value == op2.value, HType.BOOLEAN);
+      }
     }
     return node;
   }
 
   HInstruction visitTypeGuard(HTypeGuard node) {
     HInstruction value = node.inputs[0];
     return (value.type.combine(node.type) == value.type) ? value : node;
   }
 
   HInstruction visitIntegerCheck(HIntegerCheck node) {
@@ skipping 519 matching lines @@
         }
       }
       if (!canBeMoved) continue;
 
       // This is safe because we are running after GVN.
       // TODO(ngeoffray): ensure GVN has been run.
       set_.add(current);
     }
   }
 }