Use short-hand update syntax for simple updating definitions.

lib/compiler/implementation/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.
 
 interface OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
@@ skipping 969 matching lines @@
     values = new List<ValueSet>(graph.blocks.length);
     for (int i = 0; i < graph.blocks.length; i++) {
       values[graph.blocks[i].id] = new ValueSet();
     }
     visitPostDominatorTree(graph);
   }
 
   void visitBasicBlock(HBasicBlock block) {
     List<HBasicBlock> successors = block.successors;
 
-    // Phase 1: get the ValueSet of all successors, compute the
-    // intersection and move the instructions of the intersection into
-    // this block.
-    if (successors.length != 0) {
+    // Phase 1: get the ValueSet of all successors (if there are more than one),
+    // compute the intersection and move the instructions of the intersection
+    // into this block.
+    if (successors.length > 1) {
       ValueSet instructions = values[successors[0].id];
       for (int i = 1; i < successors.length; i++) {
         ValueSet other = values[successors[i].id];
         instructions = instructions.intersection(other);
       }
 
       if (!instructions.isEmpty()) {
         List<HInstruction> list = instructions.toList();
         for (HInstruction instruction in list) {
           // Move the instruction to the current block.
@@ skipping 113 matching lines @@
         // the if block terminates. So any use of the instruction
         // after the join block should be changed to the new
         // instruction.
         changeUsesDominatedBy(ifUser.joinBlock, input, convertedType);
       }
       // TODO(ngeoffray): Also change uses for the then block on a HType
       // that knows it is not of a specific Type.
     }
   }
 }