Reapply change to GVN all HFieldGet instructions.

lib/compiler/implementation/ssa/optimize.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 interface OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
   final JavaScriptBackend backend;
@@ skipping 692 matching lines @@
     node.block.addBefore(node, newInstruction);
     node.block.rewrite(node, newInstruction);
     node.block.remove(node);
   }
 }
 
 class SsaDeadCodeEliminator extends HGraphVisitor implements OptimizationPhase {
   final String name = "SsaDeadCodeEliminator";
 
   static bool isDeadCode(HInstruction instruction) {
-    // TODO(ngeoffray): the way we handle side effects is not right
-    // (e.g. branching instructions have side effects).
     return !instruction.hasSideEffects()
            && instruction.usedBy.isEmpty()
            && instruction is !HCheck
-           && instruction is !HTypeGuard;
+           && instruction is !HTypeGuard
+           && !instruction.isControlFlow();
   }
 
   void visitGraph(HGraph graph) {
     visitPostDominatorTree(graph);
   }
 
   void visitBasicBlock(HBasicBlock block) {
     HInstruction instruction = block.last;
     while (instruction !== null) {
       var previous = instruction.previous;
@@ skipping 167 matching lines @@
     }
   }
 
   bool isInputDefinedAfterDominator(HInstruction input,
                                     HBasicBlock dominator) {
     return input.block.id > dominator.id;
   }
 
   void visitBasicBlock(HBasicBlock block, ValueSet values) {
     HInstruction instruction = block.first;
+    if (block.isLoopHeader()) {
+      int flags = loopChangesFlags[block.id];
+      values.kill(flags);
+    }
     while (instruction !== null) {
       HInstruction next = instruction.next;
       int flags = instruction.getChangesFlags();
-      if (flags != 0) {
-        assert(!instruction.useGvn());
-        values.kill(flags);
-      } else if (instruction.useGvn()) {
+      assert(flags == 0 || !instruction.useGvn());
+      values.kill(flags);
+      if (instruction.useGvn()) {
         HInstruction other = values.lookup(instruction);
         if (other !== null) {
           assert(other.gvnEquals(instruction) && instruction.gvnEquals(other));
           block.rewrite(instruction, other);
           block.remove(instruction);
         } else {
           values.add(instruction);
         }
       }
       instruction = next;
@@ skipping 238 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.
     }
   }
 }