Cleanup how we handle side effects in HInstruction and put the right flags for HIs, modulo, truncat…

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

Index: sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(revision 17440)
+++ sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(working copy)
@@ -802,6 +802,7 @@
            && instruction is !HCheck
            && instruction is !HTypeGuard
            && instruction is !HParameterValue
+           && instruction is !HLocalSet
            && !instruction.isControlFlow();
   }
 
@@ -1062,7 +1063,6 @@
       int changesFlags = 0;
       HInstruction instruction = block.first;
       while (instruction != null) {
-        instruction.prepareGvn(types);
         changesFlags |= instruction.getChangesFlags();
         instruction = instruction.next;
       }