VM: Fix imprecision in array bounds check elimination.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 731699811a6446281dbc04293786c9b702ef7ae5..5530e06b5a477e83296899893239ace29bba7d8a 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -604,10 +604,13 @@ static bool CompileParsedFunctionHelper(CompilationPipeline* pipeline,
         if (FLAG_common_subexpression_elimination) {
           if (DominatorBasedCSE::Optimize(flow_graph)) {
             DEBUG_ASSERT(flow_graph->VerifyUseLists());
+            optimizer.Canonicalize();
             // Do another round of CSE to take secondary effects into account:
             // e.g. when eliminating dependent loads (a.x[0] + a.x[0])
             // TODO(fschneider): Change to a one-pass optimization pass.
-            DominatorBasedCSE::Optimize(flow_graph);
+            if (DominatorBasedCSE::Optimize(flow_graph)) {
+              optimizer.Canonicalize();
+            }
             DEBUG_ASSERT(flow_graph->VerifyUseLists());
           }
         }