Reland "Suppress canonicalization of Unbox() instruction that can deoptimize."

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 571 matching lines @@
   iterator->RemoveCurrentFromGraph();
 }
 
 
 bool FlowGraphOptimizer::Canonicalize() {
   bool changed = false;
   for (intptr_t i = 0; i < block_order_.length(); ++i) {
     BlockEntryInstr* entry = block_order_[i];
     for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
       Instruction* current = it.Current();
+      if (current->HasUnmatchedInputRepresentations()) {
+        // Can't canonicalize this instruction until all conversions for its
+        // inputs are inserted.
+        continue;
+      }
+
       Instruction* replacement = current->Canonicalize(flow_graph());
+
       if (replacement != current) {
         // For non-definitions Canonicalize should return either NULL or
         // this.
         ASSERT((replacement == NULL) || current->IsDefinition());
         ReplaceCurrentInstruction(&it, current, replacement, flow_graph_);
         changed = true;
       }
     }
   }
   return changed;
@@ skipping 9376 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, alloc->cls(), *slots);
   }
 }
 
 
 }  // namespace dart