- Canonicalize array bounds checks to avoid deopting when comparing

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 2321 matching lines @@
   // Try symbolic comparison.
   do {
     if (DependOnSameSymbol(max, length)) return max.offset() < length.offset();
   } while (CanonicalizeMaxBoundary(&max) || CanonicalizeMinBoundary(&length));
 
   // Failed to prove that maximum is bounded with array length.
   return false;
 }
 
 
+Instruction* CheckArrayBoundInstr::Canonicalize(FlowGraph* flow_graph) {
+  return IsRedundant(RangeBoundary::FromDefinition(length()->definition())) ?
+      NULL : this;
+}
+
+
 intptr_t CheckArrayBoundInstr::LengthOffsetFor(intptr_t class_id) {
   if (RawObject::IsExternalTypedDataClassId(class_id)) {
     return ExternalTypedData::length_offset();
   }
   if (RawObject::IsTypedDataClassId(class_id)) {
     return TypedData::length_offset();
   }
   switch (class_id) {
     case kGrowableObjectArrayCid:
       return GrowableObjectArray::length_offset();
@@ skipping 93 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart