Recognize pattern (a << b) & c with c being a positive Smi and allow left shift to truncate the res…

runtime/vm/flow_graph_optimizer.h

 // 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.
 
 #ifndef VM_FLOW_GRAPH_OPTIMIZER_H_
 #define VM_FLOW_GRAPH_OPTIMIZER_H_
 
 #include "vm/intermediate_language.h"
 #include "vm/flow_graph.h"
 
 namespace dart {
 
 template <typename T> class GrowableArray;
 template <typename T> class DirectChainedHashMap;
 template <typename T> class PointerKeyValueTrait;
 
 class FlowGraphOptimizer : public FlowGraphVisitor {
  public:
   explicit FlowGraphOptimizer(FlowGraph* flow_graph)
       : FlowGraphVisitor(flow_graph->reverse_postorder()),
         flow_graph_(flow_graph) { }
   virtual ~FlowGraphOptimizer() {}
 
   // Use ICData to optimize, replace or eliminate instructions.
   void ApplyICData();
 
   // Use propagated class ids to optimize, replace or eliminate instructions.
   void ApplyClassIds();
 
+  // Optimize (a << b) & c pattern: if c is a positive smi, then the
+  // shift can be a truncating Smi shift and result is always Smi.
+  void TryOptimizeLeftShiftWithBitAndPattern();
+
   void Canonicalize();
 
   void EliminateDeadPhis();
 
   void SelectRepresentations();
 
   void PropagateSminess();
 
   void InferSmiRanges();
 
@@ skipping 85 matching lines @@
                                 MethodRecognizer::Kind recognized_kind);
 
   void HandleRelationalOp(RelationalOpInstr* comp);
 
   // Visit an equality compare.  The current instruction can be the
   // comparison itself or a branch on the comparison.
   template <typename T>
   void HandleEqualityCompare(EqualityCompareInstr* comp,
                              T current_instruction);
 
+  void OptimizeLeftShiftBitAndSmiOp(Definition* bit_and_instr,
+                                    Value* left,
+                                    Value* right);
+
   FlowGraph* flow_graph_;
 
   DISALLOW_COPY_AND_ASSIGN(FlowGraphOptimizer);
 };
 
 
 class ParsedFunction;
 
 
 // Loop invariant code motion.
@@ skipping 85 matching lines @@
 
   // Worklists of blocks and definitions.
   GrowableArray<BlockEntryInstr*> block_worklist_;
   GrowableArray<Definition*> definition_worklist_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_