Implement a variation of scalar replacement for non-escaping allocations.

runtime/vm/flow_graph.h

 // 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.
 
 #ifndef VM_FLOW_GRAPH_H_
 #define VM_FLOW_GRAPH_H_
 
 #include "vm/growable_array.h"
 #include "vm/intermediate_language.h"
 #include "vm/parser.h"
@@ skipping 132 matching lines @@
   void DiscoverBlocks();
 
   // Compute information about effects occuring in different blocks and
   // discover side-effect free paths.
   void ComputeBlockEffects();
   BlockEffects* block_effects() const { return block_effects_; }
 
   // Remove the redefinition instructions inserted to inhibit code motion.
   void RemoveRedefinitions();
 
+  // Copy deoptimization target from one instruction to another if we still
+  // have to keep deoptimization environment at gotos for LICM purposes.
+  void CopyDeoptTarget(Instruction* to, Instruction* from) {
+    if (is_licm_allowed()) {
+      to->InheritDeoptTarget(from);
+    }
+  }
+
+  // Returns true if every Goto in the graph is expected to have a
+  // deoptimization environment and can be used as deoptimization target
+  // for hoisted instructions.
+  bool is_licm_allowed() const { return licm_allowed_; }
+
+  // Stop preserving environments on Goto instructions. LICM is not allowed
+  // after this point.
+  void disallow_licm() { licm_allowed_ = false; }
+
  private:
   friend class IfConverter;
   friend class BranchSimplifier;
   friend class ConstantPropagator;
 
   // SSA transformation methods and fields.
   void ComputeDominators(GrowableArray<BitVector*>* dominance_frontier);
 
   void CompressPath(
       intptr_t start_index,
@@ skipping 35 matching lines @@
   const intptr_t num_copied_params_;
   const intptr_t num_non_copied_params_;
   const intptr_t num_stack_locals_;
   GraphEntryInstr* graph_entry_;
   GrowableArray<BlockEntryInstr*> preorder_;
   GrowableArray<BlockEntryInstr*> postorder_;
   GrowableArray<BlockEntryInstr*> reverse_postorder_;
   ConstantInstr* constant_null_;
 
   BlockEffects* block_effects_;
+  bool licm_allowed_;
 };
 
 
 class LivenessAnalysis : public ValueObject {
  public:
   LivenessAnalysis(intptr_t variable_count,
                    const GrowableArray<BlockEntryInstr*>& postorder);
 
   void Analyze();
 
@@ skipping 85 matching lines @@
   // Per block sets of available blocks. Block A is available at the block B if
   // and only if A dominates B and all paths from A to B are free of side
   // effects.
   GrowableArray<BitVector*> available_at_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_H_