Simple iterative liveness analysis over SSA.

runtime/vm/flow_graph_allocator.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_ALLOCATOR_H_
 #define VM_FLOW_GRAPH_ALLOCATOR_H_
 
 #include "vm/growable_array.h"
 #include "vm/intermediate_language.h"
 
 namespace dart {
 
 class FlowGraphAllocator : public ValueObject {
  public:
-  explicit FlowGraphAllocator(const GrowableArray<BlockEntryInstr*>& blocks)
-      : blocks_(blocks) { }
+  explicit FlowGraphAllocator(const GrowableArray<BlockEntryInstr*>& postorder,

[Florian Schneider, 2012/06/25 14:38:29]

No explicit necessary.

[Vyacheslav Egorov (Google), 2012/06/25 16:58:26]

Done.

+                              intptr_t max_ssa_temp_index);
 
   void ResolveConstraints();
 
+  void AnalyzeLiveness();
+
  private:
-  const GrowableArray<BlockEntryInstr*>& blocks_;
+  void ComputeKillAndGenSets();
+  bool UpdateLiveOut(BlockEntryInstr* instr);
+  bool UpdateLiveIn(BlockEntryInstr* instr);
+  void ComputeLiveInAndLiveOutSets();
+  void DumpLiveness();
+

[srdjan, 2012/06/25 17:30:05]

It woud be nice to have comments describing briefly which state is described by
which instance field, as long as the name does not describe itself.

+  GrowableArray<BitVector*> live_out_;
+  GrowableArray<BitVector*> kill_;
+  GrowableArray<BitVector*> gen_;
+  GrowableArray<BitVector*> live_in_;
+  const GrowableArray<BlockEntryInstr*>& postorder_;
+  const intptr_t vreg_count_;
 
   DISALLOW_COPY_AND_ASSIGN(FlowGraphAllocator);
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_ALLOCATOR_H_