Revert "A simpler scheme for garbage collection of ureachable phi inputs."

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index b4fe33aa46126a307aab797502ce3d772db53708..f47d6e3b90e42ee873f3f74efc4a681f60ff1bb0 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -655,6 +655,7 @@ class BlockEntryInstr : public Instruction {
   void set_postorder_number(intptr_t number) { postorder_number_ = number; }
 
   intptr_t block_id() const { return block_id_; }
+  void set_block_id(intptr_t value) { block_id_ = value; }
 
   void set_start_pos(intptr_t pos) { start_pos_ = pos; }
   intptr_t start_pos() const { return start_pos_; }
@@ -723,11 +724,11 @@ class BlockEntryInstr : public Instruction {
   }
 
  protected:
-  BlockEntryInstr(intptr_t block_id, intptr_t try_index)
-      : block_id_(block_id),
-        try_index_(try_index),
+  explicit BlockEntryInstr(intptr_t try_index)
+      : try_index_(try_index),
         preorder_number_(-1),
         postorder_number_(-1),
+        block_id_(-1),
         dominator_(NULL),
         dominated_blocks_(1),
         last_instruction_(NULL),
@@ -738,12 +739,12 @@ class BlockEntryInstr : public Instruction {
   virtual void ClearPredecessors() = 0;
   virtual void AddPredecessor(BlockEntryInstr* predecessor) = 0;
 
-  const intptr_t block_id_;
   const intptr_t try_index_;
   intptr_t preorder_number_;
   intptr_t postorder_number_;
   // Starting and ending lifetime positions for this block.  Used by
   // the linear scan register allocator.
+  intptr_t block_id_;
   intptr_t start_pos_;
   intptr_t end_pos_;
   BlockEntryInstr* dominator_;  // Immediate dominator, NULL for graph entry.
@@ -873,8 +874,8 @@ class GraphEntryInstr : public BlockEntryInstr {
 
 class JoinEntryInstr : public BlockEntryInstr {
  public:
-  JoinEntryInstr(intptr_t block_id, intptr_t try_index)
-      : BlockEntryInstr(block_id, try_index),
+  explicit JoinEntryInstr(intptr_t try_index)
+      : BlockEntryInstr(try_index),
         predecessors_(2),  // Two is the assumed to be the common case.
         phis_(NULL),
         phi_count_(0) { }
@@ -901,13 +902,28 @@ class JoinEntryInstr : public BlockEntryInstr {
   virtual void PrintTo(BufferFormatter* f) const;
   virtual void PrintToVisualizer(BufferFormatter* f) const;
 
+  // After recomputing predecessors to eliminate unreachable ones,
+  // reorganize phi inputs to match the predecessor order and to eliminate
+  // unreachable inputs.
+  void EliminateUnreachablePhiInputs();
+
  private:
-  virtual void ClearPredecessors() { predecessors_.Clear(); }
-  virtual void AddPredecessor(BlockEntryInstr* predecessor);
+  virtual void ClearPredecessors() {
+    // Keep a 'backup' of any existing predecessors to enable garbage
+    // collection of phis after eliminating unreachable code and recomputing
+    // predecessors.
+    stale_predecessors_.Clear();
+    stale_predecessors_.AddArray(predecessors_);
+    predecessors_.Clear();
+  }
+  virtual void AddPredecessor(BlockEntryInstr* predecessor) {
+    predecessors_.Add(predecessor);
+  }
 
   GrowableArray<BlockEntryInstr*> predecessors_;
   ZoneGrowableArray<PhiInstr*>* phis_;
   intptr_t phi_count_;
+  GrowableArray<BlockEntryInstr*> stale_predecessors_;
 
   DISALLOW_COPY_AND_ASSIGN(JoinEntryInstr);
 };
@@ -915,11 +931,17 @@ class JoinEntryInstr : public BlockEntryInstr {
 
 class TargetEntryInstr : public BlockEntryInstr {
  public:
-  TargetEntryInstr(intptr_t block_id, intptr_t try_index)
-      : BlockEntryInstr(block_id, try_index),
+  explicit TargetEntryInstr(intptr_t try_index)
+      : BlockEntryInstr(try_index),
         predecessor_(NULL),
         catch_try_index_(CatchClauseNode::kInvalidTryIndex) { }
 
+  // Used for exception catch entries.
+  TargetEntryInstr(intptr_t try_index, intptr_t catch_try_index)
+      : BlockEntryInstr(try_index),
+        predecessor_(NULL),
+        catch_try_index_(catch_try_index) { }
+
   DECLARE_INSTRUCTION(TargetEntry)
 
   virtual intptr_t PredecessorCount() const {
@@ -941,7 +963,6 @@ class TargetEntryInstr : public BlockEntryInstr {
     ASSERT(IsCatchEntry());
     return catch_try_index_;
   }
-  void set_catch_try_index(intptr_t index) { catch_try_index_ = index; }
 
   virtual void PrepareEntry(FlowGraphCompiler* compiler);
 
@@ -956,7 +977,7 @@ class TargetEntryInstr : public BlockEntryInstr {
   }
 
   BlockEntryInstr* predecessor_;
-  intptr_t catch_try_index_;
+  const intptr_t catch_try_index_;
 
   DISALLOW_COPY_AND_ASSIGN(TargetEntryInstr);
 };
@@ -1145,7 +1166,7 @@ class PhiInstr : public Definition {
   virtual void PrintToVisualizer(BufferFormatter* f) const;
 
  private:
-  friend class ConstantPropagator;  // Direct access to inputs_.
+  friend class JoinEntryInstr;  // Direct access to inputs_ array.
 
   JoinEntryInstr* block_;
   GrowableArray<Value*> inputs_;