Compute immediate dominators using SEMI-NCA.

runtime/vm/intermediate_language.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_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 795 matching lines @@
   virtual void SetSuccessor(Instruction* instr) = 0;
 
   // Discover basic-block structure by performing a recursive depth first
   // traversal of the instruction graph reachable from this instruction.  As
   // a side effect, the block entry instructions in the graph are assigned
   // numbers in both preorder and postorder.  The array 'preorder' maps
   // preorder block numbers to the block entry instruction with that number
   // and analogously for the array 'postorder'.  The depth first spanning
   // tree is recorded in the array 'parent', which maps preorder block
   // numbers to the preorder number of the block's spanning-tree parent.  As
-  // a side effect, the set of basic block predecessors (e.g., block entry
-  // instructions of predecessor blocks) and also the last instruction in
-  // the block is recorded in each entry instruction.
+  // a side effect of this function76, the set of basic block predecessors

[Kevin Millikin (Google), 2012/03/19 23:25:00]

Oops.  The stray '76' is deleted.

+  // (e.g., block entry instructions of predecessor blocks) and also the
+  // last instruction in the block is recorded in each entry instruction.
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent) {
+      GrowableArray<intptr_t>* parent) {
     // Never called for instructions except block entries and branches.
     UNREACHABLE();
   }
 
 #define INSTRUCTION_TYPE_CHECK(type)                                           \
   virtual bool Is##type() const { return false; }                              \
   virtual type##Instr* As##type() { return NULL; }
 FOR_EACH_INSTRUCTION(INSTRUCTION_TYPE_CHECK)
 #undef INSTRUCTION_TYPE_CHECK
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Instruction);
 };
 
 
 // Basic block entries are administrative nodes.  Joins are the only nodes
 // with multiple predecessors.  Targets are the other basic block entries.
 // The types enforce edge-split form---joins are forbidden as the successors
 // of branches.
 class BlockEntryInstr : public Instruction {
  public:
   virtual bool IsBlockEntry() const { return true; }
 
+  virtual intptr_t PredecessorCount() const = 0;
+  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const = 0;
+
   intptr_t preorder_number() const { return preorder_number_; }
   void set_preorder_number(intptr_t number) { preorder_number_ = number; }
 
   intptr_t postorder_number() const { return postorder_number_; }
   void set_postorder_number(intptr_t number) { postorder_number_ = number; }
 
+  BlockEntryInstr* dominator() const { return dominator_; }
+  void set_dominator(BlockEntryInstr* instr) { dominator_ = instr; }
+
   Instruction* last_instruction() const { return last_instruction_; }
   void set_last_instruction(Instruction* instr) { last_instruction_ = instr; }
 
  protected:
   BlockEntryInstr()
       : preorder_number_(-1),
         postorder_number_(-1),
+        dominator_(NULL),
         last_instruction_(NULL) { }
 
  private:
   intptr_t preorder_number_;
   intptr_t postorder_number_;
+  BlockEntryInstr* dominator_;  // Immediate dominator, NULL for graph entry.
   Instruction* last_instruction_;
 
   DISALLOW_COPY_AND_ASSIGN(BlockEntryInstr);
 };
 
 
 class JoinEntryInstr : public BlockEntryInstr {
  public:
   JoinEntryInstr()
       : BlockEntryInstr(),
         predecessors_(2),  // Two is the assumed to be the common case.
         successor_(NULL) { }
 
   DECLARE_INSTRUCTION(JoinEntry)
 
+  virtual intptr_t PredecessorCount() const { return predecessors_.length(); }
+  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
+    return predecessors_[index];
+  }
+
   virtual Instruction* StraightLineSuccessor() const {
     return successor_;
   }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
     successor_ = instr;
   }
 
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
+      GrowableArray<intptr_t>* parent);
 
  private:
   ZoneGrowableArray<BlockEntryInstr*> predecessors_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(JoinEntryInstr);
 };
 
 
 class TargetEntryInstr : public BlockEntryInstr {
  public:
   TargetEntryInstr()
       : BlockEntryInstr(), predecessor_(NULL), successor_(NULL) { }
 
   DECLARE_INSTRUCTION(TargetEntry)
 
+  virtual intptr_t PredecessorCount() const {
+    return (predecessor_ == NULL) ? 0 : 1;
+  }
+  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
+    ASSERT((index == 0) && (predecessor_ != NULL));
+    return predecessor_;
+  }
+
   virtual Instruction* StraightLineSuccessor() const {
     return successor_;
   }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
     successor_ = instr;
   }
 
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
+      GrowableArray<intptr_t>* parent);
 
  private:
   BlockEntryInstr* predecessor_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(TargetEntryInstr);
 };
 
 
 // The non-optimizing compiler assumes that there is exactly one use of
@@ skipping 216 matching lines @@
   TargetEntryInstr** true_successor_address() { return &true_successor_; }
   TargetEntryInstr** false_successor_address() { return &false_successor_; }
 
   virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
       GrowableArray<BlockEntryInstr*>* postorder,
-      GrowableArray<BlockEntryInstr*>* parent);
+      GrowableArray<intptr_t>* parent);
 
  private:
   Value* value_;
   TargetEntryInstr* true_successor_;
   TargetEntryInstr* false_successor_;
 
   DISALLOW_COPY_AND_ASSIGN(BranchInstr);
 };
 
 #undef DECLARE_INSTRUCTION
@@ skipping 36 matching lines @@
   const GrowableArray<BlockEntryInstr*>& block_order_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_