Add forward iterator to iterate instructions inside a basic block.

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 1751 matching lines @@
     // condition should be handled in the graph builder
     successor_ = instr;
   }
 
   Instruction* previous() const { return previous_; }
   void set_previous(Instruction* instr) {
     ASSERT(!IsBlockEntry());
     previous_ = instr;
   }
 
-  // Remove instruction from the graph and return the instruction following the
-  // removed instruction.
-  Instruction* RemoveFromGraph();
-
   // Normal instructions can have 0 (inside a block) or 1 (last instruction in
   // a block) successors. Branch instruction with >1 successors override this
   // function.
   virtual intptr_t SuccessorCount() const;
   virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
 
   // 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
@@ skipping 143 matching lines @@
   intptr_t block_id_;
   BlockEntryInstr* dominator_;  // Immediate dominator, NULL for graph entry.
   // TODO(fschneider): Optimize the case of one child to save space.
   GrowableArray<BlockEntryInstr*> dominated_blocks_;
   Instruction* last_instruction_;
 
   DISALLOW_COPY_AND_ASSIGN(BlockEntryInstr);
 };
 
 
+class ForwardInstructionIterator : public ValueObject {
+ public:
+  explicit ForwardInstructionIterator(BlockEntryInstr* block_entry)
+      : block_entry_(block_entry), current_(block_entry) {
+    Advance();
+  }
+
+  void Advance() {
+    if (!Done()) current_ = current_->successor();
+  }
+
+  bool Done() const {
+    return current_ == block_entry_->last_instruction()->successor();
+  }
+
+  void RemoveCurrentFromGraph() {
+    ASSERT(!current_->IsBlockEntry());
+    ASSERT(!current_->IsBranch());
+    ASSERT(!current_->IsThrow());
+    ASSERT(!current_->IsReturn());
+    ASSERT(!current_->IsReThrow());
+    ASSERT(current_->previous() != NULL);
+    Instruction* next = current_->successor();
+    Instruction* prev = current_->previous();
+    prev->set_successor(next);
+    ASSERT(next != NULL);
+    if (current_ != block_entry_->last_instruction()) {
+      ASSERT(!next->IsBlockEntry());
+      next->set_previous(prev);
+    } else {
+      ASSERT(current_->IsBind());
+      // Removing the last instruction of a block.
+      // Update last_instruction of the current basic block.
+      block_entry_->set_last_instruction(prev);
+    }
+    // Reset successor and previous instruction to indicate
+    // that the instruction is removed from the graph.
+    current_->set_successor(NULL);
+    current_->set_previous(NULL);
+    current_ = prev;
+  }
+
+  Instruction* Current() const { return current_; }
+
+ private:
+  BlockEntryInstr* block_entry_;
+  Instruction* current_;
+};
+
+
 class GraphEntryInstr : public BlockEntryInstr {
  public:
   explicit GraphEntryInstr(TargetEntryInstr* normal_entry)
       : BlockEntryInstr(),
         normal_entry_(normal_entry),
         catch_entries_(),
         start_env_(NULL) { }
 
   DECLARE_INSTRUCTION(GraphEntry)
 
@@ skipping 440 matching lines @@
   const GrowableArray<BlockEntryInstr*>& block_order_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_