Add forward iterator to iterate instructions inside a basic block.

vm/intermediate_language.h

Index: vm/intermediate_language.h
===================================================================
--- vm/intermediate_language.h	(revision 9430)
+++ vm/intermediate_language.h	(working copy)
@@ -1777,7 +1777,11 @@
 
   // Remove instruction from the graph and return the instruction following the
   // removed instruction.
-  Instruction* RemoveFromGraph();
+  enum RemoveReturnValue {
+    kReturnPrevious,
+    kReturnNext
+  };
+  Instruction* RemoveFromGraph(RemoveReturnValue ret);
 
   // Normal instructions can have 0 (inside a block) or 1 (last instruction in
   // a block) successors. Branch instruction with >1 successors override this
@@ -1942,6 +1946,33 @@
 };
 
 
+class ForwardIterator : public ValueObject {

[Kevin Millikin (Google), 2012/07/06 10:44:30]

I think the class name is probably too generic.  We could call it
InstructionIterator and have it take a direction parameter.

+ public:
+  explicit ForwardIterator(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() {
+    current_ = current_->RemoveFromGraph(Instruction::kReturnPrevious);
+  }
+
+  Instruction* Current() const { return current_; }
+
+ private:
+  BlockEntryInstr* block_entry_;
+  Instruction* current_;
+};
+
+
 class GraphEntryInstr : public BlockEntryInstr {
  public:
   explicit GraphEntryInstr(TargetEntryInstr* normal_entry)