Add forward iterator to iterate instructions inside a basic block.

vm/il_printer.cc

Index: vm/il_printer.cc
===================================================================
--- vm/il_printer.cc	(revision 9430)
+++ vm/il_printer.cc	(working copy)
@@ -39,15 +39,15 @@
   for (intptr_t i = 0; i < block_order_.length(); ++i) {
     // Print the block entry.
     PrintInstruction(block_order_[i]);
-    Instruction* current = block_order_[i]->successor();
     // And all the successors until an exit, branch, or a block entry.
-    while ((current != NULL) && !current->IsBlockEntry()) {
+    ForwardInstructionIterator it(block_order_[i]);

[Kevin Millikin (Google), 2012/07/06 11:58:42]

I'm a bit uncomfortable with calling Current() on an iterator that is Done() --
it seems ill defined and relies on implementation details.  We could try:

Instruction* current = block_order_[i];
for (ForwardInstructionIterator it(current), !id.Done(), it.Advance()) {
  current = it.Current();
  // ...
}
if (current->successor() != NULL) {
  ASSERT(current->successor()->IsBlockEntry());
  OS::Print(" goto %d", current->successor()->AsBlockEntry()->block_id());
}

Is that equivalent?

[Florian Schneider, 2012/07/06 12:31:51]

Done.

+    for (; !it.Done(); it.Advance()) {
+      Instruction* current = it.Current();
       OS::Print("\n");
       PrintInstruction(current);
-      current = current->successor();
     }
     BlockEntryInstr* successor =
-        (current == NULL) ? NULL : current->AsBlockEntry();
+        (it.Current() == NULL) ? NULL : it.Current()->AsBlockEntry();
     if (successor != NULL) {
       OS::Print(" goto %d", successor->block_id());
     }