Add forward iterator to iterate instructions inside a basic block.

vm/il_printer.cc

 // 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.
 
 #include "vm/il_printer.h"
 
 #include "vm/intermediate_language.h"
 #include "vm/os.h"
 
 namespace dart {
@@ skipping 21 matching lines @@
 
 
 void FlowGraphPrinter::PrintBlocks() {
   if (!function_.IsNull()) {
     OS::Print("==== %s\n", function_.ToFullyQualifiedCString());
   }
 
   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());
     }
     OS::Print("\n");
   }
 }
 
 
 void FlowGraphPrinter::PrintInstruction(Instruction* instr) {
   char str[1000];
@@ skipping 603 matching lines @@
 void Environment::PrintTo(BufferFormatter* f) const {
   f->Print(" env={ ");
   for (intptr_t i = 0; i < values_.length(); ++i) {
     if (i > 0) f->Print(", ");
     values_[i]->PrintTo(f);
   }
   f->Print(" }");
 }
 
 }  // namespace dart