Use the instruction iterator rather than an explicit loop in more places.

runtime/vm/flow_graph_builder.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/flow_graph_builder.h"
 
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/code_descriptors.h"
 #include "vm/dart_entry.h"
@@ skipping 2202 matching lines @@
                                &assigned_vars,
                                variable_count);
   // Number blocks in reverse postorder.
   intptr_t block_count = postorder_block_entries_.length();
   for (intptr_t i = 0; i < block_count; ++i) {
     postorder_block_entries_[i]->set_block_id(block_count - i - 1);
   }
   if (for_optimized && use_ssa) {
     // Link instructions backwards for optimized compilation.
     for (intptr_t i = 0; i < block_count; ++i) {
-      Instruction* prev = postorder_block_entries_[i];
-      Instruction* current = prev->next();
-      while (current != NULL && !current->IsBlockEntry()) {
-        current->set_previous(prev);
-        prev = current;
-        current = current->next();
+      BlockEntryInstr* entry = postorder_block_entries_[i];
+      Instruction* previous = entry;
+      for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
+        Instruction* current = it.Current();
+        current->set_previous(previous);
+        previous = current;
       }
     }
     GrowableArray<BitVector*> dominance_frontier;
     ComputeDominators(&preorder_block_entries_, &parent, &dominance_frontier);
     InsertPhis(preorder_block_entries_,
                assigned_vars,
                variable_count,
                dominance_frontier);
     Rename(variable_count);
   }
@@ skipping 380 matching lines @@
   char* chars = reinterpret_cast<char*>(
       Isolate::Current()->current_zone()->Allocate(len));
   OS::SNPrint(chars, len, kFormat, function_name, reason);
   const Error& error = Error::Handle(
       LanguageError::New(String::Handle(String::New(chars))));
   Isolate::Current()->long_jump_base()->Jump(1, error);
 }
 
 
 }  // namespace dart