Add forward iterator to iterate instructions inside a basic block.

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 2493 matching lines @@
         PhiInstr* phi = (*join->phis())[i];
         if (phi != NULL) {
           (*env)[i] = new UseVal(phi);
           phi->set_ssa_temp_index(current_ssa_temp_index_++);  // New SSA temp.
         }
       }
     }
   }
 
   // 2. Process normal instructions.
-  Instruction* current = block_entry->successor();
-  while ((current != NULL) && !current->IsBlockEntry()) {
+  for (ForwardInstructionIterator it(block_entry); !it.Done(); it.Advance()) {
+    Instruction* current = it.Current();
     // Attach current environment to the instruction.
     // TODO(fschneider): Currently each instruction gets a full copy of the
     // enviroment. This should be optimized: Only instructions that can
     // deoptimize will should have uses of the environment values.
     current->set_env(new Environment(env));
 
     // 2a. Handle uses:
     // Update expression stack environment for each use.
     // For each use of a LoadLocal or StoreLocal: Replace it with the value
     // from the environment.
@@ skipping 35 matching lines @@
         } else {
           // The graph construction ensures we do not have an unused LoadLocal
           // computation.
           ASSERT(bind->is_used());
           index = load->local().BitIndexIn(var_count);
         }
         // Update expression stack and remove from graph.
         if (bind->is_used()) {
           env->Add(CopyValue((*env)[index]));
         }
-        current = current->RemoveFromGraph();
+        it.RemoveCurrentFromGraph();
       } else {
         // Not a load or store.
         if (bind->is_used()) {
           // Assign fresh SSA temporary and update expression stack.
           bind->set_ssa_temp_index(current_ssa_temp_index_++);
           env->Add(new UseVal(bind));
         }
-        current = current->successor();
       }
-    } else {
-      // Not a computation.
-      current = current->successor();
     }
   }
 
   // 3. Process dominated blocks.
   for (intptr_t i = 0; i < block_entry->dominated_blocks().length(); ++i) {
     BlockEntryInstr* block = block_entry->dominated_blocks()[i];
     ZoneGrowableArray<Value*>* new_env =
         new ZoneGrowableArray<Value*>(env->length());
     new_env->AddArray(*env);
     RenameRecursive(block, new_env, var_count);
@@ skipping 29 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