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

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index 329204c6f984e1b1f8cdaf5cc49e370d5c54bb5d..ab31e943ccd049516ce48b17aa8bec12cbfc41d5 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -93,22 +93,23 @@ void FlowGraphCompiler::VisitBlocks() {
     ASSERT(frame_register_allocator()->IsSpilled());
     assembler()->Comment("B%d", i);
     // Compile the block entry.
-    set_current_block(block_order()[i]);
-    current_block()->PrepareEntry(this);
-    Instruction* instr = current_block()->next();
+    BlockEntryInstr* entry = block_order()[i];
+    set_current_block(entry);
+    entry->PrepareEntry(this);
     // Compile all successors until an exit, branch, or a block entry.
-    while ((instr != NULL) && !instr->IsBlockEntry()) {
+    Instruction* instr = entry;
+    for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
+      instr = it.Current();
       if (FLAG_code_comments) EmitComment(instr);
       ASSERT(instr->locs() != NULL);
       EmitInstructionPrologue(instr);
       instr->EmitNativeCode(this);
-      instr = instr->next();
     }
-    BlockEntryInstr* successor =
-        (instr == NULL) ? NULL : instr->AsBlockEntry();
-    if (successor != NULL) {
+    if (instr->next() != NULL) {
+      BlockEntryInstr* successor = instr->next()->AsBlockEntry();
+      ASSERT(successor != NULL);
       frame_register_allocator()->Spill();
-      // Block ended with a "goto".  We can fall through if it is the
+      // The block ended with a "goto".  We can fall through if it is the
       // next block in the list.  Otherwise, we need a jump.
       if ((i == block_order().length() - 1) ||
           (block_order()[i + 1] != successor)) {