Disable all code motion on the final optimization attempt.

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 666 matching lines @@
       next_block_id_(0),
       info_(info),
       blocks_(8),
       values_(16),
       phi_list_(NULL) {
   start_environment_ = new HEnvironment(NULL, info->scope(), info->closure());
   start_environment_->set_ast_id(info->function()->id());
 }
 
 
-bool HGraph::AllowAggressiveOptimizations() const {
+bool HGraph::AllowCodeMotion() const {
   return info()->shared_info()->opt_count() + 1 < Compiler::kDefaultMaxOptCount;
 }
 
 
 Handle<Code> HGraph::Compile() {
   int values = GetMaximumValueID();
   if (values > LAllocator::max_initial_value_ids()) {
     if (FLAG_trace_bailout) PrintF("Function is too big\n");
     return Handle<Code>::null();
   }
@@ skipping 741 matching lines @@
         TraceGVN("Found loop invariant instruction %d\n", instr->id());
         // Move the instruction out of the loop.
         instr->Unlink();
         instr->InsertBefore(pre_header->end());
       }
     }
     instr = next;
   }
 }
 
-// Only move instructions that postdominate the loop header (i.e. are
-// always executed inside the loop). This is to avoid unnecessary
-// deoptimizations assuming the loop is executed at least once.
-// TODO(fschneider): Better type feedback should give us information
-// about code that was never executed.
+
 bool HGlobalValueNumberer::ShouldMove(HInstruction* instr,
                                       HBasicBlock* loop_header) {
-  if (FLAG_aggressive_loop_invariant_motion &&
-      !instr->IsChange() &&
-      (!instr->IsCheckInstruction() ||
-       graph_->AllowAggressiveOptimizations())) {
+  // If we've disabled code motion, don't move any instructions.
+  if (!graph_->AllowCodeMotion()) return false;
+
+  // If --aggressive-loop-invariant-motion, move everything except change
+  // instructions.
+  if (FLAG_aggressive_loop_invariant_motion && !instr->IsChange()) {
     return true;
   }
+
+  // Otherwise only move instructions that postdominate the loop header
+  // (i.e. are always executed inside the loop). This is to avoid
+  // unnecessary deoptimizations assuming the loop is executed at least
+  // once.  TODO(fschneider): Better type feedback should give us
+  // information about code that was never executed.
   HBasicBlock* block = instr->block();
   bool result = true;
   if (block != loop_header) {
     for (int i = 1; i < loop_header->predecessors()->length(); ++i) {
       bool found = false;
       HBasicBlock* pred = loop_header->predecessors()->at(i);
       while (pred != loop_header) {
         if (pred == block) found = true;
         pred = pred->dominator();
       }
@@ skipping 4402 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal