The optimizations performed by Irregexp could possible hide bugs or...

src/jsregexp.cc

Index: src/jsregexp.cc
===================================================================
--- src/jsregexp.cc	(revision 1201)
+++ src/jsregexp.cc	(working copy)
@@ -2013,7 +2013,8 @@
   // We are being asked to make a non-generic version.  Keep track of how many
   // non-generic versions we generate so as not to overdo it.
   trace_count_++;
-  if (trace_count_ < kMaxCopiesCodeGenerated &&
+  if (FLAG_irregexp_optimization &&
+      trace_count_ < kMaxCopiesCodeGenerated &&
       compiler->recursion_depth() <= RegExpCompiler::kMaxRecursion) {
     return CONTINUE;
   }
@@ -3117,7 +3118,8 @@
     new_trace.quick_check_performed()->Clear();
     alt_gen->expects_preload = preload_is_current;
     bool generate_full_check_inline = false;
-    if (try_to_emit_quick_check_for_alternative(i) &&
+    if (FLAG_irregexp_optimization &&
+        try_to_emit_quick_check_for_alternative(i) &&
         alternative.node()->EmitQuickCheck(compiler,
                                            &new_trace,
                                            preload_has_checked_bounds,
@@ -3899,7 +3901,7 @@
   bool needs_capture_clearing = !capture_registers.is_empty();
   if (body_can_be_empty) {
     body_start_reg = compiler->AllocateRegister();
-  } else if (!needs_capture_clearing) {
+  } else if (FLAG_irregexp_optimization && !needs_capture_clearing) {
     // Only unroll if there are no captures and the body can't be
     // empty.
     if (min > 0 && min <= kMaxUnrolledMinMatches) {