Some string optimizations:

src/ia32/codegen-ia32.cc

 // Copyright 2010 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 5381 matching lines @@
   Result temp = allocator()->Allocate();
   ASSERT(temp.is_valid());
   // Check if the object is a JS array or not.
   __ CmpObjectType(value.reg(), JS_ARRAY_TYPE, temp.reg());
   value.Unuse();
   temp.Unuse();
   destination()->Split(equal);
 }
 
 
+void CodeGenerator::GenerateIsRegExp(ZoneList<Expression*>* args) {
+  ASSERT(args->length() == 1);
+  Load(args->at(0));
+  Result value = frame_->Pop();
+  value.ToRegister();
+  ASSERT(value.is_valid());
+  __ test(value.reg(), Immediate(kSmiTagMask));
+  destination()->false_target()->Branch(equal);
+  // It is a heap object - get map.
+  Result temp = allocator()->Allocate();
+  ASSERT(temp.is_valid());
+  // Check if the object is a regexp.
+  __ CmpObjectType(value.reg(), JS_REGEXP_TYPE, temp.reg());
+  value.Unuse();
+  temp.Unuse();
+  destination()->Split(equal);
+}
+
+
 void CodeGenerator::GenerateIsObject(ZoneList<Expression*>* args) {
   // This generates a fast version of:
   // (typeof(arg) === 'object' || %_ClassOf(arg) == 'RegExp')
   ASSERT(args->length() == 1);
   Load(args->at(0));
   Result obj = frame_->Pop();
   obj.ToRegister();
 
   __ test(obj.reg(), Immediate(kSmiTagMask));
   destination()->false_target()->Branch(zero);
@@ skipping 928 matching lines @@
       __ test(answer.reg(), Immediate(kSmiTagMask));
       destination()->false_target()->Branch(zero);
 
       // It can be an undetectable string object.
       Result temp = allocator()->Allocate();
       ASSERT(temp.is_valid());
       __ mov(temp.reg(), FieldOperand(answer.reg(), HeapObject::kMapOffset));
       __ movzx_b(temp.reg(), FieldOperand(temp.reg(), Map::kBitFieldOffset));
       __ test(temp.reg(), Immediate(1 << Map::kIsUndetectable));
       destination()->false_target()->Branch(not_zero);
-      __ mov(temp.reg(), FieldOperand(answer.reg(), HeapObject::kMapOffset));
-      __ movzx_b(temp.reg(),
-                 FieldOperand(temp.reg(), Map::kInstanceTypeOffset));
-      __ cmp(temp.reg(), FIRST_NONSTRING_TYPE);
+      __ CmpObjectType(answer.reg(), FIRST_NONSTRING_TYPE, temp.reg());
       temp.Unuse();
       answer.Unuse();
-      destination()->Split(less);
+      destination()->Split(below);
 
     } else if (check->Equals(Heap::boolean_symbol())) {
       __ cmp(answer.reg(), Factory::true_value());
       destination()->true_target()->Branch(equal);
       __ cmp(answer.reg(), Factory::false_value());
       answer.Unuse();
       destination()->Split(equal);
 
     } else if (check->Equals(Heap::undefined_symbol())) {
       __ cmp(answer.reg(), Factory::undefined_value());
@@ skipping 4369 matching lines @@
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(ExternalReference(Runtime::kStringCompare), 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal