Some string optimizations:

src/arm/codegen-arm.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 3402 matching lines @@
   __ and_(r1, r0, Operand(kSmiTagMask));
   __ eor(r1, r1, Operand(kSmiTagMask), SetCC);
   answer.Branch(ne);
   // It is a heap object - get the map. Check if the object is a JS array.
   __ CompareObjectType(r0, r1, r1, JS_ARRAY_TYPE);
   answer.Bind();
   cc_reg_ = eq;
 }
 
 
+void CodeGenerator::GenerateIsRegExp(ZoneList<Expression*>* args) {
+  VirtualFrame::SpilledScope spilled_scope;
+  ASSERT(args->length() == 1);
+  LoadAndSpill(args->at(0));
+  JumpTarget answer;
+  // We need the CC bits to come out as not_equal in the case where the
+  // object is a smi.  This can't be done with the usual test opcode so
+  // we use XOR to get the right CC bits.
+  frame_->EmitPop(r0);
+  __ and_(r1, r0, Operand(kSmiTagMask));
+  __ eor(r1, r1, Operand(kSmiTagMask), SetCC);
+  answer.Branch(ne);
+  // It is a heap object - get the map. Check if the object is a regexp.
+  __ CompareObjectType(r0, r1, r1, JS_REGEXP_TYPE);
+  answer.Bind();
+  cc_reg_ = eq;
+}
+
+
 void CodeGenerator::GenerateIsObject(ZoneList<Expression*>* args) {
   // This generates a fast version of:
   // (typeof(arg) === 'object' || %_ClassOf(arg) == 'RegExp')
   VirtualFrame::SpilledScope spilled_scope;
   ASSERT(args->length() == 1);
   LoadAndSpill(args->at(0));
   frame_->EmitPop(r1);
   __ tst(r1, Operand(kSmiTagMask));
   false_target()->Branch(eq);
 
@@ skipping 4181 matching lines @@
 
   // Just jump to runtime to add the two strings.
   __ bind(&string_add_runtime);
   __ TailCallRuntime(ExternalReference(Runtime::kStringAdd), 2, 1);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal