Optimize the typeof operator.

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 09026cdfc8a1fd82896cab7033eb0044897cc8ab..b173e30a2bc6075fa376b8182fd6aaac71c4d555 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -5565,10 +5565,17 @@ void LCodeGen::DoFunctionLiteral(LFunctionLiteral* instr) {
 
 
 void LCodeGen::DoTypeof(LTypeof* instr) {
+  DCHECK(ToRegister(instr->value()).is(a3));
   DCHECK(ToRegister(instr->result()).is(v0));
-  Register input = ToRegister(instr->value());
-  __ push(input);
-  CallRuntime(Runtime::kTypeof, 1, instr);
+  Label end, do_call;
+  Register value_register = ToRegister(instr->value());
+  __ JumpIfNotSmi(value_register, &do_call);
+  __ li(v0, Operand(isolate()->factory()->number_string()));
+  __ jmp(&end);
+  __ bind(&do_call);
+  TypeofStub stub(isolate());
+  CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
+  __ bind(&end);
 }