Support StringLength in hydrogen (similar to ArrayLength).

src/x64/stub-cache-x64.cc

Index: src/x64/stub-cache-x64.cc
diff --git a/src/x64/stub-cache-x64.cc b/src/x64/stub-cache-x64.cc
index c86f43de2cb5e9749ec38ee86b54c19f9aeb7ea2..ca095b75ef573521112664ec2472e23f058ead16 100644
--- a/src/x64/stub-cache-x64.cc
+++ b/src/x64/stub-cache-x64.cc
@@ -307,28 +307,32 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
                                             Register receiver,
                                             Register scratch1,
                                             Register scratch2,
-                                            Label* miss) {
+                                            Label* miss,
+                                            bool support_wrappers) {
   Label check_wrapper;
 
   // Check if the object is a string leaving the instance type in the
   // scratch register.
-  GenerateStringCheck(masm, receiver, scratch1, miss, &check_wrapper);
+  GenerateStringCheck(masm, receiver, scratch1, miss,
+                      support_wrappers ? &check_wrapper : miss);
 
   // Load length directly from the string.
   __ movq(rax, FieldOperand(receiver, String::kLengthOffset));
   __ ret(0);
 
-  // Check if the object is a JSValue wrapper.
-  __ bind(&check_wrapper);
-  __ cmpl(scratch1, Immediate(JS_VALUE_TYPE));
-  __ j(not_equal, miss);
+  if (support_wrappers) {
+    // Check if the object is a JSValue wrapper.
+    __ bind(&check_wrapper);
+    __ cmpl(scratch1, Immediate(JS_VALUE_TYPE));
+    __ j(not_equal, miss);
 
-  // Check if the wrapped value is a string and load the length
-  // directly if it is.
-  __ movq(scratch2, FieldOperand(receiver, JSValue::kValueOffset));
-  GenerateStringCheck(masm, scratch2, scratch1, miss, miss);
-  __ movq(rax, FieldOperand(scratch2, String::kLengthOffset));
-  __ ret(0);
+    // Check if the wrapped value is a string and load the length
+    // directly if it is.
+    __ movq(scratch2, FieldOperand(receiver, JSValue::kValueOffset));
+    GenerateStringCheck(masm, scratch2, scratch1, miss, miss);
+    __ movq(rax, FieldOperand(scratch2, String::kLengthOffset));
+    __ ret(0);
+  }
 }
 
 
@@ -2933,7 +2937,7 @@ MaybeObject* KeyedLoadStubCompiler::CompileLoadStringLength(String* name) {
   __ Cmp(rax, Handle<String>(name));
   __ j(not_equal, &miss);
 
-  GenerateLoadStringLength(masm(), rdx, rcx, rbx, &miss);
+  GenerateLoadStringLength(masm(), rdx, rcx, rbx, &miss, true);
   __ bind(&miss);
   __ DecrementCounter(&Counters::keyed_load_string_length, 1);
   GenerateLoadMiss(masm(), Code::KEYED_LOAD_IC);