Use regular map-checks to guard string-length loading.

src/x64/stub-cache-x64.cc

 // Copyright 2012 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 286 matching lines @@
   STATIC_ASSERT(kNotStringTag != 0);
   __ testl(scratch, Immediate(kNotStringTag));
   __ j(not_zero, non_string_object);
 }
 
 
 void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
                                             Register receiver,
                                             Register scratch1,
                                             Register scratch2,
-                                            Label* miss,
-                                            bool support_wrappers) {
+                                            Label* miss) {
   Label check_wrapper;
 
   // Check if the object is a string leaving the instance type in the
   // scratch register.
-  GenerateStringCheck(masm, receiver, scratch1, miss,
-                      support_wrappers ? &check_wrapper : miss);
+  GenerateStringCheck(masm, receiver, scratch1, miss, &check_wrapper);
 
   // Load length directly from the string.
   __ movq(rax, FieldOperand(receiver, String::kLengthOffset));
   __ ret(0);
 
-  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 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);
 }
 
 
 void StubCompiler::GenerateLoadFunctionPrototype(MacroAssembler* masm,
                                                  Register receiver,
                                                  Register result,
                                                  Register scratch,
                                                  Label* miss_label) {
   __ TryGetFunctionPrototype(receiver, result, miss_label);
   if (!result.is(rax)) __ movq(rax, result);
@@ skipping 2819 matching lines @@
   // -----------------------------------
   TailCallBuiltin(masm, Builtins::kKeyedLoadIC_MissForceGeneric);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64