[stubs] Remove dead string copying code

src/x64/code-stubs-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-stubs.h"
 #include "src/api-arguments.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 1947 matching lines @@
   __ CallRuntime(Runtime::kStringCharFromCode);
   if (!result_.is(rax)) {
     __ movp(result_, rax);
   }
   call_helper.AfterCall(masm);
   __ jmp(&exit_);
 
   __ Abort(kUnexpectedFallthroughFromCharFromCodeSlowCase);
 }
 
-
-void StringHelper::GenerateCopyCharacters(MacroAssembler* masm,
-                                          Register dest,
-                                          Register src,
-                                          Register count,
-                                          String::Encoding encoding) {
-  // Nothing to do for zero characters.
-  Label done;
-  __ testl(count, count);
-  __ j(zero, &done, Label::kNear);
-
-  // Make count the number of bytes to copy.
-  if (encoding == String::TWO_BYTE_ENCODING) {
-    STATIC_ASSERT(2 == sizeof(uc16));
-    __ addl(count, count);
-  }
-
-  // Copy remaining characters.
-  Label loop;
-  __ bind(&loop);
-  __ movb(kScratchRegister, Operand(src, 0));
-  __ movb(Operand(dest, 0), kScratchRegister);
-  __ incp(src);
-  __ incp(dest);
-  __ decl(count);
-  __ j(not_zero, &loop);
-
-  __ bind(&done);
-}
-
-
 void StringHelper::GenerateFlatOneByteStringEquals(MacroAssembler* masm,
                                                    Register left,
                                                    Register right,
                                                    Register scratch1,
                                                    Register scratch2) {
   Register length = scratch1;
 
   // Compare lengths.
   Label check_zero_length;
   __ movp(length, FieldOperand(left, String::kLengthOffset));
@@ skipping 2325 matching lines @@
                            kStackUnwindSpace, nullptr, return_value_operand,
                            NULL);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64