Port the initial fast code generator to x64. For the constant true in...

src/x64/frames-x64.h

 // Copyright 2009 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
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 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef V8_X64_FRAMES_X64_H_
 #define V8_X64_FRAMES_X64_H_
 
 namespace v8 {
 namespace internal {
 
-// TODO(x64): This is a stub, mostly just a copy of the ia32 bit version.
-// This might all need to change to be correct for x64.
-
 static const int kNumRegs = 8;
 static const RegList kJSCallerSaved =
     1 << 0 |  // rax
     1 << 1 |  // rcx
     1 << 2 |  // rdx
     1 << 3 |  // rbx - used as a caller-saved register in JavaScript code
     1 << 7;   // rdi - callee function
 
 static const int kNumJSCallerSaved = 5;
 
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 inline Object* JavaScriptFrame::function_slot_object() const {
   const int offset = JavaScriptFrameConstants::kFunctionOffset;
   return Memory::Object_at(fp() + offset);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_FRAMES_X64_H_