Intrinsify some ByteArray methods.

runtime/vm/assembler_x64.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
@@ skipping 306 matching lines @@
     EmitOperand(0, operand);
     EmitImmediate(imm);
   } else {
     movq(TMP, imm);
     movq(dst, TMP);
   }
 }
 
 
 void Assembler::movsxl(Register dst, const Address& src) {
-  UNIMPLEMENTED();
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitOperandREX(dst, src, REX_W);
+  EmitUint8(0x63);
+  EmitOperand(dst & 7, src);
 }
 
 
 void Assembler::leaq(Register dst, const Address& src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitOperandREX(dst, src, REX_W);
   EmitUint8(0x8D);
   EmitOperand(dst & 7, src);
 }
 
@@ skipping 1300 matching lines @@
     comments.SetCommentAt(i, comments_[i]->comment());
   }
 
   return comments;
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64