x64: Use a short encoding of addq and subq for 32-bit immediates.

runtime/vm/code_patcher_x64.cc

 // Copyright (c) 2012, 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"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/code_patcher.h"
 #include "vm/cpu.h"
@@ skipping 252 matching lines @@
     return (bytes[0] == 0x49) && (bytes[1] == 0x8b) && (bytes[2] == 0x87);
   }
 
   RawObject* edge_counter() const {
     return object_pool_.At(InstructionPattern::IndexFromPPLoad(end_ - 4));
   }
 
  private:
   // The edge counter load is followed by the fixed-size edge counter
   // incrementing code:
-  //     49 c7 c3 02 00 00 00         movq r11,0x2
-  //     4c 01 58 17                  addq [rax+0x17],r11
-  static const intptr_t kAdjust = 11;
+  //     48 83 40 17 02             addq [rax+0x17],0x2

[Florian Schneider, 2013/10/01 11:11:05]

How about using incq to save one more byte?

+  static const intptr_t kAdjust = 5;
 
   uword end_;
   const Array& object_pool_;
 };
 
 
 RawObject* CodePatcher::GetEdgeCounterAt(uword pc, const Code& code) {
   ASSERT(code.ContainsInstructionAt(pc));
   EdgeCounter counter(pc, code);
   return counter.edge_counter();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64