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

runtime/vm/code_patcher_x64.cc

Index: runtime/vm/code_patcher_x64.cc
diff --git a/runtime/vm/code_patcher_x64.cc b/runtime/vm/code_patcher_x64.cc
index 67beae77eaaa8be0cd509c7211ecc75a51f29201..0de7bd6ace3724f2864495423ef04d062f1797ac 100644
--- a/runtime/vm/code_patcher_x64.cc
+++ b/runtime/vm/code_patcher_x64.cc
@@ -270,9 +270,8 @@ class EdgeCounter : public ValueObject {
  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_;