x64 code improvements and cleanups.

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
===================================================================
--- runtime/vm/assembler_x64.cc	(revision 33759)
+++ runtime/vm/assembler_x64.cc	(working copy)
@@ -2555,9 +2555,9 @@
 
 void Assembler::CompareObject(Register reg, const Object& object, Register pp) {
   if (CanLoadFromObjectPool(object)) {
-    ASSERT(reg != TMP);
-    LoadObject(TMP, object, pp);
-    cmpq(reg, TMP);
+    const int32_t offset =
+        Array::element_offset(FindObject(object, kNotPatchable));
+    cmpq(reg, Address::AddressBaseImm32(pp, offset - kHeapObjectTag));

[zra, 2014/03/17 19:29:58]

AddressBaseImm32 emits a fixed-size constant for the offset. If you just use
Address(pp, offset-kHeapObjectTag), you may sometimes get a shorter instruction
for the smaller constant.

[srdjan, 2014/03/17 19:54:32]

Done.

   } else {
     CompareImmediate(
         reg, Immediate(reinterpret_cast<int64_t>(object.raw())), pp);