Fix full code generator to not use --debug-code if it is in

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
===================================================================
--- src/x64/assembler-x64.cc	(revision 12237)
+++ src/x64/assembler-x64.cc	(working copy)
@@ -350,7 +350,8 @@
     : AssemblerBase(arg_isolate),
       code_targets_(100),
       positions_recorder_(this),
-      emit_debug_code_(FLAG_debug_code) {
+      emit_debug_code_(FLAG_debug_code),
+      predictable_code_size_(false) {
   if (buffer == NULL) {
     // Do our own buffer management.
     if (buffer_size <= kMinimalBufferSize) {
@@ -1234,7 +1235,7 @@
     const int long_size  = 6;
     int offs = L->pos() - pc_offset();
     ASSERT(offs <= 0);
-    if (is_int8(offs - short_size)) {
+    if (is_int8(offs - short_size) && !predictable_code_size_) {

[Jakob Kummerow, 2012/07/31 14:44:58]

A comment would be nice about why we have to disable automatic near jumps on
x64. Draft based on our offline discussion:
// On x64, when code is recompiled for debugging, some places need to be padded
// out to a certain size. The debugger is keeping track of how often it did
// this, but if the size of jump instructions can also change, that's not
// enough and the calculated offsets would be incorrect.

       // 0111 tttn #8-bit disp.
       emit(0x70 | cc);
       emit((offs - short_size) & 0xFF);
@@ -1291,7 +1292,7 @@
   if (L->is_bound()) {
     int offs = L->pos() - pc_offset() - 1;
     ASSERT(offs <= 0);
-    if (is_int8(offs - short_size)) {
+    if (is_int8(offs - short_size) && !predictable_code_size_) {
       // 1110 1011 #8-bit disp.
       emit(0xEB);
       emit((offs - short_size) & 0xFF);