Add CODE_POINTER_ALIGN, use it in Page to align generated code.

Add CODE_POINTER_ALIGN, use it in Page to align generated code.

The object's space in Page starts after Page header and is aligned to kMapAlignment which is 32 bytes on 32-bit and 8 bytes on 64-bit.

In case of 64-bit target, the current page header size is exactly 32 bytes so we get the code magically aligned at 32 bytes but it is better to have a separate CODE_POINTER_ALIGN macro to make sure the object space in Page is aligned properly for both maps and code.

There could be a small waste of bytes sometimes (since both Page header and Code header sizes are aligned separately) but it seems the optimal one would involve cross-dependencies between .h files and not clear if it's worth it.

This is a back-port from Isolates branch.

Committed: http://code.google.com/p/v8/source/detail?r=5526

[Vitaly Repeshko, 2010-09-24 15:45:38]

LGTM

http://codereview.chromium.org/3461021/diff/2001/3001
File src/globals.h (right):

http://codereview.chromium.org/3461021/diff/2001/3001#newcode218
src/globals.h:218: // Code entry points are aligned to 32 bytes (cache line size
in some CPUs).
In most of the CPUs we deal with it's actually 64. Please change the
parenthetical remark to "to improve cache line utilization".

http://codereview.chromium.org/3461021/diff/2001/3005
File src/spaces.h (right):

http://codereview.chromium.org/3461021/diff/2001/3005#newcode247
src/spaces.h:247: // code alignment to be suitabel for both.
Typo: "suitable".

[Dmitry Titov, 2010-09-24 21:49:27]

Fixed and landed.
Thanks!