Cardmarking writebarrier.

Cardmarking writebarrier.

- New сardmarking write barrier handles large objects and normal objects in a similar fashion (no more additional space for pointer tracking is required, no conditional branches in WB code).
- Changes to enable oldspaces iteration without maps decoding:
-- layout change for FixedArrays: length is stored as a smis (initial patch by
Kevin Millikin)
-- layout change for SharedFunctionInfo: integer fields are stored as smi on
arm, ia32 and rearranged on x64.
-- layout change for String: meaning of LSB bit is fliped (1 now means hash not
computed); on x64 padding is added.
-- layout of maps is _not_ changed. Map space is currently iterated in a special
way.

Committed: http://code.google.com/p/v8/source/detail?r=4715

[Vyacheslav Egorov (Chromium), 2010-05-25 12:39:06]

http://codereview.chromium.org/2144006/diff/1/11
File src/heap.cc (right):

http://codereview.chromium.org/2144006/diff/1/11#newcode1105
src/heap.cc:1105: // Save the from-space object pointer and its map pointer at
the
Here is fix for the problem occured on buildbots and real ARM hardware. 

We were scanning for pointers a very large ASCII string which happened to
contain a sequence of chars which looked like a pointer to a new space.

[Vyacheslav Egorov (Chromium), 2010-05-25 12:50:12]

Mads I also decided to tweak NewSpace::Contains(Object*),
SemiSpace::Contains(Object*) to make them match their contract. 

Please take a look.

http://codereview.chromium.org/2144006/diff/4001/5028
File src/spaces.cc (left):

http://codereview.chromium.org/2144006/diff/4001/5028#oldcode1124
src/spaces.cc:1124: object_expected_ = reinterpret_cast<uintptr_t>(start) |
kHeapObjectTag;
Change object_mask_ to match HasHeapObjectTag() implementation.
Contains(Object*) should return true iff IsHeapObject() returns true

http://codereview.chromium.org/2144006/diff/4001/5028#oldcode1328
src/spaces.cc:1328: object_expected_ = reinterpret_cast<uintptr_t>(start) |
kHeapObjectTag;
Change object_mask_ to match HasHeapObjectTag() implementation.
Contains(Object*) should return true iff IsHeapObject() returns true.

[Mads Ager (chromium), 2010-05-25 13:03:08]

LGTM, let's give it another shot!