More aggressive reuse of spill slots in the register allocator.

Two improvements:
- At phi nodes, we now try to merge operands into one spill slot and
  then reuse the spill slot for the phi.
- After register allocation we merge disjoint spill slots.

With this change, I see about 4% improvement in zlib.

BUG=
R=titzer@chromium.org

Review URL: https://codereview.chromium.org/310003003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23532 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Revert "More aggressive reuse of spill slots in the register allocator."

This reverts commit r23532 for introducing bunch of flakes.

TBR=titzer@chromium.org

Review URL: https://codereview.chromium.org/519423002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23533 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
[Auto-roll] Bump up version to 3.29.33.0

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/528443002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23534 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Reland "More aggressive reuse of spill slots in the register allocator."

This relands r23532 (https://codereview.chromium.org/310003003). Flakes seem unrelated.

TBR=titzer@chromium.org

Review URL: https://codereview.chromium.org/522173003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23536 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
[Auto-roll] Bump up version to 3.29.34.0

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/523413003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23537 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/master'