builtins.cc return PackedElementsKind where applicable

builtins.cc return PackedElementsKind where applicable

Returning a result array with holey elements kind in where we actually have a packed kind causes performance regressions.

LOG=N
BUG=chromium:531357
Committed: https://crrev.com/053d7f49e525e7b0aaab95947e8759d878ae195e
Cr-Commit-Position: refs/heads/master@{#30736}

[Camillo Bruni, 2015-09-14 13:05:40]

The CQ bit was checked by cbruni@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-14 13:05:48]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1340033002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1340033002/20001

[commit-bot: I haz the power, 2015-09-14 13:30:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-14 13:30:40]

Dry run: This issue passed the CQ dry run.

[Camillo Bruni, 2015-09-14 14:01:23]

cbruni@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Camillo Bruni, 2015-09-14 14:01:23]

PTAL

[Jakob Kummerow, 2015-09-14 15:09:47]

Looks good; but as discussed I'd beef up Map::TransitionElementsTo to ensure it
finds an existing packed elements kind map by adding something like:

// Check if we need to go back in the elements kind transition chain.
if (IsHoleyElementsKind(from_kind) && 
    to_kind == GetPackedElementsKind(from_kind) &&
    map->GetBackPointer()->IsMap() &&
    Map::cast(map->GetBackPointer())->instance_kind == to_kind)) {
  return handle(Map::cast(map->GetBackPointer()));
}

https://codereview.chromium.org/1340033002/diff/20001/src/elements.cc
File src/elements.cc (left):

https://codereview.chromium.org/1340033002/diff/20001/src/elements.cc#oldcode118
src/elements.cc:118: 
nit: keep this

[Camillo Bruni, 2015-09-15 07:34:22]

PTAL
Included Map Backtransition according to your suggestion, thanks!

[Camillo Bruni, 2015-09-15 07:34:28]

The CQ bit was checked by cbruni@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-15 07:34:40]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1340033002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1340033002/40001

[commit-bot: I haz the power, 2015-09-15 07:59:12]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-15 07:59:12]

Dry run: This issue passed the CQ dry run.

[Jakob Kummerow, 2015-09-15 08:02:39]

LGTM

https://codereview.chromium.org/1340033002/diff/40001/src/objects.cc
File src/objects.cc (right):

https://codereview.chromium.org/1340033002/diff/40001/src/objects.cc#newcode4049
src/objects.cc:4049: // Reuse map transitions for JSArrays
nit: trailing full stop please.

[Camillo Bruni, 2015-09-15 08:45:40]

The CQ bit was checked by cbruni@chromium.org

[Camillo Bruni, 2015-09-15 08:45:41]

The patchset sent to the CQ was uploaded after l-g-t-m from
jkummerow@chromium.org
Link to the patchset: https://codereview.chromium.org/1340033002/#ps60001
(title: "fullstop")

[commit-bot: I haz the power, 2015-09-15 08:45:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1340033002/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1340033002/60001

[commit-bot: I haz the power, 2015-09-15 09:08:32]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-09-15 09:08:49]

Patchset 4 (id:??) landed as
https://crrev.com/053d7f49e525e7b0aaab95947e8759d878ae195e
Cr-Commit-Position: refs/heads/master@{#30736}