[wasm][asm.js] Use x&(x-1) trick to speed up life.

[wasm][asm.js] Use x&(x-1) trick to speed up life.

Using x&(x-1) to check for power of two masks usable at runtime
speeds up the life benchmark.

Borrowing this from SimplifiedLowering for the AsmJsRemS internal
wasm opcode.

Leaving this out for general wasm as we should be doing this optimization
in LLVM.

BUG=v8:4203
TEST=None
R=bmeurer@chromium.org

Committed: https://crrev.com/4cfe91cf58e831bd8efb211184bd9c6e182e88f2
Cr-Commit-Position: refs/heads/master@{#41581}

[bradnelson, 2016-12-08 08:23:55]

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

[commit-bot: I haz the power, 2016-12-08 08:24:04]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[bradn, 2016-12-08 08:24:31]

bradnelson@google.com changed reviewers:
+ bradnelson@google.com

[commit-bot: I haz the power, 2016-12-08 08:48:49]

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

[commit-bot: I haz the power, 2016-12-08 08:48:49]

Dry run: This issue passed the CQ dry run.

[Benedikt Meurer, 2016-12-08 09:34:02]

LGTM from my side.

[bradn, 2016-12-08 09:34:42]

The CQ bit was checked by bradnelson@google.com

[commit-bot: I haz the power, 2016-12-08 09:34:52]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-08 09:36:23]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1481189682693350,
"parent_rev": "d323059ffd9b76a014a385a22c4fbaa77c01b13a", "commit_rev":
"5139b7402a8d0f4d7350a8ad9cd1acaa150b4e65"}

[commit-bot: I haz the power, 2016-12-08 09:36:27]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-12-08 09:36:42]

Description was changed from

==========
[wasm][asm.js] Use x&(x-1) trick to speed up life.

Using x&(x-1) to check for power of two masks usable at runtime
speeds up the life benchmark.

Borrowing this from SimplifiedLowering for the AsmJsRemS internal
wasm opcode.

Leaving this out for general wasm as we should be doing this optimization
in LLVM.

BUG=v8:4203
TEST=None
R=bmeurer@chromium.org
==========

to

==========
[wasm][asm.js] Use x&(x-1) trick to speed up life.

Using x&(x-1) to check for power of two masks usable at runtime
speeds up the life benchmark.

Borrowing this from SimplifiedLowering for the AsmJsRemS internal
wasm opcode.

Leaving this out for general wasm as we should be doing this optimization
in LLVM.

BUG=v8:4203
TEST=None
R=bmeurer@chromium.org

Committed: https://crrev.com/4cfe91cf58e831bd8efb211184bd9c6e182e88f2
Cr-Commit-Position: refs/heads/master@{#41581}
==========

[commit-bot: I haz the power, 2016-12-08 09:36:43]

Patchset 2 (id:??) landed as
https://crrev.com/4cfe91cf58e831bd8efb211184bd9c6e182e88f2
Cr-Commit-Position: refs/heads/master@{#41581}