[turbofan] Don't generate unnecessary minus zero checks.

[turbofan] Don't generate unnecessary minus zero checks.

When we do a checked conversion from Tagged or Float64 to Int32, we used
to always do a minus zero check, even if we already know that the input
cannot be minus zero. Now we actually do the check only if we have
evidence that the input might be minus zero.

R=epertoso@chromium.org
BUG=v8:4583
Committed: https://crrev.com/b947fff8afe6dda413033b25010c3d73a7656da5
Cr-Commit-Position: refs/heads/master@{#38308}

[Benedikt Meurer, 2016-08-03 13:05:34]

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

[commit-bot: I haz the power, 2016-08-03 13:05:43]

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

[epertoso, 2016-08-03 13:22:39]

lgtm

Nice.

[epertoso, 2016-08-03 13:22:42]

lgtm

Nice.

[commit-bot: I haz the power, 2016-08-03 13:35:17]

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

[commit-bot: I haz the power, 2016-08-03 13:35:18]

Dry run: Try jobs failed on following builders:
  v8_linux64_avx2_rel_ng on master.tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux64_avx2_rel_ng/buil...)
  v8_linux64_avx2_rel_ng_triggered on master.tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux64_avx2_rel_ng_trig...)

[Benedikt Meurer, 2016-08-03 16:14:19]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2016-08-03 16:14:19]

The patchset sent to the CQ was uploaded after l-g-t-m from
epertoso@chromium.org
Link to the patchset: https://codereview.chromium.org/2202993005/#ps20001
(title: "Err, DCHECK, meh")

[commit-bot: I haz the power, 2016-08-03 16:14:31]

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, 2016-08-03 16:34:12]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-03 16:36:24]

Description was changed from

==========
[turbofan] Don't generate unnecessary minus zero checks.

When we do a checked conversion from Tagged or Float64 to Int32, we used
to always do a minus zero check, even if we already know that the input
cannot be minus zero. Now we actually do the check only if we have
evidence that the input might be minus zero.

R=epertoso@chromium.org
BUG=v8:4583
==========

to

==========
[turbofan] Don't generate unnecessary minus zero checks.

When we do a checked conversion from Tagged or Float64 to Int32, we used
to always do a minus zero check, even if we already know that the input
cannot be minus zero. Now we actually do the check only if we have
evidence that the input might be minus zero.

R=epertoso@chromium.org
BUG=v8:4583

Committed: https://crrev.com/b947fff8afe6dda413033b25010c3d73a7656da5
Cr-Commit-Position: refs/heads/master@{#38308}
==========

[commit-bot: I haz the power, 2016-08-03 16:36:25]

Patchset 2 (id:??) landed as
https://crrev.com/b947fff8afe6dda413033b25010c3d73a7656da5
Cr-Commit-Position: refs/heads/master@{#38308}