[turbofan] Add TruncationMode for TruncateFloat64ToInt32.

[turbofan] Add TruncationMode for TruncateFloat64ToInt32.

We actually need round to zero truncation to implement the counterpart
of LDoubleToI in TurboFan, which tries to convert a double to an integer
as required for keyed load/store optimizations.

Drive-by-cleanup: Reduce some code duplication in the InstructionSelector
implementations.

R=jarin@chromium.org

Committed: https://crrev.com/4b38c15817033ccd9a65efbb3d038ae2423293c2
Cr-Commit-Position: refs/heads/master@{#29527}

[Benedikt Meurer, 2015-07-08 05:43:38]

Hey Jaro,

This adds a new truncation mode for TruncateFloat64ToInt32 (in addition to the
JavaScript mode that we already have), which will be used to implement the
DoubleToI thing in TurboFan, that is required for i.e. fast conversion of keyed
load/store indices.
Please take a look.

Thanks,
Benedikt

[Benedikt Meurer, 2015-07-08 06:26:59]

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

[commit-bot: I haz the power, 2015-07-08 06:27:04]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1225993002/1

[commit-bot: I haz the power, 2015-07-08 06:28:26]

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

[commit-bot: I haz the power, 2015-07-08 06:28:27]

Dry run: This issue passed the CQ dry run.

[Benedikt Meurer, 2015-07-08 06:28:44]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-07-08 06:28:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1225993002/1

[commit-bot: I haz the power, 2015-07-08 06:28:55]

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

[commit-bot: I haz the power, 2015-07-08 06:28:56]

No L-G-T-M from a valid reviewer yet. Only full committers are accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Jarin, 2015-07-08 06:45:09]

lgtm. (I am not wild about the VisitRR, VisitRO names, but I see that is a
preexisting technology.)

BTW, why did not you create a new opcode for this?

[Benedikt Meurer, 2015-07-08 06:47:10]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-07-08 06:47:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1225993002/1

[commit-bot: I haz the power, 2015-07-08 06:48:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-08 06:49:14]

Patchset 1 (id:??) landed as
https://crrev.com/4b38c15817033ccd9a65efbb3d038ae2423293c2
Cr-Commit-Position: refs/heads/master@{#29527}