[turbofan] Better representation selection for comparison with Float64.

[turbofan] Better representation selection for comparison with Float64.

For speculative number comparisons with SignedSmall feedback, we always
enforce either TaggedSigned or Word32 comparisons. But this is not
really beneficial if one of the inputs is already in Float64
representation; in that case it's cheaper to just convert the other
input to a Float64.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2790833004
Cr-Commit-Position: refs/heads/master@{#44327}
Committed: https://chromium.googlesource.com/v8/v8/+/8af394d6d385daf05b73765a2545ac8f266c64c7

[Benedikt Meurer, 2017-03-31 19:00:29]

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

[commit-bot: I haz the power, 2017-03-31 19:00:30]

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

[Benedikt Meurer, 2017-03-31 19:02:52]

Hey Jaro,

Spotted this in react.js, for example in updateMultiChild, where
curChildrenDOMIndex is held in a Float64 local variable in TurboFan. Don't know
if this is the desired approach, I took inspiration from the surrounding code,
but it already looks borderline understandable. Any advice on how to make this
less ad-hoc and cleaner?

Thanks,
Benedikt

[commit-bot: I haz the power, 2017-03-31 19:26:37]

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

[commit-bot: I haz the power, 2017-03-31 19:26:37]

Dry run: This issue passed the CQ dry run.

[Jarin, 2017-04-03 06:57:58]

So how much exactly does this help?

[Jarin, 2017-04-03 07:58:19]

lgtm

https://codereview.chromium.org/2790833004/diff/1/src/compiler/simplified-low...
File src/compiler/simplified-lowering.cc (right):

https://codereview.chromium.org/2790833004/diff/1/src/compiler/simplified-low...
src/compiler/simplified-lowering.cc:1627: } else if
(IsNodeRepresentationFloat64(lhs) ||
Insert a comment explaining what is going on here, please.

[Benedikt Meurer, 2017-04-03 08:00:28]

https://codereview.chromium.org/2790833004/diff/1/src/compiler/simplified-low...
File src/compiler/simplified-lowering.cc (right):

https://codereview.chromium.org/2790833004/diff/1/src/compiler/simplified-low...
src/compiler/simplified-lowering.cc:1627: } else if
(IsNodeRepresentationFloat64(lhs) ||
On 2017/04/03 07:58:19, Jarin wrote:
> Insert a comment explaining what is going on here, please.

Done.

[Benedikt Meurer, 2017-04-03 08:00:31]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2017-04-03 08:00:32]

The patchset sent to the CQ was uploaded after l-g-t-m from jarin@chromium.org
Link to the patchset: https://codereview.chromium.org/2790833004/#ps20001
(title: "REBASE and comment.")

[commit-bot: I haz the power, 2017-04-03 08:00:37]

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, 2017-04-03 08:24:04]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1491206431925410,
"parent_rev": "12faf0f87f0d180abdfe294f6646bbf2044789e8", "commit_rev":
"8af394d6d385daf05b73765a2545ac8f266c64c7"}

[commit-bot: I haz the power, 2017-04-03 08:24:09]

Description was changed from

==========
[turbofan] Better representation selection for comparison with Float64.

For speculative number comparisons with SignedSmall feedback, we always
enforce either TaggedSigned or Word32 comparisons. But this is not
really beneficial if one of the inputs is already in Float64
representation; in that case it's cheaper to just convert the other
input to a Float64.

R=jarin@chromium.org
==========

to

==========
[turbofan] Better representation selection for comparison with Float64.

For speculative number comparisons with SignedSmall feedback, we always
enforce either TaggedSigned or Word32 comparisons. But this is not
really beneficial if one of the inputs is already in Float64
representation; in that case it's cheaper to just convert the other
input to a Float64.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2790833004
Cr-Commit-Position: refs/heads/master@{#44327}
Committed:
https://chromium.googlesource.com/v8/v8/+/8af394d6d385daf05b73765a2545ac8f266...
==========

[commit-bot: I haz the power, 2017-04-03 08:24:10]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/v8/v8/+/8af394d6d385daf05b73765a2545ac8f266...

[Benedikt Meurer, 2017-04-07 10:36:45]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/2801233002/ by bmeurer@chromium.org.

The reason for reverting is: Doesn't really move the needle, but tanks
Kraken/imaging-gaussian-blur (crbug.com/709396), so reverting for now..