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deps: V8: cherry-pick 56f6a76 #25269

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@BridgeAR BridgeAR commented Dec 29, 2018

Original commit message:

[turbofan] Fix -0 check for subnormals.

Previously we'd check `x` for -0 by testing `(1.0 / x) == -Infinity`,
but this will yield the wrong results when `x` is a subnormal, i.e.
really close to 0.

In CSA we already perform bit checks to test for -0, so teach TurboFan
to do the same for comparisons to -0 (via `Object.is`). We introduce a
new NumberIsMinusZero simplified operator to handle the case where
SimplifiedLowering already knows that the input is a number.

Bug: chromium:903043, v8:6882
Change-Id: I0cb7c568029b461a92fc183104d5f359b4bfe7f4
Reviewed-on: https://chromium-review.googlesource.com/c/1328802
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57382}

Refs: v8/v8@56f6a76

Fixes: #25268

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • tests and/or benchmarks are included
  • documentation is changed or added
  • commit message follows commit guidelines

Original commit message:

    [turbofan] Fix -0 check for subnormals.

    Previously we'd check `x` for -0 by testing `(1.0 / x) == -Infinity`,
    but this will yield the wrong results when `x` is a subnormal, i.e.
    really close to 0.

    In CSA we already perform bit checks to test for -0, so teach TurboFan
    to do the same for comparisons to -0 (via `Object.is`). We introduce a
    new NumberIsMinusZero simplified operator to handle the case where
    SimplifiedLowering already knows that the input is a number.

    Bug: chromium:903043, v8:6882
    Change-Id: I0cb7c568029b461a92fc183104d5f359b4bfe7f4
    Reviewed-on: https://chromium-review.googlesource.com/c/1328802
    Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
    Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#57382}

Refs: v8/v8@56f6a76
@nodejs-github-bot nodejs-github-bot added build Issues and PRs related to build files or the CI. v8 engine Issues and PRs related to the V8 dependency. labels Dec 29, 2018
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@TimothyGu TimothyGu left a comment

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Rubber-stamp LGTM.

@devsnek
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devsnek commented Dec 29, 2018

just as a funny sidenote, we made the same mistake in node core :p #17507

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Rubber stamp LGTM

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addaleax commented Jan 8, 2019

@BridgeAR BridgeAR added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Jan 9, 2019
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BridgeAR commented Jan 9, 2019

danbev pushed a commit that referenced this pull request Jan 9, 2019
Original commit message:

    [turbofan] Fix -0 check for subnormals.

    Previously we'd check `x` for -0 by testing `(1.0 / x) == -Infinity`,
    but this will yield the wrong results when `x` is a subnormal, i.e.
    really close to 0.

    In CSA we already perform bit checks to test for -0, so teach TurboFan
    to do the same for comparisons to -0 (via `Object.is`). We introduce a
    new NumberIsMinusZero simplified operator to handle the case where
    SimplifiedLowering already knows that the input is a number.

    Bug: chromium:903043, v8:6882
    Change-Id: I0cb7c568029b461a92fc183104d5f359b4bfe7f4
    Reviewed-on: https://chromium-review.googlesource.com/c/1328802
    Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
    Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#57382}

PR-URL: #25269
Refs: v8/v8@56f6a76
Fixes: #25268
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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danbev commented Jan 9, 2019

Landed in ddbb7d7.

I updated the commit summary/subject to be deps: cherry-pick 56f6a76 from upstream V8 to avoid the issue reported by Travis CI, hope that was ok.

@danbev danbev closed this Jan 9, 2019
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addaleax commented Jan 15, 2019

@BridgeAR This would need a manual backport to v11.x-staging (it applies cleanly but does not compile)

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@addaleax I would like to backport this and it lands cleanly on v11.x but it relies on some other code and I do not know the code base well enough to backport this on my own (see also #25270 (comment)).

It would be great if the @nodejs/v8-update could have a look at backporting this.

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targos commented Feb 14, 2019

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Successfully merging this pull request may close these issues.

Object.is(-Number.MIN_VALUE, -0) broken on ≥ v10.0.0