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  1. 08 Oct, 2018 6 commits
  3. 07 Oct, 2018 3 commits
    • Benedikt Meurer's avatar
      [turbofan] Eliminate redundant Smi checks around array accesses. · bcdede0c
      Benedikt Meurer authored 
      As identified in the web-tooling-benchmark, there are specific code
patterns involving array indexed property accesses and subsequent
comparisons of those indices that lead to repeated Smi checks in the
optimized code, which in turn leads to high register pressure and
generally bad register allocation. An example of this pattern is
code like this:

```js
function f(a, n) {
  const i = a[n];
  if (n >= 1) return i;
}
```

The `a[n]` property access introduces a CheckBounds on `n`, which
later lowers to a `CheckedTaggedToInt32[dont-check-minus-zero]`,
however the `n >= 1` comparison has collected `SignedSmall` feedback
and so it introduces a `CheckedTaggedToTaggedSigned` operation. This
second Smi check is redundant and cannot easily be combined with the
earlier tagged->int32 conversion, since that also deals with heap
numbers and even truncates -0 to 0.

So we teach the RedundancyElimination to look at the inputs of these
speculative number comparisons and if there's a leading bounds check
on either of these inputs, we change the input to the result of the
bounds check. This avoids the redundant Smi checks later and generally
allows the SimplifiedLowering to do a significantly better job on the
number comparisons. We only do this in case of SignedSmall feedback
and only for inputs that are not already known to be in UnsignedSmall
range, to avoid doing too many (unnecessary) expensive lookups during
RedundancyElimination.

All of this is safe despite the fact that CheckBounds truncates -0
to 0, since the regular number comparisons in JavaScript identify
0 and -0 (unlike Object.is()). This also adds appropriate tests,
especially for the interesting cases where -0 is used only after
the code was optimized.

Bug: v8:6936, v8:7094
Change-Id: Ie37114fb6192e941ae1a4f0bfe00e9c0a8305c07
Reviewed-on: https://chromium-review.googlesource.com/c/1246181Reviewed-by: 's avatarSigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56428}
      bcdede0c
    • Benedikt Meurer's avatar
      Revert "[turbofan] Do not consume SignedSmall feedback in TurboFan anymore." · 248fd5ff
      Benedikt Meurer authored 
      This reverts commit 4fd92b25.

Reason for revert: Significant tankage on the no-mitigations bots (bad timing on the regular bots)

Original change's description:
> [turbofan] Do not consume SignedSmall feedback in TurboFan anymore.
> 
> This changes TurboFan to treat SignedSmall feedback similar to Signed32
> feedback for binary and compare operations, in order to simplify and
> unify the machinery.
> 
> This is an experiment. If this turns out to tank performance, we will
> need to revisit and ideally revert this change.
> 
> Bug: v8:7094
> Change-Id: I885769c2fe93d8413e59838fbe844650c848c3f1
> Reviewed-on: https://chromium-review.googlesource.com/c/1261442
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56411}

TBR=jarin@chromium.org,bmeurer@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:7094
Change-Id: I9fff3b40e6dc0ceb7611b55e1ca9940089470404
Reviewed-on: https://chromium-review.googlesource.com/c/1267175Reviewed-by: 's avatarBenedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56427}
      248fd5ff
    • v8-ci-autoroll-builder's avatar
      Update V8 DEPS. · c73c2dea
      v8-ci-autoroll-builder authored 
      Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/a092193..86e6b5e

TBR=machenbach@chromium.org,hablich@chromium.org,sergiyb@chromium.org

Change-Id: I70e960aca4160188ecc4100d286110f91f013964
Reviewed-on: https://chromium-review.googlesource.com/c/1266854
Commit-Queue: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Reviewed-by: 's avatarv8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#56426}
      c73c2dea
  5. 06 Oct, 2018 5 commits
  7. 05 Oct, 2018 26 commits