This changes the JSArrayIterator to always have only a single instance
type, instead of the zoo of instance types that we had before, and
which became less useful with the specification update to when "next"
is loaded from the iterator now. This greatly simplifies the baseline
implementation of the array iterator, which now only looks at the
iterated object during %ArrayIteratorPrototype%.next invocations.
In TurboFan we introduce a new JSCreateArrayIterator operator, that
holds the IterationKind and get's the iterated object as input. When
optimizing %ArrayIteratorPrototype%.next in the JSCallReducer, we
check whether the receiver is a JSCreateArrayIterator, and if so,
we try to infer maps for the iterated object from there. If we find
any, we speculatively assume that these won't have changed during
iteration (as we did before with the previous approach), and generate
fast code for both JSArray and JSTypedArray iteration.
Drive-by-fix: Drop the fast_array_iteration protector, it's not
necessary anymore since we have the deoptimization guard bit in
the JSCallReducer now.
This addresses the performance cliff noticed in webpack 4. The minimal
repro on the tracking bug goes from
console.timeEnd: mono, 124.773000
console.timeEnd: poly, 670.353000
to
console.timeEnd: mono, 118.709000
console.timeEnd: poly, 141.393000
so that's a 4.7x improvement.
Also make presubmit happy by adding the missing #undef's.
Bug: v8:7510, v7:7514
Change-Id: I79a46bfa2cd0f0710e09365ef72519b1bbb667b5
Reviewed-on: https://chromium-review.googlesource.com/946098
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51725}
