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cppgc: Use load/store instead of fetch_or

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fetch_or (lock-prefixed-or on x86) is emulated with branching on
armv7/armv8 and therefore generates more instructions.

This improves android-binary-size by 45K. It should also improve
performance.

Bug: chromium:1238884
Change-Id: I48f59b645a4bb872b3798a1fde11608fd2930ce6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3090342
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76260}
This commit is contained in:
Anton Bikineev 2021-08-12 14:37:25 +02:00 committed by V8 LUCI CQ
parent bdcda72cd1
commit 2e006255ca
1 changed files with 7 additions and 2 deletions
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9
include/cppgc/allocation.h
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@ -36,8 +36,13 @@ class V8_EXPORT MakeGarbageCollectedTraitInternal {
const_cast<uint16_t*>(reinterpret_cast<const uint16_t*>(
reinterpret_cast<const uint8_t*>(payload) -
api_constants::kFullyConstructedBitFieldOffsetFromPayload)));
atomic_mutable_bitfield->fetch_or(api_constants::kFullyConstructedBitMask,
std::memory_order_release);
// It's safe to split use load+store here (instead of a read-modify-write
// operation), since it's guaranteed that this 16-bit bitfield is only
// modified by a single thread. This is cheaper in terms of code bloat (on
// ARM) and performance.
uint16_t value = atomic_mutable_bitfield->load(std::memory_order_relaxed);
value |= api_constants::kFullyConstructedBitMask;
atomic_mutable_bitfield->store(value, std::memory_order_release);
}
template <typename U, typename CustomSpace>