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ARM: Set MaxAtomicSizeInBitsSupported appropriately.
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Authored by jyknight on Mar 4 2021, 2:30 PM.



This will result in larger atomic operations getting expanded to
__atomic_* libcalls via AtomicExpandPass. This is a part of a change
to similarly clean up atomics handling on all targets.

When ldrex is available, we can support lock-free atomics up to 32
bits. When ldrexd is available, 64 bits.

When neither are available, we can still support up to 32-bit
lock-free atomics on certain platforms, if they provide
kernel-assisted cmpxchg. In that case, we can emit native 32-bit loads
and stores, and emit rmw/cmpxchg via __sync_* libcalls. 64-bit atomics
are not supported similarly, because 64-bit loads/stores aren't

Finally, refactor/simplify the remainder of the code, which no longer
needs to try to deal with oversized atomics.

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Event Timeline

jyknight created this revision.Mar 4 2021, 2:30 PM
jyknight requested review of this revision.Mar 4 2021, 2:30 PM
Herald added a project: Restricted Project. · View Herald TranscriptMar 4 2021, 2:30 PM
jyknight updated this revision to Diff 328324.Mar 4 2021, 3:21 PM

Version where tests actually pass: I forgot to merge a fixup commit before uploading.