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[llvm-mca] Improve barriers for strict region marking #51165

Open Quuxplusone opened 2 years ago

Quuxplusone commented 2 years ago
Bugzilla Link PR52198
Status NEW
Importance P enhancement
Reported by Simon Pilgrim (llvm-dev@redking.me.uk)
Reported on 2021-10-17 10:21:08 -0700
Last modified on 2021-10-18 04:16:59 -0700
Version trunk
Hardware PC Windows NT
CC andrea.dibiagio@gmail.com, lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, matthew.davis@sony.com
Fixed by commit(s)
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Blocked by
See also PR42173

https://godbolt.org/z/er1Wsb3da

Efficiently calculating the interleaved load/store costs has been greatly hindered as the llvm-mca region markers aren't great barriers.

https://reviews.llvm.org/D111945

Even if it affects codegen, it'd be very useful if we can get llvm-mca to give us at least an estimate of costs so we can automate this a little.

Quuxplusone commented 2 years ago

+1, the UX has been rather pathetic so far.

Quuxplusone commented 2 years ago

Adding {rsp} to the asm capture does help a little, but is probably adding more memory traffic to the region block than necessary.

https://godbolt.org/z/4Pf5dncv3