[PATCH] D101349: AArch64: support i128 cmpxchg in GlobalISel.

Mon May 10 14:14:12 PDT 2021

efriedma added a comment.

This might be a bit crazy, but instead of emitting CASPX directly from globalisel, did you consider just emitting CMP_SWAP_128, then converting it to CASPX after isel?  Not sure it's worth shifting around the complexity like this, but maybe worth considering.

> - -O0, no LSE. The IR is expanded to ldxp/stxp and we need patterns & code to select them.
> - -O1, no LSE. We get G_ATOMIC_CMPXCHG, and need to produce CMP_SWAP_N pseudos. The registers are all 64-bit so this is easy in the existing framework.
> - LSE. We get G_ATOMIC_CMPXCHG and need to produce a CASP instruction with XSeqPair registers.

I think you accidentally switched -O0 and -O1.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101349/new/

https://reviews.llvm.org/D101349