[PATCH] D99565: [X86] Support replacing aligned vector moves with unaligned moves when avx is enabled.

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri added a comment.

I'm still uncomfortable with changing current status quo, even though i obviously don't get to cast the final vote here.

One should not use aligned loads in hope that they will cause an exception to detect address misalignment.
That's UBSan's job. `-fsanitize=undefined`/`-fsanitize=aligment` *should* catch it.
If it does not do so in your particular case, please file a bug, i would like to take a look.

Likewise, i don't think one should do overaligned loads and hope that they will just work.
UB is UB. The code will still be miscompiled, but you've just hidden your warning.

Likewise, even if unaligned loads can be always used, i would personally find it pretty surprising
to suddenly see unaliged loads instead of aligned ones.
Also, isn't that only possible/so when AVX is avaliable?
What happens without AVX? Do so anyways at the perfomance's cost?
Or back to exceptions?

Should this process in any form other than the UBSan changes,
i would like to first see a RFC on llvm-dev.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D99565/new/

https://reviews.llvm.org/D99565