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

Tue Apr 13 00:51:19 PDT 2021

LiuChen3 added a comment.

In D99565#2682809 <https://reviews.llvm.org/D99565#2682809>, @lebedev.ri wrote:

> 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 available?
> Also, doesn't that cause compiler lock-in?
> 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.
> Sorry about being uneasy about this. :S

We are happy to hear your voice. We will discuss this on llvm-dev later after confirming Craigs's opinion.

Repository:
  rG LLVM Github Monorepo

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

https://reviews.llvm.org/D99565