[PATCH] D88396: [X86] Support replacing aligned vector moves with unaligned moves when avx is enabled. (off by default)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D88396#2323332 <https://reviews.llvm.org/D88396#2323332>, @pengfei wrote:

> LGTM. Thanks!
> Since the pass is turned off by default, I think we can let it in. @lebedev.ri, what's your opinion?

I still retain my original opinion that this is trying to paper over broken source code,
and incorrectly so, because even if backend doesn't make use of the alignment information
that was lowered from the source code into IR, the IR will still contain incorrect alignment
information, and it is only a matter of time until that UB manifests in some other way.

As i see it, there are 4 options:

1. Don't manually vectorize the code
2. Do UBSan to catch these issues
3. Enhance clang/clang-tidy to better catch these issues
4. Don't do aligned loads https://godbolt.org/z/38jrvE
5. Add a clang (!) switch to make `__m128` unaligned

I strongly suggest that an option 4 be taken.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D88396/new/

https://reviews.llvm.org/D88396