[PATCH] D99791: [CGCall] Annotate pointer argument with alignment

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri planned changes to this revision.
lebedev.ri added a comment.

@rjmccall thank you for taking a look!

In D99791#2670333 <https://reviews.llvm.org/D99791#2670333>, @rjmccall wrote:

> The last major conversation we had about this was this RFC I sent out about five years ago:
>
>   https://lists.llvm.org/pipermail/llvm-dev/2016-January/094012.html
>
> In that RFC, I specifically argued that we should not do this, and that it should only be considered undefined behavior to actually access memory through a misaligned pointer (for a particular definition of "access memory").  At Apple, we have made that a promise to our internal users, so even if we decide to do this, we will need to not do it on Darwin.  However, as I remember it, the LLVM community did not reach a consensus to adopt my recommendation, so in principle we still have the flexibility to start doing this.  I continue to believe that doing so would be a mistake.  At any rate, you should start by reading that thread.

Thank you for the pointer!
I can for sure provide an opt-out, however note that in the end it will cause performance regressions as compared to the current LLVM optimizations.
I will start with an UBSan part then.


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https://reviews.llvm.org/D99791