llvm dev - Jan 2018 - How to remove vector.memcheck when noalias is really safe

Hi,

We are having an issue with the loop vectorizer and noalias pointers, as it is
generating `vector.memcheck` while we can guarantee that the pointers will not
overlap.

It seems that in `LoopVectorize.cpp` the function `emitMemRuntimeChecks` is
called but there are no checks to disable this behavior (like "strong
noalias")

We are actually using a technique similar to the llvm.noalias
(https://llvm.org/devmtg/2017-02-04/Restrict-Qualified-Pointers-in-LLVM.pdf),
discussed a bit here
http://lists.llvm.org/pipermail/llvm-dev/2017-September/117443.html, but we are
not using the llvm.noalias PR.

Still, from the document above, it seems that the llvm.noalias is able to get
rid off these checks, but I'm failing to see why it is related to the
introduction of this new intrinsic. I assume this optimization should work with
any noalias pointers no?, not only the ones returned by llvm.noalias...

Any ideas how to workaround this? (using the llvm.noalias PR?)

Thanks!


<https://llvm.org/devmtg/2017-02-04/Restrict-Qualified-Pointers-in-LLVM.pdf>
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