[PATCH] D129852: [AArch64][SVE] Sink op into loop if it's used by PTEST and known to zero inactive lanes.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen added a comment.

In D129852#3655395 <https://reviews.llvm.org/D129852#3655395>, @sdesmalen wrote:

> In D129852#3655364 <https://reviews.llvm.org/D129852#3655364>, @paulwalker-arm wrote:
>
>> Can you provide a C/C++ example for when this is a problem? I'm not saying there's no problem to solve but rather that I'm starting to wonder if early decisions about removing reinterpret intrinsics are now starting to bite us.
>
> https://godbolt.org/z/q6hKMsxKK
>
> In this case it doesn't have anything to do with the reinterpret intrinsics, but rather the `ptrue` that gets hoisted out which is then no longer visible to (non-Global) ISel when it lowers the `ptest`.

Just to expand on this a little bit, I experimented with disabling the removal of the reinterpret intrinsics, but found that the `convert.to.svbool` call is still outside the loop at the point of reaching codegen, meaning that it still can't fold away the ptest instruction unless it actively tries to sink the operand.


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https://reviews.llvm.org/D129852