[llvm] [DAGCombiner] Freeze maybe poison operands when folding select to logic (PR #84924)

[Nikita Popov via llvm-commits]

nikic wrote:

> I've rebased this (again). But I'm not quite sure how to proceed.
> 
>     * What remains to be solved before landing this? Any particular tests that are of concern?

I think we mainly need a solution for the "AssertZExt/AssertSExt on argument" problem.

> 
>     * Would it help if I split it up in one patch for foldBoolSelectToLogic and another one for foldVSelectToSignBitSplatMask?

Probably, especially if the latter has less test regressions?
 
>     * Should I pre-commit [e57c143](https://github.com/llvm/llvm-project/commit/e57c1432d57227969a9d6a4f19fd5469a39a4a14) (not sure if there would be any motivating test cases for that one if doing it as a pre-commit, that is why I added it as a second patch in the patch-stack here).

Yes, please. If there are no test changes as-is, you could add a test with explicit freeze.

https://github.com/llvm/llvm-project/pull/84924