[llvm-branch-commits] [llvm] release/18.x: [DAGCombiner] In mergeTruncStore, make sure we aren't storing shifted in bits. (#90939) (PR #91038)

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AtariDreams wrote:

We do not need to know how to fold every single possible permutation that comes our way, especially if they are so rare that writing compile code optimizing it isn't even worth it. We do, however, need to strive to avoid miscompiles wherever we can, no matter how esoteric the code is.

Now, this isn't always possible, but in this case, the alternative codepath given just bails the transform, which is preferable to folding something that should not be.

https://github.com/llvm/llvm-project/pull/91038