[llvm] [Loads] Support dereferenceable assumption with variable size. (PR #128436)

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annamthomas wrote:


> W/o the change the verifier will reject assumptions with just a dereferenceable bundle with non-constant sizes.

Yes, I noticed this verifier bug when trying to use these bundles downstream. I'd added a pass which identifies dereferenceability and alignment for java arrays and it would fail without the alignment bundle in the assume. 


Could you pls add a test in `early_exit_legality.ll` to show that the dereferencability and alignment bundles allow early exit vectorization without the need for statically allocated arrays (the existing tests in the patch show why predication wouldn’t be needed)? It works as expected when I tried, will be useful just to showcase that additional benefit.




https://github.com/llvm/llvm-project/pull/128436