[PATCH] D37648: [SLPVectorizer] Fix PR21780 Expansion of 256 bit vector loads fails to fold into shuffles

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a subscriber: uenoku.
jdoerfert added a comment.

With D65402 <https://reviews.llvm.org/D65402> (and later D65593 <https://reviews.llvm.org/D65593>), the Attributor will determine dereferenceability based on accesses that "must be executed".
Since the Attributor runs early in the pipeline (for now only then), this will "generally" solve the issue as unused loads are still present.
However, we lack the ability to annotate dereferenceable for pointers that are not arguments, function return values, call site arguments, or call site return values.
That means, we might determine dereferenceability early but fail to manifest it in the IR or loose the information during inlining. Though, I am unsure how much of
a problem that really is. If it turns out to be bad, I'd suggest to add an intrinsic to describe dereferenceability (among other things [alignment, max object size, ...]) of a pointer.

Long story short, I'd recommend investing the time in reviewing and testing the Attributor infrastructure and potentially thinking about a pointer property intrinsic.

If I misunderstood what is going on here, please let me know.


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https://reviews.llvm.org/D37648