[clang] [clang] add array out-of-bounds access constraints using llvm.assume (PR #159046)

[Nikita Popov via cfe-commits]

https://github.com/nikic commented:

Yes, the general problem with assumes is that, while they help some optimizations by providing additional information, they can regress others due to the added instructions/uses. Hard to say in advance whether a specific assume use it more beneficial than detrimental.

Possibly LoopVectorize should be dropping assumes altogether -- generating assume of extractelement doesn't look particularly useful to me. Adding another late run of the DropUnnecessaryAssumes pass I recently added would probably also avoid that particular issue.



https://github.com/llvm/llvm-project/pull/159046