[PATCH] D114988: [IR] `GetElementPtrInst`: per-index `inrange` support

[Nikita Popov via Phabricator via llvm-commits]

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While I support the general goal of exposing GEP offset restrictions to IR, I am quite strongly opposed to the implementation approach of extending `inrange`. The core issue is that this is strongly tied to LLVM struct types and structural GEP indexing. This will be a blow to opaque pointer usefulness and future offset canonicalization for GEPs.

I think the correct approach to `inrange`-like information is to restrict the range of GEP indices without relying on the underlying structure type. Think `inrange(0, 4) i32 %x` for `%x` between 0 and 4. This naturally integrates in purely offset-based alias analysis, and can be more generally preserved under transformation. For example, if you have `gep %base, inrange (%x + 1)`, if this is transformed into `gep (gep %base, 1), %x` there is no way to preserve `inrange` information under the current proposal, while a proper offset-based approach could easily retain information under simple transformations.


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https://reviews.llvm.org/D114988