Combining place projections in MIR makes codegen forget that NonNull is nonnull #111518

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1. scottmcm commented on May 12, 2023

   

   scottmcm

   on May 12, 2023

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   The reminds me of why I dislike the "it's just a field" approach in the first place (and thus I dislike rust-lang/rfcs#3334), and reminds me of similar problems that repr(simd) hit with looking at fields (see https://rust-lang.zulipchat.com/#narrow/stream/257879-project-portable-simd/topic/splat.20no.20longer.20compiles.20for.20release.20builds/near/351948961).

   So maybe we should use the same approach that repr(simd) is moving towards: just disallow place projections to the inner field entirely for such types. That makes this issue irrelevant -- as the project isn't there to be combined -- and the niche support ends up in the transmutes and such instead, where it sees the different types properly instead of just projections.
2. jyn514

   added

   A-MIRArea: Mid-level IR (MIR) - https://blog.rust-lang.org/2016/04/19/MIR.htmlArea: Mid-level IR (MIR) - https://blog.rust-lang.org/2016/04/19/MIR.html

   A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

   A-codegenArea: Code generationArea: Code generation

   on May 13, 2023