[PATCH] D88842: [InstCombine] inttoptr(load) -> load

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

I don't like the direction of this patch because it will remove inttoptr instructions that were present in the original program. In the same way that optimizations shouldn't introduce inttoptr, they shouldn't fuse them with loads either.
If the original program had the inttoptr cast and you fold it with a load instruction, then you are asking the load to do the cast. This sort of type punning is not ok. I strongly disagree with Chandler that LLVM's memory is not typed. It needs to distinguish between integers and pointers, otherwise I don't know how to make LLVM correct without a significant perf penalty.
If LLVM's memory was untyped, we would have to assume that every pointer load could be doing an implicit inttoptr cast, which would havoc most optimizations. The fact that some optimizations, like sroa, assume that the memory is untyped and most of the others don't is a source of miscompilations.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D88842/new/

https://reviews.llvm.org/D88842