[PATCH] D93820: [InstSimplify] Don't fold gep p, -p to null

[Nikita Popov via Phabricator via llvm-commits]

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This is a partial fix for https://bugs.llvm.org/show_bug.cgi?id=44403. Folding `gep p, q-p` to `q` is only legal if `p` and `q` have the same provenance. This fold should probably be guarded by something like `getUnderlyingObject(p) == getUnderlyingObject(q)`.

This patch is a partial fix that removes the special handling for `gep p, 0-p`, which will fold to a null pointer, which would certainly not pass an underlying object check (unless p is also null, in which case this would fold trivially anyway). Folding to a null pointer is particularly problematic due to the special handling it receives in many places, making end-to-end miscompiles more likely.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D93820

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/gep.ll

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