[PATCH] D140844: [InstCombine] Canonicalize gep of addrspacecast

[Nikita Popov via Phabricator via llvm-commits]

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With typed pointers, InstCombine will often convert gep of addrspacecast into addrspacecast of gep, see e.g. https://llvm.godbolt.org/z/fYa3oKvdh. This isn't done consistently, because it happens as a side-effect of other folds. The most common one is trivial index descaling (where no descaling actually happens, and only the addrspacecast/gep end up being swapped). These folds are disabled for opaque pointers, so we don't canonicalize in either direction there.

This adds canonicalization of `gep(ac)` to `ac(gep)`. I've limited this to the case where index types match: While this is always legal, changing index types might introduced truncs/sexts, which might be non-profitable (test diffs were a wash).

After typed pointer support is dropped, we might want to consider inverting this canonicalization and going from `ac(gep)` to `gep(ac)` instead, which seems better to me. But for now I'm matching what typed pointers were (mostly) doing.


https://reviews.llvm.org/D140844

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/gep-addrspace.ll
  llvm/test/Transforms/InstCombine/gep-vector.ll
  llvm/test/Transforms/InstCombine/non-integral-pointers.ll
  llvm/test/Transforms/InstCombine/opaque-ptr.ll

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