[InstCombine] Handle ptrtoaddr in gep of pointer sub fold (#164818)

This extends the `ptradd x, ptrtoint(y) - ptrtoint(x)` to `y`
InstCombine fold to support ptrtoaddr. In the case where x and y have
the same underlying object, this is handled by InstSimplify already. If
the underlying object may differ, the replacement can only be performed
if provenance does not matter.

For pointers with non-address bits we need to be careful here, because
the pattern will return a pointer with the non-address bits of x and the
address bits of y. As such, uses in ptrtoaddr are safe to replace, but
uses in ptrtoint are not. Whether uses in icmp are safe to replace
depends on the outcome of the pending discussion on icmp semantics (I'll
adjust this in https://github.com/llvm/llvm-project/pull/163936 if/when
that lands).

0 files changed, 0 insertions, 0 deletions