[ConstantFolding] Support ptrtoaddr in ConstantFoldCompareInstOperands (#162653)
This folds `icmp (ptrtoaddr x, ptrtoaddr y)` to `icmp (x, y)`, matching
the existing ptrtoint fold. Restrict both folds to only the case where
the result type matches the address type.
I think that all folds this can do in practice end up actually being
valid for ptrtoint to a type large than the address size as well, but I
don't really see a way to justify this generically without making
assumptions about what kind of folding the recursive calls may do.
This is based on the icmp semantics specified in
https://github.com/llvm/llvm-project/pull/163936.
llvm-project
6a25e454 - [ConstantFolding] Support ptrtoaddr in ConstantFoldCompareInstOperands (#162653)
