[llvm] Combine (X ^ Y) and (X == Y) where appropriate (PR #130922)

[Ryan Buchner via llvm-commits]

bababuck wrote:

> If %x is a function argument with the `signext` attribute we can assume the i32 is sign extended to the full register size. Likewise the `zeroext` attribute allows us to assume it is zero extended. If neither attribute is present, we can't make any assumptions. The `clang` frontend should always put `signext` on i32 function arguments to match the psABI.

Thanks for the detail.

Since we cannot make this assumption for the general case, then would it be reasonable to explicitly check for the case where the LHS is the result of an SEXT of an XOR?

https://github.com/llvm/llvm-project/pull/130922