[llvm] VNCoercion: Safely handle targets where pointers are larger than the largest legal integers. (PR #118584)

[Owen Anderson via llvm-commits]

resistor wrote:

Moving this back to draft for now.

The origins of this code in the CHERI downstream of LLVM is somewhat mysterious (it first appears in an old merge commit, without a test, and then has gotten heavily refactored in a later merge with upstream that extracted code from GVN.cpp to VNCoercion.cpp).

I believe the original intent was to stop GVN from trying to use non-integral pointer types for VN coercion. Looking at the current code `canCoerceMustAliasedValueToLoad`, I suspect this is no longer needed, and might in fact already be bit-rotted.

https://github.com/llvm/llvm-project/pull/118584