[llvm] [GlobalISel] Constant-fold G_PTR_ADD with different type sizes (PR #81473)

[Jay Foad via llvm-commits]

jayfoad wrote:

I wonder if G_PTR_ADD has the same semantics as IR getelementptr, where only the low order index-size bits of the pointer value are affected. @nikic do you know?

https://github.com/llvm/llvm-project/pull/81473