[llvm] [InstCombine] ptrmask of gep for dynamic pointer aligment (PR #80002)

[Jon Chesterfield via llvm-commits]

JonChesterfield wrote:

Added tests for non-i8 and for vector types (which don't work as implemented, it makes extracting the value messier).

Likewise this was only written for constantints as that's the main dynamic-align use case.

Could we have this as an initial patch and leave extending demanded bits for a follow on, at which point this transform might be deleted while the tests remain? I'm mainly trying to unblock test cases for variadic function lowering where the ptrmask nop gets in the way

https://github.com/llvm/llvm-project/pull/80002