[llvm] [PowerPC] Legalize i8 for read/write global name registers (PR #180805)

[Lei Huang via llvm-commits]

lei137 wrote:

> Why? I think this should stay illegal. This should provide exclusively exact match to the register type

Is there a reason we don't want this explicitly for these ops?  We do allow other instructions to have type promotions AFAIK.  For backward compact with XL compilers on powerpc, we would like to promote i8 (char) to i32 or i64.

https://github.com/llvm/llvm-project/pull/180805