[clang] [llvm] RFC: Implementing new mechanism for hard register operands to inline asm as a constraint. (PR #85846)

[Ulrich Weigand via llvm-commits]

uweigand wrote:

I can image cases where multiple register constraints may still be useful; e.g. to express that we can use any one of several hard-coded registers, or we can use a hard-coded register or some register class that doesn't contain that hard register.

It is of course superfluous to specific both a hard register and a register class containing this register.  But that's really the same issue as specifying two classes where one is a superclass of the other - and we don't explicitly forbid this either.

https://github.com/llvm/llvm-project/pull/85846