In order to properly support outputs along indirect edges of callbr, it
would be helpful to have distinct SSA values to refer to so that during
instruction selection, we can mark outputs that might come from specific
physregs as live-in and place copies to virtregs.
Please see the corresponding RFC accompanying this patch.
Link: https://github.com/llvm/llvm-project/issues/53562
Link: https://discourse.llvm.org/t/rfc-syncing-asm-goto-with-outputs-with-gcc/65453
Link: https://discourse.llvm.org/t/rfc-asm-goto-with-output-constraints/52354/4
Using CHECK-NOT like this is really fragile. I'd suggest having two tests: one that tests that valid IR isn't rejected, and one that checks that the expected diagnostics are produced for invalid IR.