[llvm] [UTC] Support to test annotated IR (PR #165419)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> Hi, @arichardson
> 
> > Should this be the default behaviour (with a --version bump)?
> 
> This change is the default behaviour, but only enabled when an extra UTC option `--check-comments` specified. And I don't think it's necessary to control it with versions.
> 
> > Being able to use CHECK-NEXT more instead of the more fragile CHECK is IMO a good thing.
> 
> This change is not introduced by this PR. And I think using `CHECK` instead of `CHECK-NEXT` is somehow reasonable, since there is an empty line between the two lines required checking:
> 
> ```llvm
> ; CHECK-NEXT:    br label [[TMP1:%.*]]
> ; CHECK:         [[TMP2:%.*]] = load i32, ptr @d, align 4
> ....
>   br label %1
> 
> ; <label>:1:                                      ; preds = %17, %0
>   %2 = load i32, ptr @d, align 4
> ```

We could add a CHECK-EMPTY: and a CHECK-NEXT for the label comment, but that should probably be a separate change.

https://github.com/llvm/llvm-project/pull/165419