[llvm-commits] [patch][pr12251] Add range metadata to llvm. Make clang produce it.

[Rafael Espíndola]

> I think you should have the ranges map exactly to the ConstantRange class,
> otherwise it is confusing to have more than one range concept inside the
> compiler (and of course being able to use the ConstantRange methods directly
> is convenient too).  As such ranges are open at the end, so { i8 0, i8 2 }
> means "Can only be 0 or 1".

That class has to be able to handle empty ranges, so it has some funny
special cases. If I understand it correctly, with i8 the range [x, x)
is empty for any x except 255 in which case it is the full range.

With closed ranges the empty range is unrepresentable, which is
probably a good thing. I this patch I have added a check to the
verifier to reject full ranges too. I don't have a strong opinion
about this, so I am fine with moving to open ranges if other prefer
it.

On the clang side the things I have changed are
* Don't output the range when an enum can take any value (would be the
full range).
* Don't output the range for C enums
* Use the desugared type to look for enums.

Cheers,
Rafael