[llvm-dev] TableGen trace facility

[Nicolai Hähnle via llvm-dev]

On Mon, Aug 3, 2020 at 6:04 PM Paul C. Anagnostopoulos via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> A question for those of you who have developed complex TableGen files: Do you think a trace facility would be useful during debugging? The idea is to add a new statement to TableGen along these lines:
>
>   trace tag : value1, value2, ... ;
>
> When encountered, the TableGen parser would display the tag along with the values of the specified value1, value2, etc. The tag is an identifier that makes it easier to distinguish multiple traces.

I'm not so sure that that's particularly useful or how it would even
work. The issue is that at the point in time where the frontend parses
those trace tags, most substitutions haven't taken place yet, so
you'll usually get fairly trivial answers that by themselves aren't
particularly helpful.

Some form of inspection of how values are substituted would indeed be
helpful, I just don't think the "trace" is quite it. In a perfect
world, we'd have some sort of "record database explorer" that doesn't
just let you look at all the final records (TableGen already allows
you to do that), but also allows you to interactively explore their
"history", i.e. how did the records come to be.

Cheers,
Nicolai

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