[LLVMdev] Proposal: type uniquing of debug info for LTO

[David Blaikie]

On Fri, Jun 21, 2013 at 4:50 PM, Manman Ren <mren at apple.com> wrote:
>
> On Jun 21, 2013, at 4:41 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
> The reason I want a flag is to avoid the need to update the existing testing
> cases while this is a work in progress.
> I believe migrating one field means updating the existing testing cases?
>
>
> It would, yes - and that's how you'd get coverage to know your change
> was stable. You'll have to update all the tests eventually anyway &
> doing so incrementally isn't substantially more expensive in my
> experience. Perhaps there's something unique to this migration that
> would make it so?
>
>
> I am going to update the existing testing cases locally to have the test
> coverage, but I don't want to check in the changes often.
> Once we turn the flag on by default and remove the other path, I will submit
> the changes on the testing cases.

I'd rather skip the flag & have the test coverage in the open along
with the changes. Having changes without testing is bad. I don't see a
benefit to you keeping the test coverage locally.

> Another point to have a flag is to check in the patches in steps: DIBuilder
> changes, changes related to the map, and DwarfDebug changes.
> Without the flag, when I migrate the first field, I have to make sure it
> works from frontend all the way to the backend.

True enough, but I don't think that's a great drawback.

Though technically, if you really wanted, you could start at the
backend & make the implementation conditional (check the type of the
field, if it's an MDNode - use that, if it's a string, do the lookup)
- implement that, then port DIBuilder, then remove the conditionality.
Though I don't like it a lot & I think the changes will be small
enough that frontend to backend will be still be understandable
patches.

>
> Hopefully that makes sense.
>
> Thanks for all your help,
> Manman