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

[Eric Christopher]

On Fri, Jun 21, 2013 at 4:59 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 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.
>

All of this.

-eric