[cfe-dev] Status of IR vs. frontend PGO (fprofile-generate vs fprofile-instr-generate)

[Xinliang David Li via cfe-dev]

On Thu, May 20, 2021 at 9:47 AM Reid Kleckner <rnk at google.com> wrote:

> On Wed, May 19, 2021 at 7:48 PM Alex Lorenz <aleksei_lorenz at apple.com>
> wrote:
>
>> As far the possible deprecation of frontend PGO, will that imply that the
>> `-fprofile-instr-generate / use` options will get removed, or will they
>> still be supported but will leverage IR PGO instead?
>>
>
> That makes sense to me, but we need to untangle the fact that
> `-fprofile-instr-generate -fcoverage-mapping` is currently used for
> coverage, so a simple alias isn't quite correct.
>
> I've always wanted a single, high-level coverage flag, and I always
> thought it should be spelled --coverage of -fcoverage, but that seems like
> it's already taken by gcov instrumentation. =/ I guess we need to bikeshed
> a new spelling.
>

Right.   -fcoverage-mapping itself does not much so it should
probably imply frontend instrumentation.

For migration purposes, if -fcoverage-mapping is used together with
-fprofile-instr-generate (which becomes IR PGO), the latter will be dropped
(or a warning is given). The tricky part is if the user uses the option to
specify the profile path, then we have a problem.

David

David
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