Re: [PATCH v7] pgo: add clang's Profile Guided Optimization infrastructure

[Nick Desaulniers]

On Thu, Jan 28, 2021 at 11:43 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
>
> Some comments:
>
> [ hash mismatches ]
>
> Observed identical warnings when doing a rebuild with GAS or Clang-IAS.
>
> [ Importance of LLVM_IAS=1 working ]
>
> Clang-LTO and Clang-CFI depend both on LLVM_IAS=1 (see for example
> "kbuild: add support for Clang LTO").
> Sooner or later we will deal with this issue (hope it is not a local problem).

If you're switching back and forth between GAS and IAS, then I would
expect a hash error if you're trying to reuse profiling data from one
with the other.  The profiling data is not portable when switching
toolchains between when the profile was collected, and when it was
used.
-- 
Thanks,
~Nick Desaulniers