Re: [PATCH 1/3] profile-count: Handle signed values in profile_probability::apply

On 8/10/2026 8:26 AM, [email protected] wrote:
> From: Kyrylo Tkachov <[email protected]>
>
> profile_probability::apply uses RDIV, which adds half the denominator
> before division.  This does not round negative values correctly.
> Multiplying the signed input by the fixed-point probability can also
> overflow for large inputs.
>
> Scale the unsigned magnitude with safe_scale_64bit, then restore the sign.
> Return the input directly for a unit probability so that the minimum
> gcov_type value remains representable.  Preserve the existing truncation
> for uninitialized probabilities.
>
> Add selftests for signed rounding, zero and unit probabilities,
> uninitialized probabilities, and the minimum and maximum gcov_type values.
>
> Bootstrapped and tested on aarch64-none-linux and x86_64-linux.
> Ok for trunk?
> Thanks,
> Kyrill
>
> gcc/ChangeLog:
>
> 	* profile-count.h (profile_probability::apply): Scale an unsigned
> 	magnitude with safe_scale_64bit.
> 	* profile-count.cc (test_profile_probability_apply): New.
> 	(profile_count_cc_tests): New.
> 	* selftest.h (profile_count_cc_tests): Declare.
> 	* selftest-run-tests.cc (selftest::run_tests): Run it.
>
> Signed-off-by: Kyrylo Tkachov <[email protected]>
OK unless Richi objects.  So give him ~48hrs before committing to chime 
back in.

jeff