On Tue, Dec 16, 2025 at 6:36 AM Andrew Pinski
<[email protected]> wrote:
>
> After r16-6104-gb5c64db0a49d46, we try to duplicate bb's
> that contain loop exit that have "never exit" but we check
> against the propability of the exit to very_unlikely. If we
> have PGO, then a loop exit might be very unlikely to be taken
> if we interate the loop more than 2000 times. So we should take
> into account if the probability is reliable or not; this basically
> says if the probability is based on profile data (or corrected profile data)
> or based on heurstics.
>
> This should fix PR 123126 but I don't have a full SPEC setup with PGO
> to be able to test it.
>
> Bootstrapped and tested on x86_64-linux-gnu.
>
> gcc/ChangeLog:
>
> * tree-ssa-loop-ch.cc (should_duplicate_loop_header_p): Check
> the reliable_p of the edge's probability.
>
> Signed-off-by: Andrew Pinski <[email protected]>
> ---
> gcc/tree-ssa-loop-ch.cc | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/tree-ssa-loop-ch.cc b/gcc/tree-ssa-loop-ch.cc
> index feecf91cf70..293720fbd04 100644
> --- a/gcc/tree-ssa-loop-ch.cc
> +++ b/gcc/tree-ssa-loop-ch.cc
> @@ -480,7 +480,8 @@ should_duplicate_loop_header_p (basic_block header, class
> loop *loop,
> or combining.
> FIXME: once we have better quality tracking,
> make this more robust. */
> - || e->probability <= profile_probability::very_unlikely ()))
> + || (!e->probability.reliable_p ()
> + && e->probability <= profile_probability::very_unlikely
> ())))
Why !e->probability.reliable_p ()? That looks backward.
Hopefully probably_never_executed_edge_p will DTRT here? I'll note
there's also edge_probability_reliable_p () which uses .probably_reliable_p ().
The profile API is too convoluted IMO :/ Possibly full of legacy stuff.
Honza?
> {
> hasone = true;
> if (dump_file && (dump_flags & TDF_DETAILS))
> --
> 2.43.0
>
