AMD General Hi
> -----Original Message----- > From: Hongtao Liu <[email protected]> > Sent: Tuesday, May 19, 2026 2:04 PM > To: Lili Cui <[email protected]> > Cc: [email protected]; [email protected]; [email protected]; Jan > Hubicka <[email protected]> > Subject: Re: [PATCH] x86: Increase generic tune branch misprediction cost > > Caution: This message originated from an External Source. Use proper caution > when opening attachments, clicking links, or responding. > > > On Fri, May 15, 2026 at 3:02 PM Lili Cui <[email protected]> wrote: > > > > Hi, > > > > This patch increases the branch misprediction scale for generic tuning to > better reflect the cost on modern CPUs with deeper pipelines. > > > > Bootstrapped and regression tested on x86_64-pc-linux-gnu. OK for trunk? > > Any comments from AMD folks? Yes, planning to run few benchmarks, will get back to you. Regards, Venkat. > > > > > Thanks, > > Lili. > > > > > > Increase the branch misprediction scale for generic tuning from > > COSTS_N_INSNS (2) to COSTS_N_INSNS (2) + 3. > > > > Modern CPUs have deeper pipelines, making branch mispredictions more > > expensive. Increasing this cost encourages if-conversion, avoiding > > pipeline stalls from mispredicted branches. > > > > This improves 544.nab_r (-O2) by 12.7% on GNR and 12.1% on Znver5 with > > single-copy. > > > > gcc/ChangeLog: > > > > * config/i386/x86-tune-costs.h (generic_cost): Increase branch > > mispredict scale from COSTS_N_INSNS (2) to COSTS_N_INSNS (2) + 3. > > --- > > gcc/config/i386/x86-tune-costs.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/gcc/config/i386/x86-tune-costs.h > > b/gcc/config/i386/x86-tune-costs.h > > index 7819fdf7c02..0c687a11a74 100644 > > --- a/gcc/config/i386/x86-tune-costs.h > > +++ b/gcc/config/i386/x86-tune-costs.h > > @@ -4274,7 +4274,7 @@ struct processor_costs generic_cost = { > > "16", /* Func alignment. */ > > 4, /* Small unroll limit. */ > > 2, /* Small unroll factor. */ > > - COSTS_N_INSNS (2), /* Branch mispredict scale. */ > > + COSTS_N_INSNS (2) + 3, /* Branch mispredict scale. */ > > }; > > > > /* core_cost should produce code tuned for Core familly of CPUs. */ > > -- > > 2.34.1 > > > > > -- > BR, > Hongtao
