On Mon, Mar 17, 2025, Thomas Gleixner wrote:
> On Fri, Mar 14 2025 at 20:06, Sean Christopherson wrote:
> > @@ -409,25 +409,28 @@ static __always_inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
> > {
> > int i, vec = FIRST_EXTERNAL_VECTOR;
> > unsigned long pir_copy[4];
> > - bool handled = false;
> > + bool found_irq = false;
> >
> > - for (i = 0; i < 4; i++)
> > + for (i = 0; i < 4; i++) {
> > pir_copy[i] = READ_ONCE(pir[i]);
> > + if (pir_copy[i])
> > + found_irq = true;
> > + }
>
> That's four extra conditional branches. You can avoid them completely. See
> delta patch below.
Huh. gcc elides the conditional branches when computing found_irq regardless of
the approach; the JEs in the changelog are from skipping the XCHG.
But clang-14 does not. I'll slot this in.
Thanks!
