On Mon, 17 Nov 2025, Hongtao Liu wrote:
> On Fri, Nov 14, 2025 at 6:04 PM Richard Biener <[email protected]> wrote:
> >
> > The following arranges for avoiding masked vector epilogues when we'll
> > eventually arrive at a vector epilogue with VF == 1 which implies no
> > scalar epilog will be necessary.
> >
> > This avoids regressing performance in OpenColorIO when the
> > avx512_masked_epilogues tuning is enabled. A testcase for one
> > example case is shown in PR122573.
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu. The testcase
> > depends on the SLP patch posted earlier.
> >
> > OK for trunk?
> >
> > Thanks,
> > Richard.
> >
> > PR tree-optimization/122573
> > * config/i386/i386.cc (ix86_vector_costs::finish_cost): Avoid
> > using masked epilogues when an SSE epilogue would have a VF of one.
> >
> > * gcc.dg/vect/costmodel/x86_64/costmodel-pr122573.c: New testcase.
> > ---
> > gcc/config/i386/i386.cc | 5 ++++
> > .../costmodel/x86_64/costmodel-pr122573.c | 30 +++++++++++++++++++
> > 2 files changed, 35 insertions(+)
> > create mode 100644
> > gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr122573.c
> >
> > diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> > index 6b6febc8870..8aac0820bc2 100644
> > --- a/gcc/config/i386/i386.cc
> > +++ b/gcc/config/i386/i386.cc
> > @@ -26609,6 +26609,11 @@ ix86_vector_costs::finish_cost (const vector_costs
> > *scalar_costs)
> > if (loop_vinfo
> > && !LOOP_VINFO_EPILOGUE_P (loop_vinfo)
> > && LOOP_VINFO_VECT_FACTOR (loop_vinfo).to_constant () > 2
> > + /* Avoid a masked epilog if cascaded epilogues eventually get us
> > + to one with VF 1 as that means no scalar epilog at all. */
> > + && !((GET_MODE_SIZE (loop_vinfo->vector_mode)
> > + / LOOP_VINFO_VECT_FACTOR (loop_vinfo).to_constant () == 16)
>
> So LOOP_VINFO_VECT_FACTOR is the "unroll factor" of the loop to be
> vectorized, and it's not always equal to TYPE_VECTOR_SUBPARTS.
> Make sense.
Yes. Is that an OK?
Thanks,
Richard.
> > + && ix86_tune_features[X86_TUNE_AVX512_TWO_EPILOGUES])
> > && ix86_tune_features[X86_TUNE_AVX512_MASKED_EPILOGUES]
> > && !OPTION_SET_P (param_vect_partial_vector_usage))
> > {
> > diff --git
> > a/gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr122573.c
> > b/gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr122573.c
> > new file mode 100644
> > index 00000000000..ca3294dca7a
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-pr122573.c
> > @@ -0,0 +1,30 @@
> > +/* { dg-do compile } */
> > +/* { dg-additional-options "-march=znver5" } */
> > +
> > +struct S {
> > + float m_col1[4];
> > + float m_col2[4];
> > + float m_col3[4];
> > + float m_col4[4];
> > +};
> > +
> > +void apply(struct S *s, const float *in, float *out, long numPixels)
> > +{
> > + for (long idx = 0; idx < numPixels; ++idx)
> > + {
> > + const float r = in[0];
> > + const float g = in[1];
> > + const float b = in[2];
> > + const float a = in[3];
> > + out[0] = r*s->m_col1[0] + g*s->m_col2[0] + b*s->m_col3[0] +
> > a*s->m_col4[0];
> > + out[1] = r*s->m_col1[1] + g*s->m_col2[1] + b*s->m_col3[1] +
> > a*s->m_col4[1];
> > + out[2] = r*s->m_col1[2] + g*s->m_col2[2] + b*s->m_col3[2] +
> > a*s->m_col4[2];
> > + out[3] = r*s->m_col1[3] + g*s->m_col2[3] + b*s->m_col3[3] +
> > a*s->m_col4[3];
> > + in += 4;
> > + out += 4;
> > + }
> > +}
> > +
> > +/* Check that we do not use a masked epilog but a SSE one with VF 1
> > + (and possibly a AVX2 one as well). */
> > +/* { dg-final { scan-tree-dump "optimized: epilogue loop vectorized using
> > 16 byte vectors and unroll factor 1" "vect" } } */
> > --
> > 2.51.0
>
>
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
