> -----Original Message-----
> From: Richard Biener <[email protected]>
> Sent: 03 June 2026 09:01
> To: Tamar Christina <[email protected]>
> Cc: [email protected]; nd <[email protected]>; [email protected]
> Subject: Re: [PATCH][vect]: gate COMPLEX_MUL on FP_CONTRACT_FAST
> [PR125431]
>
> On Wed, 3 Jun 2026, Tamar Christina wrote:
>
> > The checks for FP_CONTRACT_FAST were in the wrong place for
> complex_mul.
> >
> > The location it was in would only block FMA but not MUL. It would also not
> > really reject the forming of the FMA, it would just create an invalid
> > collection
> > of nodes which would fail analysis later on.
> >
> > However complex multiplication is also a contraction, since it's doing
> >
> > real = a*c - b*d
> > imag = a*d + b*c
> >
> > This moves the checks up to earliest possible location and actually just
> returns
> > and adds the missing check for FMS.
> >
> > Bootstrapped Regtested on aarch64-none-linux-gnu,
> > arm-none-linux-gnueabihf, x86_64-pc-linux-gnu
> > -m32, -m64 and no issues.
> >
> > Pushed.
>
> Thanks - can you also see to backport to 16 and 15 (this friday is RC
> for 15.3), but leave a short while to figure where the
> "loop vectorized" scan will fail?
Sure, will do :)
Cheers,
Tamar
>
> >
> > Thanks,
> > Tamar
> >
> > gcc/ChangeLog:
> >
> > PR tree-optimization/125431
> > * tree-vect-slp-patterns.cc (complex_mul_pattern::matches,
> > complex_fms_pattern::matches): Gate on FP contraction.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR tree-optimization/125431
> > * gfortran.dg/vect/pr125431.f90: New test.
> >
> > ---
> > diff --git a/gcc/testsuite/gfortran.dg/vect/pr125431.f90
> b/gcc/testsuite/gfortran.dg/vect/pr125431.f90
> > new file mode 100644
> > index
> 0000000000000000000000000000000000000000..fe11b5eface9978c916
> 783619677a10a7759c43d
> > --- /dev/null
> > +++ b/gcc/testsuite/gfortran.dg/vect/pr125431.f90
> > @@ -0,0 +1,16 @@
> > +! { dg-do compile }
> > +! { dg-additional-options "-O2 -ffp-contract=off" }
> > +! { dg-additional-options "-march=armv8.3-a" { target { aarch64*-*-* } } }
> > +
> > +subroutine foo(a,b,c)
> > +
> > + complex :: a(6,6)
> > + complex :: b(6,6)
> > + complex :: c(6,6)
> > +
> > + c = MATMUL(a, b)
> > +
> > +end subroutine foo
> > +
> > +! { dg-final { scan-tree-dump "LOOP VECTORIZED" "vect" { target {
> vect_float } } } }
> > +! { dg-final { scan-tree-dump-not "Found COMPLEX_MUL" "vect" } }
> > diff --git a/gcc/tree-vect-slp-patterns.cc b/gcc/tree-vect-slp-patterns.cc
> > index
> c0031a129a445160998f70bf9c18e1ef70464eed..181281c2154bedfc8e8c6
> b1bde1226e194ba99e5 100644
> > --- a/gcc/tree-vect-slp-patterns.cc
> > +++ b/gcc/tree-vect-slp-patterns.cc
> > @@ -1038,6 +1038,11 @@ complex_mul_pattern::matches
> (complex_operation_t op,
> > if (op != MINUS_PLUS)
> > return IFN_LAST;
> >
> > + /* It's only valid to form FMAs and MUL with -ffp-contract=fast. */
> > + if (flag_fp_contract_mode != FP_CONTRACT_FAST
> > + && FLOAT_TYPE_P (SLP_TREE_VECTYPE (*node)))
> > + return IFN_LAST;
> > +
> > auto childs = *ops;
> > auto l0node = SLP_TREE_CHILDREN (childs[0]);
> >
> > @@ -1050,11 +1055,8 @@ complex_mul_pattern::matches
> (complex_operation_t op,
> > auto_vec<slp_tree> left_op, right_op;
> > slp_tree add0 = NULL;
> >
> > - /* Check if we may be a multiply add. It's only valid to form FMAs
> > - with -ffp-contract=fast. */
> > + /* Check if we may be a multiply add. */
> > if (!mul0
> > - && (flag_fp_contract_mode == FP_CONTRACT_FAST
> > - || !FLOAT_TYPE_P (SLP_TREE_VECTYPE (*node)))
> > && vect_match_expression_p (l0node[0], PLUS_EXPR))
> > {
> > auto vals = SLP_TREE_CHILDREN (l0node[0]);
> > @@ -1285,6 +1287,11 @@ complex_fms_pattern::matches
> (complex_operation_t op,
> > if (!vect_match_expression_p (root, MINUS_EXPR))
> > return IFN_LAST;
> >
> > + /* It's only valid to form FMSs with -ffp-contract=fast. */
> > + if (flag_fp_contract_mode != FP_CONTRACT_FAST
> > + && FLOAT_TYPE_P (SLP_TREE_VECTYPE (*ref_node)))
> > + return IFN_LAST;
> > +
> > /* TODO: Support invariants here, with the new layout CADD now
> > can match before we get a chance to try CFMS. */
> > auto nodes = SLP_TREE_CHILDREN (root);
> >
> >
> >
>
> --
> 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)
