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?
>
> 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..fe11b5eface9978c916783619677a10a7759c43d
> --- /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..181281c2154bedfc8e8c6b1bde1226e194ba99e5
> 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)
