> -----Original Message-----
> From: Richard Biener <[email protected]>
> Sent: 15 September 2026 09:23
> To: Tamar Christina <[email protected]>
> Cc: Ezra Sitorus <[email protected]>; [email protected];
> [email protected]
> Subject: RE: [RFC PATCH 3/5] gcc: Add new COMPLEX_DOT_PROD_ROT0
> IFN/optabs
>
> On Tue, 15 Sep 2026, Tamar Christina wrote:
>
> >
> >
> > > -----Original Message-----
> > > From: [email protected] <[email protected]>
> > > Sent: 09 September 2026 19:12
> > > To: [email protected]
> > > Cc: Tamar Christina <[email protected]>; [email protected];
> > > [email protected]; Ezra Sitorus <[email protected]>
> > > Subject: [RFC PATCH 3/5] gcc: Add new COMPLEX_DOT_PROD_ROT0
> > > IFN/optabs
> > >
> > > From: Ezra Sitorus <[email protected]>
> > >
> > > Add new internal function COMPLEX_DOT_PROD_ROT0 and optab
> > > cdot_prod_rot0_optab
> > > to represent complex integer dot product.
> > >
> > > COMPLEX_DOT_PROD_ROT0 (A, B, ACC) is a lane-reducing signed integer
> > > complex
> > > dot product. The 2 input vectors contain interleaved W-bit real and
> imaginary
> > > components in even/odd numbered lanes respectively. Each 4W-bit result
> > > element
> > > accumulates the 0-rotation products of the 2 complex input pairs in the
> > > corresponding group of 4 input lanes:
> > >
> > > result[j] = acc[j]
> > > + a[k].re * b[k].re
> > > - a[k].im * b[k].im
> > > + a[k + 1].re * b[k + 1].re
> > > - a[k + 1].im * b[k + 1].im
> > >
> > > where 2*j = k.
> > >
> > > 0-rotation means that the imaginary components in the second source
> vector
> > > are
> > > negated, and so the overall operation is accumulating the real part of the
> > > complex dot product. Other rotations can be added in future patches.
>
> I other places we use _conj, not rot0:
>
> OPTAB_D (cmul_conj_optab, "cmul_conj$a3")
>
> so why not use that for consistency?
That's a different operation. complex dotprod is numerically
#include <stdint.h>
typedef struct {
int8_t real;
int8_t imag;
} cint16_t;
typedef struct {
int32_t real;
int32_t imag;
} cint32_t;
cint32_t cdot(cint16_t *a, cint16_t *b, uint32_t N)
{
cint32_t res = {0, 0};
for (uint32_t i = 0; i < N; i++) {
res.real += a[i].real * b[i].real
- a[i].imag * b[i].imag;
res.imag += a[i].real * b[i].imag
+ a[i].imag * b[i].real;
}
return res;
}
Which would be what we'd call cdot.
cdot_conj would be
#include <stdint.h>
typedef struct {
int8_t real;
int8_t imag;
} cint16_t;
typedef struct {
int32_t real;
int32_t imag;
} cint32_t;
cint32_t cdot_conj(const cint16_t *a,
const cint16_t *b,
uint32_t N)
{
cint32_t res = {0, 0};
for (uint32_t i = 0; i < N; i++) {
res.real += a[i].real * b[i].real
+ a[i].imag * b[i].imag;
res.imag += a[i].real * b[i].imag
- a[i].imag * b[i].real;
}
return res;
}
i.e. normal dual lane operations.
however this patch recognizes the single lane reduction,
#include <stdint.h>
typedef struct {
int8_t real;
int8_t imag;
} cint16_t;
int32_t cdot0(const cint16_t *a, const cint16_t *b, uint32_t N)
{
int32_t res = 0;
for (uint32_t i = 0; i < N; i++)
res += a[i].real * b[i].real
- a[i].imag * b[i].imag;
return res;
}
Which is not numerically a complex dot product. Note that the end goal
is to recognize all of these.
Thanks,
Tamar
>
> > > In internal-fn.cc: complex_dot_prod_direct is defined to { -1, 1, false }
> > > because it uses the return type as the accumulator/result type and the
> input
> > > type is either of the narrower source type.
> > >
> > > In AArch64, this corresponds to the CDOT instruction. This patch also
> teaches
> > > GCC to convert the optab into the correct define_insn pattern.
> > >
> > > gcc/ChangeLog:
> > > * config/aarch64/aarch64-sve2.md
> > > (cdot_prod_rot0<mode><vsi2qi>): New
> > > define_expand.
> > > * internal-fn.cc (complex_dot_prod_direct): New static initializers.
> > > * internal-fn.def (COMPLEX_DOT_PROD_ROT0) New internal
> > > function.
> > > * optabs.def (cdot_prod_rot0_optab): New optab.
> > > ---
> > > gcc/config/aarch64/aarch64-sve2.md | 10 ++++++++++
> > > gcc/internal-fn.cc | 5 +++++
> > > gcc/internal-fn.def | 1 +
> > > gcc/optabs.def | 1 +
> >
> > The new optabs and IFN need to be documented in ifn.texi and md.texi
> > and split the aarch64 implementation to it's own patch.
> >
> > But why not add the other rotations at the same time?
> >
> > We'd likely also later (in a different patch) need cdot_prod and
> cdot_prod_conj,
> > because then both lanes are visible the SLP tree will look much different.
> > i.e.
> >
> > #include <stdint.h>
> >
> > typedef _Complex int8_t cint16_t;
> > typedef _Complex int32_t cint32_t;
> >
> > cint32_t cdot(cint16_t *a, cint16_t *b, uint32_t N)
> > {
> > cint32_t res = 0;
> >
> > for (uint32_t i = 0; i < N; i++)
> > res += a[i] * b[i];
> >
> > return res;
> > }
> >
> > > 4 files changed, 17 insertions(+)
> > >
> > > diff --git a/gcc/config/aarch64/aarch64-sve2.md
> > > b/gcc/config/aarch64/aarch64-sve2.md
> > > index c33df283cc2a..ad4febb60bf8 100644
> > > --- a/gcc/config/aarch64/aarch64-sve2.md
> > > +++ b/gcc/config/aarch64/aarch64-sve2.md
> > > @@ -3578,6 +3578,16 @@
> > > ;; - CDOT
> > > ;;
> > > -------------------------------------------------------------------------
> > >
> > > +(define_expand "cdot_prod_rot0<mode><vsi2qi>"
> > > + [(set (match_operand:SVE_FULL_SDI 0 "register_operand")
> > > + (unspec:SVE_FULL_SDI
> > > + [(match_operand:SVE_FULL_SDI 3 "register_operand")
> > > + (match_operand:<VSI2QI> 1 "register_operand")
> > > + (match_operand:<VSI2QI> 2 "register_operand")]
> > > + UNSPEC_CDOT))]
> > > + "TARGET_SVE2"
> > > +)
> > > +
> > > (define_insn "@aarch64_sve_<optab><mode>"
> > > [(set (match_operand:SVE_FULL_SDI 0 "register_operand")
> > > (unspec:SVE_FULL_SDI
> > > diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
> > > index c57b594ac591..cc968109261b 100644
> > > --- a/gcc/internal-fn.cc
> > > +++ b/gcc/internal-fn.cc
> > > @@ -180,6 +180,7 @@ init_internal_fns ()
> > > #define unary_convert_direct { -1, 0, true }
> > > #define binary_direct { 0, 0, true }
> > > #define ternary_direct { 0, 0, true }
> > > +#define complex_dot_prod_direct { -1, 1, false }
> > > #define cond_unary_direct { 1, 1, true }
> > > #define cond_binary_direct { 1, 1, true }
> > > #define cond_ternary_direct { 1, 1, true }
> > > @@ -4315,6 +4316,9 @@ expand_reduc_sbool_optab_fn (internal_fn fn,
> > > gcall *stmt, direct_optab optab)
> > > #define expand_select_vl_optab_fn(FN, STMT, OPTAB) \
> > > expand_convert_optab_fn (FN, STMT, OPTAB, 3)
> > >
> > > +#define expand_complex_dot_prod_optab_fn(FN, STMT, OPTAB) \
> > > + expand_convert_optab_fn (FN, STMT, OPTAB, 3)
> > > +
> > > /* Expanders for optabs that can use expand_convert_optab_fn. */
> > >
> > > #define expand_unary_convert_optab_fn(FN, STMT, OPTAB) \
> > > @@ -4398,6 +4402,7 @@ multi_vector_optab_supported_p
> (convert_optab
> > > optab, tree_pair types,
> > > #define direct_unary_convert_optab_supported_p
> > > convert_optab_supported_p
> > > #define direct_binary_optab_supported_p direct_optab_supported_p
> > > #define direct_ternary_optab_supported_p direct_optab_supported_p
> > > +#define direct_complex_dot_prod_optab_supported_p
> > > convert_optab_supported_p
> > > #define direct_cond_unary_optab_supported_p
> direct_optab_supported_p
> > > #define direct_cond_binary_optab_supported_p
> direct_optab_supported_p
> > > #define direct_cond_ternary_optab_supported_p
> direct_optab_supported_p
> > > diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> > > index af9f92950c73..08bdedc30045 100644
> > > --- a/gcc/internal-fn.def
> > > +++ b/gcc/internal-fn.def
> > > @@ -453,6 +453,7 @@ DEF_INTERNAL_OPTAB_FN
> (COMPLEX_ADD_ROT90,
> > > ECF_CONST, cadd90, binary)
> > > DEF_INTERNAL_OPTAB_FN (COMPLEX_ADD_ROT270, ECF_CONST,
> cadd270,
> > > binary)
> > > DEF_INTERNAL_OPTAB_FN (COMPLEX_MUL, ECF_CONST, cmul, binary)
> > > DEF_INTERNAL_OPTAB_FN (COMPLEX_MUL_CONJ, ECF_CONST,
> cmul_conj,
> > > binary)
> > > +DEF_INTERNAL_OPTAB_FN (COMPLEX_DOT_PROD_ROT0, ECF_CONST,
> > > cdot_prod_rot0, complex_dot_prod)
> > > DEF_INTERNAL_OPTAB_FN (VEC_ADDSUB, ECF_CONST, vec_addsub,
> binary)
> > > DEF_INTERNAL_OPTAB_FN (VEC_TRUNC_ADD_HIGH, ECF_CONST |
> > > ECF_NOTHROW,
> > > vec_trunc_add_high, binary)
> > > diff --git a/gcc/optabs.def b/gcc/optabs.def
> > > index 9d95f047cb50..b30e2bec6b2b 100644
> > > --- a/gcc/optabs.def
> > > +++ b/gcc/optabs.def
> > > @@ -114,6 +114,7 @@ OPTAB_CD(vec_init_optab, "vec_init$a$b")
> > > OPTAB_CD (sdot_prod_optab, "sdot_prod$I$a$b")
> > > OPTAB_CD (udot_prod_optab, "udot_prod$I$a$b")
> > > OPTAB_CD (usdot_prod_optab, "usdot_prod$I$a$b")
> > > +OPTAB_CD (cdot_prod_rot0_optab, "cdot_prod_rot0$I$a$b")
> > >
> > > OPTAB_CD (while_ult_optab, "while_ult$a$b")
> > > OPTAB_CD (select_vl_optab, "select_vl$a$b")
> > > --
> > > 2.53.0
> >
> >
>
> --
> Richard Biener <[email protected]>
> SUSE Software Solutions Germany GmbH,
> Frankenstrasse 146, 90461 Nuernberg, Germany;
> GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri; (HRB 36809, AG Nuernberg)
