On Thu, Jan 22, 2026 at 10:31 AM Richard Biener
<[email protected]> wrote:
>
> On Wed, Jan 21, 2026 at 4:10 PM Artemiy Volkov <[email protected]> wrote:
> >
> > Currently, simplify_vector_constructor () tries to rewrite a CONSTRUCTOR
> > expression into a VEC_PERM_EXPR, as long as constructor elements all come
> > from 1 or 2 source vectors. While doing so, it protects against creating
> > VEC_PERM_EXPRs unsupported by the target by calling can_vec_perm_const_p
> > () before enacting the transformation and bailing when that returns false.
> >
> > However, we can instead allow those VEC_PERM_EXPRs to be created if we
> > know that a later vector lowering pass will legitimize them for us. IOW,
> > only if the target doesn't support the resulting permute and the
> > PROP_gimple_lvec property is already set, do we give up. This patch
> > inserts the required checks.
> >
> > This also allows us to remove the unnecessary vect_int requirement
> > (wrongly added in r16-5244-g5a2319b71e4d30) from forwprop-43.c.
> >
> > Regtested on aarch64 and x86_64, and on arm with
> > RUNTESTFLAGS=--target_board=unix/-mfpu=vfpv3-d16/-march=armv7-a.
>
> Is this a regression fix of some sorts? I'm a bit worried that the poor-mans
> lowering will create much worse code than what we produce from the
> original CTOR (and the fix should probably to vector lowering).
Oh, and we also have to be careful to not trust can_vec_perm_const_p before
IPA since we might face to be offloaded code. That's a pre-existing issue as
well.
Richard.
> Thanks,
> Richard.
>
> > PR tree-optimization/122679
> >
> > gcc/ChangeLog:
> >
> > * tree-ssa-forwprop.cc (simplify_vector_constructor): Check the
> > PROP_gimple_lvec property before bailing.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/tree-ssa/forwprop-43.c: Remove the vect_int check.
> > ---
> > gcc/testsuite/gcc.dg/tree-ssa/forwprop-43.c | 1 -
> > gcc/tree-ssa-forwprop.cc | 6 ++++--
> > 2 files changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-43.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-43.c
> > index bfda376e1f7..0e802ea5107 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-43.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-43.c
> > @@ -1,7 +1,6 @@
> > /* { dg-do compile } */
> > /* { dg-options "-O2 -fdump-tree-forwprop1" } */
> > /* { dg-require-effective-target stdint_types } */
> > -/* { dg-require-effective-target vect_int } */
> > /* { dg-additional-options "-fgimple" } */
> >
> > #include <stdint.h>
> > diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
> > index bdc63a7a71b..6c847ee7ff3 100644
> > --- a/gcc/tree-ssa-forwprop.cc
> > +++ b/gcc/tree-ssa-forwprop.cc
> > @@ -4173,7 +4173,8 @@ simplify_vector_constructor (gimple_stmt_iterator
> > *gsi)
> > ? 0 : refnelts) + i);
> > vec_perm_indices indices (sel, orig[1] ? 2 : 1, refnelts);
> > machine_mode vmode = TYPE_MODE (perm_type);
> > - if (!can_vec_perm_const_p (vmode, vmode, indices))
> > + if (!can_vec_perm_const_p (vmode, vmode, indices)
> > + && (cfun->curr_properties & PROP_gimple_lvec))
> > return false;
> > mask_type = build_vector_type (ssizetype, refnelts);
> > tree op2 = vec_perm_indices_to_tree (mask_type, indices);
> > @@ -4238,7 +4239,8 @@ simplify_vector_constructor (gimple_stmt_iterator
> > *gsi)
> > ? elts[i].second + nelts : i);
> > vec_perm_indices indices (sel, 2, nelts);
> > machine_mode vmode = TYPE_MODE (type);
> > - if (!can_vec_perm_const_p (vmode, vmode, indices))
> > + if (!can_vec_perm_const_p (vmode, vmode, indices)
> > + && (cfun->curr_properties & PROP_gimple_lvec))
> > return false;
> > mask_type = build_vector_type (ssizetype, nelts);
> > blend_op2 = vec_perm_indices_to_tree (mask_type, indices);
> > --
> > 2.43.0
> >
