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).
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
>
