On Fri, 9 Jan 2026, Richard Biener wrote:
> The following fixes enough of const VEC_PERM folding and lowering
> to deal with the fallout for the two testcases from the PR. We
> usually do not generate such problematic VEC_PERM expressions, but
> we allow those since GCC 14. As can be seen we mishandle those,
> including failure to expand/lower them by zero-extending inputs (which is
> what __builtin_shufflevector does).
>
> I'm unsure as to what extent we get such permutes but Tamar indicates
> that aarch64 can handle those at least.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu. The testcases
> failed on aarch64 as well and pass after the patch.
>
> OK?
I have pushed this now.
Richard.
> Thanks,
> Richard.
>
> PR middle-end/123175
> * match.pd (vec_perm @0 @1 @2): Fixup for inputs having a
> different number of elements than the result.
> * tree-vect-generic.cc (lower_vec_perm): Likewise.
>
> * gcc.dg/torture/pr123175-1.c: New testcase.
> * gcc.dg/torture/pr123175-2.c: Likewise.
> ---
> gcc/match.pd | 10 +++++---
> gcc/testsuite/gcc.dg/torture/pr123175-1.c | 31 +++++++++++++++++++++++
> gcc/testsuite/gcc.dg/torture/pr123175-2.c | 31 +++++++++++++++++++++++
> gcc/tree-vect-generic.cc | 13 +++++-----
> 4 files changed, 75 insertions(+), 10 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/torture/pr123175-1.c
> create mode 100644 gcc/testsuite/gcc.dg/torture/pr123175-2.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 492d88514fc..08d0810e986 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -11515,12 +11515,13 @@ and,
> {
> /* Create a vec_perm_indices for the integer vector. */
> poly_uint64 nelts = TYPE_VECTOR_SUBPARTS (type);
> + poly_uint64 nelts_in = TYPE_VECTOR_SUBPARTS (TREE_TYPE (op0));
> bool single_arg = (op0 == op1);
> - vec_perm_indices sel (builder, single_arg ? 1 : 2, nelts);
> + vec_perm_indices sel (builder, single_arg ? 1 : 2, nelts_in);
> }
> - (if (sel.series_p (0, 1, 0, 1))
> + (if (known_eq (nelts, nelts_in) && sel.series_p (0, 1, 0, 1))
> { op0; }
> - (if (sel.series_p (0, 1, nelts, 1))
> + (if (sel.series_p (0, 1, nelts_in, 1))
> { op1; }
> (with
> {
> @@ -11533,7 +11534,7 @@ and,
> op0 = op1;
> sel.rotate_inputs (1);
> }
> - else if (known_ge (poly_uint64 (sel[0]), nelts))
> + else if (known_ge (poly_uint64 (sel[0]), nelts_in))
> {
> std::swap (op0, op1);
> sel.rotate_inputs (1);
> @@ -11568,6 +11569,7 @@ and,
> in that case. But only if the vector mode is supported,
> otherwise this is invalid GIMPLE. */
> if (op_mode != BLKmode
> + && known_eq (nelts, nelts_in)
> && (TREE_CODE (cop0) == VECTOR_CST
> || TREE_CODE (cop0) == CONSTRUCTOR
> || TREE_CODE (cop1) == VECTOR_CST
> diff --git a/gcc/testsuite/gcc.dg/torture/pr123175-1.c
> b/gcc/testsuite/gcc.dg/torture/pr123175-1.c
> new file mode 100644
> index 00000000000..eea341ee2cb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr123175-1.c
> @@ -0,0 +1,31 @@
> +/* { dg-do run } */
> +/* { dg-additional-options "-fgimple" } */
> +
> +typedef int v4si __attribute__((vector_size(16)));
> +typedef int v2si __attribute__((vector_size(8)));
> +typedef char v4qi __attribute__((vector_size(4)));
> +
> +v4si res;
> +v2si a;
> +v2si b;
> +
> +void __attribute__((noipa)) __GIMPLE() foo ()
> +{
> + v2si a_;
> + v2si b_;
> + v4si res_;
> + a_ = a;
> + b_ = b;
> + res_ = __VEC_PERM (a_, b_, _Literal (v4qi) { 0, 1, 2, 3 });
> + res = res_;
> +}
> +
> +int main()
> +{
> + a = (v2si){ 4, 3 };
> + b = (v2si){ 2, 1 };
> + foo ();
> + if (res[0] != 4 || res[1] != 3 || res[2] != 2 || res[3] != 1)
> + __builtin_abort ();
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/torture/pr123175-2.c
> b/gcc/testsuite/gcc.dg/torture/pr123175-2.c
> new file mode 100644
> index 00000000000..32431bee914
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr123175-2.c
> @@ -0,0 +1,31 @@
> +/* { dg-do run } */
> +/* { dg-additional-options "-fgimple" } */
> +
> +typedef int v4si __attribute__((vector_size(16)));
> +typedef int v2si __attribute__((vector_size(8)));
> +typedef char v4qi __attribute__((vector_size(4)));
> +
> +v4si res;
> +v2si a;
> +v2si b;
> +
> +void __attribute__((noipa)) __GIMPLE() foo ()
> +{
> + v2si a_;
> + v2si b_;
> + v4si res_;
> + a_ = a;
> + b_ = b;
> + res_ = __VEC_PERM (a_, b_, _Literal (v4qi) { 0, 2, 2, 1 });
> + res = res_;
> +}
> +
> +int main()
> +{
> + a = (v2si){ 4, 3 };
> + b = (v2si){ 2, 1 };
> + foo ();
> + if (res[0] != 4 || res[1] != 2 || res[2] != 2 || res[3] != 3)
> + __builtin_abort ();
> + return 0;
> +}
> diff --git a/gcc/tree-vect-generic.cc b/gcc/tree-vect-generic.cc
> index 90b8f816e15..d34d2c5fa48 100644
> --- a/gcc/tree-vect-generic.cc
> +++ b/gcc/tree-vect-generic.cc
> @@ -1620,7 +1620,7 @@ lower_vec_perm (gimple_stmt_iterator *gsi)
> tree mask_type = TREE_TYPE (mask);
> tree vect_elt_type = TREE_TYPE (vect_type);
> tree mask_elt_type = TREE_TYPE (mask_type);
> - unsigned HOST_WIDE_INT elements;
> + unsigned HOST_WIDE_INT elements, in_elements;
> vec<constructor_elt, va_gc> *v;
> tree constr, t, si, i_val;
> tree vec0tmp = NULL_TREE, vec1tmp = NULL_TREE, masktmp = NULL_TREE;
> @@ -1628,7 +1628,8 @@ lower_vec_perm (gimple_stmt_iterator *gsi)
> location_t loc = gimple_location (gsi_stmt (*gsi));
> unsigned i;
>
> - if (!TYPE_VECTOR_SUBPARTS (res_vect_type).is_constant (&elements))
> + if (!TYPE_VECTOR_SUBPARTS (res_vect_type).is_constant (&elements)
> + || !TYPE_VECTOR_SUBPARTS (vect_type).is_constant (&in_elements))
> return;
>
> if (TREE_CODE (mask) == SSA_NAME)
> @@ -1644,7 +1645,7 @@ lower_vec_perm (gimple_stmt_iterator *gsi)
> if (TREE_CODE (mask) == VECTOR_CST
> && tree_to_vec_perm_builder (&sel_int, mask))
> {
> - vec_perm_indices indices (sel_int, 2, elements);
> + vec_perm_indices indices (sel_int, 2, in_elements);
> machine_mode vmode = TYPE_MODE (vect_type);
> tree lhs_type = TREE_TYPE (gimple_assign_lhs (stmt));
> machine_mode lhs_mode = TYPE_MODE (lhs_type);
> @@ -1729,10 +1730,10 @@ lower_vec_perm (gimple_stmt_iterator *gsi)
> unsigned HOST_WIDE_INT index;
>
> index = TREE_INT_CST_LOW (i_val);
> - if (!tree_fits_uhwi_p (i_val) || index >= elements)
> - i_val = build_int_cst (mask_elt_type, index & (elements - 1));
> + if (!tree_fits_uhwi_p (i_val) || index >= in_elements)
> + i_val = build_int_cst (mask_elt_type, index & (in_elements - 1));
>
> - if (two_operand_p && (index & elements) != 0)
> + if (two_operand_p && (index & in_elements) != 0)
> t = vector_element (gsi, vec1, i_val, &vec1tmp);
> else
> t = vector_element (gsi, vec0, i_val, &vec0tmp);
>
--
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)
