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tree-optimization/119155 - wrong aligned access for vectorized packed access

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When doing strided SLP vectorization we use the wrong alignment for
the possibly piecewise access of the vector elements for loads and
stores.  While we are carefully using element aligned loads and
stores that isn't enough for the case the original scalar accesses
are packed.  The following instead honors larger alignment when
present but correctly falls back to the original scalar alignment
used.

	PR tree-optimization/119155
	* tree-vect-stmts.cc (vectorizable_store): Do not always
	use vector element alignment for VMAT_STRIDED_SLP but
	a more correct alignment towards both ends.
	(vectorizable_load): Likewise.

	* gcc.dg/vect/pr119155.c: New testcase.
This commit is contained in:
Richard Biener 2025-03-07 12:57:42 +01:00 • committed by Richard Biener
parent 81203220af
commit adb14c7625
2 changed files with 47 additions and 4 deletions
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26
gcc/testsuite/gcc.dg/vect/pr119155.c Normal file
View file

@ -0,0 +1,26 @@
#include <stdlib.h>
#include "tree-vect.h"
struct s { int x; } __attribute__((packed));
void __attribute__((noipa))
f (char *xc, char *yc, int z)
{
for (int i = 0; i < 100; ++i)
{
struct s *x = (struct s *) xc;
struct s *y = (struct s *) yc;
x->x += y->x;
xc += z;
yc += z;
}
}
int main ()
{
check_vect ();
char *x = malloc (100 * sizeof (struct s) + 1);
char *y = malloc (100 * sizeof (struct s) + 1);
f (x + 1, y + 1, sizeof (struct s));
return 0;
}

25
gcc/tree-vect-stmts.cc
View file

@ -8904,7 +8904,15 @@ vectorizable_store (vec_info *vinfo,
}
}
}
ltype = build_aligned_type (ltype, TYPE_ALIGN (elem_type));
unsigned align;
if (alignment_support_scheme == dr_aligned)
align = known_alignment (DR_TARGET_ALIGNMENT (first_dr_info));
else
align = dr_alignment (vect_dr_behavior (vinfo, first_dr_info));
/* Alignment is at most the access size if we do multiple stores. */
if (nstores > 1)
align = MIN (tree_to_uhwi (TYPE_SIZE_UNIT (ltype)), align);
ltype = build_aligned_type (ltype, align * BITS_PER_UNIT);
ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
}
@ -10851,7 +10859,7 @@ vectorizable_load (vec_info *vinfo,
&ptype);
if (vtype != NULL_TREE)
{
dr_alignment_support dr_align = dr_aligned;
dr_alignment_support dr_align;
int mis_align = 0;
if (VECTOR_TYPE_P (ptype))
{
@ -10860,6 +10868,8 @@ vectorizable_load (vec_info *vinfo,
= vect_supportable_dr_alignment (vinfo, dr_info, ptype,
mis_align);
}
else
dr_align = dr_unaligned_supported;
if (dr_align == dr_aligned
|| dr_align == dr_unaligned_supported)
{
@ -10872,8 +10882,15 @@ vectorizable_load (vec_info *vinfo,
}
}
}
/* Else fall back to the default element-wise access. */
ltype = build_aligned_type (ltype, TYPE_ALIGN (TREE_TYPE (vectype)));
unsigned align;
if (alignment_support_scheme == dr_aligned)
align = known_alignment (DR_TARGET_ALIGNMENT (first_dr_info));
else
align = dr_alignment (vect_dr_behavior (vinfo, first_dr_info));
/* Alignment is at most the access size if we do multiple loads. */
if (nloads > 1)
align = MIN (tree_to_uhwi (TYPE_SIZE_UNIT (ltype)), align);
ltype = build_aligned_type (ltype, align * BITS_PER_UNIT);
}
if (slp)