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tree-optimization/119586 - aligned access to unaligned data

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The following reverts parts of r15-8047 which assesses alignment
analysis for VMAT_STRIDED_SLP is correct by using aligned accesses
where allowed by it.  As the PR shows this analysis is still incorrect,
so revert back to assuming we got it wrong.

	PR tree-optimization/119586
	* tree-vect-stmts.cc (vectorizable_load): Assume we got
	alignment analysis for VMAT_STRIDED_SLP wrong.
	(vectorizable_store): Likewise.

	* gcc.dg/vect/pr119586.c: New testcase.
This commit is contained in:
Richard Biener 2025-04-02 13:12:58 +02:00 • committed by Richard Biener
parent e7912d4a81
commit 574c59cfe6
2 changed files with 34 additions and 8 deletions
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21
gcc/testsuite/gcc.dg/vect/pr119586.c Normal file
View file

@ -0,0 +1,21 @@
#include "tree-vect.h"
void __attribute__((noipa)) foo (long *) {}
void __attribute__((noipa))
d()
{
long e[6][8][5];
for (int b = 0; b < 6; b++)
for (int c = 0; c < 8; c++)
{
e[b][c][0] = 1;
e[b][c][1] = 1;
e[b][c][4] = 1;
}
foo (&e[0][0][0]);
}
int main()
{
check_vect ();
d();
}

21
gcc/tree-vect-stmts.cc
View file

@ -8906,10 +8906,17 @@ vectorizable_store (vec_info *vinfo,
}
}
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));
/* ??? We'd want to use
if (alignment_support_scheme == dr_aligned)
align = known_alignment (DR_TARGET_ALIGNMENT (first_dr_info));
since doing that is what we assume we can in the above checks.
But this interferes with groups with gaps where for example
VF == 2 makes the group in the unrolled loop aligned but the
fact that we advance with step between the two subgroups
makes the access to the second unaligned. See PR119586.
We have to anticipate that here or adjust code generation to
avoid the misaligned loads by means of permutations. */
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);
@ -10884,10 +10891,8 @@ vectorizable_load (vec_info *vinfo,
}
}
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));
/* ??? The above is still wrong, see vectorizable_store. */
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);