This fixes bogus alignment computation for negative strided
grouped accesses which we now can vectorize but only through SLP.
The biasing for negative strided non-grouped accesses as supported
via VMAT_CONTIGUOUS_REVERSE does not apply there and instead causes
alignment analysis to compute wrong things. The following restricts
the biasing to non-grouped accesses for the moment, leaving bigger
refactoring for another time.
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
2021-03-25 Richard Biener <rguent...@suse.de>
PR tree-optimization/96109
* tree-vect-data-refs.c (vect_compute_data_ref_alignment):
Only bias non-grouped negative stride accesses.
* gcc.dg/vect/pr96109.c: New testcase.
---
gcc/testsuite/gcc.dg/vect/pr96109.c | 31 +++++++++++++++++++++++++++++
gcc/tree-vect-data-refs.c | 7 ++++++-
2 files changed, 37 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/pr96109.c
diff --git a/gcc/testsuite/gcc.dg/vect/pr96109.c
b/gcc/testsuite/gcc.dg/vect/pr96109.c
new file mode 100644
index 00000000000..b9bc85fa593
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr96109.c
@@ -0,0 +1,31 @@
+/* { dg-require-effective-target vect_double } */
+
+#include "tree-vect.h"
+
+static double x[1024], y[1024];
+
+void __attribute__((noipa))
+foo ()
+{
+ for (int i = 0; i < 511; ++i)
+ {
+ x[2*i] = y[1022 - 2*i - 1];
+ x[2*i+1] = y[1022 - 2*i];
+ }
+}
+
+int main()
+{
+ check_vect ();
+ for (int i = 0; i < 1024; ++i)
+ x[i] = 0, y[i] = i;
+ foo ();
+ for (int i = 0; i < 1022; ++i)
+ if (x[i] != y[1022 - (i^1)])
+ __builtin_abort ();
+ if (x[1022] != 0 || x[1023] != 0)
+ __builtin_abort ();
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump "Vectorizing an unaligned access" "vect" {
target vect_unaligned_possible } } } */
diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 97c8577ebe7..ee266ba62a8 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -1109,7 +1109,12 @@ vect_compute_data_ref_alignment (vec_info *vinfo,
dr_vec_info *dr_info)
/* If this is a backward running DR then first access in the larger
vectype actually is N-1 elements before the address in the DR.
Adjust misalign accordingly. */
- if (tree_int_cst_sgn (drb->step) < 0)
+ /* ??? The only negative stride grouped access we support is via
+ VMAT_STRIDED_SLP and that is confused by this premature adjustment
+ of misalignment which really should be done on the
+ VMAT_CONTIGUOUS_REVERSE code path instead. */
+ if (!STMT_VINFO_GROUPED_ACCESS (stmt_info)
+ && tree_int_cst_sgn (drb->step) < 0)
/* PLUS because STEP is negative. */
misalignment += ((TYPE_VECTOR_SUBPARTS (vectype) - 1)
* -TREE_INT_CST_LOW (TYPE_SIZE_UNIT (TREE_TYPE
(vectype))));
--
2.26.2
