Hi!
I admit I fully don't understand why exactly, but my experimentation so far
showed that for read/write and write/read ddrs it is ok and desirable to
ignore the dist > 0 && DDR_REVERSED_P (ddr) cases, but for write/write
ddrs it is undesirable. See the PR for further tests, perhaps I could
turn them into further testcases.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2014-01-22 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/59594
* tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Don't
ignore dist > 0 && DDR_REVERSED_P (ddr) if step is negative and both
DRs are writes.
* gcc.dg/vect/no-vfa-vect-depend-2.c: New test.
* gcc.dg/vect/pr59594.c: New test.
--- gcc/tree-vect-data-refs.c.jj 2014-01-16 20:54:59.000000000 +0100
+++ gcc/tree-vect-data-refs.c 2014-01-22 13:13:49.751362484 +0100
@@ -383,11 +383,13 @@ vect_analyze_data_ref_dependence (struct
continue;
}
- if (dist > 0 && DDR_REVERSED_P (ddr))
+ if (dist > 0 && DDR_REVERSED_P (ddr)
+ && (DR_IS_READ (dra) || DR_IS_READ (drb)))
{
/* If DDR_REVERSED_P the order of the data-refs in DDR was
reversed (to make distance vector positive), and the actual
- distance is negative. */
+ distance is negative. If both DRs are writes, we can't ignore
+ the DDR. See PR59594. */
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"dependence distance negative.\n");
--- gcc/testsuite/gcc.dg/vect/no-vfa-vect-depend-2.c.jj 2014-01-22
13:28:47.100724091 +0100
+++ gcc/testsuite/gcc.dg/vect/no-vfa-vect-depend-2.c 2014-01-22
13:41:38.736778586 +0100
@@ -0,0 +1,55 @@
+/* { dg-require-effective-target vect_int } */
+
+#include <stdarg.h>
+#include "tree-vect.h"
+
+#define N 17
+
+int ia[N] = {48,45,42,39,36,33,30,27,24,21,18,15,12,9,6,3,0};
+int ib[N] = {48,45,42,39,36,33,30,27,24,21,18,15,12,9,6,3,0};
+int res[N] = {48,192,180,168,156,144,132,120,108,96,84,72,60,48,36,24,12};
+
+__attribute__ ((noinline))
+int main1 ()
+{
+ int i;
+
+ /* Not vectorizable due to data dependence: dependence distance 1. */
+ for (i = N - 1; i >= 0; i--)
+ {
+ ia[i] = ia[i+1] * 4;
+ }
+
+ /* check results: */
+ for (i = 0; i < N; i++)
+ {
+ if (ia[i] != 0)
+ abort ();
+ }
+
+ /* Vectorizable. Dependence distance -1. */
+ for (i = N - 1; i >= 0; i--)
+ {
+ ib[i+1] = ib[i] * 4;
+ }
+
+ /* check results: */
+ for (i = 0; i < N; i++)
+ {
+ if (ib[i] != res[i])
+ abort ();
+ }
+
+ return 0;
+}
+
+int main (void)
+{
+ check_vect();
+
+ return main1 ();
+}
+
+/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" {xfail
vect_no_align } } } */
+/* { dg-final { scan-tree-dump-times "dependence distance negative" 1 "vect"
} } */
+/* { dg-final { cleanup-tree-dump "vect" } } */
--- gcc/testsuite/gcc.dg/vect/pr59594.c.jj 2014-01-22 13:39:51.362322166
+0100
+++ gcc/testsuite/gcc.dg/vect/pr59594.c 2014-01-22 13:39:43.000000000 +0100
@@ -0,0 +1,31 @@
+/* PR tree-optimization/59594 */
+
+#include "tree-vect.h"
+
+#define N 1024
+int b[N + 1];
+
+int
+main ()
+{
+ int i;
+ check_vect ();
+ for (i = 0; i < N + 1; i++)
+ {
+ b[i] = i;
+ asm ("");
+ }
+ for (i = N; i >= 0; i--)
+ {
+ b[i + 1] = b[i];
+ b[i] = 1;
+ }
+ if (b[0] != 1)
+ __builtin_abort ();
+ for (i = 0; i < N; i++)
+ if (b[i + 1] != i)
+ __builtin_abort ();
+ return 0;
+}
+
+/* { dg-final { cleanup-tree-dump "vect" } } */
Jakub
