On Fri, 24 Jan 2014, Jakub Jelinek wrote:
> 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.
Please.
> 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)))
I think that'snot sufficient. It depends
on the order of the stmts whether the dependence distance is really
negative - we are trying to catch write-after-read negative distance
here I think. We can't rely on the DDRs being formed in stmt order
(anymore, at least since 4.9 where we start to arbitrary re-order
the vector of DRs).
> {
> /* 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
>
>
--
Richard Biener <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend"orffer
