From: Yuri Rumyantsev <ysrumyan@gmail.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>,
Igor Zamyatin <izamyatin@gmail.com>
Subject: Re: [PATCH] Simple fix to enhance outer-loop vectorization.
Date: Thu, 28 May 2015 17:15:00 -0000 [thread overview]
Message-ID: <CAEoMCqQPL=ArD+dReYjWtCNW5rhTWXJdexb+1LBDXek=3NOw8w@mail.gmail.com> (raw)
In-Reply-To: <CAFiYyc3qu-1_z2URj+V9d1Cs1KyNoabo+THoznYEiDmR4YnkpQ@mail.gmail.com>
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Richard,
First of all, I don't think that it is possible to write out test for
outer-loop vectorization with zero-step reference because of possible
loop-carried dependencies and run-time aliasing is not supported for
outer-loop. If there are no such dependencies pre or pdse does
hoisting (sinking) of such invariant references. So I add a check on
it to accept zero-step references for outer loop marked with
forc-vectorize flag to guarantee absence of loop-carried dependencies
between inner-loop iterations.
I included run-time test that checks vectorization correctness.
Update patch is attached.
Yuri..
2015-05-28 14:39 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
> On Thu, May 28, 2015 at 1:00 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>> Hi All,
>>
>> Here is a simple patch which removes restriction on outer-loop
>> vectorization - allow references in inner-loop with zero step. This
>> case was found in one important benchmark.
>>
>> Bootstrap and regression testing did not show any new failures.
>> Is it OK for trunk.
>>
>> ChangeLog:
>> 2015-05-28 Yuri Rumyantsev <ysrumyan@gmail.com>
>>
>> * tree-vect-data-refs.c (vect_analyze_data_ref_access): Allow
>> consecutive accesses within outer-loop vectorization for references
>> with zero step in inner-loop.
>>
>> gcc/testsuite/ChangeLog:
>> * gcc.dg/vect/fast-math-vect-outer-1.c: New test.
>
> Can you please add a non-omp-simd testcase that triggers this as well and that
> is a runtime testcase verifying the transform is correct?
>
> Also please don't add to the strange testcase-name machinery but just
> use { dg-additional-options "-ffast-math" }
>
> Index: tree-vect-data-refs.c
> ===================================================================
> --- tree-vect-data-refs.c (revision 223653)
> +++ tree-vect-data-refs.c (working copy)
> @@ -2261,7 +2261,6 @@
> return true;
> }
>
> -
> /* Analyze the access pattern of the data-reference DR.
> In case of non-consecutive accesses call vect_analyze_group_access() to
> analyze groups of accesses. */
>
> spurious white-space change
>
>
> @@ -2291,14 +2290,8 @@
> if (loop_vinfo && integer_zerop (step))
>
> Surely the comment before this needs updating now.
>
> {
> GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt)) = NULL;
> - if (nested_in_vect_loop_p (loop, stmt))
> - {
> - if (dump_enabled_p ())
> - dump_printf_loc (MSG_NOTE, vect_location,
> - "zero step in inner loop of nest\n");
> - return false;
> - }
> - return DR_IS_READ (dr);
> + if (!nested_in_vect_loop_p (loop, stmt))
> + return DR_IS_READ (dr);
> }
>
> if (loop && nested_in_vect_loop_p (loop, stmt))
>
> so what happens after the patch? It would be nice to have a comment
> explaining what happens in the nested_in_vect_loop_p case for
> the case when the outer-loop step is zero and when it is not zero.
>
> In particular as you don't need any code generation changes - this hints
> at that you may miss something ;)
>
> Otherwise of course the patch is ok - lifting restrictions is good.
>
> Thanks,
> Richard.
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Index: testsuite/gcc.dg/vect/vect-outer-simd-1.c
===================================================================
--- testsuite/gcc.dg/vect/vect-outer-simd-1.c (revision 0)
+++ testsuite/gcc.dg/vect/vect-outer-simd-1.c (working copy)
@@ -0,0 +1,83 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_float } */
+/* { dg-require-effective-target vect_simd_clones } */
+/* { dg-additional-options "-fopenmp-simd -ffast-math" } */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "tree-vect.h"
+#define N 64
+
+float *px, *py;
+float *tx, *ty;
+float *x1, *z1, *t1, *t2;
+
+static void inline bar(const float cx, float cy,
+ float *vx, float *vy)
+{
+ int j;
+ for (j = 0; j < N; ++j)
+ {
+ const float dx = cx - px[j];
+ const float dy = cy - py[j];
+ *vx -= dx * tx[j];
+ *vy -= dy * ty[j];
+ }
+}
+
+__attribute__((noinline, noclone)) void foo1 ()
+{
+ int i;
+#pragma omp simd
+ for (i=0; i<N; i++)
+ bar(px[i], py[i], x1+i, z1+i);
+}
+
+__attribute__((noinline, noclone)) void foo2 ()
+{
+ volatile int i;
+ for (i=0; i<N; i++)
+ bar(px[i], py[i], x1+i, z1+i);
+}
+
+
+int main()
+{
+ float *X = (float*)malloc(N * 8 * sizeof (float));
+ int i;
+ check_vect ();
+ px = &X[0];
+ py = &X[N * 1];
+ tx = &X[N * 2];
+ ty = &X[N * 3];
+ x1 = &X[N * 4];
+ z1 = &X[N * 5];
+ t1 = &X[N * 6];
+ t2 = &X[N * 7];
+
+ for (i=0; i<N; i++)
+ {
+ px[i] = (float) (i+2);
+ tx[i] = (float) (i+1);
+ py[i] = (float) (i+4);
+ ty[i] = (float) (i+3);
+ x1[i] = z1[i] = 1.0f;
+ }
+ foo1 (); /* vector variant. */
+ for (i=0; i<N;i++)
+ {
+ t1[i] = x1[i]; x1[i] = 1.0f;
+ t2[i] = z1[i]; z1[i] = 1.0f;
+ }
+ foo2 (); /* scalar variant. */
+ for (i=0; i<N; i++)
+ if (x1[i] != t1[i] || z1[i] != t2[i])
+ {
+ fprintf (stderr, "Miscompare for index =%d!\n");
+ return 1;
+ }
+ fprintf (stderr, "Test passed!\n");
+ return 0;
+}
+/* { dg-final { scan-tree-dump "OUTER LOOP VECTORIZED" "vect" } } */
+/* { dg-final { cleanup-tree-dump "vect" } } */
Index: tree-vect-data-refs.c
===================================================================
--- tree-vect-data-refs.c (revision 223653)
+++ tree-vect-data-refs.c (working copy)
@@ -2287,18 +2287,17 @@
return false;
}
- /* Allow invariant loads in not nested loops. */
+ /* Allow loads with zero step in inner-loop vectorization. */
if (loop_vinfo && integer_zerop (step))
{
GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt)) = NULL;
- if (nested_in_vect_loop_p (loop, stmt))
- {
- if (dump_enabled_p ())
- dump_printf_loc (MSG_NOTE, vect_location,
- "zero step in inner loop of nest\n");
- return false;
- }
- return DR_IS_READ (dr);
+ if (!nested_in_vect_loop_p (loop, stmt))
+ return DR_IS_READ (dr);
+ /* Allow references with zero step for outer loops marked
+ with pragma omp simd only - it guarantees absence of
+ loop-carried dependencies between inner loop iterations. */
+ if (!loop->force_vectorize)
+ return false;
}
if (loop && nested_in_vect_loop_p (loop, stmt))
next prev parent reply other threads:[~2015-05-28 15:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-28 11:32 Yuri Rumyantsev
2015-05-28 11:56 ` Richard Biener
2015-05-28 17:15 ` Yuri Rumyantsev [this message]
2015-06-01 10:51 ` Richard Biener
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