[gcc r11-10167] tree-optimization/103116 - SLP permutes and peeling for gaps

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:ff408622a5f8fb395e5584a494aaaad05b3611db

commit r11-10167-gff408622a5f8fb395e5584a494aaaad05b3611db
Author: Richard Biener <rguenther@suse.de>
Date:   Wed May 4 10:43:07 2022 +0200

    tree-optimization/103116 - SLP permutes and peeling for gaps
    
    The testcase shows that we can end up with a contiguous access across
    loop iterations but by means of permutations the elements accessed
    might only cover parts of a vector.  In this case we end up with
    GROUP_GAP == 0 but still need to avoid accessing excess elements
    in the last loop iterations.  Peeling for gaps is designed to cover
    this but a single scalar iteration might not cover all of the excess
    elements.  The following ensures peeling for gaps is done in this
    situation and when that isn't sufficient because we need to peel
    more than one iteration (gcc.dg/vect/pr103116-2.c), fail the SLP
    vectorization.
    
    2022-05-04  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/103116
            * tree-vect-stmts.c (get_group_load_store_type): Handle the
            case we need peeling for gaps even though GROUP_GAP is zero.
    
            * gcc.dg/vect/pr103116-1.c: New testcase.
            * gcc.dg/vect/pr103116-2.c: Likewise.
    
    (cherry picked from commit 52b7b86f8c72eb19e637f1e72ffd10f39b8cb829)

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr103116-1.c | 50 ++++++++++++++++++++++++++++
 gcc/testsuite/gcc.dg/vect/pr103116-2.c | 59 ++++++++++++++++++++++++++++++++++
 gcc/tree-vect-stmts.c                  | 31 ++++++++++++++++++
 3 files changed, 140 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/vect/pr103116-1.c b/gcc/testsuite/gcc.dg/vect/pr103116-1.c
new file mode 100644
index 00000000000..d3639fc8cfd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr103116-1.c
@@ -0,0 +1,50 @@
+/* { dg-require-effective-target mmap } */
+
+#include <sys/mman.h>
+#include <stdio.h>
+
+#define COUNT 128
+#define MMAP_SIZE 0x20000
+#define ADDRESS 0x1122000000
+#define TYPE unsigned int
+
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
+void __attribute__((noipa))
+loop (TYPE *restrict x, TYPE *restrict y)
+{
+  for (int i = 0; i < COUNT; ++i)
+    {
+      x[i * 4] = y[i * 2] + 1;
+      x[i * 4 + 1] = y[i * 2] + 2;
+      x[i * 4 + 2] = y[i * 2 + 1] + 3;
+      x[i * 4 + 3] = y[i * 2 + 1] + 4;
+    }
+}
+
+TYPE x[COUNT * 4];
+
+int
+main (void)
+{
+  void *y;
+  TYPE *end_y;
+
+  y = mmap ((void *) ADDRESS, MMAP_SIZE, PROT_READ | PROT_WRITE,
+            MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (y == MAP_FAILED)
+    {
+      perror ("mmap");
+      return 1;
+    }
+
+  end_y = (TYPE *) ((char *) y + MMAP_SIZE);
+
+  loop (x, end_y - COUNT * 2);
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "Data access with gaps requires scalar epilogue loop" "vect" { target { vect_perm && vect_int } } } } */
diff --git a/gcc/testsuite/gcc.dg/vect/pr103116-2.c b/gcc/testsuite/gcc.dg/vect/pr103116-2.c
new file mode 100644
index 00000000000..2f4ed0f404c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr103116-2.c
@@ -0,0 +1,59 @@
+/* { dg-require-effective-target mmap } */
+/* { dg-additional-options "-mssse3" { target x86_64-*-* i?86-*-* } } */
+
+#include <sys/mman.h>
+#include <stdio.h>
+#include "tree-vect.h"
+
+#define COUNT 128
+#define MMAP_SIZE 0x20000
+#define ADDRESS 0x1122000000
+#define TYPE unsigned short
+#define GROUP_SIZE 2
+
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
+void __attribute__((noipa))
+loop (TYPE *restrict x, TYPE *restrict y)
+{
+  for (int i = 0; i < COUNT; ++i)
+    {
+      x[i * 8] = y[i * GROUP_SIZE] + 1;
+      x[i * 8 + 1] = y[i * GROUP_SIZE] + 2;
+      x[i * 8 + 2] = y[i * GROUP_SIZE + 1] + 3;
+      x[i * 8 + 3] = y[i * GROUP_SIZE + 1] + 4;
+      x[i * 8 + 4] = y[i * GROUP_SIZE] + 5;
+      x[i * 8 + 5] = y[i * GROUP_SIZE] + 6;
+      x[i * 8 + 6] = y[i * GROUP_SIZE + 1] + 7;
+      x[i * 8 + 7] = y[i * GROUP_SIZE + 1] + 8;
+    }
+}
+
+TYPE x[COUNT * 4];
+
+int
+main (void)
+{
+  void *y;
+  TYPE *end_y;
+
+  check_vect ();
+
+  y = mmap ((void *) ADDRESS, MMAP_SIZE, PROT_READ | PROT_WRITE,
+            MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (y == MAP_FAILED)
+    {
+      perror ("mmap");
+      return 1;
+    }
+
+  end_y = (TYPE *) ((char *) y + MMAP_SIZE);
+
+  loop (x, end_y - COUNT * GROUP_SIZE);
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "peeling for gaps insufficient for access" "vect" { target { vect_perm_short } } } } */
diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
index 0d61b0f51d0..973c6dcea18 100644
--- a/gcc/tree-vect-stmts.c
+++ b/gcc/tree-vect-stmts.c
@@ -2207,6 +2207,37 @@ get_group_load_store_type (vec_info *vinfo, stmt_vec_info stmt_info,
 	      gcc_assert (!loop_vinfo || cmp > 0);
 	      *memory_access_type = VMAT_CONTIGUOUS;
 	    }
+
+	  /* When we have a contiguous access across loop iterations
+	     but the access in the loop doesn't cover the full vector
+	     we can end up with no gap recorded but still excess
+	     elements accessed, see PR103116.  Make sure we peel for
+	     gaps if necessary and sufficient and give up if not.  */
+	  if (loop_vinfo
+	      && *memory_access_type == VMAT_CONTIGUOUS
+	      && SLP_TREE_LOAD_PERMUTATION (slp_node).exists ()
+	      && !multiple_p (group_size * LOOP_VINFO_VECT_FACTOR (loop_vinfo),
+			      nunits))
+	    {
+	      unsigned HOST_WIDE_INT cnunits, cvf;
+	      if (!can_overrun_p
+		  || !nunits.is_constant (&cnunits)
+		  || !LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant (&cvf)
+		  /* Peeling for gaps assumes that a single scalar iteration
+		     is enough to make sure the last vector iteration doesn't
+		     access excess elements.
+		     ???  Enhancements include peeling multiple iterations
+		     or using masked loads with a static mask.  */
+		  || (group_size * cvf) % cnunits + group_size < cnunits)
+		{
+		  if (dump_enabled_p ())
+		    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+				     "peeling for gaps insufficient for "
+				     "access\n");
+		  return false;
+		}
+	      overrun_p = true;
+	    }
 	}
     }
   else