[gcc r11-11465] vect: Fix access size alignment assumption [PR115192]

[Richard Sandiford]

https://gcc.gnu.org/g:741ea10418987ac02eb8e680f2946a6e5928eb23

commit r11-11465-g741ea10418987ac02eb8e680f2946a6e5928eb23
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Jun 4 13:47:34 2024 +0100

    vect: Fix access size alignment assumption [PR115192]
    
    create_intersect_range_checks checks whether two access ranges
    a and b are alias-free using something equivalent to:
    
      end_a <= start_b || end_b <= start_a
    
    It has two ways of doing this: a "vanilla" way that calculates
    the exact exclusive end pointers, and another way that uses the
    last inclusive aligned pointers (and changes the comparisons
    accordingly).  The comment for the latter is:
    
          /* Calculate the minimum alignment shared by all four pointers,
             then arrange for this alignment to be subtracted from the
             exclusive maximum values to get inclusive maximum values.
             This "- min_align" is cumulative with a "+ access_size"
             in the calculation of the maximum values.  In the best
             (and common) case, the two cancel each other out, leaving
             us with an inclusive bound based only on seg_len.  In the
             worst case we're simply adding a smaller number than before.
    
    The problem is that the associated code implicitly assumed that the
    access size was a multiple of the pointer alignment, and so the
    alignment could be carried over to the exclusive end pointer.
    
    The testcase started failing after g:9fa5b473b5b8e289b6542
    because that commit improved the alignment information for
    the accesses.
    
    gcc/
            PR tree-optimization/115192
            * tree-data-ref.c (create_intersect_range_checks): Take the
            alignment of the access sizes into account.
    
    gcc/testsuite/
            PR tree-optimization/115192
            * gcc.dg/vect/pr115192.c: New test.
    
    (cherry picked from commit a0fe4fb1c8d7804515845dd5d2a814b3c7a1ccba)

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr115192.c | 28 ++++++++++++++++++++++++++++
 gcc/tree-data-ref.c                  |  5 ++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr115192.c b/gcc/testsuite/gcc.dg/vect/pr115192.c
new file mode 100644
index 00000000000..923d377c1bb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr115192.c
@@ -0,0 +1,28 @@
+#include "tree-vect.h"
+
+int data[4 * 16 * 16] __attribute__((aligned(16)));
+
+__attribute__((noipa)) void
+foo (__SIZE_TYPE__ n)
+{
+  for (__SIZE_TYPE__ i = 1; i < n; ++i)
+    {
+      data[i * n * 4] = data[(i - 1) * n * 4] + 1;
+      data[i * n * 4 + 1] = data[(i - 1) * n * 4 + 1] + 2;
+    }
+}
+
+int
+main ()
+{
+  check_vect ();
+
+  data[0] = 10;
+  data[1] = 20;
+
+  foo (3);
+
+  if (data[24] != 12 || data[25] != 24)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-data-ref.c b/gcc/tree-data-ref.c
index b3dd2f0ca41..d127aba8792 100644
--- a/gcc/tree-data-ref.c
+++ b/gcc/tree-data-ref.c
@@ -73,6 +73,7 @@ along with GCC; see the file COPYING3.  If not see
 
 */
 
+#define INCLUDE_ALGORITHM
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
@@ -2629,7 +2630,9 @@ create_intersect_range_checks (class loop *loop, tree *cond_expr,
 	 Because the maximum values are inclusive, there is an alias
 	 if the maximum value of one segment is equal to the minimum
 	 value of the other.  */
-      min_align = MIN (dr_a.align, dr_b.align);
+      min_align = std::min (dr_a.align, dr_b.align);
+      min_align = std::min (min_align, known_alignment (dr_a.access_size));
+      min_align = std::min (min_align, known_alignment (dr_b.access_size));
       cmp_code = LT_EXPR;
     }