[gcc r12-8297] tree-optimization/105219 - bogus max iters for vectorized epilogue

[gcc r12-8297] tree-optimization/105219 - bogus max iters for vectorized epilogue

[Richard Biener]

https://gcc.gnu.org/g:f27848a5dc4d3b16cd4112bddcb59e0916eba623

commit r12-8297-gf27848a5dc4d3b16cd4112bddcb59e0916eba623
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Apr 27 14:06:12 2022 +0200

    tree-optimization/105219 - bogus max iters for vectorized epilogue
    
    The following makes sure to take into account prologue peeling
    when trying to narrow down the maximum number of iterations
    computed for the vectorized epilogue.  A similar issue exists when
    peeling for gaps.
    
    2022-04-27  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/105219
            * tree-vect-loop.cc (vect_transform_loop): Disable
            special code narrowing the vectorized epilogue max
            iterations when peeling for alignment or gaps was in effect.
    
            * gcc.dg/vect/pr105219.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr105219.c | 29 +++++++++++++++++++++++++++++
 gcc/tree-vect-loop.cc                |  6 +++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr105219.c b/gcc/testsuite/gcc.dg/vect/pr105219.c
new file mode 100644
index 00000000000..0cb7ae2f4d6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr105219.c
@@ -0,0 +1,29 @@
+/* { dg-do run } */
+/* { dg-additional-options "-O3" } */
+/* { dg-additional-options "-mtune=intel" { target x86_64-*-* i?86-*-* } } */
+
+#include "tree-vect.h"
+
+int data[128];
+
+void __attribute((noipa))
+foo (int *data, int n)
+{
+  for (int i = 0; i < n; ++i)
+    data[i] = i;
+}
+
+int main()
+{
+  check_vect ();
+  for (int start = 0; start < 16; ++start)
+    for (int n = 1; n < 3*16; ++n)
+      {
+        __builtin_memset (data, 0, sizeof (data));
+        foo (&data[start], n);
+        for (int j = 0; j < n; ++j)
+          if (data[start + j] != j)
+            __builtin_abort ();
+      }
+  return 0;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index d7bc34636bd..f53a634a390 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -9977,7 +9977,11 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
 			    lowest_vf) - 1
 	   : wi::udiv_floor (loop->nb_iterations_upper_bound + bias_for_lowest,
 			     lowest_vf) - 1);
-      if (main_vinfo)
+      if (main_vinfo
+	  /* Both peeling for alignment and peeling for gaps can end up
+	     with the scalar epilogue running for more than VF-1 iterations.  */
+	  && !main_vinfo->peeling_for_alignment
+	  && !main_vinfo->peeling_for_gaps)
 	{
 	  unsigned int bound;
 	  poly_uint64 main_iters