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 --git a/gcc/testsuite/gcc.dg/vect/pr105219.c b/gcc/testsuite/gcc.dg/vect/pr105219.c
new file mode 100644 (file)
index 0000000..0cb7ae2
--- /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 d7bc34636bd52b2f67cdecd3dc16fcff684dba07..f53a634a390c389df13f83a4ba8eb5bfa4aaddad 100644 (file)
--- 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