[gcc r13-8679] tree-optimization/114485 - neg induction with partial vectors

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:a676581ddc49a6ead8edced7bb4b92aeceebde56

commit r13-8679-ga676581ddc49a6ead8edced7bb4b92aeceebde56
Author: Richard Biener <rguent...@suse.de>
Date:   Thu Apr 4 10:00:51 2024 +0200

    tree-optimization/114485 - neg induction with partial vectors
    
    We can't use vect_update_ivs_after_vectorizer for partial vectors,
    the following fixes vect_can_peel_nonlinear_iv_p accordingly.
    
            PR tree-optimization/114485
            * tree-vect-loop-manip.cc (vect_can_peel_nonlinear_iv_p):
            vect_step_op_neg isn't OK for partial vectors but only
            for unknown niter.
    
            * gcc.dg/vect/pr114485.c: New testcase.
    
    (cherry picked from commit 85621f98d245004a6c9787dde21e0acc17ab2c50)

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr114485.c | 18 ++++++++++++++++++
 gcc/tree-vect-loop-manip.cc          | 17 ++++++++++-------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr114485.c 
b/gcc/testsuite/gcc.dg/vect/pr114485.c
new file mode 100644
index 00000000000..6536806e350
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr114485.c
@@ -0,0 +1,18 @@
+#include "tree-vect.h"
+
+int b, c = 8, d;
+int e[23];
+int main()
+{
+  check_vect ();
+
+  int *h = e;
+  for (int i = 1; i < b + 21; i += 2)
+    {
+      c *= -1;
+      d = h[i] ? i : 0;
+    }
+  if (c != 8)
+    abort ();
+  return 0;
+}
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 767b19b15a1..9049a4b01e4 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1401,17 +1401,20 @@ vect_can_peel_nonlinear_iv_p (loop_vec_info loop_vinfo,
      For shift, when shift mount >= precision, there would be UD.
      For mult, don't known how to generate
      init_expr * pow (step, niters) for variable niters.
-     For neg, it should be ok, since niters of vectorized main loop
-     will always be multiple of 2.  */
-  if ((!LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
-       || !LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant ())
-      && induction_type != vect_step_op_neg)
+     For neg unknown niters are ok, since niters of vectorized main loop
+     will always be multiple of 2.
+     See also PR113163,  PR114196 and PR114485.  */
+  if (!LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant ()
+      || LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo)
+      || (!LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
+         && induction_type != vect_step_op_neg))
     {
       if (dump_enabled_p ())
        dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
                         "Peeling for epilogue is not supported"
-                        " for nonlinear induction except neg"
-                        " when iteration count is unknown.\n");
+                        " for this nonlinear induction"
+                        " when iteration count is unknown or"
+                        " when using partial vectorization.\n");
       return false;
     }