[gcc r13-6503] tree-optimization/109025 - fixup double reduction detection

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

https://gcc.gnu.org/g:c1873079b05e399355eb79e4828ed9ba2d0c6968

commit r13-6503-gc1873079b05e399355eb79e4828ed9ba2d0c6968
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Mar 6 10:43:13 2023 +0100

    tree-optimization/109025 - fixup double reduction detection
    
    The following closes a gap in double reduction detection where we
    in the outer loop analysis fail to verify the inner LC PHI use is
    the latch definition of the inner loop PHI.  That latch definition
    is used to detect that an inner loop is part of a double reduction
    when later doing the inner loop analysis.
    
            PR tree-optimization/109025
            * tree-vect-loop.cc (vect_is_simple_reduction): Verify
            the inner LC PHI use is the inner loop PHI latch definition
            before classifying an outer PHI as double reduction.
    
            * gcc.dg/vect/pr109025.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr109025.c | 14 ++++++++++++++
 gcc/tree-vect-loop.cc                |  6 +++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr109025.c b/gcc/testsuite/gcc.dg/vect/pr109025.c
new file mode 100644
index 00000000000..13fb0ce4ba9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr109025.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3" } */
+
+int func_4(int t, int b)
+{
+  for (int tt1 = 0; tt1 < 128 ; tt1 ++)
+    {
+      for (int tt = 0; tt < 128; tt ++)
+	if (b)
+	  t |= 3;
+      t |= 3;
+    }
+  return t;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index b17e8745d3f..320c15f144b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -3894,6 +3894,8 @@ vect_is_simple_reduction (loop_vec_info loop_info, stmt_vec_info phi_info,
           return NULL;
         }
 
+      /* Verify there is an inner cycle composed of the PHI phi_use_stmt
+	 and the latch definition op1.  */
       gimple *def1 = SSA_NAME_DEF_STMT (op1);
       if (gimple_bb (def1)
 	  && flow_bb_inside_loop_p (loop, gimple_bb (def_stmt))
@@ -3901,7 +3903,9 @@ vect_is_simple_reduction (loop_vec_info loop_info, stmt_vec_info phi_info,
 	  && flow_bb_inside_loop_p (loop->inner, gimple_bb (def1))
 	  && (is_gimple_assign (def1) || is_gimple_call (def1))
 	  && is_a <gphi *> (phi_use_stmt)
-	  && flow_bb_inside_loop_p (loop->inner, gimple_bb (phi_use_stmt)))
+	  && flow_bb_inside_loop_p (loop->inner, gimple_bb (phi_use_stmt))
+	  && (op1 == PHI_ARG_DEF_FROM_EDGE (phi_use_stmt,
+					    loop_latch_edge (loop->inner))))
         {
           if (dump_enabled_p ())
             report_vect_op (MSG_NOTE, def_stmt,