[PATCH] tree-optimization/109025 - fixup double reduction detection

[PATCH] tree-optimization/109025 - fixup double reduction detection

[Richard Biener]

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.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	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.
---
 gcc/testsuite/gcc.dg/vect/pr109025.c | 14 ++++++++++++++
 gcc/tree-vect-loop.cc                |  6 +++++-
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr109025.c

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,
-- 
2.35.3