From: Richard Biener <rguenther@suse.de>
Date: Mon, 6 Mar 2023 09:43:13 +0000 (+0100)
Subject: tree-optimization/109025 - fixup double reduction detection
X-Git-Tag: basepoints/gcc-14~704
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c1873079b05e399355eb79e4828ed9ba2d0c6968;p=thirdparty%2Fgcc.git

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 --git a/gcc/testsuite/gcc.dg/vect/pr109025.c b/gcc/testsuite/gcc.dg/vect/pr109025.c
new file mode 100644
index 000000000000..13fb0ce4ba98
--- /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 b17e8745d3fb..320c15f144ba 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,