From: Richard Biener <rguenther@suse.de>
Date: Thu, 25 Feb 2021 08:36:33 +0000 (+0100)
Subject: tree-optimization/99253 - fix reduction path check
X-Git-Tag: releases/gcc-10.3.0~217
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=65767abfdc07547b5435083a5af6ab085e013a4d;p=thirdparty%2Fgcc.git

tree-optimization/99253 - fix reduction path check

This fixes an ordering problem with verifying that no intermediate
computations in a reduction path are used outside of the chain.  The
check was disabled for value-preserving conversions at the tail
but whether a stmt was a conversion or not was only computed after
the first use.  The following fixes this by re-ordering things
accordingly.

2021-02-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/99253
	* tree-vect-loop.c (check_reduction_path): First compute
	code, then verify out-of-loop uses.

	* gcc.dg/vect/pr99253.c: New testcase.

(cherry picked from commit 1193d05465acd39b6e3c7095274d8351a1e2cd44)
---

diff --git a/gcc/testsuite/gcc.dg/vect/pr99253.c b/gcc/testsuite/gcc.dg/vect/pr99253.c
new file mode 100644
index 000000000000..9e3345025bab
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr99253.c
@@ -0,0 +1,22 @@
+/* { dg-do run } */
+
+#include "tree-vect.h"
+
+int a = 0;
+static int b = 0;
+long c = 0;
+
+int
+main()
+{
+  check_vect ();
+  for (int d = 0; d < 8; d++)
+    {
+      a ^= c;
+      b = a;
+      a ^= 1;
+    }
+  if (a != 0 || b != 1)
+    __builtin_abort();
+  return 0;
+}
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index cfeeac5f84e2..899b56087451 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -3030,34 +3030,6 @@ pop:
 	  fail = true;
 	  break;
 	}
-      /* Check there's only a single stmt the op is used on.  For the
-	 not value-changing tail and the last stmt allow out-of-loop uses.
-	 ???  We could relax this and handle arbitrary live stmts by
-	 forcing a scalar epilogue for example.  */
-      imm_use_iterator imm_iter;
-      gimple *op_use_stmt;
-      unsigned cnt = 0;
-      FOR_EACH_IMM_USE_STMT (op_use_stmt, imm_iter, op)
-	if (!is_gimple_debug (op_use_stmt)
-	    && (*code != ERROR_MARK
-		|| flow_bb_inside_loop_p (loop, gimple_bb (op_use_stmt))))
-	  {
-	    /* We want to allow x + x but not x < 1 ? x : 2.  */
-	    if (is_gimple_assign (op_use_stmt)
-		&& gimple_assign_rhs_code (op_use_stmt) == COND_EXPR)
-	      {
-		use_operand_p use_p;
-		FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
-		  cnt++;
-	      }
-	    else
-	      cnt++;
-	  }
-      if (cnt != 1)
-	{
-	  fail = true;
-	  break;
-	}
       tree_code use_code = gimple_assign_rhs_code (use_stmt);
       if (use_code == MINUS_EXPR)
 	{
@@ -3087,6 +3059,34 @@ pop:
 	  fail = true;
 	  break;
 	}
+      /* Check there's only a single stmt the op is used on.  For the
+	 not value-changing tail and the last stmt allow out-of-loop uses.
+	 ???  We could relax this and handle arbitrary live stmts by
+	 forcing a scalar epilogue for example.  */
+      imm_use_iterator imm_iter;
+      gimple *op_use_stmt;
+      unsigned cnt = 0;
+      FOR_EACH_IMM_USE_STMT (op_use_stmt, imm_iter, op)
+	if (!is_gimple_debug (op_use_stmt)
+	    && (*code != ERROR_MARK
+		|| flow_bb_inside_loop_p (loop, gimple_bb (op_use_stmt))))
+	  {
+	    /* We want to allow x + x but not x < 1 ? x : 2.  */
+	    if (is_gimple_assign (op_use_stmt)
+		&& gimple_assign_rhs_code (op_use_stmt) == COND_EXPR)
+	      {
+		use_operand_p use_p;
+		FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
+		  cnt++;
+	      }
+	    else
+	      cnt++;
+	  }
+      if (cnt != 1)
+	{
+	  fail = true;
+	  break;
+	}
     }
   return ! fail && ! neg && *code != ERROR_MARK;
 }