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.

diff --git a/gcc/testsuite/gcc.dg/vect/pr99253.c b/gcc/testsuite/gcc.dg/vect/pr99253.c
new file mode 100644 (file)
index 0000000..9e33450
--- /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 27845c0..3e973e7 100644 (file)
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -3432,34 +3432,6 @@ 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)
        {
@@ -3489,6 +3461,34 @@ 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;
 }