Fix EXTRACT_LAST_REDUCTION segfault

This code:

      /* Make sure we don't accidentally use the old condition.  */
      cond_expr = NULL_TREE;

was misplaced, since it triggered even when we needed to force the
original unmodified cond_expr into a mask temporary and then invert it.

2019-12-31  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-stmts.c (vectorizable_condition): Only nullify cond_expr
	if we've created a new condition.  Don't nullify it if we've decided
	to keep it and then invert the result.

gcc/testsuite/
	* gcc.dg/vect/vect-cond-reduc-6.c: New test.

From-SVN: r279804

gcc/ChangeLog

 2020-12-31  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* tree-vect-stmts.c (vectorizable_condition): Only nullify cond_expr
+	if we've created a new condition.  Don't nullify it if we've decided
+	to keep it and then invert the result.
+
+2020-12-31  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* tree-vect-loop-manip.c (create_lcssa_for_virtual_phi): Return
 	the incoming virtual operand definition.
 	(vect_do_peeling): When vectorizing an epilogue loop, handle the

gcc/testsuite/ChangeLog

 2020-12-31  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* gcc.dg/vect/vect-cond-reduc-6.c: New test.
+
+2020-12-31  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* gcc.dg/vect/vect-epilogues-2.c: New test.
 
 2019-12-30  Olivier Hainque  <hainque@adacore.com>

gcc/testsuite/gcc.dg/vect/vect-cond-reduc-6.c

+/* { dg-do compile } */
+
+int
+f (int *y)
+{
+  int res = 0;
+  for (int i = 0; i < 100; ++i)
+    res = (y[i] & 1) == 0 && (y[i] < 10) ? res : 1;
+  return res;
+}

gcc/tree-vect-stmts.c

@@ -10033,10 +10033,12 @@ vectorizable_condition (stmt_vec_info stmt_info, gimple_stmt_iterator *gsi,
 	  if (new_code == ERROR_MARK)
 	    must_invert_cmp_result = true;
 	  else
-	    cond_code = new_code;
+	    {
+	      cond_code = new_code;
+	      /* Make sure we don't accidentally use the old condition.  */
+	      cond_expr = NULL_TREE;
+	    }
 	}
-      /* Make sure we don't accidentally use the old condition.  */
-      cond_expr = NULL_TREE;
       std::swap (then_clause, else_clause);
     }