[PATCH] Fix endless recursion in BIT_AND_EXPR folding (PR middle-end/40204)

Richard Guenther richard.guenther@gmail.com
Wed May 20 21:03:00 GMT 2009


On Wed, May 20, 2009 at 11:01 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> On the attached testcase we endlessly recurse between fold_binary
> (BIT_AND_EXPR, ...) and fold_build2 (BIT_AND_EXPR, ...).  The problem
> is in the PR29749 optimization, if op1 has a smaller precision type,
> newmask might be different from mask, yet build_int_cst_type
> might strip the extra bits again, yielding identical constant as arg1.
>
> Fixed by checking for this and not recursing in that case.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk/4.4?

Ok.

Thanks,
Richard.

> 2009-05-20  Jakub Jelinek  <jakub@redhat.com>
>
>        PR middle-end/40204
>        * fold-const.c (fold_binary) <case BIT_AND_EXPR>: Avoid infinite
>        recursion if build_int_cst_type returns the same INTEGER_CST as
>        arg1.
>
>        * gcc.c-torture/compile/pr40204.c: New test.
>
> --- gcc/fold-const.c.jj 2009-05-19 10:51:32.000000000 +0200
> +++ gcc/fold-const.c    2009-05-20 18:18:04.000000000 +0200
> @@ -11375,6 +11375,8 @@ fold_binary (enum tree_code code, tree t
>              if (prec < HOST_BITS_PER_WIDE_INT
>                  || newmask == ~(unsigned HOST_WIDE_INT) 0)
>                {
> +                 tree newmaskt;
> +
>                  if (shift_type != TREE_TYPE (arg0))
>                    {
>                      tem = fold_build2 (TREE_CODE (arg0), shift_type,
> @@ -11385,9 +11387,9 @@ fold_binary (enum tree_code code, tree t
>                    }
>                  else
>                    tem = op0;
> -                 return fold_build2 (BIT_AND_EXPR, type, tem,
> -                                     build_int_cst_type (TREE_TYPE (op1),
> -                                                         newmask));
> +                 newmaskt = build_int_cst_type (TREE_TYPE (op1), newmask);
> +                 if (!tree_int_cst_equal (newmaskt, arg1))
> +                   return fold_build2 (BIT_AND_EXPR, type, tem, newmaskt);
>                }
>            }
>        }
> --- gcc/testsuite/gcc.c-torture/compile/pr40204.c.jj    2009-05-20 18:20:41.000000000 +0200
> +++ gcc/testsuite/gcc.c-torture/compile/pr40204.c       2009-05-20 18:20:19.000000000 +0200
> @@ -0,0 +1,14 @@
> +/* PR middle-end/40204 */
> +
> +struct S
> +{
> +  unsigned int a : 4;
> +  unsigned int b : 28;
> +} s;
> +char c;
> +
> +void
> +f (void)
> +{
> +  s.a = (c >> 4) & ~(1 << 4);
> +}
>
>        Jakub
>



More information about the Gcc-patches mailing list