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Re: [PATCH] Fix endless recursion in BIT_AND_EXPR folding (PR middle-end/40204)
- From: Richard Guenther <richard dot guenther at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 20 May 2009 23:03:15 +0200
- Subject: Re: [PATCH] Fix endless recursion in BIT_AND_EXPR folding (PR middle-end/40204)
- References: <20090520210145.GI5781@tyan-ft48-01.lab.bos.redhat.com>
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
>