Fix combine_blocks (PR tree-optimization/48975)

Hi!

combine_blocks at the end removes most of the bbs, keeps around just
loop header, maybe latch and maybe exit_bb.  We need to free bb->aux
through free_bb_predicate, but that is done in the caller, using array of
(former) loop bbs, with the new loop->num_nodes count (at most 3).
While that properly frees bb->aux for loop->header, it might very well
access bb->aux of deleted bbs and free that, for most of the deleted
bbs will leak memory and might keep around bb->aux for latch and/or exit_bb
(which is incorrect as following passes expect that bb->aux is NULL upon
entry - shouldn't we with ENABLE_CHECKING verify bb->aux is NULL after
every pass instead of just testing it at the beginning of a couple of
passes?).  Fixed by calling free_bb_predicate already before deleting
any bbs, for all bbs in the loop, and making sure the caller doesn't do it
again.

Bootstrapped/regtested on x86_64linux and i686-linux, ok for trunk?

2011-05-12  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/48975
	* tree-if-conv.c (combine_blocks): Call free_bb_predicate
	on all bbs here and free and clear ifc_bbs at the end.

	* gcc.dg/pr48975.c: New test.


	Jakub

On Thu, May 12, 2011 at 4:42 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> combine_blocks at the end removes most of the bbs, keeps around just
> loop header, maybe latch and maybe exit_bb.  We need to free bb->aux
> through free_bb_predicate, but that is done in the caller, using array of
> (former) loop bbs, with the new loop->num_nodes count (at most 3).
> While that properly frees bb->aux for loop->header, it might very well
> access bb->aux of deleted bbs and free that, for most of the deleted
> bbs will leak memory and might keep around bb->aux for latch and/or exit_bb
> (which is incorrect as following passes expect that bb->aux is NULL upon
> entry - shouldn't we with ENABLE_CHECKING verify bb->aux is NULL after
> every pass instead of just testing it at the beginning of a couple of
> passes?).

I think verify_flow might be a good place to check this.

>  Fixed by calling free_bb_predicate already before deleting
> any bbs, for all bbs in the loop, and making sure the caller doesn't do it
> again.
>
> Bootstrapped/regtested on x86_64linux and i686-linux, ok for trunk?

Ok.

Thanks,
Richard.

> 2011-05-12  Jakub Jelinek  <jakub@redhat.com>
>
>        PR tree-optimization/48975
>        * tree-if-conv.c (combine_blocks): Call free_bb_predicate
>        on all bbs here and free and clear ifc_bbs at the end.
>
>        * gcc.dg/pr48975.c: New test.
>
> --- gcc/tree-if-conv.c.jj       2011-05-02 18:39:28.000000000 +0200
> +++ gcc/tree-if-conv.c  2011-05-12 12:20:33.000000000 +0200
> @@ -1637,6 +1637,7 @@ combine_blocks (struct loop *loop)
>   for (i = 0; i < orig_loop_num_nodes; i++)
>     {
>       bb = ifc_bbs[i];
> +      free_bb_predicate (bb);
>       if (bb_with_exit_edge_p (loop, bb))
>        {
>          exit_bb = bb;
> @@ -1712,6 +1713,9 @@ combine_blocks (struct loop *loop)
>       && exit_bb != loop->header
>       && can_merge_blocks_p (loop->header, exit_bb))
>     merge_blocks (loop->header, exit_bb);
> +
> +  free (ifc_bbs);
> +  ifc_bbs = NULL;
>  }
>
>  /* If-convert LOOP when it is legal.  For the moment this pass has no
> --- gcc/testsuite/gcc.dg/pr48975.c.jj   2011-05-12 12:23:59.000000000 +0200
> +++ gcc/testsuite/gcc.dg/pr48975.c      2011-05-12 12:23:51.000000000 +0200
> @@ -0,0 +1,18 @@
> +/* PR tree-optimization/48975 */
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -ffast-math -fno-tree-slp-vectorize" } */
> +
> +static int
> +foo (int x)
> +{
> +  return (x > 0) ? 0 : x + 1;
> +}
> +
> +void
> +bar (unsigned int x)
> +{
> +  int l = 1;
> +lab:
> +  while (x)
> +    x = foo (x);
> +}
>
>        Jakub
>