Re: [PATCH] Fix PR 63748

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Nov 10, 2014 at 2:33 AM, Patrick Palka <patrick@parcs.ath.cx>
wrote:
> PR 63748 reports a false-positive uninitialized warning under the
> presence of abnormal edges.  The statements for which the uninitialized
> warnings are emitted all look like:
>
>   buf_117(ab) = buf_317(D)(ab);
>
> This PR is similar to PR 57287 which also reports false-positive
> uninitialized warnings under the presence of abnormal edges.  That PR
> fixed the reported issue by allowing to propagate default definitions
> which appear in abnormal PHI nodes.  That is, it allowed propagating the
> following kinds of copies:
>
>   buf_24 = buf_16(D)(ab);
>
> But it still did not allow propagating copies whose destination operand
> occurs in an abnormal PHI node.  To fix PR 63748, this patch extends the
> fix to PR 57287 to allow propagating such copies too.

Thus you allow

   buf_24(ab) = buf_16(D)(ab);

to be propagated.

This is only valid if you propagate into all uses of buf_24(ab) as otherwise
you create overlapping life-ranges with the default definition.  Which
may be a moot issue now as Marcs patch to ignore undefined SSA names
in the out-of-SSA live compute, thus ...

> Full bootstrap + regtesting on x86_64-unknown-linux-gnu is in progress.
> Is this patch OK if testing succeeds with no new regressions?

... ok.  But please watch for fallout.

Thanks,
Richard.

> 2014-11-10  Patrick Palka  <ppalka@gcc.gnu.org>
>
> gcc/
>         PR middle-end/63748
>         * tree-ssa-propagate.c (may_propagate_copy): Allow propagating
>         SSA copies whose source and destination names both occur in
>         abnormal edges.
>
> gcc/testsuite/
>         PR middle-end/63748
>         * gcc.dg/pr63748.c: New testcase.
> ---
>  gcc/testsuite/gcc.dg/pr63748.c | 36 ++++++++++++++++++++++++++++++++++++
>  gcc/tree-ssa-propagate.c       | 27 +++++++++++++++------------
>  2 files changed, 51 insertions(+), 12 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/pr63748.c
>
> diff --git a/gcc/testsuite/gcc.dg/pr63748.c b/gcc/testsuite/gcc.dg/pr63748.c
> new file mode 100644
> index 0000000..2e50445
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr63748.c
> @@ -0,0 +1,36 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wall" } */
> +
> +#include <setjmp.h>
> +
> +jmp_buf *alloc_jmp_buf ();
> +int foo (void *);
> +
> +int
> +test (int op, int noside)
> +{
> +  void *argvec = 0;
> +
> +  if (op)
> +    {
> +      jmp_buf *buf = alloc_jmp_buf (); /* { dg-bogus "uninitialized" } */
> +      setjmp (*buf);
> +
> +      if (noside)
> +        goto nosideret;
> +
> +    do_call_it:
> +
> +      if (noside)
> +        goto nosideret;
> +
> +      return foo (argvec);
> +    }
> +
> +  argvec = __builtin_alloca (1);
> +  goto do_call_it;
> +
> +nosideret:
> +  return 1;
> +}
> +
> diff --git a/gcc/tree-ssa-propagate.c b/gcc/tree-ssa-propagate.c
> index 9f4d381..9e61baf 100644
> --- a/gcc/tree-ssa-propagate.c
> +++ b/gcc/tree-ssa-propagate.c
> @@ -1275,21 +1275,24 @@ may_propagate_copy (tree dest, tree orig)
>    tree type_d = TREE_TYPE (dest);
>    tree type_o = TREE_TYPE (orig);
>
> -  /* If ORIG flows in from an abnormal edge, it cannot be propagated.  */
> +  /* If ORIG is a default definition which flows in from an abnormal edge
> +     then the copy can be propagated.  It is important that we do so to avoid
> +     uninitialized regular copies.  */
>    if (TREE_CODE (orig) == SSA_NAME
>        && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig)
> -      /* If it is the default definition and an automatic variable then
> -         we can though and it is important that we do to avoid
> -        uninitialized regular copies.  */
> -      && !(SSA_NAME_IS_DEFAULT_DEF (orig)
> -          && (SSA_NAME_VAR (orig) == NULL_TREE
> -              || TREE_CODE (SSA_NAME_VAR (orig)) == VAR_DECL)))
> +      && SSA_NAME_IS_DEFAULT_DEF (orig)
> +      && (SSA_NAME_VAR (orig) == NULL_TREE
> +         || TREE_CODE (SSA_NAME_VAR (orig)) == VAR_DECL))
> +    ;
> +  /* Otherwise if ORIG just flows in from an abnormal edge then the copy cannot
> +     be propagated.  */
> +  else if (TREE_CODE (orig) == SSA_NAME
> +          && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
>      return false;
> -
> -  /* If DEST is an SSA_NAME that flows from an abnormal edge, then it
> -     cannot be replaced.  */
> -  if (TREE_CODE (dest) == SSA_NAME
> -      && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))
> +  /* Similarly if DEST flows in from an abnormal edge then the copy cannot be
> +     propagated.  */
> +  else if (TREE_CODE (dest) == SSA_NAME
> +          && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))
>      return false;
>
>    /* Do not copy between types for which we *do* need a conversion.  */
> --
> 2.2.0.rc0.18.ga1ad247
>