[Bug tree-optimization/34677] PREs insert_fake_stores is mostly useless

[dberlin at dberlin dot org]

------- Comment #4 from dberlin at gcc dot gnu dot org  2008-01-04 17:31 -------
Subject: Re:  PREs insert_fake_stores is mostly useless

FRE will handle DECL's, and VN will value number them.
I've made small attempts at make PRE work with globals, but i'm lazy
and haven't done it for real yet :)
It is trickier than it would initially seem.

On 4 Jan 2008 17:00:21 -0000, rguenth at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #2 from rguenth at gcc dot gnu dot org  2008-01-04 17:00 -------
> The plain DECL does not work because
>
>   1) we don't do the storetmp
>   2) can_PRE_operation and can_value_number_operation return false (so we
>      do not enter a into EXP_GEN
>   3) create_value_expr_from cannot handle it
>
> most of the rest of PRE looks like it may handle DECLs, but if you fix the
> above, vn_lookup_with_vuses still not finds VH.10, because it is not ANTIC_IN.
>
>
>
> --
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34677
>
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-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34677