[Bug middle-end/38533] [4.2/4.3/4.4 regression] tree-ssa-reassoc.c increases register pressure several times

["dberlin at dberlin dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #4 from dberlin at gcc dot gnu dot org  2008-12-16 17:00 -------
Subject: Re:  [4.2/4.3/4.4 regression] tree-ssa-reassoc.c increases register
pressure several times

Yes, that looks like a bug.
There are also numerous ways in which the placement can be improved.
A few people had talked about rewriting it to be a balanced tree
placement, etc, so i've never bothered to do even the small cleanups.
If you want to change placement, go for it.
:)

On Tue, Dec 16, 2008 at 11:57 AM, jakub at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #3 from jakub at gcc dot gnu dot org  2008-12-16 16:57 -------
> In particular, the problem is in linearize_expr_tree.  The |s are already
> perfectly linearized (in all but the innermost recursive linearize_expr_tree
> binlhsisreassoc is 1 and binrhsisreassoc is 0, in the innermost both are 0),
> yet:
> 1645  gsinow = gsi_for_stmt (stmt);
> 1646  gsilhs = gsi_for_stmt (SSA_NAME_DEF_STMT (binlhs));
> 1647  gsi_move_before (&gsilhs, &gsinow);
> moves all of them to one spot.  Couldn't that moving be deferred till we
> actually know it is worthwhile to reassociate something, not blindly just in
> case something will be needed?
>
>
> --
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38533
>
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38533