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[Bug tree-optimization/54146] Very slow compile with attribute((flatten))
- From: "stevenb.gcc at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 06 Aug 2012 09:09:02 +0000
- Subject: [Bug tree-optimization/54146] Very slow compile with attribute((flatten))
- Auto-submitted: auto-generated
- References: <bug-54146-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54146
--- Comment #20 from stevenb.gcc at gmail dot com <stevenb.gcc at gmail dot com> 2012-08-06 09:09:02 UTC ---
On Mon, Aug 6, 2012 at 10:45 AM, rguenth at gcc dot gnu.org
<gcc-bugzilla@gcc.gnu.org> wrote:
> Ick, I suppose similar issues exist on the tree level for passes that
> think that memory / compile-time usage O(number-of-ssa-names or basic-blocks)
> is "ok" (and I suppose it really _is_ ok ...?)
I think this is OK, yes. In general, anything linear in some measure
of the function should be OK.
NB, this thing in ifcvt is *not* O(max_reg_num()) but
O(max_reg_num()*n_basic_blocks).
I suspect that in the tree optimizers, a non-linear issue exists for
rewriting into loop-closed SSA form. It looks like it is
O(num_ssa_names*n_basic_blocks). I'm trying to confirm that (in my
evening free time, so don't hold your breath ;-).