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Re: [PATCH] Remove basic_block->loop_depth
- From: Richard Guenther <rguenther at suse dot de>
- To: Ulrich Weigand <uweigand at de dot ibm dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 14 Aug 2012 12:48:21 +0200 (CEST)
- Subject: Re: [PATCH] Remove basic_block->loop_depth
- References: <201208141016.q7EAGHMF012074@d06av02.portsmouth.uk.ibm.com>
On Tue, 14 Aug 2012, Ulrich Weigand wrote:
> Richard Guenther wrote:
> > Accessing loop_depth (bb->loop_father) isn't very expensive. The
> > following removes the duplicate info in basic-blocks which is not
> > properly kept up-to-date at the moment.
> Looks like this broke SPU build, since spu_machine_dependent_reorg
> accesses ->loop_depth. According to comments in the code, this
> was done because of concerns that loop_father may no longer be set up
> this late in compilation, so I'm wondering whether just replacing
> this by loop_depth (bb->loop_father) would work here ...
Well, if loops are no longer set up (thus ->loop_father is NULL) then
the loop_depth information was stale and possibly wrong.
> /* If this branch is a loop exit then propagate to previous
> fallthru block. This catches the cases when it is a simple
> loop or when there is an initial branch into the loop. */
> if (prev && (loop_exit || simple_loop)
> && prev->loop_depth <= bb->loop_depth)
> prop = prev;
> /* If there is only one adjacent predecessor. Don't propagate
> outside this loop. This loop_depth test isn't perfect, but
> I'm not sure the loop_father member is valid at this point. */
> else if (prev && single_pred_p (bb)
> && prev->loop_depth == bb->loop_depth)
> prop = prev;
> Any suggestions?
If SPU md reorg would like to look at loop structures it should
compute them. Simply call flow_loops_find, which hopefully works
in CFG RTL mode (which I think is the mode available from md reorg?).
I was simply throwing away loops after RTL loop optimizers not only
because IRA for some weird reason decides to re-compute them in
non-standard ways and because loop verification fails between
ira / reload passes. So the other way would be to preserve loops
for a longer period.