RE: [PATCH][6/n] Merge from match-and-simplify, make forwprop fold all stmts

["Zhenqiang Chen" <zhenqiang.chen@arm.com>]

The patch leads to big regression for float operators on target without hard
fpu support due to register shuffle.

Please refer https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63743 for more
detail.

Thanks!
-Zhenqiang

> -----Original Message-----
> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
> owner@gcc.gnu.org] On Behalf Of Jeff Law
> Sent: Saturday, October 25, 2014 1:48 AM
> To: Richard Biener; gcc-patches@gcc.gnu.org
> Cc: Jakub Jelinek
> Subject: Re: [PATCH][6/n] Merge from match-and-simplify, make forwprop
> fold all stmts
> 
> On 10/24/14 07:16, Richard Biener wrote:
> >
> > This patch makes GIMPLE forwprop fold all statements, following
> > single-use SSA edges only (as suggested by Jeff and certainly how this
> > will regress the least until we replace manual simplification code
> > that does not restrict itself this way).
> >
> > forwprop is run up to 4 times at the moment (once only for -Og, not at
> > all for -O0), which still seems reasonable.  IMHO the forwprop pass
> > immediately after inlining is somewhat superfluous, it was added there
> > just for its ADDR_EXPR propagation.  We should eventually split this
> > pass into two.
> >
> > Note that just folding what we propagated into (like the SSA
> > propagators do during substitute-and-fold phase) will miss cases where
> > we propagate into a stmt feeding the one we could simplify.  Unless we
> > always fold all single-use (and their use) stmts we have to fold
> > everything from time to time.  Changing how / when we fold stuff is
> > certainly sth to look after with fold_stmt now being able to follow
> > SSA edges.
> >
> > Bootstrapped on x86_64-unknown-linux-gnu, testing still in progress.
> >
> >  From earlier testing I remember I need to adjust a few testcases that
> > don't expect the early folding - notably two strlenopt cases
> > (previously XFAILed but then PASSed again).
> >
> > I also expect to massage the single-use heuristic as I get to merging
> > the patterns I added for the various forwprop manual pattern matchings
> > to trunk (a lot of them do not restrict themselves this way).
> >
> > Does this otherwise look ok?
> >
> > Thanks,
> > Richard.
> >
> > 2014-10-24  Richard Biener  <rguenther@suse.de>
> >
> > 	* tree-ssa-forwprop.c: Include tree-cfgcleanup.h and
tree-into-ssa.h.
> > 	(lattice): New global.
> > 	(fwprop_ssa_val): New function.
> > 	(fold_all_stmts): Likewise.
> > 	(pass_forwprop::execute): Finally fold all stmts.
> Seems reasonable.  After all, we can iterate on the single-use heuristic.
> 
> jeff
>