On Wed, 26 Aug 2020, Jeff Law wrote:
> On Tue, 2020-08-25 at 23:58 -0400, Hans-Peter Nilsson wrote:
> > On Mon, 24 Aug 2020, Jeff Law via Gcc wrote:
> > > On Thu, 2020-08-20 at 21:36 +0530, Senthil Kumar Selvaraj via Gcc wrote:
> > > > The post-reload splitter introduces the clobber. The wiki
> > > > suggests that approach if most insns clobber REG_CC, perhaps because of
> > > > the missed optimizations you describe below?
> > > If most patterns set/clobber the flags, then yes, it's slightly better to
> > > only
> > > expose them after reload. Various passes that directly grub through RTL
> > > rather
> > > than using helpers like single_set will optimize things better.
> >
> > The "slightly" being omissions like the one fixed in combine.c
> > last month. ;-) There's one in reload too ("Discard obvious
> > no-ops, even without -O"), but it seems to be acting the other
> > way(!)
> Yea, this is the kind of thing I'm thinking of when I say "slightly".
JFTR, I'd like to stress that point: contrary to my initial
fears, my experience with the CRIS de-cc0ration is that the
straight-set insn assumptions in gcc are few and far-between
enough to be ignored as a factor regarding missed optimizations,
when picking a strategy.
brgds, H-P
