[PATCH, v2] (9e) Update "startwith" logic for pass-skipping to handle __RTL functions
David Malcolm
dmalcolm@redhat.com
Fri Jan 20 14:57:00 GMT 2017
On Fri, 2017-01-20 at 09:06 +0100, Richard Biener wrote:
> On Thu, Jan 19, 2017 at 6:22 PM, David Malcolm <dmalcolm@redhat.com>
> wrote:
> > On Mon, 2017-01-16 at 14:42 -0700, Jeff Law wrote:
> > > On 01/09/2017 07:38 PM, David Malcolm wrote:
> > > > gcc/ChangeLog:
> > > > * passes.c: Include "insn-addr.h".
> > > > (should_skip_pass_p): Add logging. Update logic for
> > > > running
> > > > "expand" to be compatible with both __GIMPLE and __RTL.
> > > > Guard
> > > > property-provider override so it is only done for gimple
> > > > passes.
> > > > Don't skip dfinit.
> > > > (skip_pass): New function.
> > > > (execute_one_pass): Call skip_pass when skipping passes.
> > > > ---
> > > > gcc/passes.c | 65
> > > > +++++++++++++++++++++++++++++++++++++++++++++++++++++-------
> > > > 1 file changed, 58 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/gcc/passes.c b/gcc/passes.c
> > > > index 31262ed..6954d1e 100644
> > > > --- a/gcc/passes.c
> > > > +++ b/gcc/passes.c
> > > > @@ -59,6 +59,7 @@ along with GCC; see the file COPYING3. If
> > > > not
> > > > see
> > > > #include "cfgrtl.h"
> > > > #include "tree-ssa-live.h" /* For remove_unused_locals. */
> > > > #include "tree-cfgcleanup.h"
> > > > +#include "insn-addr.h" /* for INSN_ADDRESSES_ALLOC. */
> > > insn-addr? Yuk.
> > >
> > >
> > > >
> > > > using namespace gcc;
> > > >
> > > > @@ -2315,26 +2316,73 @@ should_skip_pass_p (opt_pass *pass)
> > > > if (!cfun->pass_startwith)
> > > > return false;
> > > >
> > > > - /* We can't skip the lowering phase yet -- ideally we'd
> > > > - drive that phase fully via properties. */
> > > > - if (!(cfun->curr_properties & PROP_ssa))
> > > > - return false;
> > > > + /* For __GIMPLE functions, we have to at least start when we
> > > > leave
> > > > + SSA. */
> > > > + if (pass->properties_destroyed & PROP_ssa)
> > > > + {
> > > > + if (!quiet_flag)
> > > > + fprintf (stderr, "starting anyway when leaving SSA: %s\n",
> > > > pass->name);
> > > > + cfun->pass_startwith = NULL;
> > > > + return false;
> > > > + }
> > > This seems to need a comment -- it's not obvious how destroying
> > > the
> > > SSA
> > > property maps to a pass that can not be skipped.
> >
> > Added:
> >
> > /* For __GIMPLE functions, we have to at least start when we
> > leave
> > SSA. Hence, we need to detect the "expand" pass, and stop
> > skipping
> > when we encounter it. A cheap way to identify "expand" is it
> > to
> > detect the destruction of PROP_ssa.
> > For __RTL functions, we invoke "rest_of_compilation" directly,
> > which
> > is after "expand", and hence we don't reach this conditional.
> > */
> >
> > > > - /* And also run any property provider. */
> > > > - if (pass->properties_provided != 0)
> > > > + /* Run any property provider. */
> > > > + if (pass->type == GIMPLE_PASS
> > > > + && pass->properties_provided != 0)
> > > > return false;
> > > So comment needed here too. I read this as "if a gimple pass
> > > provides a
> > > property then it should not be skipped. Which means that an RTL
> > > pass
> > > that provides a property can?
> >
> > Added:
> >
> > /* For GIMPLE passes, run any property provider (but continue
> > skipping
> > afterwards).
> > We don't want to force running RTL passes that are property
> > providers:
> > "expand" is covered above, and the only pass other than
> > "expand" that
> > provides a property is "into_cfglayout" (PROP_cfglayout),
> > which does
> > too much for a dumped __RTL function. */
> >
> > ...the problem being that into_cfglayout's execute vfunc calls
> > cfg_layout_initialize, which does a lot more that just
> > cfg_layout_rtl_register_cfg_hooks (the skip hack does just the
> > latter).
> >
> > > > + /* Don't skip df init; later RTL passes need it. */
> > > > + if (strstr (pass->name, "dfinit") != NULL)
> > > > + return false;
> > > Which seems like a failing in RTL passes saying they need DF
> > > init.
> >
> > There isn't a "PROP_df"; should there be?
> > Or is this hack accepable?
> >
> > > > +/* Skip the given pass, for handling passes before "startwith"
> > > > + in __GIMPLE and__RTL-marked functions.
> > > > + In theory, this ought to be a no-op, but some of the RTL
> > > > passes
> > > > + need additional processing here. */
> > > > +
> > > > +static void
> > > > +skip_pass (opt_pass *pass)
> > > ...
> > > This all feels like a failing in how we handle state in the RTL
> > > world.
> > > And I suspect it's prone to error. Imagine if I'm hacking on
> > > something
> > > in the RTL world and my code depends on something else being set
> > > up.
> > > I
> > > really ought to have a way within my pass to indicate what I
> > > depend
> > > on.
> > > Having it hidden away in passes.c makes it easy to miss/forget.
> >
> > Indeed, it's a hack. I preferred the vfunc idea, but Richi prefers
> > to keep it all in one place.
> >
> > > > +{
> > > > + /* Pass "reload" sets the global "reload_completed", and
> > > > many
> > > > + things depend on this (e.g. instructions in .md files).
> > > > */
> > > > + if (strcmp (pass->name, "reload") == 0)
> > > > + reload_completed = 1;
> > > Seems like this ought to be a property provided by LRA/reload.
> >
> > If we have a __RTL function with a "startwith" of a pass after
> > reload,
> > we don't want to run "reload" when iterating through the pass list
> > to
> > reach the start pass, since presumably it could change the insns.
> > So
> > if LRA/reload provide a property, say PROP_reload_completed, we'd
> > still
> > need a way to *not* run reload, whilst setting the reload_completed
> > global. So I don't think that a property necessarily buys us much
> > here (it'd still be a hack either way...).
> >
> > Or is your observation more about having a way to identify the pass
> > without doing a strcmp?
> >
> > > > +
> > > > + /* The INSN_ADDRESSES vec is normally set up by
> > > > + shorten_branches; set it up for the benefit of passes
> > > > that
> > > > + run after this. */
> > > > + if (strcmp (pass->name, "shorten") == 0)
> > > > + INSN_ADDRESSES_ALLOC (get_max_uid ());
> > > Similarly ought to be provided by shorten-branches
> >
> > Similar to the reload_completed discussion above.
> >
> >
> > > > +
> > > > + /* Update the cfg hooks as appropriate. */
> > > > + if (strcmp (pass->name, "into_cfglayout") == 0)
> > > > + {
> > > > + cfg_layout_rtl_register_cfg_hooks ();
> > > > + cfun->curr_properties |= PROP_cfglayout;
> > > > + }
> > > > + if (strcmp (pass->name, "outof_cfglayout") == 0)
> > > > + {
> > > > + rtl_register_cfg_hooks ();
> > > > + cfun->curr_properties &= ~PROP_cfglayout;
> > > > + }
> > > > +}
> > > This feels somewhat different, but still a hack.
> > >
> > > I don't have strong suggestions on how to approach this, but what
> > > we've
> > > got here feels like a hack and one prone to bitrot.
> >
> > Given that Richi seems to prefer the "contain it all in once place"
> > to the virtual function idea, there's not much more I can offer to
> > fix it.
> >
> > Updated version of the patch attached (just adding the missing
> > comments)
> >
> > Is this version OK?
>
> Ok.
>
> Richard.
[...snip...]
Thanks.
Current status of the RTL "frontend" is that patches 1-8 are in trunk,
so that we're building the code for reading RTL dumps, but patch 9 (the
code to wire that up to cc1 with "__RTL" so that it's actually usable
from DejaGnu) isn't.
I believe the only remaining part of patch 9 that hasn't been approved
yet is:
"[PATCH 9f] Add a way for the C frontend to compile __RTL-tagged
functions"
https://gcc.gnu.org/ml/gcc-patches/2017-01/msg00590.html
Richi: if that patch is approved, are you OK with patch 9 in early
stage 4?
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