On Wed, 2020-04-22 at 12:26 -0600, Jeff Law wrote:
> On Fri, 2020-04-10 at 16:40 -0500, will schmidt via Gcc-patches
> wrote:
> > [RFC][PR target/90000] Compile time hog w/impossible asm constraint
> > lra loop
> >
> > Hi,
> > RFC for a bandaid/patch to partially address target PR/90000.
> >
> > This adds an escape condition from the forever loop where
> > LRA gets stuck while attempting to handle constraints from an
> > instruction that has previously suffered an impossible constraint
> > error.
> >
> > This is somewhat inspired by MAX_RELOAD_INSNS_NUMBER as
> > seen in lra-constraints.c lra_constraints(). This utilizes the
> > existing counter variable lra_constraint_iter.
> >
> > More needs to be done here, as this does replace a spin-forever
> > situation with an ICE.
> >
> > Thanks
> > -Will
> >
> >
> > gcc/
> > 2020-04-10 Will Schmidt <will_schm...@vnet.ibm.com>
> >
> > * lra.c: Add include of rtl-error.h.
> > (MAX_LRA_CONSTRAINT_PASSES): New define.
> > (lra): Add check of lra_constraint_iter value.
>
> Doesn't this argue that there's some other datastructure that needs
> to be updated
> when we removed the impossible asm?
Yes, i think so. I'm just not sure exactly what or where.
The submitted patch is minimally allowing for manageable-in-size reload
dumps for my continued debug. :-)
There is an old patch that addressed what looks like a similar issue,
but i wasn't able to directly apply that to this situation without
failing in other places.
>commit e86c0101ae59b32c3f10edcca78398cbf8848eaa
>Author: Steven Bosscher <ste...@gcc.gnu.org>
>Date: Thu Jan 24 10:30:26 2013 +0000
> re PR inline-asm/55934 (LRA inline asm error recovery)
Which does a bit more, but at it's core is this:
+ PATTERN (insn) = gen_rtx_USE (VOIDmode, const0_rtx);
+ lra_set_insn_deleted (insn);
I suspect this particular scenario with the testcase is a dependency across
several 'insns', so marking just one as deleted is not enough.
(but i'm not sure,..
void foo (void)
{
register float __attribute__ ((mode(SD))) r31 __asm__ ("r31");
register float __attribute__ ((mode(SD))) fr1 __asm__ ("fr1");
__asm__ ("#" : "=d" (fr1));
r31 = fr1;
__asm__ ("#" : : "r" (r31));
}
thanks
-Will
>
> Jeff
> >
>
>
