On Mon, 2019-11-25 at 16:47 -0600, Segher Boessenkool wrote:
>
> > > - sh (that's sh4-linux):
> > >
> > > /home/segher/src/kernel/net/ipv4/af_inet.c: In function
> > > 'snmp_get_cpu_field':
> > > /home/segher/src/kernel/net/ipv4/af_inet.c:1638:1: error: unable to find
> > > a register to spill in class 'R0_REGS'
> > > 1638 | }
> > > | ^
> > > /home/segher/src/kernel/net/ipv4/af_inet.c:1638:1: error: this is the
> > > insn:
> > > (insn 18 17 19 2 (set (reg:SI 0 r0)
> > > (mem:SI (plus:SI (reg:SI 4 r4 [178])
> > > (reg:SI 6 r6 [171])) [17 *_3+0 S4 A32]))
> > > "/home/segher/src/kernel/net/ipv4/af_inet.c":1638:1 188 {movsi_i}
> > > (expr_list:REG_DEAD (reg:SI 4 r4 [178])
> > > (expr_list:REG_DEAD (reg:SI 6 r6 [171])
> > > (nil))))
> > > /home/segher/src/kernel/net/ipv4/af_inet.c:1638: confused by earlier
> > > errors, bailing out
> >
> > Would have to look more at this one. Seems odd that it can't allocate
> > R0 when it's already the destination and when R0 can't be live before
> > the insn. But there again, this is reload, so my enthuasiasm for looking
> > is a bit limited :-)
>
> It wants to use r0 in some other insn, so it needs to spill it here, but
> cannot. This is what class_likely_spilled is for.
>
Hmm ... the R0 problem ... SH doesn't override class_likely_spilled
explicitly, but it's got a R0_REGS class with only one said reg in it.
So the default impl of class_likely_spilled should do its thing.
LRA is available on SH and often fixes the R0 problems -- but not
always. Maybe it got better over time, haven't checked.
Could you re-run the SH build tests with -mlra, please ?
Cheers,
Oleg
