https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38629
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
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Assignee|hubicka at gcc dot gnu.org |unassigned at gcc dot
gnu.org
--- Comment #10 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #9)
> (In reply to Jan Hubicka from comment #6)
> > OK, at -Os the issue is that function is called once so inlining is a win.
> > Making multiple copies of it leads to GCC making clone:
> > delay_wait_us_ms.constprop.0:
> > .LFB3:
> > movl $136, %edi
> > jmp delay_wait_us
> > .LFE3:
> > and then calling it
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > call delay_wait_us_ms.constprop.0
> > at -Os,that is
> >
> > With -O2 it is different story, we end up inlining everything. We get:
> > Analyzing function body size: delay_wait_us
> > freq: 1000 size: 1 time: 1 __asm__ __volatile__("wdr");
> > freq: 1000 size: 1 time: 1 MEM[(volatile unsigned char *)82B] ={v}
> > timeout_2(D);
> > freq: 1000 size: 1 time: 1 D.2719_5 ={v} MEM[(volatile unsigned char
> > *)88B];
> > freq: 1000 size: 1 time: 1 D.2720_6 = D.2719_5 | 1;
> > freq: 1000 size: 1 time: 1 MEM[(volatile unsigned char *)88B] ={v}
> > D.2720_6;
> > freq: 11111 size: 1 time: 1 D.2721_8 ={v} MEM[(volatile unsigned char
> > *)88B];
> > freq: 11111 size: 0 time: 0 D.2722_9 = (int) D.2721_8;
> > freq: 11111 size: 1 time: 1 D.2723_10 = D.2722_9 & 1;
> > freq: 11111 size: 2 time: 2 if (D.2723_10 == 0)
> > freq: 1000 size: 1 time: 2 return;
> > Likely eliminated
> > Overall function body time: 51-2 size: 10-1
> > With function call overhead time: 51-13 size: 10-3
> >
> > that fits in early-inlining-insns. With --param early-inlining-insns=0 we
> > get it right. GCC inliner is guessing here that inlining such a small leaf
> > function will result in enough optimization so it pays back. I am not sure
> > what we can do here, early-inlining-insns is being pushed up by C++ code...
> >
> > It is not terribly bad tradeoff even at -O2. I will try to get some data how
> > much early inlining insns cost us at -O2 and if it is too much, I will
> > disable the allowed growth for functions not declared inline.
>
> Are you still working on this?
No reply, unassigning
