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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CC| |egallager at gcc dot gnu.org
--- Comment #9 from Eric Gallager <egallager at gcc dot gnu.org> ---
(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?
