https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38629
Eric Gallager <egallager at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- 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