On 20-12-13 09:48:35, Segher Boessenkool wrote: > Hi! > > On Sun, Dec 13, 2020 at 03:34:57PM +0100, Piotr Kubaj wrote: > > this is only default tuning (-mtune, not -mcpu). > > It is both, actually (-mcpu= implies -mtune=) Yes, but -mtune doesn't imply -mcpu. If I set up only -mtune, -mcpu is the generic one (ppc970 for BE) > > > Linux also does similarly in linux64.h: > > 74 #undef PROCESSOR_DEFAULT > > 75 #define PROCESSOR_DEFAULT PROCESSOR_POWER7 > > 76 #undef PROCESSOR_DEFAULT64 > > 77 #define PROCESSOR_DEFAULT64 PROCESSOR_POWER8 > > Yes, but we still default to power4 on BE Linux (and power8 on LE). I > get lost in the macro maze here, not sure how that works :-) > > > Although there is hard to explain (for me) setting to tune for POWER7 on > > 32-bits. POWER7 is 64-bit and it should be more reasonable to optimize for > > the last 32-bit machines that still may be in use (so G4). > > 7450 has very different optimisation than 970. Power7 and 970 have > largely similar pipelines. Yes, but the point is that users on 32-bit machines don't use POWER7, but most likely G4.
>
> > That said, on the 64-bit front, we will just match the Linux setting.
>
> Compile a very simple test and look at the .machine in the generated .s?
> Does that do what you want?
Yes, I just tested it (on BE).
pkubaj@talos:$/usr/home/pkubaj$ cat test.c
#include <stdio.h>
int main()
{
printf("Hello world!");
}
I built it twice, with GCC 9.3 without my patch and with GCC 10.1 with my
patch. The only difference is:
pkubaj@talos:$/usr/home/pkubaj$ diff -u test.s.9 test.s.10
--- test.s.9 2020-12-14 15:51:43.203263000 +0100
+++ test.s.10 2020-12-14 15:52:01.147238000 +0100
@@ -43,5 +43,5 @@
.cfi_endproc
.LFE1:
.size main,.-main
- .ident "GCC: (FreeBSD Ports Collection) 9.3.0"
+ .ident "GCC: (FreeBSD Ports Collection) 10.2.0"
.section .note.GNU-stack,"",@progbits
Both have .machine power4:
pkubaj@talos:$/usr/home/pkubaj$ grep .machine test.s.*
test.s.10: .machine power4
test.s.9: .machine power4
I'm not sure where GCC sets power8 for LE, but it's definitely somewhere else.
So IMO this patch is good to go.
Thanks,
Piotr Kubaj.
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