Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return

[Quentin Lambert]

On 27/11/2014 13:25, David Laight wrote:
> From: Joe Perches
> > On Wed, 2014-11-26 at 10:34 -0800, Alexei Starovoitov wrote:
> > > On Wed, Nov 26, 2014 at 10:02 AM, Joe Perches <joe@xxxxxxxxxxx> wrote:
> > > > On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote:
> > > > > On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches <joe@xxxxxxxxxxx> wrote:
> > > > > > Is there any value in reordering these tests for frequency
> > > > > > or maybe using | instead of || to avoid multiple jumps?
> > > > > probably not. It's not a critical path.
> > > > > compiler may fuse conditions depending on values anyway.
> > > > > If it was a critical path, we could have used
> > > > > (1 << reg) & mask trick.
> > > > > I picked explicit 'return true' else 'return false' here,
> > > > > because it felt easier to read. Just a matter of taste.
> > > > There is a size difference though: (allyesconfig)
> > > >
> > > > $ size arch/x86/net/built-in.o*
> > > >     text    data     bss     dec     hex filename
> > > >    12999    1012    4336   18347    47ab arch/x86/net/built-in.o.new
> > > >    13177    1076    4592   18845    499d arch/x86/net/built-in.o.old
> > > interesting. Compiler obviously thinks that 178 byte increase
> > > with -O2 is the right trade off. Which I agree with :)
> > >
> > > If I think dropping 'inline' and using -Os will give bigger savings...
> > This was allyesconfig which already uses -Os
> >
> > Using -O2, there is no difference using inline
> > or not, but the size delta with the bitmask is
> > much larger
> >
> > $ size arch/x86/net/built-in.o* (allyesconfig, but not -Os)
> >     text	   data	    bss	    dec	    hex	filename
> >    13410	    820	   3624	  17854	   45be	arch/x86/net/built-in.o.new
> >    16130	    884	   4200	  21214	   52de	arch/x86/net/built-in.o.old
> >    16130	    884	   4200	  21214	   52de	arch/x86/net/built-in.o.static
> That is quite a big % change in the code size.
> Why the change in data?
>
> 	David
Do you want me to propose a second version, or should I just
drop it all together ?

I am a new contributor so I have no experience in that sort of thing.

Quentin
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