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Message-ID: <1409482237.4476.277.camel@eris.loria.fr>
Date: Sun, 31 Aug 2014 12:50:37 +0200
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: Re: [PATCH 7/8] add the thrd_xxxxxx functions
Am Sonntag, den 31.08.2014, 13:51 +0400 schrieb Alexander Monakov:
> On Sun, 31 Aug 2014, Jens Gustedt wrote:
> > > > @@ -234,7 +253,10 @@ static int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restr
> > > > new->canary = self->canary;
> > > >
> > > > a_inc(&libc.threads_minus_1);
> > > > - ret = __clone(start, stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);
> > > > + if (c11)
> > > > + ret = __clone(start_c11, stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);
> > > > + else
> > > > + ret = __clone(start, stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);
> > >
> > > Couldn't this be "c11 ? start_c11 : start" to avoid duplicating the
> > > rest of the call?
> >
> > I think that the ternary expression together with the other
> > parenthesized paramenter and the length of the line would make the
> > line barely readable.
> >
> > This are some of the pivots lines of the implementation, I'd rather
> > have them stick out.
> >
> > Also the assembler that is produced should be identical.
>
> It probably won't be with GCC. Try:
>
> echo 'int g(int); int f(int y){if (y) return g(0); else return g(1);}' |
> gcc -xc - -S -o- -O
>
> And try varying optimization levels. With gcc-4.8 on x86-64 I get two calls
> except with -Os, and even with -Os it's worse than with a ternary operator.
Interesting remark, but your example is a bit flawed. It has the types
of the arguments for f and g the same, int. This has gcc attempt to
save things in the entry register for the first argument of the call.
As expected with the following, more complete example I see no
difference for the assembler for f or h, but for the names of the
labels. This holds for gcc and clang.
echo 'int g(void*); int a; int b; int f(int y){ if (y) return g(&a); else return g(&b);} int h(int y) { return y ? g(&a) : g(&b); }' | gcc -xc - -S -o- -O
Jens
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