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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