adding -fnoalias ... would a patch be accepted ?

[torbenh]

On Tue, Jan 05, 2010 at 04:27:33PM +0100, Richard Guenther wrote:
> On Tue, Jan 5, 2010 at 4:03 PM, torbenh <torbenh@gmx.de> wrote:
> > On Tue, Jan 05, 2010 at 02:46:30PM +0100, Richard Guenther wrote:
> >> On Tue, Jan 5, 2010 at 2:40 PM, torbenh <torbenh@gmx.de> wrote:
> >>
> >> The -fno-alias-X things do not make much sense for user code (they
> >> have been historically used from Frontends). Â If restrict doesn't work
> >> for you (do you have a testcase that can reproduce your issue?)
> >> then you probably need to wait for IPA pointer analysis to be
> >> fixed in GCC 4.6.
> >
> > sorry... forget the attachment :S
> 
> Yes, in this case you can fix it by making ramp static.  Otherwise its
> address may be takein in another translation unit.  For Fortran we
> have the DECL_RESTRICTED_P which we could expose to other
> languages via an attribute.  It tells that a decl is not aliased by
> restrict qualified pointers, so
> 
> struct Ramp {
>     float phase;
>     inline float process() { return phase++; }
> } ramp __attribute__((restrict));
> 
> void fill_buffer( float * __restrict buf, size_t nframes )
> {
>     for( size_t i=0; i<nframes; i++ )
>         buf[i] = ramp.process();
> }

would that also work with this stuff:


template<typename ... Args>
class Mixer;

template<typename T1, typename ... Args>
class Mixer<T1, Args...> : public Block
{
    private:
	T1 t1 __attribute__((restrict));
	Mixer<Args...> t2;
    public:
	inline float process() {
	    return t1.process() + t2.process();
	}
};

template<typename T1, typename T2>
class Mixer<T1,T2> : public Block
{
    private:
	T1 t1 __attribute__((restrict));
	T2 t2 __attribute__((restrict));
    public:
	inline float process() {
	    return t1.process() + t2.process();
	}
};

Mixer<Ramp,Ramp,Ramp,Ramp> mix __attribute__((restrict))

?

i still dont understand whats the problem with -fnolias,
as in attached patch.

> 
> would then be optimized as well.  Can you file an enhancement
> bugreport according to this?
> 
> Thanks,
> Richard.

-- 
torben Hohn
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