Re: [avr-gcc-list] Unused registers saves/restores ?

[Dmitry K.]

10 Jun 2003 09:20 Eric wrote:
> > 10 Jun 2003 08:12 Eric wrote:
> > > > Hello all,
> > > >
> > > > Compiler:
> > > >         avr-gcc --version
> > > >         avr-gcc (GCC) 3.3.1 20030519 (prerelease)
> > > >
> > > > Programm:
> > > >         typedef struct { long a; int b; } lo_in;
> > > >
> > > >         lo_in foo_lo_in (void)
> > > >         {
> > > >             lo_in x;
> > > >             x.a = 1;
> > > >             x.b = 2;
> > > >             return x;
> > > >         };
> > > >
> > > > Compile with:
> > > >         avr-gcc -O3 -S foo_lo_in.c
> > > >
> > > > Result: r2,3,4,7,... not used, but saved/restored:
> > >
> > > Do you get the same with other optimizations?
>
> Including -Os?
>
> > > Eric
> >
> > avr-gcc -Os -S foo_lo_in.c  ==>  roughly the same
>

> Is there an optimization level where it doesn't produce a
> problem? (i.e. -O0, -O1, -O2)
>
> Eric

avr-gcc -O0 -S  ==> best result:
        /* File "foo_lo_in.c": code   75 = 0x004b (  40), prologues  18, 
epilogues                      
17 */
        Body is greate, but prologue/epilogue small.