SV *tmp = newSVsv(foo);
do_something(tmp);
SvREFCNT_dec(tmp);

##</code><code>##

SV *tmp = sv_2mortal(newSVsv(foo));
do_something(tmp);
/* no clean up code required here */

##</code><code>##

SV *tmp = sv_2mortal(newSVsv(foo));
if (av_store(av, ix, tmp)) SvREFCNT_inc(tmp);