According to newSVrv, it's 

SV_CHECK_THINKFIRST_COW_DROP(rv);
(void)SvAMAGIC_off(rv);

if (SvTYPE(rv) >= SVt_PVMG) {
    const U32 refcnt = SvREFCNT(rv);
    SvREFCNT(rv) = 0;
    sv_clear(rv);
    SvFLAGS(rv) = 0;
    SvREFCNT(rv) = refcnt;

    sv_upgrade(rv, SVt_IV);
} else if (SvROK(rv)) {
    SvREFCNT_dec(SvRV(rv));
} else if (SvTYPE(rv) < SVt_PV && SvTYPE(rv) != SVt_IV) {
    sv_upgrade(rv, SVt_IV);
} else if (SvTYPE(rv) >= SVt_PV) {
    SvPV_free(rv);
    SvLEN_set(rv, 0);
    SvCUR_set(rv, 0);
}

SvOK_off(rv);
SvRV_set(rv, sv);
SvROK_on(rv);

SvREFCNT_inc(sv);

SvSETMAGIC(rv);

[download]

Or you could use 

sv_replace(rv, newRV_inc(sv))
SvSETMAGIC(rv);

[download]

Update: Fixed ref count as per reply.

In reply to Re: where is sv_setrv? by ikegami
in thread where is sv_setrv? by patcat88

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