see:
PL_in_my = KEY_my
(op.c)
PADOFFSET
Perl_allocmy(pTHX_ const char *const name, const STRLEN len, const U32 flags)
it calls:
off = pad_add_name(name, len, ...)
(toke.c)
pl_yylval.opval = newOP(OP_PADANY, 0);
pl_yylval.opval->op_targ = allocmy(PL_tokenbuf, tokenbuf_len, 0);