1 /* This file is part of the autovivification Perl module.
2 * See http://search.cpan.org/dist/autovivification/ */
4 #define PERL_NO_GET_CONTEXT
9 #define __PACKAGE__ "autovivification"
10 #define __PACKAGE_LEN__ (sizeof(__PACKAGE__)-1)
12 /* --- Compatibility wrappers ---------------------------------------------- */
14 #define A_HAS_PERL(R, V, S) (PERL_REVISION > (R) || (PERL_REVISION == (R) && (PERL_VERSION > (V) || (PERL_VERSION == (V) && (PERL_SUBVERSION >= (S))))))
16 #ifndef A_WORKAROUND_REQUIRE_PROPAGATION
17 # define A_WORKAROUND_REQUIRE_PROPAGATION !A_HAS_PERL(5, 10, 1)
20 /* --- Helpers ------------------------------------------------------------- */
22 #if A_WORKAROUND_REQUIRE_PROPAGATION
24 #define A_ENCODE_UV(B, U) \
26 while (len < sizeof(UV)) { \
27 (B)[len++] = (U) & 0xFF; \
31 #define A_DECODE_UV(U, B) \
34 (U) = ((U) << 8) | (B)[--len];
36 #if A_WORKAROUND_REQUIRE_PROPAGATION
37 STATIC UV a_require_tag(pTHX) {
38 #define a_require_tag() a_require_tag(aTHX)
41 for (si = PL_curstackinfo; si; si = si->si_prev) {
44 for (cxix = si->si_cxix; cxix >= 0; --cxix) {
45 const PERL_CONTEXT *cx = si->si_cxstack + cxix;
47 if (CxTYPE(cx) == CXt_EVAL && cx->blk_eval.old_op_type == OP_REQUIRE)
54 #endif /* A_WORKAROUND_REQUIRE_PROPAGATION */
56 STATIC SV *a_tag(pTHX_ UV bits) {
57 #define a_tag(B) a_tag(aTHX_ (B))
61 unsigned char buf[sizeof(UV) * 2];
64 cxreq = a_require_tag();
65 A_ENCODE_UV(buf, cxreq);
66 A_ENCODE_UV(buf + sizeof(UV), bits);
67 hint = newSVpvn(buf, sizeof buf);
73 STATIC UV a_detag(pTHX_ const SV *hint) {
74 #define a_detag(H) a_detag(aTHX_ (H))
76 UV cxreq = 0, bits = 0;
80 if (!(hint && SvOK(hint)))
85 A_DECODE_UV(cxreq, buf);
86 if (a_require_tag() != cxreq)
89 A_DECODE_UV(bits, buf + sizeof(UV));
94 #else /* A_WORKAROUND_REQUIRE_PROPAGATION */
96 #define a_tag(B) newSVuv(B)
97 #define a_detag(H) (((H) && SvOK(H)) ? SvUVX(H) : 0)
99 #endif /* !A_WORKAROUND_REQUIRE_PROPAGATION */
101 /* Used both for hints and op flags */
102 #define A_HINT_STRICT 1
103 #define A_HINT_WARN 2
104 #define A_HINT_FETCH 4
105 #define A_HINT_STORE 8
106 #define A_HINT_EXISTS 16
107 #define A_HINT_DELETE 32
108 #define A_HINT_NOTIFY (A_HINT_STRICT|A_HINT_WARN)
109 #define A_HINT_DO (A_HINT_FETCH|A_HINT_STORE|A_HINT_EXISTS|A_HINT_DELETE)
110 #define A_HINT_MASK (A_HINT_NOTIFY|A_HINT_DO)
112 /* Only used in op flags */
113 #define A_HINT_ROOT 64
114 #define A_HINT_DEREF 128
116 STATIC U32 a_hash = 0;
118 STATIC UV a_hint(pTHX) {
119 #define a_hint() a_hint(aTHX)
121 #if A_HAS_PERL(5, 9, 5)
122 hint = Perl_refcounted_he_fetch(aTHX_ PL_curcop->cop_hints_hash,
124 __PACKAGE__, __PACKAGE_LEN__,
128 SV **val = hv_fetch(GvHV(PL_hintgv), __PACKAGE__, __PACKAGE_LEN__, a_hash);
133 return a_detag(hint);
136 /* ... op => info map ...................................................... */
144 #define PTABLE_NAME ptable_map
145 #define PTABLE_VAL_FREE(V) PerlMemShared_free(V)
149 /* PerlMemShared_free() needs the [ap]PTBLMS_? default values */
150 #define ptable_map_store(T, K, V) ptable_map_store(aPTBLMS_ (T), (K), (V))
152 STATIC ptable *a_op_map = NULL;
155 STATIC perl_mutex a_op_map_mutex;
158 STATIC const a_op_info *a_map_fetch(const OP *o, a_op_info *oi) {
159 const a_op_info *val;
162 MUTEX_LOCK(&a_op_map_mutex);
165 val = ptable_fetch(a_op_map, o);
172 MUTEX_UNLOCK(&a_op_map_mutex);
178 STATIC const a_op_info *a_map_store_locked(pPTBLMS_ const OP *o, OP *(*old_pp)(pTHX), void *next, UV flags) {
179 #define a_map_store_locked(O, PP, N, F) a_map_store_locked(aPTBLMS_ (O), (PP), (N), (F))
182 if (!(oi = ptable_fetch(a_op_map, o))) {
183 oi = PerlMemShared_malloc(sizeof *oi);
184 ptable_map_store(a_op_map, o, oi);
194 STATIC void a_map_store(pPTBLMS_ const OP *o, OP *(*old_pp)(pTHX), void *next, UV flags) {
195 #define a_map_store(O, PP, N, F) a_map_store(aPTBLMS_ (O), (PP), (N), (F))
198 MUTEX_LOCK(&a_op_map_mutex);
201 a_map_store_locked(o, old_pp, next, flags);
204 MUTEX_UNLOCK(&a_op_map_mutex);
208 STATIC void a_map_delete(pTHX_ const OP *o) {
209 #define a_map_delete(O) a_map_delete(aTHX_ (O))
211 MUTEX_LOCK(&a_op_map_mutex);
214 ptable_map_store(a_op_map, o, NULL);
217 MUTEX_UNLOCK(&a_op_map_mutex);
221 STATIC const OP *a_map_descend(const OP *o) {
222 switch (PL_opargs[o->op_type] & OA_CLASS_MASK) {
226 case OA_BASEOP_OR_UNOP:
227 return cUNOPo->op_first;
230 return cLISTOPo->op_last;
236 STATIC void a_map_store_root(pPTBLMS_ const OP *root, OP *(*old_pp)(pTHX), UV flags) {
237 #define a_map_store_root(R, PP, F) a_map_store_root(aPTBLMS_ (R), (PP), (F))
238 const a_op_info *roi;
243 MUTEX_LOCK(&a_op_map_mutex);
246 roi = a_map_store_locked(o, old_pp, (OP *) root, flags | A_HINT_ROOT);
248 while (o->op_flags & OPf_KIDS) {
249 o = a_map_descend(o);
252 if ((oi = ptable_fetch(a_op_map, o))) {
253 oi->flags &= ~A_HINT_ROOT;
254 oi->next = (a_op_info *) roi;
260 MUTEX_UNLOCK(&a_op_map_mutex);
266 STATIC void a_map_update_flags_topdown(const OP *root, UV flags) {
271 MUTEX_LOCK(&a_op_map_mutex);
274 flags &= ~A_HINT_ROOT;
277 if ((oi = ptable_fetch(a_op_map, o)))
278 oi->flags = (oi->flags & A_HINT_ROOT) | flags;
279 if (!(o->op_flags & OPf_KIDS))
281 o = a_map_descend(o);
285 MUTEX_UNLOCK(&a_op_map_mutex);
291 #define a_map_cancel(R) a_map_update_flags_topdown((R), 0)
293 STATIC void a_map_update_flags_bottomup(const OP *o, UV flags, UV rflags) {
297 MUTEX_LOCK(&a_op_map_mutex);
300 flags &= ~A_HINT_ROOT;
301 rflags |= A_HINT_ROOT;
303 oi = ptable_fetch(a_op_map, o);
304 while (!(oi->flags & A_HINT_ROOT)) {
311 MUTEX_UNLOCK(&a_op_map_mutex);
317 /* ... Decide whether this expression should be autovivified or not ........ */
319 STATIC UV a_map_resolve(const OP *o, a_op_info *oi) {
320 UV flags = 0, rflags;
324 while (!(roi->flags & A_HINT_ROOT))
329 rflags = roi->flags & ~A_HINT_ROOT;
334 if (root->op_flags & OPf_MOD) {
335 if (rflags & A_HINT_STORE)
336 flags = (A_HINT_STORE|A_HINT_DEREF);
337 } else if (rflags & A_HINT_FETCH)
338 flags = (A_HINT_FETCH|A_HINT_DEREF);
342 a_map_update_flags_bottomup(o, 0, 0);
346 flags |= (rflags & A_HINT_NOTIFY);
347 a_map_update_flags_bottomup(o, flags, 0);
349 return oi->flags & A_HINT_ROOT ? 0 : flags;
352 /* ... Lightweight pp_defined() ............................................ */
354 STATIC bool a_defined(pTHX_ SV *sv) {
355 #define a_defined(S) a_defined(aTHX_ (S))
356 bool defined = FALSE;
358 switch (SvTYPE(sv)) {
360 if (AvMAX(sv) >= 0 || SvGMAGICAL(sv)
361 || (SvRMAGICAL(sv) && mg_find(sv, PERL_MAGIC_tied)))
365 if (HvARRAY(sv) || SvGMAGICAL(sv)
366 || (SvRMAGICAL(sv) && mg_find(sv, PERL_MAGIC_tied)))
376 /* --- PP functions -------------------------------------------------------- */
378 /* Be aware that we restore PL_op->op_ppaddr from the pointer table old_pp
379 * value, another extension might have saved our pp replacement as the ppaddr
380 * for this op, so this doesn't ensure that our function will never be called
381 * again. That's why we don't remove the op info from our map, so that it can
382 * still run correctly if required. */
384 /* ... pp_rv2av ............................................................ */
386 STATIC OP *a_pp_rv2av(pTHX) {
391 a_map_fetch(PL_op, &oi);
394 if (flags & A_HINT_DEREF) {
396 /* We always need to push an empty array to fool the pp_aelem() that comes
400 av = sv_2mortal((SV *) newAV());
405 PL_op->op_ppaddr = oi.old_pp;
408 return CALL_FPTR(oi.old_pp)(aTHX);
411 /* ... pp_rv2hv ............................................................ */
413 STATIC OP *a_pp_rv2hv_simple(pTHX) {
418 a_map_fetch(PL_op, &oi);
421 if (flags & A_HINT_DEREF) {
425 PL_op->op_ppaddr = oi.old_pp;
428 return CALL_FPTR(oi.old_pp)(aTHX);
431 STATIC OP *a_pp_rv2hv(pTHX) {
436 a_map_fetch(PL_op, &oi);
439 if (flags & A_HINT_DEREF) {
443 hv = sv_2mortal((SV *) newHV());
448 PL_op->op_ppaddr = oi.old_pp;
451 return CALL_FPTR(oi.old_pp)(aTHX);
454 /* ... pp_deref (aelem,helem,rv2sv,padsv) .................................. */
456 STATIC OP *a_pp_deref(pTHX) {
461 a_map_fetch(PL_op, &oi);
464 if (flags & A_HINT_DEREF) {
469 old_private = PL_op->op_private;
470 PL_op->op_private = ((old_private & ~OPpDEREF) | OPpLVAL_DEFER);
471 o = CALL_FPTR(oi.old_pp)(aTHX);
472 PL_op->op_private = old_private;
474 if (flags & (A_HINT_NOTIFY|A_HINT_STORE)) {
477 if (flags & A_HINT_STRICT)
478 croak("Reference vivification forbidden");
479 else if (flags & A_HINT_WARN)
480 warn("Reference was vivified");
481 else /* A_HINT_STORE */
482 croak("Can't vivify reference");
487 } else if ((flags & ~A_HINT_ROOT)
488 && (PL_op->op_private & OPpDEREF || flags & A_HINT_ROOT)) {
489 /* Decide if the expression must autovivify or not.
490 * This branch should be called only once by expression. */
491 flags = a_map_resolve(PL_op, &oi);
493 /* We need the updated flags value in the deref branch. */
494 if (flags & A_HINT_DEREF)
498 /* This op doesn't need to skip autovivification, so restore the original
500 PL_op->op_ppaddr = oi.old_pp;
502 return CALL_FPTR(oi.old_pp)(aTHX);
505 /* ... pp_root (exists,delete,keys,values) ................................. */
507 STATIC OP *a_pp_root_unop(pTHX) {
511 if (!a_defined(TOPs)) {
513 /* Can only be reached by keys or values */
514 if (GIMME_V == G_SCALAR) {
521 a_map_fetch(PL_op, &oi);
523 return CALL_FPTR(oi.old_pp)(aTHX);
526 STATIC OP *a_pp_root_binop(pTHX) {
530 if (!a_defined(TOPm1s)) {
533 if (PL_op->op_type == OP_EXISTS)
539 a_map_fetch(PL_op, &oi);
541 return CALL_FPTR(oi.old_pp)(aTHX);
544 /* --- Check functions ----------------------------------------------------- */
546 STATIC void a_recheck_rv2xv(pTHX_ OP *o, OPCODE type, OP *(*new_pp)(pTHX)) {
547 #define a_recheck_rv2xv(O, T, PP) a_recheck_rv2xv(aTHX_ (O), (T), (PP))
550 if (o->op_type == type && o->op_ppaddr != new_pp
551 && cUNOPo->op_first->op_type != OP_GV
552 && a_map_fetch(o, &oi)) {
553 a_map_store(o, o->op_ppaddr, oi.next, oi.flags);
554 o->op_ppaddr = new_pp;
560 /* ... ck_pad{any,sv} ...................................................... */
562 /* Sadly, the PADSV OPs we are interested in don't trigger the padsv check
563 * function, but are instead manually mutated from a PADANY. This is why we set
564 * PL_ppaddr[OP_PADSV] in the padany check function so that PADSV OPs will have
565 * their op_ppaddr set to our pp_padsv. PL_ppaddr[OP_PADSV] is then reset at the
566 * beginning of every ck_pad{any,sv}. Some unwanted OPs can still call our
567 * pp_padsv, but much less than if we would have set PL_ppaddr[OP_PADSV]
570 STATIC OP *(*a_pp_padsv_saved)(pTHX) = 0;
572 STATIC void a_pp_padsv_save(void) {
573 if (a_pp_padsv_saved)
576 a_pp_padsv_saved = PL_ppaddr[OP_PADSV];
577 PL_ppaddr[OP_PADSV] = a_pp_deref;
580 STATIC void a_pp_padsv_restore(OP *o) {
581 if (!a_pp_padsv_saved)
584 if (o->op_ppaddr == a_pp_deref)
585 o->op_ppaddr = a_pp_padsv_saved;
587 PL_ppaddr[OP_PADSV] = a_pp_padsv_saved;
588 a_pp_padsv_saved = 0;
591 STATIC OP *(*a_old_ck_padany)(pTHX_ OP *) = 0;
593 STATIC OP *a_ck_padany(pTHX_ OP *o) {
596 a_pp_padsv_restore(o);
598 o = CALL_FPTR(a_old_ck_padany)(aTHX_ o);
601 if (hint & A_HINT_DO) {
603 a_map_store_root(o, a_pp_padsv_saved, hint);
610 STATIC OP *(*a_old_ck_padsv)(pTHX_ OP *) = 0;
612 STATIC OP *a_ck_padsv(pTHX_ OP *o) {
615 a_pp_padsv_restore(o);
617 o = CALL_FPTR(a_old_ck_padsv)(aTHX_ o);
620 if (hint & A_HINT_DO) {
621 a_map_store_root(o, o->op_ppaddr, hint);
622 o->op_ppaddr = a_pp_deref;
629 /* ... ck_deref (aelem,helem,rv2sv) ........................................ */
631 /* Those ops appear both at the root and inside an expression but there's no
632 * way to distinguish both situations. Worse, we can't even know if we are in a
633 * modifying context, so the expression can't be resolved yet. It will be at the
634 * first invocation of a_pp_deref() for this expression. */
636 STATIC OP *(*a_old_ck_aelem)(pTHX_ OP *) = 0;
637 STATIC OP *(*a_old_ck_helem)(pTHX_ OP *) = 0;
638 STATIC OP *(*a_old_ck_rv2sv)(pTHX_ OP *) = 0;
640 STATIC OP *a_ck_deref(pTHX_ OP *o) {
641 OP * (*old_ck)(pTHX_ OP *o) = 0;
644 switch (o->op_type) {
646 old_ck = a_old_ck_aelem;
647 if ((hint & A_HINT_DO) && !(hint & A_HINT_STRICT))
648 a_recheck_rv2xv(cUNOPo->op_first, OP_RV2AV, a_pp_rv2av);
651 old_ck = a_old_ck_helem;
652 if ((hint & A_HINT_DO) && !(hint & A_HINT_STRICT))
653 a_recheck_rv2xv(cUNOPo->op_first, OP_RV2HV, a_pp_rv2hv_simple);
656 old_ck = a_old_ck_rv2sv;
659 o = CALL_FPTR(old_ck)(aTHX_ o);
661 if (hint & A_HINT_DO) {
662 a_map_store_root(o, o->op_ppaddr, hint);
663 o->op_ppaddr = a_pp_deref;
670 /* ... ck_rv2xv (rv2av,rv2hv) .............................................. */
672 /* Those ops also appear both inisde and at the root, hence the caveats for
673 * a_ck_deref() still apply here. Since a padsv/rv2sv must appear before a
674 * rv2[ah]v, resolution is handled by the first call to a_pp_deref() in the
677 STATIC OP *(*a_old_ck_rv2av)(pTHX_ OP *) = 0;
678 STATIC OP *(*a_old_ck_rv2hv)(pTHX_ OP *) = 0;
680 STATIC OP *a_ck_rv2xv(pTHX_ OP *o) {
681 OP * (*old_ck)(pTHX_ OP *o) = 0;
682 OP * (*new_pp)(pTHX) = 0;
685 switch (o->op_type) {
686 case OP_RV2AV: old_ck = a_old_ck_rv2av; new_pp = a_pp_rv2av; break;
687 case OP_RV2HV: old_ck = a_old_ck_rv2hv; new_pp = a_pp_rv2hv_simple; break;
689 o = CALL_FPTR(old_ck)(aTHX_ o);
691 if (cUNOPo->op_first->op_type == OP_GV)
695 if (hint & A_HINT_DO && !(hint & A_HINT_STRICT)) {
696 a_map_store_root(o, o->op_ppaddr, hint);
697 o->op_ppaddr = new_pp;
704 /* ... ck_xslice (aslice,hslice) ........................................... */
706 /* I think those are only found at the root, but there's nothing that really
707 * prevent them to be inside the expression too. We only need to update the
708 * root so that the rest of the expression will see the right context when
709 * resolving. That's why we don't replace the ppaddr. */
711 STATIC OP *(*a_old_ck_aslice)(pTHX_ OP *) = 0;
712 STATIC OP *(*a_old_ck_hslice)(pTHX_ OP *) = 0;
714 STATIC OP *a_ck_xslice(pTHX_ OP *o) {
715 OP * (*old_ck)(pTHX_ OP *o) = 0;
718 switch (o->op_type) {
720 old_ck = a_old_ck_aslice;
723 old_ck = a_old_ck_hslice;
724 if (hint & A_HINT_DO)
725 a_recheck_rv2xv(cUNOPo->op_first->op_sibling, OP_RV2HV, a_pp_rv2hv);
728 o = CALL_FPTR(old_ck)(aTHX_ o);
730 if (hint & A_HINT_DO) {
731 a_map_store_root(o, 0, hint);
738 /* ... ck_root (exists,delete,keys,values) ................................. */
740 /* Those ops are only found at the root of a dereferencing expression. We can
741 * then resolve at compile time if vivification must take place or not. */
743 STATIC OP *(*a_old_ck_exists)(pTHX_ OP *) = 0;
744 STATIC OP *(*a_old_ck_delete)(pTHX_ OP *) = 0;
745 STATIC OP *(*a_old_ck_keys) (pTHX_ OP *) = 0;
746 STATIC OP *(*a_old_ck_values)(pTHX_ OP *) = 0;
748 STATIC OP *a_ck_root(pTHX_ OP *o) {
749 OP * (*old_ck)(pTHX_ OP *o) = 0;
750 OP * (*new_pp)(pTHX) = 0;
751 bool enabled = FALSE;
754 switch (o->op_type) {
756 old_ck = a_old_ck_exists;
757 new_pp = a_pp_root_binop;
758 enabled = hint & A_HINT_EXISTS;
761 old_ck = a_old_ck_delete;
762 new_pp = a_pp_root_binop;
763 enabled = hint & A_HINT_DELETE;
766 old_ck = a_old_ck_keys;
767 new_pp = a_pp_root_unop;
768 enabled = hint & A_HINT_FETCH;
771 old_ck = a_old_ck_values;
772 new_pp = a_pp_root_unop;
773 enabled = hint & A_HINT_FETCH;
776 o = CALL_FPTR(old_ck)(aTHX_ o);
778 if (hint & A_HINT_DO) {
780 a_map_update_flags_topdown(o, hint | A_HINT_DEREF);
781 a_map_store_root(o, o->op_ppaddr, hint);
782 o->op_ppaddr = new_pp;
792 STATIC U32 a_initialized = 0;
794 /* --- XS ------------------------------------------------------------------ */
796 MODULE = autovivification PACKAGE = autovivification
802 if (!a_initialized++) {
805 a_op_map = ptable_new();
807 MUTEX_INIT(&a_op_map_mutex);
810 PERL_HASH(a_hash, __PACKAGE__, __PACKAGE_LEN__);
812 a_old_ck_padany = PL_check[OP_PADANY];
813 PL_check[OP_PADANY] = MEMBER_TO_FPTR(a_ck_padany);
814 a_old_ck_padsv = PL_check[OP_PADSV];
815 PL_check[OP_PADSV] = MEMBER_TO_FPTR(a_ck_padsv);
817 a_old_ck_aelem = PL_check[OP_AELEM];
818 PL_check[OP_AELEM] = MEMBER_TO_FPTR(a_ck_deref);
819 a_old_ck_helem = PL_check[OP_HELEM];
820 PL_check[OP_HELEM] = MEMBER_TO_FPTR(a_ck_deref);
821 a_old_ck_rv2sv = PL_check[OP_RV2SV];
822 PL_check[OP_RV2SV] = MEMBER_TO_FPTR(a_ck_deref);
824 a_old_ck_rv2av = PL_check[OP_RV2AV];
825 PL_check[OP_RV2AV] = MEMBER_TO_FPTR(a_ck_rv2xv);
826 a_old_ck_rv2hv = PL_check[OP_RV2HV];
827 PL_check[OP_RV2HV] = MEMBER_TO_FPTR(a_ck_rv2xv);
829 a_old_ck_aslice = PL_check[OP_ASLICE];
830 PL_check[OP_ASLICE] = MEMBER_TO_FPTR(a_ck_xslice);
831 a_old_ck_hslice = PL_check[OP_HSLICE];
832 PL_check[OP_HSLICE] = MEMBER_TO_FPTR(a_ck_xslice);
834 a_old_ck_exists = PL_check[OP_EXISTS];
835 PL_check[OP_EXISTS] = MEMBER_TO_FPTR(a_ck_root);
836 a_old_ck_delete = PL_check[OP_DELETE];
837 PL_check[OP_DELETE] = MEMBER_TO_FPTR(a_ck_root);
838 a_old_ck_keys = PL_check[OP_KEYS];
839 PL_check[OP_KEYS] = MEMBER_TO_FPTR(a_ck_root);
840 a_old_ck_values = PL_check[OP_VALUES];
841 PL_check[OP_VALUES] = MEMBER_TO_FPTR(a_ck_root);
843 stash = gv_stashpvn(__PACKAGE__, __PACKAGE_LEN__, 1);
844 newCONSTSUB(stash, "A_HINT_STRICT", newSVuv(A_HINT_STRICT));
845 newCONSTSUB(stash, "A_HINT_WARN", newSVuv(A_HINT_WARN));
846 newCONSTSUB(stash, "A_HINT_FETCH", newSVuv(A_HINT_FETCH));
847 newCONSTSUB(stash, "A_HINT_STORE", newSVuv(A_HINT_STORE));
848 newCONSTSUB(stash, "A_HINT_EXISTS", newSVuv(A_HINT_EXISTS));
849 newCONSTSUB(stash, "A_HINT_DELETE", newSVuv(A_HINT_DELETE));
850 newCONSTSUB(stash, "A_HINT_MASK", newSVuv(A_HINT_MASK));
858 RETVAL = a_tag(SvOK(hint) ? SvUV(hint) : 0);
868 RETVAL = newSVuv(a_detag(tag));