diff options
Diffstat (limited to 'generic/regc_nfa.c')
| -rw-r--r-- | generic/regc_nfa.c | 655 |
1 files changed, 601 insertions, 54 deletions
diff --git a/generic/regc_nfa.c b/generic/regc_nfa.c index 1d572c3..20eb3ba 100644 --- a/generic/regc_nfa.c +++ b/generic/regc_nfa.c @@ -34,6 +34,7 @@ #define NISERR() VISERR(nfa->v) #define NERR(e) VERR(nfa->v, (e)) +#define STACK_TOO_DEEP(x) (0) /* - newnfa - set up an NFA @@ -883,6 +884,20 @@ specialcolors( - optimize - optimize an NFA ^ static long optimize(struct nfa *, FILE *); */ + + /* + * The main goal of this function is not so much "optimization" (though it + * does try to get rid of useless NFA states) as reducing the NFA to a form + * the regex executor can handle. The executor, and indeed the cNFA format + * that is its input, can only handle PLAIN and LACON arcs. The output of + * the regex parser also includes EMPTY (do-nothing) arcs, as well as + * ^, $, AHEAD, and BEHIND constraint arcs, which we must get rid of here. + * We first get rid of EMPTY arcs and then deal with the constraint arcs. + * The hardest part of either job is to get rid of circular loops of the + * target arc type. We would have to do that in any case, though, as such a + * loop would otherwise allow the executor to cycle through the loop endlessly + * without making any progress in the input string. + */ static long /* re_info bits */ optimize( struct nfa *nfa, @@ -904,6 +919,7 @@ optimize( if (verbose) { fprintf(f, "\nconstraints:\n"); } + fixconstraintloops(nfa, f); /* get rid of constraint loops */ pullback(nfa, f); /* pull back constraints backward */ pushfwd(nfa, f); /* push fwd constraints forward */ if (verbose) { @@ -914,7 +930,7 @@ optimize( } /* - - pullback - pull back constraints backward to (with luck) eliminate them + - pullback - pull back constraints backward to eliminate them ^ static VOID pullback(struct nfa *, FILE *); */ static void @@ -954,6 +970,12 @@ pullback( return; } + /* + * Any ^ constraints we were able to pull to the start state can now be + * replaced by PLAIN arcs referencing the BOS or BOL colors. There should + * be no other ^ or BEHIND arcs left in the NFA, though we do not check + * that here (compact() will fail if so). + */ for (a=nfa->pre->outs ; a!=NULL ; a=nexta) { nexta = a->outchain; if (a->type == '^') { @@ -982,10 +1004,7 @@ pull( struct arc *nexta; struct state *s; - if (from == to) { /* circular constraint is pointless */ - freearc(nfa, con); - return 1; - } + assert(from != to); /* should have gotten rid of this earlier */ if (from->flag) { /* can't pull back beyond start */ return 0; } @@ -995,25 +1014,6 @@ pull( } /* - * DGP 2007-11-15: Cloning a state with a circular constraint on its list - * of outs can lead to trouble [Bug 1810038], so get rid of them first. - */ - - for (a = from->outs; a != NULL; a = nexta) { - nexta = a->outchain; - switch (a->type) { - case '^': - case '$': - case BEHIND: - case AHEAD: - if (from == a->to) { - freearc(nfa, a); - } - break; - } - } - - /* * First, clone from state if necessary to avoid other outarcs. */ @@ -1022,7 +1022,6 @@ pull( if (NISERR()) { return 0; } - assert(to != from); /* con is not an inarc */ copyins(nfa, from, s, 1); /* duplicate inarcs */ cparc(nfa, con, s, to); /* move constraint arc */ freearc(nfa, con); @@ -1071,7 +1070,7 @@ pull( } /* - - pushfwd - push forward constraints forward to (with luck) eliminate them + - pushfwd - push forward constraints forward to eliminate them ^ static VOID pushfwd(struct nfa *, FILE *); */ static void @@ -1111,6 +1110,12 @@ pushfwd( return; } + /* + * Any $ constraints we were able to push to the post state can now be + * replaced by PLAIN arcs referencing the EOS or EOL colors. There should + * be no other $ or AHEAD arcs left in the NFA, though we do not check + * that here (compact() will fail if so). + */ for (a = nfa->post->ins; a != NULL; a = nexta) { nexta = a->inchain; if (a->type == '$') { @@ -1139,10 +1144,7 @@ push( struct arc *nexta; struct state *s; - if (to == from) { /* circular constraint is pointless */ - freearc(nfa, con); - return 1; - } + assert(to != from); /* should have gotten rid of this earlier */ if (to->flag) { /* can't push forward beyond end */ return 0; } @@ -1152,28 +1154,6 @@ push( } /* - * DGP 2007-11-15: Here we duplicate the same protections as appear - * in pull() above to avoid troubles with cloning a state with a - * circular constraint on its list of ins. It is not clear whether - * this is necessary, or is protecting against a "can't happen". - * Any test case that actually leads to a freearc() call here would - * be a welcome addition to the test suite. - */ - - for (a = to->ins; a != NULL; a = nexta) { - nexta = a->inchain; - switch (a->type) { - case '^': - case '$': - case BEHIND: - case AHEAD: - if (a->from == to) { - freearc(nfa, a); - } - break; - } - } - /* * First, clone to state if necessary to avoid other inarcs. */ @@ -1503,6 +1483,573 @@ replaceempty( copyins(nfa, from, to, 0); } + +/* + * isconstraintarc - detect whether an arc is of a constraint type + */ +static inline int +isconstraintarc(struct arc * a) +{ + switch (a->type) + { + case '^': + case '$': + case BEHIND: + case AHEAD: + case LACON: + return 1; + } + return 0; +} + +/* + * hasconstraintout - does state have a constraint out arc? + */ +static int +hasconstraintout(struct state * s) +{ + struct arc *a; + + for (a = s->outs; a != NULL; a = a->outchain) { + if (isconstraintarc(a)) { + return 1; + } + } + return 0; +} + +/* + * fixconstraintloops - get rid of loops containing only constraint arcs + * + * A loop of states that contains only constraint arcs is useless, since + * passing around the loop represents no forward progress. Moreover, it + * would cause infinite looping in pullback/pushfwd, so we need to get rid + * of such loops before doing that. + */ +static void +fixconstraintloops( + struct nfa * nfa, + FILE *f) /* for debug output; NULL none */ +{ + struct state *s; + struct state *nexts; + struct arc *a; + struct arc *nexta; + int hasconstraints; + + /* + * In the trivial case of a state that loops to itself, we can just drop + * the constraint arc altogether. This is worth special-casing because + * such loops are far more common than loops containing multiple states. + * While we're at it, note whether any constraint arcs survive. + */ + hasconstraints = 0; + for (s = nfa->states; s != NULL && !NISERR(); s = nexts) { + nexts = s->next; + /* while we're at it, ensure tmp fields are clear for next step */ + assert(s->tmp == NULL); + for (a = s->outs; a != NULL && !NISERR(); a = nexta) { + nexta = a->outchain; + if (isconstraintarc(a)) { + if (a->to == s) { + freearc(nfa, a); + } else { + hasconstraints = 1; + } + } + } + /* If we removed all the outarcs, the state is useless. */ + if (s->nouts == 0 && !s->flag) { + dropstate(nfa, s); + } + } + + /* Nothing to do if no remaining constraint arcs */ + if (NISERR() || !hasconstraints) { + return; + } + + /* + * Starting from each remaining NFA state, search outwards for a + * constraint loop. If we find a loop, break the loop, then start the + * search over. (We could possibly retain some state from the first scan, + * but it would complicate things greatly, and multi-state constraint + * loops are rare enough that it's not worth optimizing the case.) + */ + restart: + for (s = nfa->states; s != NULL && !NISERR(); s = s->next) { + if (findconstraintloop(nfa, s)) { + goto restart; + } + } + + if (NISERR()) { + return; + } + + /* + * Now remove any states that have become useless. (This cleanup is not + * very thorough, and would be even less so if we tried to combine it with + * the previous step; but cleanup() will take care of anything we miss.) + * + * Because findconstraintloop intentionally doesn't reset all tmp fields, + * we have to clear them after it's done. This is a convenient place to + * do that, too. + */ + for (s = nfa->states; s != NULL; s = nexts) { + nexts = s->next; + s->tmp = NULL; + if ((s->nins == 0 || s->nouts == 0) && !s->flag) { + dropstate(nfa, s); + } + } + + if (f != NULL) { + dumpnfa(nfa, f); + } +} + +/* + * findconstraintloop - recursively find a loop of constraint arcs + * + * If we find a loop, break it by calling breakconstraintloop(), then + * return 1; otherwise return 0. + * + * State tmp fields are guaranteed all NULL on a success return, because + * breakconstraintloop does that. After a failure return, any state that + * is known not to be part of a loop is marked with s->tmp == s; this allows + * us not to have to re-prove that fact on later calls. (This convention is + * workable because we already eliminated single-state loops.) + * + * Note that the found loop doesn't necessarily include the first state we + * are called on. Any loop reachable from that state will do. + * + * The maximum recursion depth here is one more than the length of the longest + * loop-free chain of constraint arcs, which is surely no more than the size + * of the NFA, and in practice will be a lot less than that. + */ +static int +findconstraintloop(struct nfa * nfa, struct state * s) +{ + struct arc *a; + + /* Since this is recursive, it could be driven to stack overflow */ + if (STACK_TOO_DEEP(nfa->v->re)) { + NERR(REG_ETOOBIG); + return 1; /* to exit as quickly as possible */ + } + + if (s->tmp != NULL) { + /* Already proven uninteresting? */ + if (s->tmp == s) { + return 0; + } + /* Found a loop involving s */ + breakconstraintloop(nfa, s); + /* The tmp fields have been cleaned up by breakconstraintloop */ + return 1; + } + for (a = s->outs; a != NULL; a = a->outchain) { + if (isconstraintarc(a)) { + struct state *sto = a->to; + + assert(sto != s); + s->tmp = sto; + if (findconstraintloop(nfa, sto)) { + return 1; + } + } + } + + /* + * If we get here, no constraint loop exists leading out from s. Mark it + * with s->tmp == s so we need not rediscover that fact again later. + */ + s->tmp = s; + return 0; +} + +/* + * breakconstraintloop - break a loop of constraint arcs + * + * sinitial is any one member state of the loop. Each loop member's tmp + * field links to its successor within the loop. (Note that this function + * will reset all the tmp fields to NULL.) + * + * We can break the loop by, for any one state S1 in the loop, cloning its + * loop successor state S2 (and possibly following states), and then moving + * all S1->S2 constraint arcs to point to the cloned S2. The cloned S2 should + * copy any non-constraint outarcs of S2. Constraint outarcs should be + * dropped if they point back to S1, else they need to be copied as arcs to + * similarly cloned states S3, S4, etc. In general, each cloned state copies + * non-constraint outarcs, drops constraint outarcs that would lead to itself + * or any earlier cloned state, and sends other constraint outarcs to newly + * cloned states. No cloned state will have any inarcs that aren't constraint + * arcs or do not lead from S1 or earlier-cloned states. It's okay to drop + * constraint back-arcs since they would not take us to any state we've not + * already been in; therefore, no new constraint loop is created. In this way + * we generate a modified NFA that can still represent every useful state + * sequence, but not sequences that represent state loops with no consumption + * of input data. Note that the set of cloned states will certainly include + * all of the loop member states other than S1, and it may also include + * non-loop states that are reachable from S2 via constraint arcs. This is + * important because there is no guarantee that findconstraintloop found a + * maximal loop (and searching for one would be NP-hard, so don't try). + * Frequently the "non-loop states" are actually part of a larger loop that + * we didn't notice, and indeed there may be several overlapping loops. + * This technique ensures convergence in such cases, while considering only + * the originally-found loop does not. + * + * If there is only one S1->S2 constraint arc, then that constraint is + * certainly satisfied when we enter any of the clone states. This means that + * in the common case where many of the constraint arcs are identically + * labeled, we can merge together clone states linked by a similarly-labeled + * constraint: if we can get to the first one we can certainly get to the + * second, so there's no need to distinguish. This greatly reduces the number + * of new states needed, so we preferentially break the given loop at a state + * pair where this is true. + * + * Furthermore, it's fairly common to find that a cloned successor state has + * no outarcs, especially if we're a bit aggressive about removing unnecessary + * outarcs. If that happens, then there is simply not any interesting state + * that can be reached through the predecessor's loop arcs, which means we can + * break the loop just by removing those loop arcs, with no new states added. + */ +static void +breakconstraintloop(struct nfa * nfa, struct state * sinitial) +{ + struct state *s; + struct state *shead; + struct state *stail; + struct state *sclone; + struct state *nexts; + struct arc *refarc; + struct arc *a; + struct arc *nexta; + + /* + * Start by identifying which loop step we want to break at. + * Preferentially this is one with only one constraint arc. (XXX are + * there any other secondary heuristics we want to use here?) Set refarc + * to point to the selected lone constraint arc, if there is one. + */ + refarc = NULL; + s = sinitial; + do { + nexts = s->tmp; + assert(nexts != s); /* should not see any one-element loops */ + if (refarc == NULL) { + int narcs = 0; + + for (a = s->outs; a != NULL; a = a->outchain) { + if (a->to == nexts && isconstraintarc(a)) { + refarc = a; + narcs++; + } + } + assert(narcs > 0); + if (narcs > 1) { + refarc = NULL; /* multiple constraint arcs here, no good */ + } + } + s = nexts; + } while (s != sinitial); + + if (refarc) { + /* break at the refarc */ + shead = refarc->from; + stail = refarc->to; + assert(stail == shead->tmp); + } else { + /* for lack of a better idea, break after sinitial */ + shead = sinitial; + stail = sinitial->tmp; + } + + /* + * Reset the tmp fields so that we can use them for local storage in + * clonesuccessorstates. (findconstraintloop won't mind, since it's just + * going to abandon its search anyway.) + */ + for (s = nfa->states; s != NULL; s = s->next) { + s->tmp = NULL; + } + + /* + * Recursively build clone state(s) as needed. + */ + sclone = newstate(nfa); + if (sclone == NULL) { + assert(NISERR()); + return; + } + + clonesuccessorstates(nfa, stail, sclone, shead, refarc, + NULL, NULL, nfa->nstates); + + if (NISERR()) { + return; + } + + /* + * It's possible that sclone has no outarcs at all, in which case it's + * useless. (We don't try extremely hard to get rid of useless states + * here, but this is an easy and fairly common case.) + */ + if (sclone->nouts == 0) { + freestate(nfa, sclone); + sclone = NULL; + } + + /* + * Move shead's constraint-loop arcs to point to sclone, or just drop them + * if we discovered we don't need sclone. + */ + for (a = shead->outs; a != NULL; a = nexta) { + nexta = a->outchain; + if (a->to == stail && isconstraintarc(a)) { + if (sclone) { + cparc(nfa, a, shead, sclone); + } + freearc(nfa, a); + if (NISERR()) { + break; + } + } + } +} + +/* + * clonesuccessorstates - create a tree of constraint-arc successor states + * + * ssource is the state to be cloned, and sclone is the state to copy its + * outarcs into. sclone's inarcs, if any, should already be set up. + * + * spredecessor is the original predecessor state that we are trying to build + * successors for (it may not be the immediate predecessor of ssource). + * refarc, if not NULL, is the original constraint arc that is known to have + * been traversed out of spredecessor to reach the successor(s). + * + * For each cloned successor state, we transiently create a "donemap" that is + * a boolean array showing which source states we've already visited for this + * clone state. This prevents infinite recursion as well as useless repeat + * visits to the same state subtree (which can add up fast, since typical NFAs + * have multiple redundant arc pathways). Each donemap is a char array + * indexed by state number. The donemaps are all of the same size "nstates", + * which is nfa->nstates as of the start of the recursion. This is enough to + * have entries for all pre-existing states, but *not* entries for clone + * states created during the recursion. That's okay since we have no need to + * mark those. + * + * curdonemap is NULL when recursing to a new sclone state, or sclone's + * donemap when we are recursing without having created a new state (which we + * do when we decide we can merge a successor state into the current clone + * state). outerdonemap is NULL at the top level and otherwise the parent + * clone state's donemap. + * + * The successor states we create and fill here form a strict tree structure, + * with each state having exactly one predecessor, except that the toplevel + * state has no inarcs as yet (breakconstraintloop will add its inarcs from + * spredecessor after we're done). Thus, we can examine sclone's inarcs back + * to the root, plus refarc if any, to identify the set of constraints already + * known valid at the current point. This allows us to avoid generating extra + * successor states. + */ +static void +clonesuccessorstates( + struct nfa * nfa, + struct state * ssource, + struct state * sclone, + struct state * spredecessor, + struct arc * refarc, + char *curdonemap, + char *outerdonemap, + int nstates) +{ + char *donemap; + struct arc *a; + + /* Since this is recursive, it could be driven to stack overflow */ + if (STACK_TOO_DEEP(nfa->v->re)) { + NERR(REG_ETOOBIG); + return; + } + + /* If this state hasn't already got a donemap, create one */ + donemap = curdonemap; + if (donemap == NULL) { + donemap = (char *) MALLOC(nstates * sizeof(char)); + if (donemap == NULL) { + NERR(REG_ESPACE); + return; + } + + if (outerdonemap != NULL) { + /* + * Not at outermost recursion level, so copy the outer level's + * donemap; this ensures that we see states in process of being + * visited at outer levels, or already merged into predecessor + * states, as ones we shouldn't traverse back to. + */ + memcpy(donemap, outerdonemap, nstates * sizeof(char)); + } else { + /* At outermost level, only spredecessor is off-limits */ + memset(donemap, 0, nstates * sizeof(char)); + assert(spredecessor->no < nstates); + donemap[spredecessor->no] = 1; + } + } + + /* Mark ssource as visited in the donemap */ + assert(ssource->no < nstates); + assert(donemap[ssource->no] == 0); + donemap[ssource->no] = 1; + + /* + * We proceed by first cloning all of ssource's outarcs, creating new + * clone states as needed but not doing more with them than that. Then in + * a second pass, recurse to process the child clone states. This allows + * us to have only one child clone state per reachable source state, even + * when there are multiple outarcs leading to the same state. Also, when + * we do visit a child state, its set of inarcs is known exactly, which + * makes it safe to apply the constraint-is-already-checked optimization. + * Also, this ensures that we've merged all the states we can into the + * current clone before we recurse to any children, thus possibly saving + * them from making extra images of those states. + * + * While this function runs, child clone states of the current state are + * marked by setting their tmp fields to point to the original state they + * were cloned from. This makes it possible to detect multiple outarcs + * leading to the same state, and also makes it easy to distinguish clone + * states from original states (which will have tmp == NULL). + */ + for (a = ssource->outs; a != NULL && !NISERR(); a = a->outchain) { + struct state *sto = a->to; + + /* + * We do not consider cloning successor states that have no constraint + * outarcs; just link to them as-is. They cannot be part of a + * constraint loop so there is no need to make copies. In particular, + * this rule keeps us from trying to clone the post state, which would + * be a bad idea. + */ + if (isconstraintarc(a) && hasconstraintout(sto)) { + struct state *prevclone; + int canmerge; + struct arc *a2; + + /* + * Back-link constraint arcs must not be followed. Nor is there a + * need to revisit states previously merged into this clone. + */ + assert(sto->no < nstates); + if (donemap[sto->no] != 0) { + continue; + } + + /* + * Check whether we already have a child clone state for this + * source state. + */ + prevclone = NULL; + for (a2 = sclone->outs; a2 != NULL; a2 = a2->outchain) { + if (a2->to->tmp == sto) { + prevclone = a2->to; + break; + } + } + + /* + * If this arc is labeled the same as refarc, or the same as any + * arc we must have traversed to get to sclone, then no additional + * constraints need to be met to get to sto, so we should just + * merge its outarcs into sclone. + */ + if (refarc && a->type == refarc->type && a->co == refarc->co) { + canmerge = 1; + } else { + struct state *s; + + canmerge = 0; + for (s = sclone; s->ins; s = s->ins->from) { + if (s->nins == 1 && + a->type == s->ins->type && a->co == s->ins->co) { + canmerge = 1; + break; + } + } + } + + if (canmerge) { + /* + * We can merge into sclone. If we previously made a child + * clone state, drop it; there's no need to visit it. (This + * can happen if ssource has multiple pathways to sto, and we + * only just now found one that is provably a no-op.) + */ + if (prevclone) { + dropstate(nfa, prevclone); /* kills our outarc, too */ + } + + /* Recurse to merge sto's outarcs into sclone */ + clonesuccessorstates(nfa, sto, sclone, spredecessor, refarc, + donemap, outerdonemap, nstates); + /* sto should now be marked as previously visited */ + assert(NISERR() || donemap[sto->no] == 1); + } else if (prevclone) { + /* + * We already have a clone state for this successor, so just + * make another arc to it. + */ + cparc(nfa, a, sclone, prevclone); + } else { + /* + * We need to create a new successor clone state. + */ + struct state *stoclone; + + stoclone = newstate(nfa); + if (stoclone == NULL) { + assert(NISERR()); + break; + } + /* Mark it as to what it's a clone of */ + stoclone->tmp = sto; + /* ... and add the outarc leading to it */ + cparc(nfa, a, sclone, stoclone); + } + } else { + /* + * Non-constraint outarcs just get copied to sclone, as do outarcs + * leading to states with no constraint outarc. + */ + cparc(nfa, a, sclone, sto); + } + } + + /* + * If we are at outer level for this clone state, recurse to all its child + * clone states, clearing their tmp fields as we go. (If we're not + * outermost for sclone, leave this to be done by the outer call level.) + * Note that if we have multiple outarcs leading to the same clone state, + * it will only be recursed-to once. + */ + if (curdonemap == NULL) { + for (a = sclone->outs; a != NULL && !NISERR(); a = a->outchain) { + struct state *stoclone = a->to; + struct state *sto = stoclone->tmp; + + if (sto != NULL) { + stoclone->tmp = NULL; + clonesuccessorstates(nfa, sto, stoclone, spredecessor, refarc, + NULL, donemap, nstates); + } + } + + /* Don't forget to free sclone's donemap when done with it */ + FREE(donemap); + } +} /* - cleanup - clean up NFA after optimizations @@ -1618,7 +2165,7 @@ analyze( } /* - - compact - compact an NFA + - compact - construct the compact representation of an NFA ^ static VOID compact(struct nfa *, struct cnfa *); */ static void @@ -1687,7 +2234,7 @@ compact( cnfa->flags |= HASLACONS; break; default: - assert(NOTREACHED); + NERR(REG_ASSERT); break; } } |