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-rw-r--r--ChangeLog7
-rw-r--r--generic/regc_nfa.c334
-rw-r--r--generic/regcomp.c12
3 files changed, 258 insertions, 95 deletions
diff --git a/ChangeLog b/ChangeLog
index 696c2a1..88e698f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2013-03-06 Don Porter <dgp@users.sourceforge.net>
+
+ * generic/regc_nfa.c: [Bugs 3604074,3606683] Rewrite of the
+ * generic/regcomp.c: fixempties() routine (and supporting
+ routines) to completely eliminate the infinite loop hazard.
+ Thanks to Tom Lane for the much improved solution.
+
2013-02-28 Don Porter <dgp@users.sourceforge.net>
* generic/tclLiteral.c: Revise TclReleaseLiteral() to tolerate a
diff --git a/generic/regc_nfa.c b/generic/regc_nfa.c
index 65147d4..2fe2b27 100644
--- a/generic/regc_nfa.c
+++ b/generic/regc_nfa.c
@@ -497,6 +497,62 @@ freearc(
}
/*
+ - hasnonemptyout - Does state have a non-EMPTY out arc?
+ ^ static int hasnonemptyout(struct state *);
+ */
+static int
+hasnonemptyout(
+ struct state *s)
+{
+ struct arc *a;
+
+ for (a = s->outs; a != NULL; a = a->outchain) {
+ if (a->type != EMPTY) {
+ return 1;
+ }
+ }
+ return 0;
+}
+
+/*
+ - nonemptyouts - count non-EMPTY out arcs of a state
+ ^ static int nonemptyouts(struct state *);
+ */
+static int
+nonemptyouts(
+ struct state *s)
+{
+ int n = 0;
+ struct arc *a;
+
+ for (a = s->outs; a != NULL; a = a->outchain) {
+ if (a->type != EMPTY) {
+ n++;
+ }
+ }
+ return n;
+}
+
+/*
+ - nonemptyins - count non-EMPTY in arcs of a state
+ ^ static int nonemptyins(struct state *);
+ */
+static int
+nonemptyins(
+ struct state *s)
+{
+ int n = 0;
+ struct arc *a;
+
+ for (a = s->ins; a != NULL; a = a->inchain) {
+ if (a->type != EMPTY) {
+ n++;
+ }
+ }
+ return n;
+}
+
+/*
- findarc - find arc, if any, from given source with given type and color
* If there is more than one such arc, the result is random.
^ static struct arc *findarc(struct state *, int, pcolor);
@@ -559,21 +615,25 @@ moveins(
}
/*
- - copyins - copy all in arcs of a state to another state
- ^ static void copyins(struct nfa *, struct state *, struct state *);
+ - copyins - copy in arcs of a state to another state
+ * Either all arcs, or only non-empty ones as determined by all value.
+ ^ static VOID copyins(struct nfa *, struct state *, struct state *, int);
*/
static void
copyins(
struct nfa *nfa,
struct state *oldState,
- struct state *newState)
+ struct state *newState,
+ int all)
{
struct arc *a;
assert(oldState != newState);
for (a=oldState->ins ; a!=NULL ; a=a->inchain) {
- cparc(nfa, a, a->from, newState);
+ if (all || a->type != EMPTY) {
+ cparc(nfa, a, a->from, newState);
+ }
}
}
@@ -598,21 +658,25 @@ moveouts(
}
/*
- - copyouts - copy all out arcs of a state to another state
- ^ static void copyouts(struct nfa *, struct state *, struct state *);
+ - copyouts - copy out arcs of a state to another state
+ * Either all arcs, or only non-empty ones as determined by all value.
+ ^ static VOID copyouts(struct nfa *, struct state *, struct state *, int);
*/
static void
copyouts(
struct nfa *nfa,
struct state *oldState,
- struct state *newState)
+ struct state *newState,
+ int all)
{
struct arc *a;
assert(oldState != newState);
for (a=oldState->outs ; a!=NULL ; a=a->outchain) {
- cparc(nfa, a, newState, a->to);
+ if (all || a->type != EMPTY) {
+ cparc(nfa, a, newState, a->to);
+ }
}
}
@@ -970,9 +1034,9 @@ pull(
if (NISERR()) {
return 0;
}
- assert(to != from); /* con is not an inarc */
- copyins(nfa, from, s); /* duplicate inarcs */
- cparc(nfa, con, s, to); /* move constraint arc */
+ 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);
from = s;
con = from->outs;
@@ -1130,7 +1194,7 @@ push(
if (NISERR()) {
return 0;
}
- copyouts(nfa, to, s); /* duplicate outarcs */
+ copyouts(nfa, to, s, 1); /* duplicate outarcs */
cparc(nfa, con, from, s); /* move constraint */
freearc(nfa, con);
to = s;
@@ -1247,118 +1311,206 @@ fixempties(
FILE *f) /* for debug output; NULL none */
{
struct state *s;
+ struct state *s2;
struct state *nexts;
- struct state *to;
struct arc *a;
struct arc *nexta;
- int progress;
/*
- * Find and eliminate empties until there are no more.
+ * First, get rid of any states whose sole out-arc is an EMPTY,
+ * since they're basically just aliases for their successor. The
+ * parsing algorithm creates enough of these that it's worth
+ * special-casing this.
*/
+ for (s = nfa->states; s != NULL && !NISERR(); s = nexts) {
+ nexts = s->next;
+ if (s->flag || s->nouts != 1) {
+ continue;
+ }
+ a = s->outs;
+ assert(a != NULL && a->outchain == NULL);
+ if (a->type != EMPTY) {
+ continue;
+ }
+ if (s != a->to) {
+ moveins(nfa, s, a->to);
+ }
+ dropstate(nfa, s);
+ }
- do {
- progress = 0;
- for (s = nfa->states; s != NULL && !NISERR(); s = nexts) {
- nexts = s->next;
- for (a = s->outs; a != NULL && !NISERR(); a = a->outchain) {
- if (a->type == EMPTY) {
-
- /*
- * Mark a for deletion; copy arcs to preserve graph
- * connectivity after it is gone.
- */
-
- unempty(nfa, a);
- }
- }
+ /*
+ * Similarly, get rid of any state with a single EMPTY in-arc, by
+ * folding it into its predecessor.
+ */
+ for (s = nfa->states; s != NULL && !NISERR(); s = nexts) {
+ nexts = s->next;
+ /* Ensure tmp fields are clear for next step */
+ assert(s->tmp = NULL);
+ if (s->flag || s->nins != 1) {
+ continue;
+ }
+ a = s->ins;
+ assert(a != NULL && a->inchain == NULL);
+ if (a->type != EMPTY) {
+ continue;
+ }
+ if (s != a->from) {
+ moveouts(nfa, s, a->from);
+ }
+ dropstate(nfa, s);
+ }
+ /*
+ * For each remaining NFA state, find all other states that are
+ * reachable from it by a chain of one or more EMPTY arcs. Then
+ * generate new arcs that eliminate the need for each such chain.
+ *
+ * If we just do this straightforwardly, the algorithm gets slow in
+ * complex graphs, because the same arcs get copied to all
+ * intermediate states of an EMPTY chain, and then uselessly pushed
+ * repeatedly to the chain's final state; we waste a lot of time in
+ * newarc's duplicate checking. To improve matters, we decree that
+ * any state with only EMPTY out-arcs is "doomed" and will not be
+ * part of the final NFA. That can be ensured by not adding any new
+ * out-arcs to such a state. Having ensured that, we need not update
+ * the state's in-arcs list either; all arcs that might have gotten
+ * pushed forward to it will just get pushed directly to successor
+ * states. This eliminates most of the useless duplicate arcs.
+ */
+ for (s = nfa->states; s != NULL && !NISERR(); s = s->next) {
+ for (s2 = emptyreachable(s, s); s2 != s && !NISERR();
+ s2 = nexts) {
/*
- * Now pass through and delete the marked arcs. Doing all the
- * deletion after all the marking prevents arc copying from
- * resurrecting deleted arcs which can cause failure to converge.
- * [Tcl Bug 3604074]
+ * If s2 is doomed, we decide that (1) we will always push
+ * arcs forward to it, not pull them back to s; and (2) we
+ * can optimize away the push-forward, per comment above.
+ * So do nothing.
*/
+ if (s2->flag || hasnonemptyout(s2)) {
+ replaceempty(nfa, s, s2);
+ }
- for (a = s->outs; a != NULL; a = nexta) {
- nexta = a->outchain;
- if (a->from == NULL) {
- progress = 1;
- to = a->to;
- a->from = s;
- freearc(nfa, a);
- if (to->nins == 0) {
- while ((a = to->outs)) {
- freearc(nfa, a);
- }
- if (nexts == to) {
- nexts = to->next;
- }
- freestate(nfa, to);
- }
- if (s->nouts == 0) {
- while ((a = s->ins)) {
- freearc(nfa, a);
- }
- freestate(nfa, s);
- }
- }
+ /* Reset the tmp fields as we walk back */
+ nexts = s2->tmp;
+ s2->tmp = NULL;
+ }
+ s->tmp = NULL;
+ }
+
+ /*
+ * Remove all the EMPTY arcs, since we don't need them anymore.
+ */
+ for (s = nfa->states; s != NULL; s = s->next) {
+ for (a = s->outs; a != NULL; a = nexta) {
+ nexta = a->outchain;
+ if (a->type == EMPTY) {
+ freearc(nfa, a);
}
}
- if (progress && f != NULL) {
- dumpnfa(nfa, f);
+ }
+
+ /*
+ * And 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.)
+ */
+ for (s = nfa->states; s != NULL && !NISERR(); s = nexts) {
+ nexts = s->next;
+ if ((s->nins == 0 || s->nouts == 0) && !s->flag) {
+ dropstate(nfa, s);
}
- } while (progress && !NISERR());
+ }
+
+ if (f != NULL && !NISERR()) {
+ dumpnfa(nfa, f);
+ }
}
/*
- - unempty - optimize out an EMPTY arc, if possible
- * Actually, as it stands this function always succeeds, but the return value
- * is kept with an eye on possible future changes.
- ^ static int unempty(struct nfa *, struct arc *);
+ - emptyreachable - recursively find all states reachable from s by EMPTY arcs
+ * The return value is the last such state found. Its tmp field links back
+ * to the next-to-last such state, and so on back to s, so that all these
+ * states can be located without searching the whole NFA.
+ * The maximum recursion depth here is equal to the length of the longest
+ * loop-free chain of EMPTY arcs, which is surely no more than the size of
+ * the NFA, and in practice will be a lot less than that.
+ ^ static struct state *emptyreachable(struct state *, struct state *);
*/
-static int /* 0 couldn't, 1 could */
-unempty(
- struct nfa *nfa,
- struct arc *a)
+static struct state *
+emptyreachable(
+ struct state *s,
+ struct state *lastfound)
{
- struct state *from = a->from;
- struct state *to = a->to;
-
- assert(a->type == EMPTY);
- assert(from != nfa->pre && to != nfa->post);
+ struct arc *a;
- if (from == to) { /* vacuous loop */
- freearc(nfa, a);
- return 1;
+ s->tmp = lastfound;
+ lastfound = s;
+ for (a = s->outs; a != NULL; a = a->outchain) {
+ if (a->type == EMPTY && a->to->tmp == NULL) {
+ lastfound = emptyreachable(a->to, lastfound);
+ }
}
+ return lastfound;
+}
+
+/*
+ - replaceempty - replace an EMPTY arc chain with some non-empty arcs
+ * The EMPTY arc(s) should be deleted later, but we can't do it here because
+ * they may still be needed to identify other arc chains during fixempties().
+ ^ static void replaceempty(struct nfa *, struct state *, struct state *);
+ */
+static void
+replaceempty(
+ struct nfa *nfa,
+ struct state *from,
+ struct state *to)
+{
+ int fromouts;
+ int toins;
+
+ assert(from != to);
/*
- * Mark arc for deletion.
+ * Create replacement arcs that bypass the need for the EMPTY chain. We
+ * can do this either by pushing arcs forward (linking directly from
+ * "from"'s predecessors to "to") or by pulling them back (linking
+ * directly from "from" to "to"'s successors). In general, we choose
+ * whichever way creates greater fan-out or fan-in, so as to improve the
+ * odds of reducing the other state to zero in-arcs or out-arcs and
+ * thereby being able to delete it. However, if "from" is doomed (has no
+ * non-EMPTY out-arcs), we must keep it so, so always push forward in that
+ * case.
+ *
+ * The fan-out/fan-in comparison should count only non-EMPTY arcs. If
+ * "from" is doomed, we can skip counting "to"'s arcs, since we want to
+ * force taking the copynonemptyins path in that case.
*/
+ fromouts = nonemptyouts(from);
+ toins = (fromouts == 0) ? 1 : nonemptyins(to);
- a->from = NULL;
-
- if (from->nouts > to->nins) {
- copyouts(nfa, to, from);
- return 1;
+ if (fromouts > toins) {
+ copyouts(nfa, to, from, 0);
+ return;
}
- if (from->nouts < to->nins) {
- copyins(nfa, from, to);
- return 1;
+ if (fromouts < toins) {
+ copyins(nfa, from, to, 0);
+ return;
}
/*
- * from->nouts == to->nins . decide on secondary issue: copy fewest arcs
+ * fromouts == toins. Decide on secondary issue: copy fewest arcs.
+ *
+ * Doesn't seem to be worth the trouble to exclude empties from these
+ * comparisons; that takes extra time and doesn't seem to improve the
+ * resulting graph much.
*/
-
if (from->nins > to->nouts) {
- copyouts(nfa, to, from);
- return 1;
+ copyouts(nfa, to, from, 0);
+ return;
}
- copyins(nfa, from, to);
- return 1;
+ copyins(nfa, from, to, 0);
}
/*
diff --git a/generic/regcomp.c b/generic/regcomp.c
index b15117b..c93eb24 100644
--- a/generic/regcomp.c
+++ b/generic/regcomp.c
@@ -121,12 +121,15 @@ static void destroystate(struct nfa *, struct state *);
static void newarc(struct nfa *, int, pcolor, struct state *, struct state *);
static struct arc *allocarc(struct nfa *, struct state *);
static void freearc(struct nfa *, struct arc *);
+static int hasnonemptyout(struct state *);
+static int nonemptyouts(struct state *);
+static int nonemptyins(struct state *);
static struct arc *findarc(struct state *, int, pcolor);
static void cparc(struct nfa *, struct arc *, struct state *, struct state *);
static void moveins(struct nfa *, struct state *, struct state *);
-static void copyins(struct nfa *, struct state *, struct state *);
+static void copyins(struct nfa *, struct state *, struct state *, int);
static void moveouts(struct nfa *, struct state *, struct state *);
-static void copyouts(struct nfa *, struct state *, struct state *);
+static void copyouts(struct nfa *, struct state *, struct state *, int);
static void cloneouts(struct nfa *, struct state *, struct state *, struct state *, int);
static void delsub(struct nfa *, struct state *, struct state *);
static void deltraverse(struct nfa *, struct state *, struct state *);
@@ -144,7 +147,8 @@ static int push(struct nfa *, struct arc *);
#define COMPATIBLE 3 /* compatible but not satisfied yet */
static int combine(struct arc *, struct arc *);
static void fixempties(struct nfa *, FILE *);
-static int unempty(struct nfa *, struct arc *);
+static struct state *emptyreachable(struct state *, struct state *);
+static void replaceempty(struct nfa *, struct state *, struct state *);
static void cleanup(struct nfa *);
static void markreachable(struct nfa *, struct state *, struct state *, struct state *);
static void markcanreach(struct nfa *, struct state *, struct state *, struct state *);
@@ -607,7 +611,7 @@ makesearch(
for (s=slist ; s!=NULL ; s=s2) {
s2 = newstate(nfa);
- copyouts(nfa, s, s2);
+ copyouts(nfa, s, s2, 1);
for (a=s->ins ; a!=NULL ; a=b) {
b = a->inchain;
generated by cgit v0.12 at 2024-11-25 18:25:34 (GMT)