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NFA merging: permit different reports

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For cases where the edges from start are not to a mix of accept and
acceptEod, report sets can be combined.
This commit is contained in:
Justin Viiret 2016-02-10 15:14:49 +11:00 committed by Matthew Barr
parent 42d34f19d1
commit 670eff5bc0
1 changed files with 39 additions and 49 deletions
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88
src/nfagraph/ng_uncalc_components.cpp
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@ -486,53 +486,49 @@ void buildNfaMergeQueue(const vector<NGHolder *> &cluster,
}
}
/** True if the graphs have compatible starts for merging, i.e. they are NOT
* both vacuous with different reports on the starts. */
/**
* True if the graphs have mergeable starts.
*
* Nowadays, this means that any vacuous edges must have the same tops. In
* addition, mixed-accept cases need to have matching reports.
*/
static
bool mergeableStarts(const NGHolder &h1, const NGHolder &h2) {
bool vac1 = isVacuous(h1), vac2 = isVacuous(h2);
// Safety tests: reports should be empty on non-vacuous graphs.
if (!vac1) {
assert(h1[h1.start].reports.empty());
assert(h1[h1.startDs].reports.empty());
}
if (!vac2) {
assert(h2[h2.start].reports.empty());
assert(h2[h2.startDs].reports.empty());
if (!isVacuous(h1) || !isVacuous(h2)) {
return true;
}
if (vac1 && vac2) {
// Graphs must have the same reports on their starts to be mergeable
// (and top on start->accept).
if (h1[h1.start].reports
!= h2[h2.start].reports) {
// Vacuous edges from startDs should not occur: we have better ways to
// implement true dot-star relationships. Just in case they do, ban them
// from being merged unless they have identical reports.
if (is_match_vertex(h1.startDs, h1) || is_match_vertex(h2.startDs, h2)) {
assert(0);
return false;
}
// If both graphs have edge (start, accept), the tops must match.
auto e1_accept = edge(h1.start, h1.accept, h1);
auto e2_accept = edge(h2.start, h2.accept, h2);
if (e1_accept.second && e2_accept.second &&
h1[e1_accept.first].top != h2[e2_accept.first].top) {
return false;
}
// If both graphs have edge (start, acceptEod), the tops must match.
auto e1_eod = edge(h1.start, h1.acceptEod, h1);
auto e2_eod = edge(h2.start, h2.acceptEod, h2);
if (e1_eod.second && e2_eod.second &&
h1[e1_eod.first].top != h2[e2_eod.first].top) {
return false;
}
// If one graph has an edge to accept and the other has an edge to
// acceptEod, the reports must match for the merge to be safe.
if ((e1_accept.second && e2_eod.second) ||
(e2_accept.second && e1_eod.second)) {
if (h1[h1.start].reports != h2[h2.start].reports) {
return false;
}
if (h1[h1.startDs].reports
!= h2[h2.startDs].reports) {
return false;
}
pair<NFAEdge, bool> e1, e2;
e1 = edge(h1.start, h1.accept, h1);
e2 = edge(h2.start, h2.accept, h2);
if (e1.second || e2.second) {
if (e1.second && e2.second &&
h1[e1.first].top != h2[e2.first].top) {
return false;
}
}
e1 = edge(h1.start, h1.acceptEod, h1);
e2 = edge(h2.start, h2.acceptEod, h2);
if (e1.second || e2.second) {
if (e1.second && e2.second &&
h1[e1.first].top != h2[e2.first].top) {
return false;
}
}
}
return true;
@ -545,20 +541,14 @@ bool mergeNfaPair(NGHolder &ga, NGHolder &gb, const ReportManager *rm,
auto a_state_ids = numberStates(ga);
auto b_state_ids = numberStates(gb);
// At the moment, since our vertices can only have one report ID each,
// we must ensure that our start vertices have the same report ID,
// otherwise they can't be merged. This happens in vacuous NFAs, used
// by Rose.
// XXX: the multi-top code has this limitation, too.
// Vacuous NFAs require special checks on their starts to ensure that tops
// match, and that reports match for mixed-accept cases.
if (!mergeableStarts(ga, gb)) {
DEBUG_PRINTF("starts aren't mergeable\n");
return false;
}
// NOTE: states must be numbered already.
u32 cpl = commonPrefixLength(ga, a_state_ids, gb, b_state_ids);
if (!shouldMerge(gb, b_state_ids, ga, a_state_ids, cpl, rm, cc)) {
return false;
}