From 62f651cd909d72f203bc9bd7e88607835b082c37 Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Thu, 20 Feb 2020 13:35:11 +0100
Subject: [PATCH] "taint" memoized follow sets that came from intermediate
results
tentative commit. this should solve issue 92, but isn't working, yet.
the idea is to taint any memoized follow set that hit a recursive loop,
directly or indirectly. the recursive calls (h_follow_rec) are allowed to use
these intermediates, but propagate the taint. the top-level routine (h_follow)
places the original taint on its result and may remove it at the end. it will
not return memoized results that are tainted (but compute them afresh).
---
src/cfgrammar.c | 115 ++++++++++++++++++++++++++++++++++--------------
src/cfgrammar.h | 1 +
2 files changed, 82 insertions(+), 34 deletions(-)
diff --git a/src/cfgrammar.c b/src/cfgrammar.c
index 9697e12b..22442376 100644
--- a/src/cfgrammar.c
+++ b/src/cfgrammar.c
@@ -240,6 +240,7 @@ HStringMap *h_stringmap_new(HArena *a)
m->end_branch = NULL;
m->char_branches = h_hashtable_new(a, h_eq_ptr, h_hash_ptr);
m->arena = a;
+ m->taint = false;
return m;
}
@@ -452,7 +453,7 @@ static bool any_string_shorter(size_t k, const HStringMap *m);
typedef const HStringMap *(*StringSetFun)(size_t, HCFGrammar *, HCFChoice **);
// helper for h_first_seq and h_follow
-static void stringset_extend(HCFGrammar *g, HStringMap *ret,
+static bool stringset_extend(HCFGrammar *g, HStringMap *ret,
size_t k, const HStringMap *as,
StringSetFun f, HCFChoice **tail);
@@ -546,44 +547,25 @@ static void remove_all_shorter(size_t k, HStringMap *m)
}
// h_follow adapted to the signature of StringSetFun
-static inline
-const HStringMap *h_follow_(size_t k, HCFGrammar *g, HCFChoice **s)
+static const HStringMap *
+h_follow_(size_t k, HCFGrammar *g, HCFChoice **s)
{
return h_follow(k, g, *s);
}
-const HStringMap *h_follow(size_t k, HCFGrammar *g, const HCFChoice *x)
-{
- // consider all occurances of X in g
- // the follow set of X is the union of:
- // {$} if X is the start symbol
- // given a production "A -> alpha X tail":
- // first_k(tail follow_k(A))
-
- // first_k(tail follow_k(A)) =
- // { a b | a <- first_k(tail), b <- follow_l(A), l=k-|a| }
+static const HStringMap *h_follow_rec(size_t k, HCFGrammar *g, HCFChoice **s);
- HStringMap *ret;
-
- // shortcut: follow_0(X) is always {""}
- if (k==0) {
- return g->singleton_epsilon;
- }
- // memoize via g->follow
- ensure_k(g, k);
- ret = h_hashtable_get(g->follow[k], x);
- if (ret != NULL) {
- return ret;
- }
- ret = h_stringmap_new(g->arena);
- assert(ret != NULL);
- h_hashtable_put(g->follow[k], x, ret);
+static bool
+follow_work(size_t k, HCFGrammar *g, const HCFChoice *x, HStringMap *ret)
+{
+ bool taint = false;
// if X is the start symbol, the end token is in its follow set
if (x == g->start) {
h_stringmap_put_end(ret, INSET);
}
- // iterate over g->nts
+
+ // iterate over g->nts, looking for X
size_t i;
HHashTableEntry *hte;
int x_found=0;
@@ -608,7 +590,7 @@ const HStringMap *h_follow(size_t k, HCFGrammar *g, const HCFChoice *x)
const HStringMap *first_tail = h_first_seq(k, g, tail);
// extend the elems of first_k(tail) up to length k from follow(A)
- stringset_extend(g, ret, k, first_tail, h_follow_, &a);
+ taint |= stringset_extend(g, ret, k, first_tail, h_follow_rec, &a);
}
}
}
@@ -616,7 +598,66 @@ const HStringMap *h_follow(size_t k, HCFGrammar *g, const HCFChoice *x)
}
assert(x_found || x == g->start); // no orphan non-terminals
- h_hashtable_del(g->follow[k], x);
+ return taint;
+}
+
+// inner (recursion) variant of h_follow
+static const HStringMap *h_follow_rec(size_t k, HCFGrammar *g, HCFChoice **s)
+{
+ HStringMap *ret;
+ HCFChoice *x = *s;
+
+ // shortcut: follow_0(X) is always {""}
+ if (k==0) {
+ return g->singleton_epsilon;
+ }
+
+ // memoize via g->follow
+ assert(k <= g->kmax);
+ ret = h_hashtable_get(g->follow[k], x);
+ if (ret != NULL) { // return regardless of taint
+ return ret;
+ }
+ ret = h_stringmap_new(g->arena);
+ assert(ret != NULL);
+ h_hashtable_put(g->follow[k], x, ret);
+
+ ret->taint = true;
+ ret->taint = follow_work(k, g, x, ret);
+ return ret;
+}
+
+const HStringMap *h_follow(size_t k, HCFGrammar *g, const HCFChoice *x)
+{
+ // consider all occurances of X in g
+ // the follow set of X is the union of:
+ // {$} if X is the start symbol
+ // given a production "A -> alpha X tail":
+ // first_k(tail follow_k(A))
+
+ // first_k(tail follow_k(A)) =
+ // { a b | a <- first_k(tail), b <- follow_l(A), l=k-|a| }
+
+ HStringMap *ret;
+
+ // shortcut: follow_0(X) is always {""}
+ if (k==0) {
+ return g->singleton_epsilon;
+ }
+
+ // memoize via g->follow
+ ensure_k(g, k);
+ ret = h_hashtable_get(g->follow[k], x);
+ if (ret != NULL && !ret->taint) {
+ return ret;
+ }
+ ret = h_stringmap_new(g->arena);
+ assert(ret != NULL);
+ h_hashtable_put(g->follow[k], x, ret);
+
+ ret->taint = true;
+ follow_work(k, g, x, ret);
+ ret->taint = false;
return ret;
}
@@ -643,13 +684,17 @@ HStringMap *h_predict(size_t k, HCFGrammar *g,
}
// add the set { a b | a <- as, b <- f_l(S), l=k-|a| } to ret
-static void stringset_extend(HCFGrammar *g, HStringMap *ret,
+static bool stringset_extend(HCFGrammar *g, HStringMap *ret,
size_t k, const HStringMap *as,
StringSetFun f, HCFChoice **tail)
{
+ bool taint = false;
+
if (as->epsilon_branch) {
// for a="", add f_k(tail) to ret
- h_stringmap_update(ret, f(k, g, tail));
+ const HStringMap *f_tail = f(k, g, tail);
+ taint |= f_tail->taint;
+ h_stringmap_update(ret, f_tail);
}
if (as->end_branch) {
@@ -676,9 +721,11 @@ static void stringset_extend(HCFGrammar *g, HStringMap *ret,
HStringMap *ret_ = h_stringmap_new(g->arena);
h_stringmap_put_after(ret, c, ret_);
- stringset_extend(g, ret_, k-1, as_, f, tail);
+ taint |= stringset_extend(g, ret_, k-1, as_, f, tail);
}
}
+
+ return taint;
}
diff --git a/src/cfgrammar.h b/src/cfgrammar.h
index 2e8ba83c..6068a2bc 100644
--- a/src/cfgrammar.h
+++ b/src/cfgrammar.h
@@ -37,6 +37,7 @@ typedef struct HStringMap_ {
void *end_branch; // points to leaf value
HHashTable *char_branches; // maps to inner nodes (HStringMaps)
HArena *arena;
+ bool taint; // for use by h_follow() and h_first()
} HStringMap;
HStringMap *h_stringmap_new(HArena *a);
--
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