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* Memoise checkVarDefs since internally produced terms (i.e., not the

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result of parsing) can have very heavy sharing, causing exponential
  complexity if we naively recurse into them.  ATerms are graphs, not
  trees!
This commit is contained in:
Eelco Dolstra 2005-11-04 15:17:05 +00:00
parent 1f285cf556
commit 5bf939885a
1 changed files with 24 additions and 9 deletions
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33
src/libexpr/nixexpr.cc
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@ -301,8 +301,16 @@ Expr substitute(const ATermMap & subs, Expr e)
} }
void checkVarDefs(const ATermMap & defs, Expr e) /* We use memoisation to prevent exponential complexity on heavily
shared ATerms (remember, an ATerm is a graph, not a tree!). Note
that using an STL set is fine here wrt to ATerm garbage collection
since all the ATerms in the set are already reachable from
somewhere else. */
static void checkVarDefs2(set<Expr> & done, const ATermMap & defs, Expr e)
{ {
if (done.find(e) != done.end()) return;
done.insert(e);
ATerm name, pos, value; ATerm name, pos, value;
ATermList formals; ATermList formals;
ATerm with, body; ATerm with, body;
@ -320,22 +328,22 @@ void checkVarDefs(const ATermMap & defs, Expr e)
Expr deflt; Expr deflt;
if (!matchNoDefFormal(*i, name)) if (!matchNoDefFormal(*i, name))
if (matchDefFormal(*i, name, deflt)) if (matchDefFormal(*i, name, deflt))
checkVarDefs(defs, deflt); checkVarDefs2(done, defs, deflt);
else else
abort(); abort();
defs2.set(name, (ATerm) ATempty); defs2.set(name, (ATerm) ATempty);
} }
checkVarDefs(defs2, body); checkVarDefs2(done, defs2, body);
} }
else if (matchFunction1(e, name, body, pos)) { else if (matchFunction1(e, name, body, pos)) {
ATermMap defs2(defs); ATermMap defs2(defs);
defs2.set(name, (ATerm) ATempty); defs2.set(name, (ATerm) ATempty);
checkVarDefs(defs2, body); checkVarDefs2(done, defs2, body);
} }
else if (matchRec(e, rbnds, nrbnds)) { else if (matchRec(e, rbnds, nrbnds)) {
checkVarDefs(defs, (ATerm) nrbnds); checkVarDefs2(done, defs, (ATerm) nrbnds);
ATermMap defs2(defs); ATermMap defs2(defs);
for (ATermIterator i(rbnds); i; ++i) { for (ATermIterator i(rbnds); i; ++i) {
if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */ if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */
@ -345,25 +353,32 @@ void checkVarDefs(const ATermMap & defs, Expr e)
if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */ if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */
defs2.set(name, (ATerm) ATempty); defs2.set(name, (ATerm) ATempty);
} }
checkVarDefs(defs2, (ATerm) rbnds); checkVarDefs2(done, defs2, (ATerm) rbnds);
} }
else if (matchWith(e, with, body, pos)) { else if (matchWith(e, with, body, pos)) {
/* We can't check the body without evaluating the definitions /* We can't check the body without evaluating the definitions
(which is an arbitrary expression), so we don't do that (which is an arbitrary expression), so we don't do that
here but only when actually evaluating the `with'. */ here but only when actually evaluating the `with'. */
checkVarDefs(defs, with); checkVarDefs2(done, defs, with);
} }
else if (ATgetType(e) == AT_APPL) { else if (ATgetType(e) == AT_APPL) {
int arity = ATgetArity(ATgetAFun(e)); int arity = ATgetArity(ATgetAFun(e));
for (int i = 0; i < arity; ++i) for (int i = 0; i < arity; ++i)
checkVarDefs(defs, ATgetArgument(e, i)); checkVarDefs2(done, defs, ATgetArgument(e, i));
} }
else if (ATgetType(e) == AT_LIST) else if (ATgetType(e) == AT_LIST)
for (ATermIterator i((ATermList) e); i; ++i) for (ATermIterator i((ATermList) e); i; ++i)
checkVarDefs(defs, *i); checkVarDefs2(done, defs, *i);
}
void checkVarDefs(const ATermMap & defs, Expr e)
{
set<Expr> done;
checkVarDefs2(done, defs, e);
} }