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c++: bad ggc_free in try_class_unification [PR109556]

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Aside from correcting how try_class_unification copies multi-dimensional
'targs', r13-377-g3e948d645bc908 also made it ggc_free this copy as an
optimization.  But this is wrong since the call to unify within might've
captured the args in persistent memory such as the satisfaction cache
(as part of constrained auto deduction).

	PR c++/109556

gcc/cp/ChangeLog:

	* pt.cc (try_class_unification): Don't ggc_free the copy of
	'targs'.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-placeholder13.C: New test.
This commit is contained in:
Patrick Palka 2023-04-19 13:07:46 -04:00
parent 6fc8e25cb6
commit 5e284ebbc3
2 changed files with 18 additions and 5 deletions
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5
gcc/cp/pt.cc
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@ -23895,11 +23895,6 @@ try_class_unification (tree tparms, tree targs, tree parm, tree arg,
err = unify (tparms, targs, CLASSTYPE_TI_ARGS (parm),
CLASSTYPE_TI_ARGS (arg), UNIFY_ALLOW_NONE, explain_p);
if (TMPL_ARGS_HAVE_MULTIPLE_LEVELS (targs))
for (tree level : tree_vec_range (targs))
ggc_free (level);
ggc_free (targs);
return err ? NULL_TREE : arg;
}

18
gcc/testsuite/g++.dg/cpp2a/concepts-placeholder13.C Normal file
View file

@ -0,0 +1,18 @@
// PR c++/109556
// { dg-do compile { target c++20 } }
template<class T, auto N>
concept C = (N != 0);
template<auto N, auto M>
struct A { };
template<auto N, C<N> auto M>
void f(A<N, M>);
int main() {
f(A<1, 42>{});
f(A<2, 42>{});
f(A<1, 43>{});
f(A<2, 43>{});
}