From 90361bc6f4ffffedb444e86380b6d1e08475fa74 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Wed, 19 Apr 2023 13:07:46 -0400
Subject: [PATCH] c++: bad ggc_free in try_class_unification [PR109556]
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.
(cherry picked from commit 5e284ebbc3082c5a8974d24e3a0977aa48f3cc60)
---
gcc/cp/pt.cc | 5 -----
.../g++.dg/cpp2a/concepts-placeholder13.C | 18 ++++++++++++++++++
2 files changed, 18 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-placeholder13.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index e065ace5c55c..68a056acf8b6 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -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;
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder13.C b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder13.C
new file mode 100644
index 000000000000..ac9f84524d31
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-placeholder13.C
@@ -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>{});
+}
--
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