Regtested on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
When processing inherited CTAD in C++23, type_targs_deducible_from can
be called with a synthetic alias template whose TREE_VALUE is a type
alias. Since TYPE_TEMPLATE_INFO_MAYBE_ALIAS can return NULL for type
aliases, we need to fall back to TYPE_TEMPLATE_INFO to get the template
info of the underlying type before calling TI_TEMPLATE, and otherwise
return NULL_TREE when the type lacks template info, indicating it can't
be deduced.
PR c++/122070
gcc/cp/ChangeLog:
* pt.cc (type_targs_deducible_from): Fall back to
TYPE_TEMPLATE_INFO when TYPE_TEMPLATE_INFO_MAYBE_ALIAS is NULL.
gcc/testsuite/ChangeLog:
* g++.dg/cpp23/class-deduction-inherited10.C: New test.
* g++.dg/cpp23/class-deduction-inherited9.C: New test.
Signed-off-by: Egas Ribeiro <[email protected]>
---
gcc/cp/pt.cc | 12 ++++++-
.../cpp23/class-deduction-inherited10.C | 10 ++++++
.../g++.dg/cpp23/class-deduction-inherited9.C | 31 +++++++++++++++++++
3 files changed, 52 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C
create mode 100644 gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 341e5ab8808..50d1cac5a7a 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -31641,7 +31641,17 @@ type_targs_deducible_from (tree tmpl, tree type)
per alias_ctad_tweaks. */
tparms = INNERMOST_TEMPLATE_PARMS (TREE_PURPOSE (tmpl));
ttype = TREE_VALUE (tmpl);
- tmpl = TI_TEMPLATE (TYPE_TEMPLATE_INFO_MAYBE_ALIAS (ttype));
+ tree ti = TYPE_TEMPLATE_INFO_MAYBE_ALIAS (ttype);
+
+ /* Fallback to using TYPE_TEMPLATE_INFO if
+ TYPE_TEMPLATE_INFO_MAYBE_ALIAS is NULL_TREE. */
+ if (!ti)
+ {
+ ti = TYPE_TEMPLATE_INFO (ttype);
+ if (!ti)
+ return NULL_TREE;
+ }
+ tmpl = TI_TEMPLATE (ti);
}
int len = TREE_VEC_LENGTH (tparms);
diff --git a/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C
b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C
new file mode 100644
index 00000000000..7f9c9f21645
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++23 } }
+// PR c++/122070
+template<class T> struct A { A(T) {}; };
+
+using B = A<int>;
+
+template<class T=void>
+struct C : B { using B::B; };
+
+C c = 0;
diff --git a/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C
b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C
new file mode 100644
index 00000000000..b13394bf8f9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C
@@ -0,0 +1,31 @@
+// { dg-do compile { target c++23 } }
+// PR c++/122070
+
+namespace std {
+ using size_t = decltype(sizeof(0));
+ template<typename CharT>
+ struct basic_string_view {
+ const CharT* ptr;
+ size_t len;
+ constexpr basic_string_view(const CharT* p) : ptr(p), len(0) { while
(p && p[len]) ++len; }
+ };
+ using string_view = basic_string_view<char>;
+}
+
+template<std::size_t N>
+struct sized_string_view: std::string_view {
+ using std::string_view::string_view;
+};
+template<std::size_t N>
+sized_string_view(const char (&str)[N]) -> sized_string_view<N - 1>;
+
+constexpr auto string_builder(auto first, auto second, auto... trailing) {
+ constexpr auto is_last = sizeof...(trailing) == 0;
+ auto buffer = 1;
+ if constexpr (is_last) {
+ return buffer;
+ } else
+ return string_builder(buffer, trailing...);
+}
+
+constexpr auto copyright = string_builder(sized_string_view("a"),
sized_string_view("b"), sized_string_view("c"));
--
2.52.0
