c++: Fix ICE with type aliases in inherited CTAD [PR122070]

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, which should
always be non-NULL when called from inherited_ctad_tweaks.

	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 <egas.g.ribeiro@gmail.com>
Co-authored-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 20a1177ffab768e34fa63a014b947f30a61fa969..ccbc6eb5410a90923b42dc1028b590c1cdbcc38d 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -31631,7 +31631,11 @@ 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);
+      if (!ti)
+       /* TTYPE is a typedef to a template-id.  */
+       ti = TYPE_TEMPLATE_INFO (ttype);
+      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 (file)
index 0000000..d3b1b18
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C
@@ -0,0 +1,11 @@
+// PR c++/122070
+// { dg-do compile { target c++23 } }
+
+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 (file)
index 0000000..c7d2720
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C
@@ -0,0 +1,31 @@
+// PR c++/122070
+// { dg-do compile { target c++23 } }
+
+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"));