[gcc r13-7517] c++: NSDMI instantiation during overload resolution [PR110468]

[gcc r13-7517] c++: NSDMI instantiation during overload resolution [PR110468]

[Patrick Palka]

https://gcc.gnu.org/g:23c64450cbce916547142519a72075d1930c8282

commit r13-7517-g23c64450cbce916547142519a72075d1930c8282
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jun 29 16:10:18 2023 -0400

    c++: NSDMI instantiation during overload resolution [PR110468]
    
    Here we find ourselves instantiating the NSDMI for A<1>::m when
    computing argument conversions during overload resolution, and
    thus tf_conv is set.  The flag causes mark_used for the constructor
    used in the NSDMI to exit early and not instantiate its noexcept-spec,
    which eventually leads to an ICE from nothrow_spec_p.
    
    This patch fixes this by clearing any special tsubst flags during
    instantiation of an NSDMI, since the result should be independent of
    the context that requires the instantiation.
    
            PR c++/110468
    
    gcc/cp/ChangeLog:
    
            * init.cc (maybe_instantiate_nsdmi_init): Mask out all
            tsubst flags except for tf_warning_or_error.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/noexcept79.C: New test.
    
    (cherry picked from commit 9479da4515f7d019b4ef282d0e21536431c44f71)

Diff:
---
 gcc/cp/init.cc                          |  4 ++++
 gcc/testsuite/g++.dg/cpp0x/noexcept79.C | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index de9cd1f06dd..52b33d48844 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -579,6 +579,10 @@ maybe_instantiate_nsdmi_init (tree member, tsubst_flags_t complain)
   tree init = DECL_INITIAL (member);
   if (init && DECL_LANG_SPECIFIC (member) && DECL_TEMPLATE_INFO (member))
     {
+      /* Clear any special tsubst flags; the result of NSDMI instantiation
+	 should be independent of the substitution context.  */
+      complain &= tf_warning_or_error;
+
       init = DECL_INITIAL (DECL_TI_TEMPLATE (member));
       location_t expr_loc
 	= cp_expr_loc_or_loc (init, DECL_SOURCE_LOCATION (member));
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept79.C b/gcc/testsuite/g++.dg/cpp0x/noexcept79.C
new file mode 100644
index 00000000000..d1f54d14431
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept79.C
@@ -0,0 +1,18 @@
+// PR c++/110468
+// { dg-do compile { target c++11 } }
+
+template<int T>
+struct variant {
+  variant() noexcept(T > 0);
+};
+
+template<int N>
+struct A {
+  variant<N> m = {};
+};
+
+struct B {
+  B(A<1>);
+};
+
+B b = {{}};