c++: dependence of member noexcept-spec [PR104079]

Here a stale TYPE_DEPENDENT_P/_P_VALID value for f's function type
after replacing the type's DEFERRED_NOEXCEPT with the parsed dependent
noexcept-spec causes us to try to instantiate g's noexcept-spec ahead
of time (since it in turn appears non-dependent), leading to an ICE.

This patch fixes this by clearing TYPE_DEPENDENT_P_VALID in
fixup_deferred_exception_variants appropriately (as in
build_cp_fntype_variant).

That turns out to fix the testcase for C++17 but not for C++11/14,
because it's not until C++17 that a noexcept-spec is part of (and
therefore affects dependence of) the function type.  Since dependence of
NOEXCEPT_EXPR is defined in terms of instantiation dependence, the most
appropriate fix for earlier dialects seems to be to make instantiation
dependence consider dependence of a noexcept-spec.

	PR c++/104079

gcc/cp/ChangeLog:

	* pt.cc (value_dependent_noexcept_spec_p): New predicate split
	out from ...
	(dependent_type_p_r): ... here.
	(instantiation_dependent_r): Use value_dependent_noexcept_spec_p
	to consider dependence of a noexcept-spec before C++17.
	* tree.cc (fixup_deferred_exception_variants): Clear
	TYPE_DEPENDENT_P_VALID.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/noexcept74.C: New test.
	* g++.dg/cpp0x/noexcept74a.C: New test.

gcc/cp/pt.cc

@@ -27003,6 +27003,24 @@ invalid_nontype_parm_type_p (tree type, tsubst_flags_t complain)
   return true;
 }
 
+/* Returns true iff the noexcept-specifier for TYPE is value-dependent.  */
+
+static bool
+value_dependent_noexcept_spec_p (tree type)
+{
+  if (tree spec = TYPE_RAISES_EXCEPTIONS (type))
+    if (tree noex = TREE_PURPOSE (spec))
+      /* Treat DEFERRED_NOEXCEPT as non-dependent, since it doesn't
+	 affect overload resolution and treating it as dependent breaks
+	 things.  Same for an unparsed noexcept expression.  */
+      if (TREE_CODE (noex) != DEFERRED_NOEXCEPT
+	  && TREE_CODE (noex) != DEFERRED_PARSE
+	  && value_dependent_expression_p (noex))
+	return true;
+
+  return false;
+}
+
 /* Returns TRUE if TYPE is dependent, in the sense of [temp.dep.type].
    Assumes that TYPE really is a type, and not the ERROR_MARK_NODE.*/
 
@@ -27055,17 +27073,10 @@ dependent_type_p_r (tree type)
 	   arg_type = TREE_CHAIN (arg_type))
 	if (dependent_type_p (TREE_VALUE (arg_type)))
 	  return true;
-      if (cxx_dialect >= cxx17)
+      if (cxx_dialect >= cxx17
+	  && value_dependent_noexcept_spec_p (type))
 	/* A value-dependent noexcept-specifier makes the type dependent.  */
-	if (tree spec = TYPE_RAISES_EXCEPTIONS (type))
-	  if (tree noex = TREE_PURPOSE (spec))
-	    /* Treat DEFERRED_NOEXCEPT as non-dependent, since it doesn't
-	       affect overload resolution and treating it as dependent breaks
-	       things.  Same for an unparsed noexcept expression.  */
-	    if (TREE_CODE (noex) != DEFERRED_NOEXCEPT
-		&& TREE_CODE (noex) != DEFERRED_PARSE
-		&& value_dependent_expression_p (noex))
-	      return true;
+	return true;
       return false;
     }
   /* -- an array type constructed from any dependent type or whose
@@ -27874,6 +27885,17 @@ instantiation_dependent_r (tree *tp, int *walk_subtrees,
 	return *tp;
       break;
 
+    case TEMPLATE_DECL:
+    case FUNCTION_DECL:
+      /* Before C++17, a noexcept-specifier isn't part of the function type
+	 so it doesn't affect type dependence, but we still want to consider it
+	 for instantiation dependence.  */
+      if (cxx_dialect < cxx17
+	  && DECL_DECLARES_FUNCTION_P (*tp)
+	  && value_dependent_noexcept_spec_p (TREE_TYPE (*tp)))
+	return *tp;
+      break;
+
     default:
       break;
     }

gcc/cp/tree.cc

@@ -2839,6 +2839,10 @@ fixup_deferred_exception_variants (tree type, tree raises)
 	  }
 	else
 	  TYPE_RAISES_EXCEPTIONS (variant) = raises;
+
+	if (!TYPE_DEPENDENT_P (variant))
+	  /* We no longer know that it's not type-dependent.  */
+	  TYPE_DEPENDENT_P_VALID (variant) = false;
       }
 }
 

gcc/testsuite/g++.dg/cpp0x/noexcept74.C

@@ -0,0 +1,11 @@
+// PR c++/104079
+// { dg-do compile { target c++11 } }
+
+template<bool B>
+struct AT {
+  static void f() noexcept(B);
+
+  void g() noexcept(noexcept(f())) {
+    static_assert(noexcept(f()), "");
+  }
+};

gcc/testsuite/g++.dg/cpp0x/noexcept74a.C

@@ -0,0 +1,12 @@
+// PR c++/104079
+// { dg-do compile { target c++11 } }
+// A variant of noexcept74.C where f is a function template.
+
+template<bool B>
+struct AT {
+  template<class...> static void f() noexcept(B);
+
+  void g() noexcept(noexcept(f())) {
+    static_assert(noexcept(f()), "");
+  }
+};