c++: ICE with delayed noexcept and attribute used [PR97966]

Another ICE with delayed noexcept parsing, but a bit gnarlier.

A function definition marked with __attribute__((used)) ought to be
emitted even when it is not referenced in the TU.  For a member function
template marked with __attribute__((used)) this means that it will
be instantiated: in instantiate_class_template_1 we have

11971               /* Instantiate members marked with attribute used.  */
11972               if (r != error_mark_node && DECL_PRESERVE_P (r))
11973                 mark_used (r);

It is not so surprising that this doesn't work well with delayed
noexcept parsing: when we're processing the function template we delay
the parsing, so the member "foo" is found, but then when we're
instantiating it, "foo" hasn't yet been seen, which creates a
discrepancy and a crash ensues.  "foo" hasn't yet been seen because
instantiate_class_template_1 just loops over the class members and
instantiates right away.

To make it work, this patch uses a vector to keep track of members
marked with attribute used and uses it to instantiate such members
only after we're done with the class; in particular, after we have
called finish_member_declaration for each member.  And we ought to
be verifying that we did emit such members, so I've added a bunch
of dg-finals.

gcc/cp/ChangeLog:

	PR c++/97966
	* pt.c (instantiate_class_template_1): Instantiate members
	marked with attribute used only after we're done instantiating
	the class.

gcc/testsuite/ChangeLog:

	PR c++/97966
	* g++.dg/cpp0x/noexcept63.C: New test.

1 files changed, 10 insertions, 2 deletions

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 373f827..63a0a11 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -11895,6 +11895,9 @@ instantiate_class_template_1 (tree type)
      relative to the scope of the class.  */
   pop_to_parent_deferring_access_checks ();
 
+  /* A vector to hold members marked with attribute used. */
+  auto_vec<tree> used;
+
   /* Now members are processed in the order of declaration.  */
   for (member = CLASSTYPE_DECL_LIST (pattern);
        member; member = TREE_CHAIN (member))
@@ -11968,7 +11971,7 @@ instantiate_class_template_1 (tree type)
 	      finish_member_declaration (r);
 	      /* Instantiate members marked with attribute used.  */
 	      if (r != error_mark_node && DECL_PRESERVE_P (r))
-		mark_used (r);
+		used.safe_push (r);
 	      if (TREE_CODE (r) == FUNCTION_DECL
 		  && DECL_OMP_DECLARE_REDUCTION_P (r))
 		cp_check_omp_declare_reduction (r);
@@ -12034,7 +12037,7 @@ instantiate_class_template_1 (tree type)
 			     /*flags=*/0);
 			  /* Instantiate members marked with attribute used. */
 			  if (r != error_mark_node && DECL_PRESERVE_P (r))
-			    mark_used (r);
+			    used.safe_push (r);
 			}
 		      else if (TREE_CODE (r) == FIELD_DECL)
 			{
@@ -12225,6 +12228,11 @@ instantiate_class_template_1 (tree type)
   if (TYPE_CONTAINS_VPTR_P (type) && CLASSTYPE_KEY_METHOD (type))
     vec_safe_push (keyed_classes, type);
 
+  /* Now that we've gone through all the members, instantiate those
+     marked with attribute used.  */
+  for (tree x : used)
+    mark_used (x);
+
   return type;
 }