c: Handle C_TYPE_INCOMPLETE_VARS even for ENUMERAL_TYPEs [PR94172]

The following testcases ICE, because they contain extern variable
declarations with incomplete enum types that is later completed and after
that those variables are accessed.  The ICEs are because the vars then may have
incorrect DECL_MODE etc., e.g. in the first case the var has SImode
DECL_MODE (the guessed mode for the enum), but the enum then actually has
DImode because its enumerators don't fit into unsigned int.

The following patch fixes it by using C_TYPE_INCOMPLETE_VARS not just on
incomplete struct/union types, but also incomplete enum types.
TYPE_VFIELD can't be used as it is TYPE_MIN_VALUE on ENUMERAL_TYPE,
thankfully TYPE_LANG_SLOT_1 has been used in the C FE only on
FUNCTION_TYPEs.

2020-03-17  Jakub Jelinek  <jakub@redhat.com>

	PR c/94172
	* c-tree.h (C_TYPE_INCOMPLETE_VARS): Define to TYPE_LANG_SLOT_1
	instead of TYPE_VFIELD, and support it on {RECORD,UNION,ENUMERAL}_TYPE.
	(TYPE_ACTUAL_ARG_TYPES): Check that it is only used on FUNCTION_TYPEs.
	* c-decl.c (pushdecl): Push C_TYPE_INCOMPLETE_VARS also to
	ENUMERAL_TYPEs.
	(finish_incomplete_vars): New function, moved from finish_struct.  Use
	relayout_decl instead of layout_decl.
	(finish_struct): Remove obsolete comment about C_TYPE_INCOMPLETE_VARS
	being TYPE_VFIELD.  Use finish_incomplete_vars.
	(finish_enum): Clear C_TYPE_INCOMPLETE_VARS.  Call
	finish_incomplete_vars.
	* c-typeck.c (c_build_qualified_type): Clear C_TYPE_INCOMPLETE_VARS
	also on ENUMERAL_TYPEs.

	* gcc.dg/pr94172-1.c: New test.
	* gcc.dg/pr94172-2.c: New test.

1 files changed, 27 insertions, 23 deletions

diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index 87a0734..ed5163d 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -3312,7 +3312,8 @@ pushdecl (tree x)
 	element = TREE_TYPE (element);
       element = TYPE_MAIN_VARIANT (element);
 
-      if (RECORD_OR_UNION_TYPE_P (element)
+      if ((RECORD_OR_UNION_TYPE_P (element)
+	   || TREE_CODE (element) == ENUMERAL_TYPE)
 	  && (TREE_CODE (x) != TYPE_DECL
 	      || TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE)
 	  && !COMPLETE_TYPE_P (element))
@@ -8354,6 +8355,26 @@ field_decl_cmp (const void *x_p, const void *y_p)
   return 1;
 }
 
+/* If this structure or union completes the type of any previous
+   variable declaration, lay it out and output its rtl.  */
+static void
+finish_incomplete_vars (tree incomplete_vars, bool toplevel)
+{
+  for (tree x = incomplete_vars; x; x = TREE_CHAIN (x))
+    {
+      tree decl = TREE_VALUE (x);
+      if (TREE_CODE (TREE_TYPE (decl)) == ARRAY_TYPE)
+	layout_array_type (TREE_TYPE (decl));
+      if (TREE_CODE (decl) != TYPE_DECL)
+	{
+	  relayout_decl (decl);
+	  if (c_dialect_objc ())
+	    objc_check_decl (decl);
+	  rest_of_decl_compilation (decl, toplevel, 0);
+	}
+    }
+}
+
 /* Fill in the fields of a RECORD_TYPE or UNION_TYPE node, T.
    LOC is the location of the RECORD_TYPE or UNION_TYPE's definition.
    FIELDLIST is a chain of FIELD_DECL nodes for the fields.
@@ -8612,13 +8633,6 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
       warning_at (loc, 0, "union cannot be made transparent");
     }
 
-  /* Note: C_TYPE_INCOMPLETE_VARS overloads TYPE_VFIELD which is used
-     in dwarf2out via rest_of_decl_compilation below and means
-     something totally different.  Since we will be clearing
-     C_TYPE_INCOMPLETE_VARS shortly after we iterate through them,
-     clear it ahead of time and avoid problems in dwarf2out.  Ideally,
-     C_TYPE_INCOMPLETE_VARS should use some language specific
-     node.  */
   tree incomplete_vars = C_TYPE_INCOMPLETE_VARS (TYPE_MAIN_VARIANT (t));
   for (x = TYPE_MAIN_VARIANT (t); x; x = TYPE_NEXT_VARIANT (x))
     {
@@ -8639,21 +8653,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
   /* Finish debugging output for this type.  */
   rest_of_type_compilation (t, toplevel);
 
-  /* If this structure or union completes the type of any previous
-     variable declaration, lay it out and output its rtl.  */
-  for (x = incomplete_vars; x; x = TREE_CHAIN (x))
-    {
-      tree decl = TREE_VALUE (x);
-      if (TREE_CODE (TREE_TYPE (decl)) == ARRAY_TYPE)
-	layout_array_type (TREE_TYPE (decl));
-      if (TREE_CODE (decl) != TYPE_DECL)
-	{
-	  layout_decl (decl, 0);
-	  if (c_dialect_objc ())
-	    objc_check_decl (decl);
-	  rest_of_decl_compilation (decl, toplevel, 0);
-	}
-    }
+  finish_incomplete_vars (incomplete_vars, toplevel);
 
   /* If we're inside a function proper, i.e. not file-scope and not still
      parsing parameters, then arrange for the size of a variable sized type
@@ -8932,8 +8932,10 @@ finish_enum (tree enumtype, tree values, tree attributes)
   TYPE_LANG_SPECIFIC (enumtype) = lt;
 
   /* Fix up all variant types of this enum type.  */
+  tree incomplete_vars = C_TYPE_INCOMPLETE_VARS (TYPE_MAIN_VARIANT (enumtype));
   for (tem = TYPE_MAIN_VARIANT (enumtype); tem; tem = TYPE_NEXT_VARIANT (tem))
     {
+      C_TYPE_INCOMPLETE_VARS (tem) = NULL_TREE;
       if (tem == enumtype)
 	continue;
       TYPE_VALUES (tem) = TYPE_VALUES (enumtype);
@@ -8952,6 +8954,8 @@ finish_enum (tree enumtype, tree values, tree attributes)
   /* Finish debugging output for this type.  */
   rest_of_type_compilation (enumtype, toplevel);
 
+  finish_incomplete_vars (incomplete_vars, toplevel);
+
   /* If this enum is defined inside a struct, add it to
      struct_types.  */
   if (warn_cxx_compat