d: Fix ICE in must_pass_in_stack_var_size_or_pad with D enums [PR123411]

An `enum : enum A` type caused the already computed underlying type size
of `enum A` to be overwritten with NULL_TREE.  To fix, don't finish the
enum with layout_type unless we're handling the main variant type.

	PR d/123411

gcc/d/ChangeLog:

	* types.cc (TypeVisitor::visit (TypeEnum *)): Only call layout_type on
	the TYPE_MAIN_VARIANT of the enum.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr123411.d: New test.

Author: ibuclaw

gcc/d/types.cc

@@ -1181,33 +1181,35 @@ class TypeVisitor : public Visitor
     /* Finish the enumeration type.  */
     if (TREE_CODE (t->ctype) == ENUMERAL_TYPE)
       {
-	TYPE_MIN_VALUE (t->ctype) = TYPE_MIN_VALUE (basetype);
-	TYPE_MAX_VALUE (t->ctype) = TYPE_MAX_VALUE (basetype);
-	TYPE_UNSIGNED (t->ctype) = TYPE_UNSIGNED (basetype);
-	SET_TYPE_ALIGN (t->ctype, TYPE_ALIGN (basetype));
-	TYPE_SIZE (t->ctype) = NULL_TREE;
-	TYPE_PRECISION (t->ctype) = dmd::size (t, t->sym->loc) * 8;
+	tree type = TYPE_MAIN_VARIANT (t->ctype);
 
-	layout_type (t->ctype);
+	if (type == t->ctype)
+	  {
+	    TYPE_MIN_VALUE (type) = TYPE_MIN_VALUE (basetype);
+	    TYPE_MAX_VALUE (type) = TYPE_MAX_VALUE (basetype);
+	    TYPE_UNSIGNED (type) = TYPE_UNSIGNED (basetype);
+	    SET_TYPE_ALIGN (type, TYPE_ALIGN (basetype));
+	    TYPE_SIZE (type) = NULL_TREE;
+	    TYPE_PRECISION (type) = dmd::size (t, t->sym->loc) * 8;
+
+	    layout_type (type);
+	  }
 
 	/* Fix up all forward-referenced variants of this enum type.  */
-	for (tree v = TYPE_MAIN_VARIANT (t->ctype); v;
-	     v = TYPE_NEXT_VARIANT (v))
+	for (tree variant = TYPE_NEXT_VARIANT (type); variant;
+	     variant = TYPE_NEXT_VARIANT (variant))
 	  {
-	    if (v == t->ctype)
-	      continue;
-
-	    TYPE_VALUES (v) = TYPE_VALUES (t->ctype);
-	    TYPE_LANG_SPECIFIC (v) = TYPE_LANG_SPECIFIC (t->ctype);
-	    TYPE_MIN_VALUE (v) = TYPE_MIN_VALUE (t->ctype);
-	    TYPE_MAX_VALUE (v) = TYPE_MAX_VALUE (t->ctype);
-	    TYPE_UNSIGNED (v) = TYPE_UNSIGNED (t->ctype);
-	    TYPE_SIZE (v) = TYPE_SIZE (t->ctype);
-	    TYPE_SIZE_UNIT (v) = TYPE_SIZE_UNIT (t->ctype);
-	    SET_TYPE_MODE (v, TYPE_MODE (t->ctype));
-	    TYPE_PRECISION (v) = TYPE_PRECISION (t->ctype);
-	    SET_TYPE_ALIGN (v, TYPE_ALIGN (t->ctype));
-	    TYPE_USER_ALIGN (v) = TYPE_USER_ALIGN (t->ctype);
+	    TYPE_VALUES (variant) = TYPE_VALUES (type);
+	    TYPE_LANG_SPECIFIC (variant) = TYPE_LANG_SPECIFIC (type);
+	    TYPE_MIN_VALUE (variant) = TYPE_MIN_VALUE (type);
+	    TYPE_MAX_VALUE (variant) = TYPE_MAX_VALUE (type);
+	    TYPE_UNSIGNED (variant) = TYPE_UNSIGNED (type);
+	    TYPE_SIZE (variant) = TYPE_SIZE (type);
+	    TYPE_SIZE_UNIT (variant) = TYPE_SIZE_UNIT (type);
+	    SET_TYPE_MODE (variant, TYPE_MODE (type));
+	    TYPE_PRECISION (variant) = TYPE_PRECISION (type);
+	    SET_TYPE_ALIGN (variant, TYPE_ALIGN (type));
+	    TYPE_USER_ALIGN (variant) = TYPE_USER_ALIGN (type);
 	  }
 
 	/* Complete forward-referenced fields of this enum type.  */

gcc/testsuite/gdc.dg/pr123411.d

@@ -0,0 +1,15 @@
+// { dg-do compile }
+module object;
+enum E
+{
+    unknown
+}
+enum : E
+{
+    E_UNKNOWN
+}
+
+E test()
+{
+    return E.unknown;
+}