+(defglobal %%simple-array-n-bits%% (make-array (1+ sb!vm:widetag-mask)))
+#.(loop for info across sb!vm:*specialized-array-element-type-properties*
+ collect `(setf (aref %%simple-array-n-bits%% ,(sb!vm:saetp-typecode info))
+ ,(sb!vm:saetp-n-bits info)) into forms
+ finally (return `(progn ,@forms)))
+
+(defun allocate-vector-with-widetag (widetag length &optional n-bits)