The problem here was that with -fcompare-debug, 
execute_cleanup_cfg_post_optimizing wants to print out all the decls 
used in a function, which involves printing the DECL_INITIAL, and the 
instantiation of a FIELD_DECL with an NSDMI had an uninstantiated 
DECL_INITIAL, so the dumper got confused by the C++ tree codes.  Fixed 
by setting DECL_INITIAL of instantiated FIELD_DECLs to error_mark_node 
and using DECL_TEMPLATE_INFO to look up the original NSDMI instead.

Tested x86_64-pc-linux-gnu, applying to trunk.