structs: deal with initialization diamond problem.

Until now it has been documented that if a struct type
inherits a supertype two or more times, then the supertype
initialization occurs that many times.

This change fixes the behavior: bases are initialized once.

* struct.c (struct struct_type): New members, ndsupers, dsus
providing a flat array for tracking duplicate supertypes.
(get_all_supers, get_duplicate_supers): New static functions.
(make_struct_type): Calculate the duplicate supers, and store
them in the dsus array. Under 242 or lower compat mode,
pretend there are duplicates, which defeats the duplicate
detecting mechanism
(struct_type_destroy): Free the dsus array.
(call_inittfun_chain, call_postinitfun_chain): Take new
arguments: the root type from which the recursion started, and
a stack-allocated bit vector indicating which duplicate bases
have already been initialized. If the given type appears in
the duplicate bases list of the root type, and its bit is
already set, then skip all initialization for it. Otherwise
set its bit and proceed.
(alloc_seen, clear_seen): New macros to help with allocating
the bitvector of duplicate bases.
(make_struct_impl, lazy_struct_init, reset_struct): Use
alloc_seen and clear_seen macros to manage the bitvector of
duplicate bases for calling call_initfun_chain and
call_postinitfun_chain.

* txr.1: Updated doc with new paragraph about duplicated
supertypes, and compat note added.

0 files changed, 0 insertions, 0 deletions