/*************************************************************************
*									 *
*	 YAP Prolog 							 *
*									 *
*	Yap Prolog was developed at NCCUP - Universidade do Porto	 *
*									 *
* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997	 *
*									 *
**************************************************************************
*									 *
* File:		eval.yap						 *
* Last rev:								 *
* mods:									 *
* comments:	optimise disjunction handling				 *
*									 *
*************************************************************************/

:- system_module( '$_eval', [], ['$full_clause_optimisation'/4]).

:- use_system_module( terms, [new_variables_in_term/3,
        variables_within_term/3]).


%, portray_clause((H:-BF))
'$full_clause_optimisation'(H, M, B0, BF) :-
	'$localise_vars_opt'(H, M, B0, BF), !.

% the idea here is to make global variables in disjunctions
% local.
'$localise_vars_opt'(H, M, (B1;B2), (NB1;NB2)) :-
	'$variables_in_term'(H, [], LV),
	'$localise_vars'(B1, M, NB1, LV, LV, []),
	'$localise_disj_vars'(B2, M, NB2, LV, LV, []).

'$localise_disj_vars'((B;B2), M, (NB ; NB2), LV, LV0, LEqs) :- !,
	'$localise_vars'(B, M, NB, LV, LV0, LEqs),
	'$localise_disj_vars'(B2, M, NB2, LV, LV0, LEqs).	
'$localise_disj_vars'(B2, M, NB, LV, LV0, LEqs) :-
	'$localise_vars'(B2, M, NB, LV, LV0, LEqs).

'$localise_vars'((A->B), M, (A->NB), LV, LV0, LEqs) :-
	'$safe_guard'(A, M), !,
	'$variables_in_term'(A, LV, LV1),
	'$localise_vars'(B, M,  NB, LV1, LV0, LEqs).
'$localise_vars'((A;B), M, (NA;NB), LV1, LV0, LEqs) :- !,
	'$localise_vars'(A, M,  NA, LV1, LV0, LEqs),
	'$localise_disj_vars'(B, M,  NB, LV1, LV0, LEqs).
'$localise_vars'(((A,B),C), M, NG, LV, LV0, LEqs) :- !,
	'$flatten_bd'((A,B),C,NB),
	'$localise_vars'(NB, M, NG, LV, LV0, LEqs).
'$localise_vars'((!,B), M, (!,NB), LV, LV0, LEqs) :- !,
	'$localise_vars'(B, M,  NB, LV, LV0, LEqs).
'$localise_vars'((X=Y,B), M, (X=Y,NB1), LV, LV0, LEqs) :-
	var(X), var(Y), !,
	'$localise_vars'(B, M,  NB1, LV, LV0, [X,Y|LEqs]).
'$localise_vars'((G,B), M, (G,NB1), LV, LV0, LEqs) :-
	'$safe_builtin'(G, M), !,
	'$variables_in_term'(G, LV, LV1),
	'$add_extra_safe'(G, NLV0, LV0),
	'$localise_vars'(B, M,  NB1, LV1, NLV0, LEqs).
'$localise_vars'((G1,B1), _, O, LV, LV0, LEqs) :- !,
	terms:variables_within_term(LV, B1, Commons),
	terms:new_variables_in_term(LV, B1, New),
	copy_term(Commons+New+LEqs+B1, NCommons+NNew+NLEqs+NB1),
	NNew = New,
	NLEqs = LEqs,
	'$gen_equals'(Commons, NCommons, LV0, (G1,NB1), O).
'$localise_vars'(G, _, G, _, _, _).

'$gen_equals'([], [], _, O, O).
'$gen_equals'([V|Commons],[NV|NCommons], LV0, O, NO) :- V == NV, !,
	'$gen_equals'(Commons,NCommons, LV0, O, NO).
'$gen_equals'([V|Commons],[NV|NCommons], LV0, O, OO) :-
	'$vmember'(V,LV0),
         OO = (V=NV,'$safe'(NV),NO),
	'$gen_equals'(Commons,NCommons, LV0, O, NO).
'$gen_equals'([V|Commons],[NV|NCommons], LV0, O, OO) :- 
         OO = (V=NV,NO),
	'$gen_equals'(Commons,NCommons, LV0, O, NO).

'$safe_guard'((A,B), M) :- !,
	    '$safe_guard'(A, M),
	    '$safe_guard'(B, M).
'$safe_guard'((A;B), M) :- !,
	    '$safe_guard'(A, M),
	    '$safe_guard'(B, M).
'$safe_guard'(A, M) :- !,
	    '$safe_builtin'(A, M).

'$safe_builtin'(G, Mod) :-
	'$flags'(G, Mod, Fl, Fl),
	Fl /\ 0x00008880 =\= 0.

'$vmember'(V,[V1|_]) :- V == V1, !.
'$vmember'(V,[_|LV0]) :-
	'$vmember'(V,LV0).

'$flatten_bd'((A,B),R,NB) :- !,
	'$flatten_bd'(B,R,R1),
	'$flatten_bd'(A,R1,NB).
'$flatten_bd'(A,R,(A,R)).

'$add_extra_safe'('$plus'(_,_,V)) --> !, [V].
'$add_extra_safe'('$minus'(_,_,V)) --> !, [V].
'$add_extra_safe'('$times'(_,_,V)) --> !, [V].
'$add_extra_safe'('$div'(_,_,V)) --> !, [V].
'$add_extra_safe'('$and'(_,_,V)) --> !, [V].
'$add_extra_safe'('$or'(_,_,V)) --> !, [V].
'$add_extra_safe'('$sll'(_,_,V)) --> !, [V].
'$add_extra_safe'('$slr'(_,_,V)) --> !, [V].
'$add_extra_safe'(C=D,A,B) :-
   !,
   ( compound(C) ->
     '$variables_in_term'(C,E,A)
   ;
     E=A
   ),
   ( compound(D) ->
     '$variables_in_term'(D,B,E)
   ;
     B=E
   ).
'$add_extra_safe'(_) --> [].