wrap op_sibling field access in OP_SIBLING* macros

Remove (almost all) direct access to the op_sibling field of OP structs,
and use these three new macros instead:

    OP_SIBLING(o);
    OP_HAS_SIBLING(o);
    OP_SIBLING_set(o, new_value);

OP_HAS_SIBLING is intended to be a slightly more efficient version of
OP_SIBLING when only boolean context is needed.

For now these three macros are just defined in the obvious way:

    #define OP_SIBLING(o)          (0 + (o)->op_sibling)
    #define OP_HAS_SIBLING(o)      (cBOOL((o)->op_sibling))
    #define OP_SIBLING_set(o, sib) ((o)->op_sibling = (sib))

but abstracting them out will allow us shortly to make the last pointer in
an op_sibling chain point back to the parent rather than being null, with
a new flag indicating whether this is the last op.

Perl_ck_fun() still has a couple of direct uses of op_sibling, since it
takes the field's address, which is not covered by these macros.

1 files changed, 1 insertions, 1 deletions

diff --git a/pp_sort.c b/pp_sort.c
index e205201968..f75ecd9f03 100644
--- a/pp_sort.c
+++ b/pp_sort.c
@@ -1507,7 +1507,7 @@ PP(pp_sort)
     SAVEVPTR(PL_sortcop);
     if (flags & OPf_STACKED) {
 	if (flags & OPf_SPECIAL) {
-	    OP *nullop = cLISTOP->op_first->op_sibling;	/* pass pushmark */
+	    OP *nullop = OP_SIBLING(cLISTOP->op_first);	/* pass pushmark */
             assert(nullop->op_type == OP_NULL);
 	    PL_sortcop = nullop->op_next;
 	}