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, 2 insertions, 2 deletions

diff --git a/util.c b/util.c
index 21f51ba50b..c4707e243f 100644
--- a/util.c
+++ b/util.c
@@ -1323,7 +1323,7 @@ Perl_closest_cop(pTHX_ const COP *cop, const OP *o, const OP *curop,
 
     if (o->op_flags & OPf_KIDS) {
 	const OP *kid;
-	for (kid = cUNOPo->op_first; kid; kid = kid->op_sibling) {
+	for (kid = cUNOPo->op_first; kid; kid = OP_SIBLING(kid)) {
 	    const COP *new_cop;
 
 	    /* If the OP_NEXTSTATE has been optimised away we can still use it
@@ -1416,7 +1416,7 @@ Perl_mess_sv(pTHX_ SV *basemsg, bool consume)
 	 */
 
 	const COP *cop =
-	    closest_cop(PL_curcop, PL_curcop->op_sibling, PL_op, FALSE);
+	    closest_cop(PL_curcop, OP_SIBLING(PL_curcop), PL_op, FALSE);
 	if (!cop)
 	    cop = PL_curcop;