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, 13 insertions, 0 deletions

diff --git a/op.h b/op.h
index 100514c6ad..598e20156f 100644
--- a/op.h
+++ b/op.h
@@ -1016,6 +1016,15 @@ is also available as well as C<OP_TYPE_IS_OR_WAS_NN>
 and C<OP_TYPE_ISNT_AND_WASNT_NN> which elide
 the NULL pointer check.
 
+=for apidoc Am|bool|OP_HAS_SIBLING|OP *o
+Returns true if o has a sibling
+
+=for apidoc Am|bool|OP_SIBLING|OP *o
+Returns the sibling of o, or NULL if there is no sibling
+
+=for apidoc Am|bool|OP_SIBLING_set|OP *o|OP *sib
+Sets the sibling of o to sib
+
 =cut
 */
 
@@ -1052,6 +1061,10 @@ the NULL pointer check.
 #define OP_TYPE_ISNT_AND_WASNT(o, type) \
     ( (o) && OP_TYPE_ISNT_AND_WASNT_NN(o, type) )
 
+#define OP_HAS_SIBLING(o)      (cBOOL((o)->op_sibling))
+#define OP_SIBLING(o)          (0 + (o)->op_sibling)
+#define OP_SIBLING_set(o, sib) ((o)->op_sibling = (sib))
+
 #define newATTRSUB(f, o, p, a, b) Perl_newATTRSUB_x(aTHX_  f, o, p, a, b, FALSE)
 #define newSUB(f, o, p, b)	newATTRSUB((f), (o), (p), NULL, (b))