Return fresh scalar from join(const,const)

$ perl5.20.1 -Ilib  -le 'for(1,2) { push @_, \join "x", 1 } print for @_'
SCALAR(0x7fb131005438)
SCALAR(0x7fb131005648)
$ ./perl -Ilib  -le 'for(1,2) { push @_, \join "x", 1 } print for @_'
SCALAR(0x7fe612831b30)
SCALAR(0x7fe612831b30)

Notice how we now get two references to the same scalar.  I broke this
accidentally in 987c9691.  If join has two arguments, it gets con-
verted to a stringify op.  The stringify op might get constant-folded,
and folding of stringify is special, because the parser uses it
itself to implement qq().  So I had ck_join set op_folded to flag
the op as being a folded join.  Only that came too late, because
op_convert_list(OP_STRINGIFY,...) folds the op before it returns it.
Hence, the folded constant was flagged the wrong way, and stopped
being implicitly copied by refgen (\).

1 files changed, 4 insertions, 0 deletions

diff --git a/op.h b/op.h
index 161c1a5eea..befdc79ee4 100644
--- a/op.h
+++ b/op.h
@@ -139,6 +139,10 @@ Deprecated.  Use C<GIMME_V> instead.
                                 /*  On OP_PADRANGE, push @_ */
                                 /*  On OP_DUMP, has no label */
                                 /*  On OP_UNSTACK, in a C-style for loop */
+/* There is no room in op_flags for this one, so it has its own bit-
+   field member (op_folded) instead.  The flag is only used to tell
+   op_convert_list to set op_folded.  */
+#define OPf_FOLDED      1<<16
 
 /* old names; don't use in new code, but don't break them, either */
 #define OPf_LIST	OPf_WANT_LIST