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, 5 insertions, 3 deletions

diff --git a/op.c b/op.c
index 476d1544c1..1ca2cd35cf 100644
--- a/op.c
+++ b/op.c
@@ -4225,7 +4225,8 @@ S_fold_constants(pTHX_ OP *o)
     folded = cBOOL(o->op_folded);
     op_free(o);
     assert(sv);
-    if (type == OP_STRINGIFY) SvPADTMP_off(sv);
+    if (type == OP_STRINGIFY && !folded)
+	SvPADTMP_off(sv);
     else if (!SvIMMORTAL(sv)) {
 	SvPADTMP_on(sv);
 	SvREADONLY_on(sv);
@@ -4450,6 +4451,8 @@ Perl_op_convert_list(pTHX_ I32 type, I32 flags, OP *o)
 
     CHANGE_TYPE(o, type);
     o->op_flags |= flags;
+    if (flags & OPf_FOLDED)
+	o->op_folded = 1;
 
     o = CHECKOP(type, o);
     if (o->op_type != (unsigned)type)
@@ -10973,10 +10976,9 @@ Perl_ck_join(pTHX_ OP *o)
 	if (bairn && !OP_HAS_SIBLING(bairn) /* single-item list */
 	 && PL_opargs[bairn->op_type] & OA_RETSCALAR)
 	{
-	    OP * const ret = op_convert_list(OP_STRINGIFY, 0,
+	    OP * const ret = op_convert_list(OP_STRINGIFY, OPf_FOLDED,
 				     op_sibling_splice(o, kid, 1, NULL));
 	    op_free(o);
-	    ret->op_folded = 1;
 	    return ret;
 	}
     }