S_fold_constants: folded sv should note be a PADTMP

op.c

@@ -4976,14 +4976,11 @@ S_fold_constants(pTHX_ OP *const o)
     is_stringify = type == OP_STRINGIFY && !o->op_folded;
     op_free(o);
     assert(sv);
-    if (is_stringify)
-        SvPADTMP_off(sv);
-    else if (!SvIMMORTAL(sv)) {
-        SvPADTMP_on(sv);
-        /* Do not set SvREADONLY(sv) here. newSVOP will call
-         * Perl_ck_svconst, which will do it. Setting it early
-         * here prevents Perl_ck_svconst from setting SvIsCOW(sv).*/
-    }
+    /* sv may have swiped the TARG from a PADTMP OP, but that flag
+     * should be off when sv is attached to the new CONST OP. */
+    SvPADTMP_off(sv);
+    /* Perl_ck_svconst will try to set READONLY and IsCOW flags on
+     * sv as part of the new CONST OP creation. */
     newop = newSVOP(OP_CONST, 0, MUTABLE_SV(sv));
     if (!is_stringify) newop->op_folded = 1;
     return newop;