Turn on read-only flag for some unchangeable inversion lists

These lists are read-only.  Turning on the flag may allow some
optimisations to be done, including some that may be added in the
future.

1 files changed, 3 insertions, 0 deletions

diff --git a/utf8.c b/utf8.c
index f4b9dc6109..1b198bf955 100644
--- a/utf8.c
+++ b/utf8.c
@@ -2735,6 +2735,8 @@ Perl__core_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 m
 	    else SvREFCNT_inc_simple_void_NN(swash_invlist);
 	}
 
+        SvREADONLY_on(swash_invlist);
+
         /* Use the inversion list stand-alone if small enough */
         if ((int) _invlist_len(swash_invlist) <= invlist_swash_boundary) {
 	    SvREFCNT_dec(retval);
@@ -3840,6 +3842,7 @@ Perl__swash_to_invlist(pTHX_ SV* const swash)
 	sv_free(other); /* through with it! */
     }
 
+    SvREADONLY_on(invlist);
     return invlist;
 }