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, 2 insertions, 0 deletions

diff --git a/regcomp.c b/regcomp.c
index d53105355d..decbe4a7ad 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -7686,6 +7686,8 @@ Perl__new_invlist_C_array(pTHX_ const UV* const list)
     /* Initialize the iteration pointer. */
     invlist_iterfinish(invlist);
 
+    SvREADONLY_on(invlist);
+
     return invlist;
 }
 #endif /* ifndef PERL_IN_XSUB_RE */