sv.c: Don’t cache utf8 length on gmagical SVs

The cache will just be invalidate on the next fetch.  This commit avoids
extra work in those cases that are detectable.  We still have to invali-
date caches in mg_get, because caches can be created while magic is
being called and SvMAGICAL is off.

diff --git a/sv.c b/sv.c
index 493ab7b..641b56f 100644 (file)
--- a/sv.c
+++ b/sv.c
@@ -6837,7 +6837,7 @@ S_utf8_mg_len_cache_update(pTHX_ SV *const sv, MAGIC **const mgp,
                           const STRLEN ulen)
 {
     PERL_ARGS_ASSERT_UTF8_MG_LEN_CACHE_UPDATE;
-    if (SvREADONLY(sv) || !SvPOK(sv))
+    if (SvREADONLY(sv) || SvGMAGICAL(sv) || !SvPOK(sv))
        return;
 
     if (!*mgp && (SvTYPE(sv) < SVt_PVMG ||