change HvENAME_HEK() to HvENAME_HEK_NN() where NULLs would crash anyway

gcc 12 was producing a confusing message complaining that
references to with hek_key[] were beyond the end of the array,
even though a properly HEK has bytes beyond the first we declare.

From experimentation I theorize the confusing message was produced
because HvENAME_HEK() can return a NULL pointer, and the array
pointed to by any NULL pointer is zero length, producing the
array bounds warning we were seeing.

Fixed by changing each hv_(fetch|delete)hek() call to use the
HvENAME_HEK_NN() macro variant, which doesn't include an explicit
NULL return value.

mro_method_changed_in() was a bit special, it evaluated the
hv_fetchhek() before the check for an anonymous stash, so I reordered
the code to take advantage of C99, checking the assertions before we
dereference the stash pointer, checking we have a name before trying
to look it up.

2 files changed, 11 insertions, 10 deletions

diff --git a/hv.c b/hv.c
index 5fc9ea122d..669f766705 100644
--- a/hv.c
+++ b/hv.c
@@ -2286,8 +2286,8 @@ Perl_hv_undef_flags(pTHX_ HV *hv, U32 flags)
             mro_isa_changed_in(hv);
         if (PL_stashcache) {
             DEBUG_o(Perl_deb(aTHX_ "hv_undef_flags clearing PL_stashcache for effective name '%"
-                             HEKf "'\n", HEKfARG(HvENAME_HEK(hv))));
-            (void)hv_deletehek(PL_stashcache, HvENAME_HEK(hv), G_DISCARD);
+                             HEKf "'\n", HEKfARG(HvENAME_HEK_NN(hv))));
+            (void)hv_deletehek(PL_stashcache, HvENAME_HEK_NN(hv), G_DISCARD);
         }
       }
 
@@ -2300,8 +2300,8 @@ Perl_hv_undef_flags(pTHX_ HV *hv, U32 flags)
       {
         if (name && PL_stashcache) {
             DEBUG_o(Perl_deb(aTHX_ "hv_undef_flags clearing PL_stashcache for name '%"
-                             HEKf "'\n", HEKfARG(HvNAME_HEK(hv))));
-            (void)hv_deletehek(PL_stashcache, HvNAME_HEK(hv), G_DISCARD);
+                             HEKf "'\n", HEKfARG(HvNAME_HEK_NN(hv))));
+            (void)hv_deletehek(PL_stashcache, HvNAME_HEK_NN(hv), G_DISCARD);
         }
         hv_name_set(hv, NULL, 0, flags);
       }
diff --git a/mro_core.c b/mro_core.c
index 2be181e102..3bd05af901 100644
--- a/mro_core.c
+++ b/mro_core.c
@@ -1327,17 +1327,18 @@ via, C<mro::method_changed_in(classname)>.
 void
 Perl_mro_method_changed_in(pTHX_ HV *stash)
 {
-    const char * const stashname = HvENAME_get(stash);
-    const STRLEN stashname_len = HvENAMELEN_get(stash);
-
-    SV ** const svp = hv_fetchhek(PL_isarev, HvENAME_HEK(stash), 0);
-    HV * const isarev = svp ? MUTABLE_HV(*svp) : NULL;
-
     PERL_ARGS_ASSERT_MRO_METHOD_CHANGED_IN;
 
+    const char * const stashname = HvENAME_get(stash);
+
     if(!stashname)
         Perl_croak(aTHX_ "Can't call mro_method_changed_in() on anonymous symbol table");
 
+    const STRLEN stashname_len = HvENAMELEN_get(stash);
+
+    SV ** const svp = hv_fetchhek(PL_isarev, HvENAME_HEK_NN(stash), 0);
+    HV * const isarev = svp ? MUTABLE_HV(*svp) : NULL;
+
     /* Inc the package generation, since a local method changed */
     HvMROMETA(stash)->pkg_gen++;