Perl_setlocale(): Same code for all param2 == NULL

Calling Perl_setlocale() with a NULL 2nd parameter returns the current
locale, rather than changing it.  Previously LC_NUMERIC and LC_ALL were
treated specially; other categories were lumped in with the code that
changes the locale.

Changing some categories involves a non-trivial amount of work.  This
commit avoids that by moving all queries to the same 'if' branch.
LC_NUMERIC and LC_ALL still have to be treated specially, but now it's
all within the same outer 'if', and the unnecessarily executing code
for when the locale changes is avoided.

locale.c

@@ -2233,16 +2233,19 @@ Perl_setlocale(const int category, const char * locale)
     unsigned int cat_index;
     dSAVEDERRNO;
     dTHX;
+
+    /* A NULL locale means only query what the current one is. */
+    if (locale == NULL) {
+
+#  ifdef USE_LOCALE_NUMERIC
+#    ifdef LC_ALL
+
     DECLARATION_FOR_LC_NUMERIC_MANIPULATION;
 
-#ifdef USE_LOCALE_NUMERIC
+#    endif
 
-    /* A NULL locale means only query what the current one is.  We have the
-     * LC_NUMERIC name saved, because we are normally switched into the C
-     * (or equivalent) locale for it.  For an LC_ALL query, switch back to get
-     * the correct results.  All other categories don't require special
-     * handling */
-    if (locale == NULL) {
+        /* We have the LC_NUMERIC name saved, because we are normally switched
+         * into the C locale (or equivalent) for it. */
         if (category == LC_NUMERIC) {
 
             /* We don't have to copy this return value, as it is a per-thread
@@ -2252,29 +2255,35 @@ Perl_setlocale(const int category, const char * locale)
 
 #  ifdef LC_ALL
 
-        else if (category == LC_ALL) {
+        /* For an LC_ALL query, switch back to the underlying numeric locale
+         * (if we aren't there already) so as to get the correct results.  Our
+         * records for all the other categories are valid without switching */
+        if (category == LC_ALL) {
             STORE_LC_NUMERIC_FORCE_TO_UNDERLYING();
         }
 
 #  endif
+#  endif    /* End of has LC_NUMERIC */
+
+        retval = save_to_buffer(querylocale_r(category),
+                                &PL_setlocale_buf, &PL_setlocale_bufsize, 0);
 
+#  if defined(USE_LOCALE_NUMERIC) && defined(LC_ALL)
+
+        if (category == LC_ALL) {
+            RESTORE_LC_NUMERIC();
     }
 
-#endif
+#  endif
+
+        return retval;
+    } /* End of querying the current locale */
 
     cat_index = get_category_index(category, NULL);
     retval = save_to_buffer(setlocale_i(cat_index, locale),
                             &PL_setlocale_buf, &PL_setlocale_bufsize, 0);
     SAVE_ERRNO;
 
-#if defined(USE_LOCALE_NUMERIC) && defined(LC_ALL)
-
-    if (locale == NULL && category == LC_ALL) {
-        RESTORE_LC_NUMERIC();
-    }
-
-#endif
-
     DEBUG_L(PerlIO_printf(Perl_debug_log,
         "%s:%d: %s\n", __FILE__, __LINE__,
             setlocale_debug_string_r(category, locale, retval)));
@@ -2285,11 +2294,6 @@ Perl_setlocale(const int category, const char * locale)
         return NULL;
     }
 
-    /* If locale == NULL, we are just querying the state */
-    if (locale == NULL) {
-        return retval;
-    }
-
     /* Now that have changed locales, we have to update our records to
      * correspond.  Only certain categories have extra work to update. */
     if (update_functions[cat_index]) {