regcomp.c: Allow search to work on empty inversion lists

You cannot retrieve the array of an empty inversion list, so the code
has to be reordered to do that after the list is known to be non-empty.
I haven't been able to find a case where this currently fails, but
future commits open up the possibility.

diff --git a/regcomp.c b/regcomp.c
index eb7655e..263b7b4 100644 (file)
--- a/regcomp.c
+++ b/regcomp.c
@@ -7323,16 +7323,24 @@ Perl__invlist_search(pTHX_ SV* const invlist, const UV cp)
 
     IV low = 0;
     IV high = invlist_len(invlist);
-    const UV * const array = invlist_array(invlist);
+    const IV highest_element = high - 1;
+    const UV* array;
 
     PERL_ARGS_ASSERT__INVLIST_SEARCH;
 
-    /* If list is empty or the code point is before the first element, return
-     * failure. */
-    if (high == 0 || cp < array[0]) {
+    /* If list is empty, return failure. */
+    if (high == 0) {
        return -1;
     }
 
+    /* If the code point is before the first element, return failure.  (We
+     * can't combine this with the test above, because we can't get the array
+     * unless we know the list is non-empty) */
+    array = invlist_array(invlist);
+    if (cp < array[0]) {
+        return -1;
+    }
+
     /* Binary search.  What we are looking for is <i> such that
      * array[i] <= cp < array[i+1]
      * The loop below converges on the i+1. */