perldelta for optimized match count idiom [GH #24558]

Author: richardleach

pod/perldelta.pod

@@ -99,6 +99,18 @@ There may well be none in a stable release.
 
 =item *
 
+Counting the number of matches within a string using the following common
+idiom is now more streamlined.
+
+    C<my $count =()= $str =~ /$pat/g;>
+
+Instead of pushing all matches to the stack in mortal SVs just so that
+the list assignment can count them, C<pp_match> maintains an internal
+count during matching and pushes only that at the completion of matching.
+[GH #24558]
+
+=item *
+
 XXX
 
 =back