Issue 18774: Update news and whatsnew for the set optimizations

Doc/whatsnew/3.4.rst

@@ -389,6 +389,12 @@ Major performance enhancements have been added:
 
 * The UTF-32 decoder is now 3x to 4x faster.
 
+* The cost of hash collisions for sets is now reduced.  Each hash table
+  probe now checks a second key/hash pair for each cache line retrieved.
+  This exploits cache locality to make collision resolution less expensive.
+
+  (Contributed by Raymond Hetting in :issue"`18771`.)
+
 
 Build and C API Changes
 =======================

Misc/NEWS

@@ -12,6 +12,10 @@ Core and Builtins
 
 - Issue #18774: Remove last bits of GNU PTH thread code and thread_pth.h.
 
+- Issue #18771: Add optimization to set object lookups to reduce the cost
+  of hash collisions.  The core idea is to inspect a second key/hash pair
+  for each cache line retrieved.
+
 - Issue #16105: When a signal handler fails to write to the file descriptor
   registered with ``signal.set_wakeup_fd()``, report an exception instead
   of ignoring the error.