Mention devirtualization in release notes

[hans]

lgtm

Can you write something about this option for UsersManual.rst too? Then we could make this note link to it.

[Prazek]

Added link to documentation

[Prazek]

Pushed on branch

docs/ReleaseNotes.rst

 
 Major New Features
 ------------------
 
 - The ``diagnose_if`` attribute has been added to clang. This attribute allows
   clang to emit a warning or error if a function call meets one or more
   user-specified conditions.
 
+- Enhanced devirtualization with
+  '-fstrict-vtable-pointers <http://clang.llvm.org/docs/UsersManual.html#cmdoption-fstrict-vtable-pointers>`_.
+  Clang devirtualizes across different basic blocks, like loops:
+
+  .. code-block:: c++
+       struct A {
+           virtual void foo();
+       };
+       void indirect(A &a, int n) {
+           for (int i = 0 ; i < n; i++)
+               a.foo();
+       }
+       void test(int n) {
+           A a;
+           indirect(a, n);
+       }
+
+
 -  ...
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 -  ...
 
 New Compiler Flags