I've committed this patch to document recent addition.
Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
retrieving revision 1.14
diff -u -r1.14 changes.html
--- changes.html 14 Jul 2015 12:55:08 -0000 1.14
+++ changes.html 21 Jul 2015 09:29:51 -0000
@@ -43,6 +43,10 @@
<li>A new command-line option <code>-Wshift-negative-value</code> has been
added for the C and C++ compilers, which warns about left shifting
a negative value.</li>
+ <li>A new command-line option <code>-Wshift-overflow</code> has been
+ added for the C and C++ compilers, which warns about left shift
+ overflows. <code>-Wshift-overflow=2</code> also warns about
+ left-shifting 1 into the sign bit.</li>
</ul>
<h3 id="c">C</h3>
Marek
