From 33086098769d3c593f783a0fbfa7649c136c140e Mon Sep 17 00:00:00 2001
From: Denis Davydov <davydden@gmail.com>
Date: Fri, 6 Jan 2017 20:19:41 +0100
Subject: [PATCH] add a note on -Og and -O0 debug flags

---
 doc/readme.html | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/doc/readme.html b/doc/readme.html
index 1b4a74681d..7f3bb705ce 100644
--- a/doc/readme.html
+++ b/doc/readme.html
@@ -288,6 +288,15 @@
 	  are usually found almost instantaneously, displaying the file
 	  name and line number of where the problem occurred.
 	</p>
+	<p>
+	  Debug mode, by default, uses the <code>-Og</code> flag. It promises most of the
+	  debugging experience of <code>-O0</code> but at a better performance.
+	  This is a reasonable choice for unit tests and enables numerous asserts
+	  within the library. Sometimes, however, one needs Debug mode to use
+	  <code>-O0</code> (e.g. GCC 6.2.0 optimizes out local variables with <code>-Og</code>).
+	  This can be achieved by configuring <acronym>deal.II</acronym> with
+	  <code>-DDEAL_II_HAVE_FLAG_Og=false</code>.
+	</p>
 	</li>
 
 	<li> <i>Optimized mode</i>: You will want to link with this version of
-- 
2.39.5