updated doc for fast cycle detection

doc/faq.txt

@@ -67,6 +67,13 @@ compilation but it will also use more memory because
 resulting in a trade off between speed of compilation and memory
 usage.
 
+Alternatively, if the graph is big, using the flag ``cycle_detection=fast``
+will speedup the computations by removing some of the inplace
+optimizations. This would allow theano to skip a time consuming cycle
+detection algorithm. If the graph is big enough,we suggest that you use
+this flag instead of ``optimizer_excluding=inplace``. It will result in a
+computation time that is in between fast compile and fast run.
+
 Theano flag `reoptimize_unpickled_function` controls if an unpickled
 theano function should reoptimize its graph or not. Theano users can
 use the standard python pickle tools to save a compiled theano

doc/tutorial/modes.txt

@@ -225,7 +225,8 @@ stabilize          "+++++"       "++"            Only applies stability opts
 =================  ============  ==============  ==================================================
 
 For a detailed list of the specific optimizations applied for each of these
-optimizers, see :ref:`optimizations`. Also, see :ref:`unsafe_optimization`.
+optimizers, see :ref:`optimizations`. Also, see :ref:`unsafe_optimization` and
+:ref:`faster-theano-function-compilation`.
 
 
 .. _using_debugmode: