[Docs] Add a note clarifying how to get good test performances.
Differential Revision: https://reviews.llvm.org/D56337
llvm-svn: 351885
diff --git a/llvm/docs/TestingGuide.rst b/llvm/docs/TestingGuide.rst
index e3db60d..ceb2023 100644
--- a/llvm/docs/TestingGuide.rst
+++ b/llvm/docs/TestingGuide.rst
@@ -107,6 +107,13 @@
% make check-llvm
+In order to get reasonable testing performance, build LLVM and subprojects
+in release mode, i.e.
+
+.. code-block:: bash
+
+ % cmake -DCMAKE_BUILD_TYPE="Release"
+
If you have `Clang <http://clang.llvm.org/>`_ checked out and built, you
can run the LLVM and Clang tests simultaneously using: