Index: llvm/trunk/CMakeLists.txt
===================================================================
--- llvm/trunk/CMakeLists.txt
+++ llvm/trunk/CMakeLists.txt
@@ -2,6 +2,11 @@
 
 cmake_minimum_required(VERSION 2.8.8)
 
+if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+  message(STATUS "No build type selected, default to Debug")
+  set(CMAKE_BUILD_TYPE "Debug")
+endif()
+
 # FIXME: It may be removed when we use 2.8.12.
 if(CMAKE_VERSION VERSION_LESS 2.8.12)
   # Invalidate a couple of keywords.