From a3bfa6f566da184ddceba6583f357125a2f21b9a Mon Sep 17 00:00:00 2001
From: Alexander Alekhin <alexander.alekhin@intel.com>
Date: Tue, 8 Nov 2016 18:00:03 +0300
Subject: [PATCH] cmake: ccache

---
 CMakeLists.txt                      |  2 ++
 cmake/OpenCVCompilerOptions.cmake   | 34 +++++++++++++++++++++++++++++
 cmake/OpenCVDetectCXXCompiler.cmake |  4 ----
 3 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 007b80d4da..91a6462012 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -217,6 +217,7 @@ OCV_OPTION(INSTALL_TESTS            "Install accuracy and performance test binar
 
 # OpenCV build options
 # ===================================================
+OCV_OPTION(ENABLE_CCACHE              "Use ccache"                                               (UNIX AND NOT IOS AND (CMAKE_GENERATOR MATCHES "Makefile" OR CMAKE_GENERATOR MATCHES "Ninja")) )
 OCV_OPTION(ENABLE_DYNAMIC_CUDA        "Enabled dynamic CUDA linkage"                             ON   IF ANDROID )
 OCV_OPTION(ENABLE_PRECOMPILED_HEADERS "Use precompiled headers"                                  ON   IF (NOT IOS) )
 OCV_OPTION(ENABLE_SOLUTION_FOLDERS    "Solution folder in Visual Studio or in other IDEs"        (MSVC_IDE OR CMAKE_GENERATOR MATCHES Xcode) IF (CMAKE_VERSION VERSION_GREATER "2.8.0") )
@@ -731,6 +732,7 @@ else()
   status("    Linker flags (Release):" ${CMAKE_SHARED_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS_RELEASE})
   status("    Linker flags (Debug):"   ${CMAKE_SHARED_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS_DEBUG})
 endif()
+status("    ccache:"                  CMAKE_COMPILER_IS_CCACHE THEN YES ELSE NO)
 status("    Precompiled headers:"     PCHSupport_FOUND AND ENABLE_PRECOMPILED_HEADERS THEN YES ELSE NO)
 
 # ========================== OpenCV modules ==========================
diff --git a/cmake/OpenCVCompilerOptions.cmake b/cmake/OpenCVCompilerOptions.cmake
index 499061e28c..57d142eb0b 100644
--- a/cmake/OpenCVCompilerOptions.cmake
+++ b/cmake/OpenCVCompilerOptions.cmake
@@ -1,3 +1,33 @@
+if(ENABLE_CCACHE AND NOT CMAKE_COMPILER_IS_CCACHE)
+  # This works fine with Unix Makefiles and Ninja generators
+  find_host_program(CCACHE_PROGRAM ccache)
+  if(CCACHE_PROGRAM)
+    message(STATUS "Looking for ccache - found (${CCACHE_PROGRAM})")
+    get_property(__OLD_RULE_LAUNCH_COMPILE GLOBAL PROPERTY RULE_LAUNCH_COMPILE)
+    if(__OLD_RULE_LAUNCH_COMPILE)
+      message(STATUS "Can't replace CMake compiler launcher")
+    else()
+      set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CCACHE_PROGRAM}")
+      # NOTE: Actually this check doesn't work as expected.
+      # "RULE_LAUNCH_COMPILE" is ignored by CMake during try_compile() step.
+      # ocv_check_compiler_flag(CXX "" IS_CCACHE_WORKS)
+      set(IS_CCACHE_WORKS 1)
+      if(IS_CCACHE_WORKS)
+        set(CMAKE_COMPILER_IS_CCACHE 1)
+      else()
+        message(STATUS "Unable to compile program with enabled ccache, reverting...")
+        set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${__OLD_RULE_LAUNCH_COMPILE}")
+      endif()
+    else()
+      message(STATUS "Looking for ccache - not found")
+    endif()
+  endif()
+endif()
+
+if((CMAKE_COMPILER_IS_CLANGCXX OR CMAKE_COMPILER_IS_CLANGCC OR CMAKE_COMPILER_IS_CCACHE) AND NOT CMAKE_GENERATOR MATCHES "Xcode")
+  set(ENABLE_PRECOMPILED_HEADERS OFF CACHE BOOL "" FORCE)
+endif()
+
 if(MINGW OR (X86 AND UNIX AND NOT APPLE))
   # mingw compiler is known to produce unstable SSE code with -O3 hence we are trying to use -O2 instead
   if(CMAKE_COMPILER_IS_GNUCXX)
@@ -111,6 +141,10 @@ if(CMAKE_COMPILER_IS_GNUCXX)
     add_extra_compiler_option(-pthread)
   endif()
 
+  if(CMAKE_COMPILER_IS_CLANGCXX)
+    add_extra_compiler_option(-Qunused-arguments)
+  endif()
+
   if(OPENCV_WARNINGS_ARE_ERRORS)
     add_extra_compiler_option(-Werror)
   endif()
diff --git a/cmake/OpenCVDetectCXXCompiler.cmake b/cmake/OpenCVDetectCXXCompiler.cmake
index aa7a8b6a6f..b53f8d7363 100644
--- a/cmake/OpenCVDetectCXXCompiler.cmake
+++ b/cmake/OpenCVDetectCXXCompiler.cmake
@@ -14,10 +14,6 @@ if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
   set(CMAKE_COMPILER_IS_CLANGCC 1)
 endif()
 
-if((CMAKE_COMPILER_IS_CLANGCXX OR CMAKE_COMPILER_IS_CLANGCC) AND NOT CMAKE_GENERATOR MATCHES "Xcode")
-  set(ENABLE_PRECOMPILED_HEADERS OFF CACHE BOOL "" FORCE)
-endif()
-
 # ----------------------------------------------------------------------------
 # Detect Intel ICC compiler -- for -fPIC in 3rdparty ( UNIX ONLY ):
 #  see  include/opencv/cxtypes.h file for related   ICC & CV_ICC defines.