Use depfiles in FindComputeCpp.cmake (#130)

Adds `DEPFILE` to the custom command that invokes the device compiler to
trigger rebuilds of the integration header once an included header changed when
using the Ninja generator and CMake 3.7 and up.

Also, ComputeCpp_ROOT_DIR is set based on the location of the INCLUDE
directory. These locatons are derived from the cache variable passed
by the user, if present, failing that an environment variable, and if
neither are passed, the standard system locations.

Additionally removes a trailing whitespace.

cmake/Modules/FindComputeCpp.cmake

@@ -59,42 +59,42 @@ find_package(OpenCL REQUIRED)
 # Find ComputeCpp package
 
 # Try to read the environment variable
-if(DEFINED ENV{COMPUTECPP_DIR})
-  if(NOT ComputeCpp_DIR)
-    set(ComputeCpp_ROOT_DIR $ENV{COMPUTECPP_DIR} CACHE PATH
-      "The root of the ComputeCpp install")
-  endif()
-else()
-  set(ComputeCpp_ROOT_DIR ${ComputeCpp_DIR} CACHE PATH
-    "The root of the ComputeCpp install")
+if(DEFINED ComputeCpp_DIR)
+  set(computecpp_find_hint ${ComputeCpp_DIR})
+elseif(DEFINED ENV{COMPUTECPP_DIR})
+  set(computecpp_find_hint $ENV{COMPUTECPP_DIR})
 endif()
 
 find_program(ComputeCpp_DEVICE_COMPILER_EXECUTABLE compute++
-  PATHS ${ComputeCpp_ROOT_DIR}
+  PATHS ${computecpp_find_hint}
   PATH_SUFFIXES bin)
 
 find_program(ComputeCpp_INFO_EXECUTABLE computecpp_info
-  PATHS ${ComputeCpp_ROOT_DIR}
+  PATHS ${computecpp_find_hint}
   PATH_SUFFIXES bin)
 
 find_library(COMPUTECPP_RUNTIME_LIBRARY
   NAMES ComputeCpp ComputeCpp_vs2015
-  PATHS ${ComputeCpp_ROOT_DIR}
+  PATHS ${computecpp_find_hint}
   PATH_SUFFIXES lib
   DOC "ComputeCpp Runtime Library")
 
 find_library(COMPUTECPP_RUNTIME_LIBRARY_DEBUG
   NAMES ComputeCpp ComputeCpp_vs2015_d
-  PATHS ${ComputeCpp_ROOT_DIR}
+  PATHS ${computecpp_find_hint}
   PATH_SUFFIXES lib
   DOC "ComputeCpp Debug Runtime Library")
 
 find_path(ComputeCpp_INCLUDE_DIRS
   NAMES "CL/sycl.hpp"
-  PATHS ${ComputeCpp_ROOT_DIR}/include
+  PATHS ${computecpp_find_hint}/include
   DOC "The ComputeCpp include directory")
 get_filename_component(ComputeCpp_INCLUDE_DIRS ${ComputeCpp_INCLUDE_DIRS} ABSOLUTE)
 
+get_filename_component(computecpp_canonical_root_dir "${ComputeCpp_INCLUDE_DIRS}/.." ABSOLUTE)
+set(ComputeCpp_ROOT_DIR "${computecpp_canonical_root_dir}" CACHE PATH
+    "The root of the ComputeCpp install")
+
 execute_process(COMMAND ${ComputeCpp_INFO_EXECUTABLE} "--dump-version"
   OUTPUT_VARIABLE ComputeCpp_VERSION
   RESULT_VARIABLE ComputeCpp_INFO_EXECUTABLE_RESULT OUTPUT_STRIP_TRAILING_WHITESPACE)
@@ -174,7 +174,7 @@ set_target_properties(ComputeCpp::ComputeCpp PROPERTIES
   IMPORTED_LOCATION_RELWITHDEBINFO "${COMPUTECPP_RUNTIME_LIBRARY_DEBUG}"
   IMPORTED_LOCATION                "${COMPUTECPP_RUNTIME_LIBRARY}"
   INTERFACE_INCLUDE_DIRECTORIES    "${ComputeCpp_INCLUDE_DIRS}"
-  INTERFACE_LINK_LIBRARIES         "OpenCL::OpenCL" 
+  INTERFACE_LINK_LIBRARIES         "OpenCL::OpenCL"
 )
 
 # This property allows targets to specify that their sources should be
@@ -234,6 +234,7 @@ function(__build_ir)
 
   # Set the path to the integration header.
   set(outputSyclFile ${CMAKE_CURRENT_BINARY_DIR}/${sourceFileName}.sycl)
+  set(depFileName ${CMAKE_CURRENT_BINARY_DIR}/${sourceFileName}.sycl.d)
 
   set(include_directories "$<TARGET_PROPERTY:${SDK_BUILD_IR_TARGET},INCLUDE_DIRECTORIES>")
   set(compile_definitions "$<TARGET_PROPERTY:${SDK_BUILD_IR_TARGET},COMPILE_DEFINITIONS>")
@@ -281,6 +282,14 @@ function(__build_ir)
     endforeach()
   endif()
 
+  # Depfile support was only added in CMake 3.7
+  # CMake throws an error if it is unsupported by the generator (i. e. not ninja)
+  if((NOT CMAKE_VERSION VERSION_LESS 3.7.0) AND
+          CMAKE_GENERATOR MATCHES "Ninja")
+      set(generate_depfile -MMD -MF ${depFileName})
+      set(enable_depfile "DEPFILE ${depFileName}")
+  endif()
+
   # Add custom command for running compute++
   add_custom_command(
     OUTPUT ${outputSyclFile}
@@ -292,8 +301,10 @@ function(__build_ir)
             ${generated_compile_definitions}
             -o ${outputSyclFile}
             -c ${SDK_BUILD_IR_SOURCE}
+            ${generate_depfile}
     DEPENDS ${ir_dependencies}
     IMPLICIT_DEPENDS CXX ${SDK_BUILD_IR_SOURCE}
+    ${enable_depfile}
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
     COMMENT "Building ComputeCpp integration header file ${outputSyclFile}")