macOS: add support for OpenMP, making smoke/fluid/cloth simulations faster.

This bring macOS on par with Windows and Linux. It uses the OpenMP library
added to our precompiled libraries.

Custom flags are set because FindOpenMP from CMake below 3.12 does not support
AppleClang, and more recent versions do not work with our custom directory
location either.

Differential Revision: https://developer.blender.org/D4257

3 files changed, 21 insertions, 7 deletions

diff --git a/build_files/build_environment/cmake/harvest.cmake b/build_files/build_environment/cmake/harvest.cmake
index d79d91f2b90..a281eb900e3 100644
--- a/build_files/build_environment/cmake/harvest.cmake
+++ b/build_files/build_environment/cmake/harvest.cmake
@@ -131,6 +131,10 @@ harvest(lame/lib ffmpeg/lib "*.a")
 harvest(clang/bin llvm/bin "clang-format")
 harvest(llvm/bin llvm/bin "llvm-config")
 harvest(llvm/lib llvm/lib "libLLVM*.a")
+if(APPLE)
+	harvest(openmp/lib openmp/lib "*")
+	harvest(openmp/include openmp/include "*.h")
+endif()
 harvest(ogg/lib ffmpeg/lib "*.a")
 harvest(openal/include openal/include "*.h")
 if(UNIX AND NOT APPLE)
diff --git a/build_files/build_environment/cmake/openmp.cmake b/build_files/build_environment/cmake/openmp.cmake
index ba8e6248126..d8224020ecf 100644
--- a/build_files/build_environment/cmake/openmp.cmake
+++ b/build_files/build_environment/cmake/openmp.cmake
@@ -23,7 +23,8 @@ ExternalProject_Add(external_openmp
 	URL_HASH MD5=${OPENMP_HASH}
 	PREFIX ${BUILD_DIR}/openmp
 	CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${LIBDIR}/openmp ${DEFAULT_CMAKE_FLAGS}
-	INSTALL_DIR ${LIBDIR}/clang
+	INSTALL_COMMAND cd ${BUILD_DIR}/openmp/src/external_openmp-build && install_name_tool -id '@executable_path/../Resources/lib/libomp.dylib' runtime/src/libomp.dylib && make install
+	INSTALL_PATH ${LIBDIR}/openmp
 )
 
 add_dependencies(
diff --git a/build_files/cmake/platform/platform_apple.cmake b/build_files/cmake/platform/platform_apple.cmake
index 4e78737fd9e..1b3b844642e 100644
--- a/build_files/cmake/platform/platform_apple.cmake
+++ b/build_files/cmake/platform/platform_apple.cmake
@@ -383,13 +383,22 @@ if(WITH_CYCLES_EMBREE)
 	set(PLATFORM_LINKFLAGS "${PLATFORM_LINKFLAGS} -Xlinker -stack_size -Xlinker 0x100000")
 endif()
 
+# CMake FindOpenMP doesn't know about AppleClang before 3.12, so provide custom flags.
 if(WITH_OPENMP)
-	execute_process(COMMAND ${CMAKE_C_COMPILER} --version OUTPUT_VARIABLE COMPILER_VENDOR)
-	string(SUBSTRING "${COMPILER_VENDOR}" 0 5 VENDOR_NAME) # truncate output
-	if(${VENDOR_NAME} MATCHES "Apple") # Apple does not support OpenMP reliable with gcc and not with clang
-		set(WITH_OPENMP OFF)
-	else() # vanilla gcc or clang_omp support OpenMP
-		message(STATUS "Using special OpenMP enabled compiler !") # letting find_package(OpenMP) module work for gcc
+	if(CMAKE_C_COMPILER_ID MATCHES "AppleClang" AND CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL "7.0")
+		# Use OpenMP from our precompiled libraries.
+		message(STATUS "Using ${LIBDIR}/openmp for OpenMP")
+		set(OPENMP_CUSTOM ON)
+		set(OPENMP_FOUND ON)
+		set(OpenMP_C_FLAGS "-Xclang -fopenmp -I${LIBDIR}/openmp/include")
+		set(OpenMP_CXX_FLAGS "-Xclang -fopenmp -I${LIBDIR}/openmp/include")
+		set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -L${LIBDIR}/openmp/lib -lomp")
+
+		# Copy libomp.dylib to allow executables like datatoc to work.
+		execute_process(
+			COMMAND mkdir -p ${CMAKE_BINARY_DIR}/Resources/lib
+			COMMAND cp -p ${LIBDIR}/openmp/lib/libomp.dylib ${CMAKE_BINARY_DIR}/Resources/lib/libomp.dylib
+		)
 	endif()
 endif()