CMake: Pass OpenMP compiler and linker flags through CMake targets

ywwry66 · ywwry66 · commit a6e21835a264 · 2025-03-12T22:03:32.000-04:00
Using `OpenMP::OpenMP_LANG` targets for CMake is less error-prone than
passing the compiler and linker flags manually. Furthermore, it allows
the user to customize those flags by setting `OpenMP_LANG_FLAGS`,
`OpenMP_LANG_LIB_NAMES`, and `OpenMP_omp_LIBRARY`.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -110,7 +110,8 @@ endif()
 message(WARNING "CMake support is experimental. It does not yet support all build options and may not produce the same Makefiles that OpenBLAS ships with.")
 
 if (USE_OPENMP)
-  find_package(OpenMP REQUIRED)
+  find_package(OpenMP COMPONENTS C REQUIRED)
+  set(CCOMMON_OPT "${CCOMMON_OPT} -DUSE_OPENMP")
 endif ()
 
 include("${PROJECT_SOURCE_DIR}/cmake/utils.cmake")
@@ -230,6 +231,12 @@ endif ()
 # add objects to the openblas lib
 if(NOT NO_LAPACK)
   add_library(LAPACK_OVERRIDES OBJECT ${LA_SOURCES})
+  if (USE_OPENMP AND (NOT NOFORTRAN))
+    # Disable OpenMP for LAPACK Fortran codes on Windows.
+    if(NOT ${CMAKE_SYSTEM_NAME} STREQUAL "Windows")
+      target_link_libraries(LAPACK_OVERRIDES OpenMP::OpenMP_Fortran)
+    endif()
+  endif()
   list(APPEND TARGET_OBJS "$<TARGET_OBJECTS:LAPACK_OVERRIDES>")
 endif()
 if(NOT NO_LAPACKE)
diff --git a/cmake/arch.cmake b/cmake/arch.cmake
@@ -31,17 +31,6 @@ if (${CMAKE_C_COMPILER_ID} STREQUAL "Intel")
   set(CCOMMON_OPT "${CCOMMON_OPT} -wd981")
 endif ()
 
-if (USE_OPENMP)
-  # USE_SIMPLE_THREADED_LEVEL3 = 1
-  # NO_AFFINITY = 1
-  find_package(OpenMP REQUIRED)
-  if (OpenMP_FOUND)
-    set(CCOMMON_OPT "${CCOMMON_OPT} ${OpenMP_C_FLAGS} -DUSE_OPENMP")
-    set(FCOMMON_OPT "${FCOMMON_OPT} ${OpenMP_Fortran_FLAGS}")
-  endif()
-endif ()
-
-
 if (DYNAMIC_ARCH)
   if (ARM64)
     set(DYNAMIC_CORE ARMV8 CORTEXA53 CORTEXA57 THUNDERX THUNDERX2T99 TSV110 EMAG8180 NEOVERSEN1 THUNDERX3T110)
diff --git a/cmake/f_check.cmake b/cmake/f_check.cmake
@@ -24,6 +24,9 @@ include(CheckLanguage)
 check_language(Fortran)
 if(CMAKE_Fortran_COMPILER)
   enable_language(Fortran)
+  if (USE_OPENMP)
+    find_package(OpenMP COMPONENTS Fortran REQUIRED)
+  endif ()
 else()
   set (NOFORTRAN 1)
   if (NOT NO_LAPACK)
diff --git a/cmake/fc.cmake b/cmake/fc.cmake
@@ -7,7 +7,7 @@ if (${F_COMPILER} STREQUAL "FLANG" AND NOT CMAKE_Fortran_COMPILER_ID STREQUAL "L
   # This is for classic Flang. LLVM Flang is handled with gfortran below.
   set(CCOMMON_OPT "${CCOMMON_OPT} -DF_INTERFACE_FLANG")
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -fopenmp")
+    set(OpenMP_Fortran_FLAGS "-fopenmp")
   endif ()
   set(FCOMMON_OPT "${FCOMMON_OPT} -Mrecursive -Kieee")
 endif ()
@@ -117,7 +117,7 @@ if (${F_COMPILER} STREQUAL "GFORTRAN" OR ${F_COMPILER} STREQUAL "F95" OR CMAKE_F
   endif ()
 
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -fopenmp")
+    set(OpenMP_Fortran_FLAGS "-fopenmp")
   endif ()
 endif ()
 
@@ -128,14 +128,14 @@ if (${F_COMPILER} STREQUAL "INTEL" OR CMAKE_Fortran_COMPILER_ID MATCHES "Intel")
   endif ()
   set(FCOMMON_OPT "${FCOMMON_OPT} -recursive -fp-model=consistent")
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -openmp")
+    set(OpenMP_Fortran_FLAGS "-openmp")
   endif ()
 endif ()
 
 if (${F_COMPILER} STREQUAL "FUJITSU")
   set(CCOMMON_OPT "${CCOMMON_OPT} -DF_INTERFACE_FUJITSU")
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -openmp")
+    set(OpenMP_Fortran_FLAGS "-openmp")
   endif ()
 endif ()
 
@@ -151,7 +151,7 @@ if (${F_COMPILER} STREQUAL "IBM")
     set(FCOMMON_OPT "${FCOMMON_OPT} -q32")
   endif ()
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -openmp")
+    set(OpenMP_Fortran_FLAGS "-openmp")
   endif ()
 endif ()
 
@@ -168,7 +168,7 @@ if (${F_COMPILER} STREQUAL "PGI" OR ${F_COMPILER} STREQUAL "PGF95")
   endif ()
   set(FCOMMON_OPT "${FCOMMON_OPT} -Mrecursive")
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -mp")
+    set(OpenMP_Fortran_FLAGS "-mp")
   endif ()
 endif ()
 
@@ -195,7 +195,7 @@ if (${F_COMPILER} STREQUAL "PATHSCALE")
   endif ()
 
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -mp")
+    set(OpenMP_Fortran_FLAGS "-mp")
   endif ()
 endif ()
 
@@ -233,7 +233,7 @@ if (${F_COMPILER} STREQUAL "OPEN64")
 
   if (USE_OPENMP)
     set(FEXTRALIB "${FEXTRALIB} -lstdc++")
-    set(FCOMMON_OPT "${FCOMMON_OPT} -mp")
+    set(OpenMP_Fortran_FLAGS "-mp")
   endif ()
 endif ()
 
@@ -245,14 +245,14 @@ if (${F_COMPILER} STREQUAL "SUN")
     set(FCOMMON_OPT "${FCOMMON_OPT} -m64")
   endif ()
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -xopenmp=parallel")
+    set(OpenMP_Fortran_FLAGS "-xopenmp=parallel")
   endif ()
 endif ()
 
 if (${F_COMPILER} STREQUAL "COMPAQ")
   set(CCOMMON_OPT "${CCOMMON_OPT} -DF_INTERFACE_COMPAQ")
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -openmp")
+    set(OpenMP_Fortran_FLAGS "-openmp")
   endif ()
 endif ()
 
@@ -265,7 +265,7 @@ if (${F_COMPILER} STREQUAL "CRAY")
   if (NOT USE_OPENMP)
     set(FCOMMON_OPT "${FCOMMON_OPT} -fno-openmp")
   else ()
-    set(FCOMMON_OPT "${FCOMMON_OPT} -fopenmp")
+    set(OpenMP_Fortran_FLAGS "-fopenmp")
   endif ()
 endif ()
 
@@ -290,7 +290,7 @@ if (${F_COMPILER} STREQUAL "NAGFOR")
   # -w=unused: Suppress warning messages about unused variables
   set(FCOMMON_OPT "${FCOMMON_OPT} -w=x77 -w=ques -w=unused")
   if (USE_OPENMP)
-    set(FCOMMON_OPT "${FCOMMON_OPT} -openmp")
+    set(OpenMP_Fortran_FLAGS "-openmp")
   endif ()
 endif ()
 
diff --git a/cmake/system.cmake b/cmake/system.cmake
@@ -655,15 +655,6 @@ if (LAPACK_STRLEN)
 endif()
 set(LAPACK_FPFLAGS "${LAPACK_FPFLAGS} ${FPFLAGS}")
 
-#Disable -fopenmp for LAPACK Fortran codes on Windows.
-if (${CMAKE_SYSTEM_NAME} STREQUAL "Windows")
-  set(FILTER_FLAGS "-fopenmp;-mp;-openmp;-xopenmp=parallel")
-  foreach (FILTER_FLAG ${FILTER_FLAGS})
-    string(REPLACE ${FILTER_FLAG} "" LAPACK_FFLAGS ${LAPACK_FFLAGS})
-    string(REPLACE ${FILTER_FLAG} "" LAPACK_FPFLAGS ${LAPACK_FPFLAGS})
-  endforeach ()
-endif ()
-
 if (CMAKE_Fortran_COMPILER)
   if ("${F_COMPILER}" STREQUAL "NAGFOR" OR "${F_COMPILER}" STREQUAL "CRAY" OR CMAKE_Fortran_COMPILER_ID MATCHES "LLVMFlang.*")
     set(FILTER_FLAGS "-msse3;-mssse3;-msse4.1;-mavx;-mavx2,-mskylake-avx512")
diff --git a/driver/level2/CMakeLists.txt b/driver/level2/CMakeLists.txt
@@ -223,3 +223,7 @@ if (USE_THREAD)
 endif ()
 
 add_library(driver_level2 OBJECT ${OPENBLAS_SRC})
+
+if (USE_OPENMP)
+  target_link_libraries(driver_level2 OpenMP::OpenMP_C)
+endif()
diff --git a/driver/level3/CMakeLists.txt b/driver/level3/CMakeLists.txt
@@ -171,3 +171,7 @@ endforeach ()
 #
 
 add_library(driver_level3 OBJECT ${OPENBLAS_SRC})
+
+if (USE_OPENMP)
+  target_link_libraries(driver_level3 OpenMP::OpenMP_C)
+endif()
diff --git a/driver/others/CMakeLists.txt b/driver/others/CMakeLists.txt
@@ -88,3 +88,7 @@ endif ()
 #endif
 
 add_library(driver_others OBJECT ${OPENBLAS_SRC} ${MEMORY} ${SMP_SOURCES} ${COMMON_SOURCES})
+
+if (USE_OPENMP)
+  target_link_libraries(driver_others OpenMP::OpenMP_C)
+endif()
diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
@@ -250,3 +250,7 @@ if ( BUILD_COMPLEX16 AND NOT  BUILD_DOUBLE)
 endif ()
 
 add_library(interface OBJECT ${OPENBLAS_SRC})
+
+if (USE_OPENMP)
+  target_link_libraries(interface OpenMP::OpenMP_C)
+endif()
diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
@@ -1364,6 +1364,9 @@ endif ()
     if (USE_GEMM3M)
       target_compile_definitions(kernel${TSUFFIX} PRIVATE USE_GEMM3M)
     endif()
+    if (USE_OPENMP)
+      target_link_libraries(kernel${TSUFFIX} OpenMP::OpenMP_C)
+    endif()
 endfunction ()
 
 
diff --git a/lapack/CMakeLists.txt b/lapack/CMakeLists.txt
@@ -117,3 +117,7 @@ GenerateCombinationObjects("${UNIT_SOURCES}" "UNIT" "N" "" 4)
 GenerateCombinationObjects("${UNIT_SOURCES2}" "UNIT" "N" "" 0 "" "" 3)
 
 add_library(lapack OBJECT ${OPENBLAS_SRC})
+
+if (USE_OPENMP)
+  target_link_libraries(lapack OpenMP::OpenMP_C)
+endif()

Original file line number	Diff line number	Diff line change
`@@ -171,3 +171,7 @@ endforeach ()`
`171`	`171`	`#`
`172`	`172`
`173`	`173`	`add_library(driver_level3 OBJECT ${OPENBLAS_SRC})`
	`174`	`+`
	`175`	`+if (USE_OPENMP)`
	`176`	`+ target_link_libraries(driver_level3 OpenMP::OpenMP_C)`
	`177`	`+endif()`