CMake: Check for known bad configurations with LLVM Flang

.github/workflows/dynamic_arch.yml

@@ -167,9 +167,6 @@ jobs:
             idx: int32
             target-prefix: mingw-w64-clang-x86_64
             fc-pkg: fc
-            # Compiling with Flang 16 seems to cause test errors on machines
-            # with AVX512 instructions. Revisit after MSYS2 distributes Flang 17.
-            no-avx512-flags: -DNO_AVX512=1
           - msystem: CLANG32
             idx: int32
             target-prefix: mingw-w64-clang-i686
@@ -185,9 +182,6 @@ jobs:
             idx64-flags: -DBINARY=64 -DINTERFACE64=1
             target-prefix: mingw-w64-clang-x86_64
             fc-pkg: fc
-            # Compiling with Flang 16 seems to cause test errors on machines
-            # with AVX512 instructions. Revisit after MSYS2 distributes Flang 17.
-            no-avx512-flags: -DNO_AVX512=1
           - msystem: MINGW64
             idx: int32
             target-prefix: mingw-w64-x86_64
@@ -274,7 +268,6 @@ jobs:
                 -DTARGET=CORE2 \
                 ${{ matrix.idx64-flags }} \
                 ${{ matrix.c-lapack-flags }} \
-                ${{ matrix.no-avx512-flags }} \
                 -DCMAKE_C_COMPILER_LAUNCHER=ccache \
                 -DCMAKE_Fortran_COMPILER_LAUNCHER=ccache \
                 ..

CMakeLists.txt

@@ -93,6 +93,38 @@ 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(NOT NOFORTRAN)
+  # Check for working Fortran compiler
+  include(CheckLanguage)
+  check_language(Fortran)
+  if(CMAKE_Fortran_COMPILER)
+    enable_language(Fortran)
+  else()
+    set(NOFORTRAN 1)
+  endif()
+endif()
+
+if (NOT NOFORTRAN AND CMAKE_Fortran_COMPILER_ID STREQUAL "LLVMFlang")
+  if (CMAKE_Fortran_COMPILER_VERSION VERSION_LESS 17 OR WIN32)
+    # The *blas3 tests fail on hardware with AVX512 instruction when using
+    # LLVM Flang before version 17 or when using LLVM Flang on Windows.
+    # Tested with LLVM Flang 16 and LLVM Flang 17 on Windows (MSYS2/CLANG64).
+    # FIXME: Revisit with LLVM Flang 18.
+    if (NOT NO_AVX512)
+      message(STATUS "Disabling AVX512 instructions for LLVM Flang before version 17 or on Windows.")
+    endif()
+    set(NO_AVX512 1)
+  endif()
+
+  if (CMAKE_Fortran_COMPILER_VERSION VERSION_LESS 17)
+    # LLVM Flang before version 17 doesn't support necessary OpenMP constructs.
+    if (USE_OPENMP)
+      message(STATUS "Disabling OpenMP for LLVM Flang before version 17.")
+      set(USE_OPENMP 0)
+    endif()
+  endif()
+endif()
+
 include("${PROJECT_SOURCE_DIR}/cmake/utils.cmake")
 include("${PROJECT_SOURCE_DIR}/cmake/system.cmake")
 

cmake/f_check.cmake

@@ -20,12 +20,7 @@
 # NEEDBUNDERSCORE
 # NEED2UNDERSCORES
 
-include(CheckLanguage)
-check_language(Fortran)
-if(CMAKE_Fortran_COMPILER)
-  enable_language(Fortran)
-else()
-  set (NOFORTRAN 1)
+if(NOT CMAKE_Fortran_COMPILER)
   if (NOT NO_LAPACK)
      if (NOT XXXXX)
 	message(STATUS "No Fortran compiler found, can build only BLAS and f2c-converted LAPACK")