[openmp] Tighten flang detection in offloading test

[elmcdonough]

Summary

This patch ensures that the locally built version of flang when building in-tree. find_program sometimes used the wrong executable if a different copy of flang was installed.

[jdoerfert]

didn't the docs say something about specifying a flang compiler via cmake? Is that still a thing?

[elmcdonough]

In D159161#4628422, @jdoerfert wrote:

didn't the docs say something about specifying a flang compiler via cmake? Is that still a thing?

If you're building out of tree, you can specify where flang by setting OPENMP_TEST_Fortran_COMPILER manually. The first version of this patch attempted to check if flang was present by reading the LLVM_ENABLE_PROJECTS value, but that didn't work as intended. That value was always blank when the tests were being built.

[jdoerfert]

In D159161#4628813, @elmcdonough wrote:

In D159161#4628422, @jdoerfert wrote:

didn't the docs say something about specifying a flang compiler via cmake? Is that still a thing?

If you're building out of tree, you can specify where flang by setting OPENMP_TEST_Fortran_COMPILER manually. The first version of this patch attempted to check if flang was present by reading the LLVM_ENABLE_PROJECTS value, but that didn't work as intended. That value was always blank when the tests were being built.

But will this not overwrite that flag and render it useless? I am confused.

[elmcdonough]

In D159161#4633167, @jdoerfert wrote:

In D159161#4628813, @elmcdonough wrote:

In D159161#4628422, @jdoerfert wrote:

didn't the docs say something about specifying a flang compiler via cmake? Is that still a thing?

If you're building out of tree, you can specify where flang by setting OPENMP_TEST_Fortran_COMPILER manually. The first version of this patch attempted to check if flang was present by reading the LLVM_ENABLE_PROJECTS value, but that didn't work as intended. That value was always blank when the tests were being built.

But will this not overwrite that flag and render it useless? I am confused.

This only applies if the project is built in-tree. A compiler can be specified in a standalone build.

[jdoerfert]

I c. Thx, LG

openmp/CMakeLists.txt

else()
   if (NOT MSVC)
     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)
     set(OPENMP_TEST_CXX_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++)
   else()
     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang.exe)
     set(OPENMP_TEST_CXX_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++.exe)
   endif()
 
-  find_program(OPENMP_TEST_Fortran_COMPILER flang-new PATHS LLVM_RUNTIME_OUTPUT_INTDIR)
-  if (NOT OPENMP_TEST_Fortran_COMPILER)
-    unset(OPENMP_TEST_Fortran_COMPILER CACHE)
+  # Check for flang
+  if (NOT MSVC)
+    set(OPENMP_TEST_Fortran_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/flang-new)
+  else()
+    set(OPENMP_TEST_Fortran_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/flang-new.exe)
+  endif()
+
+  # Set fortran test compiler if flang is found
+  if (EXISTS "${OPENMP_TEST_Fortran_COMPILER}")
+    message("Using local flang build at ${OPENMP_TEST_Fortran_COMPILER}")
+  else()
+    unset(OPENMP_TEST_Fortran_COMPILER)
   endif()
 
   # If not standalone, set CMAKE_CXX_STANDARD but don't set the global cache value,
   # only set it locally for OpenMP.
   set(CMAKE_CXX_STANDARD 17)
   set(CMAKE_CXX_STANDARD_REQUIRED NO)
   set(CMAKE_CXX_EXTENSIONS NO)
 endif()