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[openmp] Allow testing OpenMP without a full clang build tree #182470

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Merged
mstorsjo merged 3 commits into from
Feb 23, 2026
Merged

[openmp] Allow testing OpenMP without a full clang build tree #182470

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62b5c0d
[openmp] Allow testing OpenMP without a full clang build tree
mstorsjo Feb 20, 2026
f53f189
Allow overriding OPENMP_TEST_C_COMPILER even if Clang is available
mstorsjo Feb 20, 2026
cdf9d49
Apply the two remaining suggestions.
mstorsjo Feb 23, 2026
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33 changes: 19 additions & 14 deletions openmp/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -41,13 +41,26 @@ else()
"Path where built OpenMP libraries should be installed.")
endif()

if (NOT MSVC)
set(OPENMP_TEST_C_COMPILER ${LLVM_TOOLS_BINARY_DIR}/clang)
set(OPENMP_TEST_CXX_COMPILER ${LLVM_TOOLS_BINARY_DIR}/clang++)
else()
set(OPENMP_TEST_C_COMPILER ${LLVM_TOOLS_BINARY_DIR}/clang.exe)
set(OPENMP_TEST_CXX_COMPILER ${LLVM_TOOLS_BINARY_DIR}/clang++.exe)
set(OPENMP_TEST_C_COMPILER_default "${LLVM_TOOLS_BINARY_DIR}/clang${CMAKE_EXECUTABLE_SUFFIX}")
set(OPENMP_TEST_CXX_COMPILER_default "${LLVM_TOOLS_BINARY_DIR}/clang++${CMAKE_EXECUTABLE_SUFFIX}")
set(OPENMP_TEST_Fortran_COMPILER_default "${LLVM_TOOLS_BINARY_DIR}/flang${CMAKE_EXECUTABLE_SUFFIX}")
if (NOT TARGET "clang")
set(OPENMP_TEST_C_COMPILER_default "${CMAKE_C_COMPILER}")
set(OPENMP_TEST_CXX_COMPILER_default "${CMAKE_CXX_COMPILER}")
endif()
if (NOT TARGET "flang")
if (CMAKE_Fortran_COMPILER)
set(OPENMP_TEST_Fortran_COMPILER_default "${CMAKE_Fortran_COMPILER}")
else()
unset(OPENMP_TEST_Fortran_COMPILER_default)
endif()
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endif()
set(OPENMP_TEST_C_COMPILER "${OPENMP_TEST_C_COMPILER_default}" CACHE STRING
"C compiler to use for testing OpenMP runtime libraries.")
set(OPENMP_TEST_CXX_COMPILER "${OPENMP_TEST_CXX_COMPILER_default}" CACHE STRING
"C++ compiler to use for testing OpenMP runtime libraries.")
set(OPENMP_TEST_Fortran_COMPILER "${OPENMP_TEST_Fortran_COMPILER_default}" CACHE STRING
"Fortran compiler to use for testing OpenMP runtime libraries.")

# Set fortran test compiler if flang is found
if (EXISTS "${OPENMP_TEST_Fortran_COMPILER}")
Expand Down Expand Up @@ -85,14 +98,6 @@ math(EXPR LIBOMP_VERSION_BUILD_MONTH_DAY "${LIBOMP_VERSION_BUILD}%10000")
set(LIBOMP_BUILD_DATE "No_Timestamp")


# Check for flang
set(OPENMP_TEST_Fortran_COMPILER_default "")
if (CMAKE_Fortran_COMPILER)
set(OPENMP_TEST_Fortran_COMPILER_default "${CMAKE_Fortran_COMPILER}")
endif ()
set(OPENMP_TEST_Fortran_COMPILER "${OPENMP_TEST_Fortran_COMPILER_default}" CACHE STRING
"Fortran compiler to use for testing OpenMP runtime libraries.")

set(LIBOMP_FORTRAN_MODULES FALSE CACHE BOOL
"Create Fortran module files? (requires fortran compiler)")

Expand Down
8 changes: 6 additions & 2 deletions openmp/cmake/OpenMPTesting.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -127,19 +127,23 @@ function(add_openmp_testsuite target comment)
set_property(GLOBAL APPEND PROPERTY OPENMP_LIT_DEPENDS ${ARG_DEPENDS})
endif()

unset(EXTRA_CHECK_DEPENDS)

@Meinersbur Meinersbur Feb 20, 2026 •
edited
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Suggested change
unset(EXTRA_CHECK_DEPENDS)
set(EXTRA_CHECK_DEPENDS "")

By set(EXTRA_CHECK_DEPENDS) and unset(EXTRA_CHECK_DEPENDS) being equivalent I meant to not use it. unsettin the value will mean that the value of outer namespace becomes visible:

function(foo)
  set(EXTRA_CHECK_DEPENDS) # or unset(EXTRA_CHECK_DEPENDS) 
  message("EXTRA_CHECK_DEPENDS='${EXTRA_CHECK_DEPENDS}'")
endfunction()


set(EXTRA_CHECK_DEPENDS "Outer namespace value" CACHE STRING "Example variable")
foo()
$ cmake -P unset.cmake
EXTRA_CHECK_DEPENDS='Outer namespace value'

The CMake manual puts it like this:

Image

@mstorsjo mstorsjo Feb 23, 2026

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Oh, right, sorry, I missed the point there! Will fix.

if (TARGET "clang")
list(APPEND EXTRA_CHECK_DEPENDS clang)
endif()
if (ARG_EXCLUDE_FROM_CHECK_ALL)
add_lit_testsuite(${target}
${comment}
${ARG_UNPARSED_ARGUMENTS}
EXCLUDE_FROM_CHECK_ALL
DEPENDS clang FileCheck not ${ARG_DEPENDS}
DEPENDS ${EXTRA_CHECK_DEPENDS} FileCheck not ${ARG_DEPENDS}
ARGS ${ARG_ARGS}
)
else()
add_lit_testsuite(${target}
${comment}
${ARG_UNPARSED_ARGUMENTS}
DEPENDS clang FileCheck not ${ARG_DEPENDS}
DEPENDS ${EXTRA_CHECK_DEPENDS} FileCheck not ${ARG_DEPENDS}
ARGS ${ARG_ARGS}
)
endif()
Expand Down
12 changes: 10 additions & 2 deletions openmp/docs/Building.md
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Original file line number Diff line number Diff line change
Expand Up @@ -136,8 +136,8 @@ is expected to have been built from the same Git commit as OpenMP. It will,
however, use the compiler detected by CMake, usually gcc.
To also make it use Clang, add
`-DCMAKE_C_COMPILER=../build/bin/clang -DCMAKE_C_COMPILER=../build/bin/clang++`.
In any case, it will use Clang from `LLVM_BINARY_DIR` for running the regression
tests. `LLVM_BINARY_DIR` can also be omitted in which case testing
It will use Clang from `LLVM_BINARY_DIR` for running the regression tests, if Clang is included in that build.

@Meinersbur Meinersbur Feb 20, 2026

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Consider adding that you need OPENMP_TEST_C_COMPILER/OPENMP_TEST_CXX_COMPILER if you want testing without clang in LLVM_BINARY_DIR

@Meinersbur Meinersbur Feb 20, 2026

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Suggested change
It will use Clang from `LLVM_BINARY_DIR` for running the regression tests, if Clang is included in that build.
Clang/Flang from `LLVM_BINARY_DIR` will be used for testing if available, otherwise `CMAKE_C_COMPILER`/`CMAKE_CXX_COMPILER`/`CMAKE_Fortran_COMPILER`. Tests are also only expected to work with Clang/Flang built from the same Git commit, so `OPENMP_TEST_C_COMPILER`/`OPENMP_TEST_CXX_COMPILER`/`OPENMP_TEST_Fortran_COMPILER` can be used to explicitly set the test compilers.

`LLVM_BINARY_DIR` can also be omitted in which case testing
(`ninja check-openmp`) is disabled.

The `CMAKE_INSTALL_PREFIX` can be the same, but does not need to. Using the same
Expand Down Expand Up @@ -269,6 +269,14 @@ tests.
: Location, relative to [`CMAKE_INSTALL_PREFIX`][CMAKE_INSTALL_PREFIX], where to
install the OpenMP libraries (`.a` and `.so`)

**OPENMP_TEST_C_COMPILER**:STRING (default: Clang built in the same build configuration, or **CMAKE_C_COMPILER**)
: C compiler to use for testing OpenMP runtime libraries.

**OPENMP_TEST_CXX_COMPILER**:STRING (default: Clang built in the same build configuration, or **CMAKE_CXX_COMPILER**)
: C++ compiler to use for testing OpenMP runtime libraries.

**OPENMP_TEST_Fortran_COMPILER**:STRING (default: Flang built in the same build configuration, or **CMAKE_Fortran_COMPILER**)
: Fortran compiler to use for testing OpenMP runtime libraries.

### Options for `libomp`

Expand Down
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