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[CMake] Change how the default value of USE_OPENMP is set.

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This change means if the user explicitly passes `-DUSE_OPENMP=ON` to
CMake during the first configure and the compiler does not support
OpenMP the configure will fail but if the user doesn't specify it the
build system will automatically enable/disable OpenMP support depending
on whether it is supported by the compiler.

This is an improvement on the previous behaviour because previously we
would just emit a warning if `-DUSE_OPENMP=ON` was passed and the
compiler didn't support OpenMP.
This commit is contained in:
Dan Liew 2017-08-12 18:09:38 +01:00
parent 7b47b0380e
commit e898f515f7
1 changed files with 27 additions and 23 deletions
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50
CMakeLists.txt
View file

@ -281,33 +281,37 @@ endif()
################################################################################
# OpenMP support
################################################################################
option(USE_OPENMP "Use OpenMP" ON)
set(OPENMP_FOUND FALSE)
if (USE_OPENMP)
# Because this is on by default we make the configure succeed with a warning
# if OpenMP support is not detected.
find_package(OpenMP)
if (NOT OPENMP_FOUND)
message(WARNING "OpenMP support was requested but your compiler doesn't support it")
endif()
endif()
find_package(OpenMP)
if (OPENMP_FOUND)
list(APPEND Z3_COMPONENT_CXX_FLAGS ${OpenMP_CXX_FLAGS})
# GCC and Clang need to have additional flags passed to the linker.
# We can't do ``target_link_libraries(libz3 INTERFACE ${OpenMP_CXX_FLAGS})``
# because ``/openmp`` is interpreted as file name rather than a linker
# flag by MSVC and breaks the build
if (("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang") OR
("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU"))
list(APPEND Z3_DEPENDENT_EXTRA_CXX_LINK_FLAGS ${OpenMP_CXX_FLAGS})
endif()
unset(CMAKE_REQUIRED_FLAGS)
message(STATUS "Using OpenMP")
set(USE_OPENMP_DEFAULT ON)
else()
set(USE_OPENMP_DEFAULT OFF)
endif()
# By setting `USE_OPENMP` this way configuration will fail during the first
# configure if the user explicitly passes `-DUSE_OPENMP=ON` and the compiler
# does not support OpenMP. However if the option is not set explicitly during
# the first configure OpenMP support will be automatically enabled/disabled
# depending on whether OpenMP is available.
option(USE_OPENMP "Use OpenMP" ${USE_OPENMP_DEFAULT})
if (USE_OPENMP)
if (NOT OPENMP_FOUND)
message(FATAL_ERROR "USE_OPENMP is ON but your compiler does not support OpenMP")
endif()
list(APPEND Z3_COMPONENT_CXX_FLAGS ${OpenMP_CXX_FLAGS})
# GCC and Clang need to have additional flags passed to the linker.
# We can't do ``target_link_libraries(libz3 INTERFACE ${OpenMP_CXX_FLAGS})``
# because ``/openmp`` is interpreted as file name rather than a linker
# flag by MSVC and breaks the build
if (("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang") OR
("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU"))
list(APPEND Z3_DEPENDENT_EXTRA_CXX_LINK_FLAGS ${OpenMP_CXX_FLAGS})
endif()
message(STATUS "Using OpenMP")
else()
list(APPEND Z3_COMPONENT_CXX_DEFINES "-D_NO_OMP_")
message(STATUS "Not using OpenMP")
set(USE_OPENMP OFF CACHE BOOL "Use OpenMP" FORCE)
endif()
################################################################################