Merge pull request #2256 from akohlmey/cmake-use-alternate-linker

Use alternate/faster linker if available

cmake/CMakeLists.txt

@@ -747,6 +747,12 @@ if (${_index} GREATER -1)
 endif()
 message(STATUS "<<< Linker flags: >>>")
 message(STATUS "Executable name:  ${LAMMPS_BINARY}")
+if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
+  get_target_property(OPTIONS lammps LINK_OPTIONS)
+  if(OPTIONS)
+    message(STATUS "Linker options:   ${OPTIONS}")
+  endif()
+endif()
 if(CMAKE_EXE_LINKER_FLAGS)
   message(STATUS "Executable linker flags: ${CMAKE_EXE_LINKER_FLAGS}")
 endif()

cmake/Modules/Testing.cmake

@@ -16,6 +16,33 @@ if(ENABLE_TESTING)
   set(MEMORYCHECK_COMMAND "${VALGRIND_BINARY}" CACHE FILEPATH "Memory Check Command")
   set(MEMORYCHECK_COMMAND_OPTIONS "${VALGRIND_DEFAULT_OPTIONS}" CACHE STRING "Memory Check Command Options")
 
+  # check if a faster linker is available.
+  # only verified with GNU and Clang compilers and new CMake
+  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
+    if((${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
+        OR (${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang"))
+      include(CheckCXXCompilerFlag)
+      set(CMAKE_CUSTOM_LINKER_DEFAULT default)
+      check_cxx_compiler_flag(-fuse-ld=lld HAVE_LLD_LINKER)
+      check_cxx_compiler_flag(-fuse-ld=gold HAVE_GOLD_LINKER)
+      check_cxx_compiler_flag(-fuse-ld=bfd HAVE_BFD_LINKER)
+      if(HAVE_LLD_LINKER)
+        set(CMAKE_CUSTOM_LINKER_DEFAULT lld)
+      elseif(HAVE_GOLD_LINKER)
+        set(CMAKE_CUSTOM_LINKER_DEFAULT gold)
+      elseif(HAVE_BFD_LINKER)
+        set(CMAKE_CUSTOM_LINKER_DEFAULT bfd)
+      endif()
+      set(CMAKE_CUSTOM_LINKER_VALUES lld gold bfd default)
+      set(CMAKE_CUSTOM_LINKER ${CMAKE_CUSTOM_LINKER_DEFAULT} CACHE STRING "Choose a custom linker for faster linking (lld, gold, bfd, default)")
+      validate_option(CMAKE_CUSTOM_LINKER CMAKE_CUSTOM_LINKER_VALUES)
+      mark_as_advanced(CMAKE_CUSTOM_LINKER)
+      if(NOT "${CMAKE_CUSTOM_LINKER}" STREQUAL "default")
+        target_link_options(lammps PUBLIC -fuse-ld=${CMAKE_CUSTOM_LINKER})
+      endif()
+    endif()
+  endif()
+
   include(CTest)
 
   enable_testing()

doc/src/Build_development.rst

@@ -259,6 +259,23 @@ and working.
      of mis-compiled code (or an undesired large loss of precision due
      to significant reordering of operations and thus less error cancellation).
 
+Use custom linker for faster link times when ENABLE_TESTING is active
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When compiling LAMMPS with enabled tests, most test executables will
+need to be linked against the LAMMPS library.  Since this can be a
+large with many C++ objects when many packages are enabled, link times
+can become very long on machines that use the GNU BFD linker (e.g.
+Linux systems).  Alternatives like the ``lld`` linker of the LLVM project
+or the ``gold`` linker available with GNU binutils can speed up this step
+substantially. CMake will by default test if any of the two can be
+enabled and use it when ``ENABLE_TESTING`` is active.  It can also be
+selected manually through the ``CMAKE_CUSTOM_LINKER`` CMake variable.
+Allowed values are ``lld``, ``gold``, ``bfd``, or ``default``.  The
+``default`` option will use the system default linker otherwise, the
+linker is chosen explicitly.  This option is only available for the
+GNU or Clang C++ compiler.
+
 Tests for other components and utility functions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

doc/utils/sphinx-config/false_positives.txt

@@ -236,6 +236,7 @@ bilayer
 bilayers
 binsize
 binstyle
+binutils
 biomolecular
 biomolecule
 Biomolecules