Merge pull request #2989 from MRtrix3/mrtrix_use_lld_option

Disable the use of LLD by default

CMakeLists.txt

@@ -24,6 +24,7 @@ option(MRTRIX_STRIP_CONDA "Strip ananconda/mininconda from PATH to avoid conflic
 option(MRTRIX_USE_PCH "Use precompiled headers" ON)
 option(MRTRIX_PYTHON_SOFTLINK "Build directory softlink to Python source code rather than copying" ON)
 option(MRTRIX_BUILD_NON_CORE_STATIC "Build MRtrix's non-core code as a static library" OFF)
+option(MRTRIX_USE_LLD "Use lld as the linker" OFF)
 
 set(MRTRIX_DEPENDENCIES_DIR "" CACHE PATH
     "An optional local directory containing all thirdparty dependencies:\n \

cmake/LinkerSetup.cmake

@@ -1,25 +1,33 @@
-# On Linux we want to use the LLVM linker if available as it is faster than the default GNU linker.
+# The LLVM linker is faster than the default GNU linker.
 # Unfortunately, lld is not able to perform LTO when compiling with GCC.
+if(MRTRIX_USE_LLD)
+    include(CheckCXXCompilerFlag)
 
-if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_INTERPROCEDURAL_OPTIMIZATION)
-    set(GCC_LTO TRUE)
-else()
-    set(GCC_LTO FALSE)
-endif()
+    if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+        set(GCC_LTO TRUE)
+        message(WARNING "LLD cannot be used with GCC when LTO is enabled. Please another compiler or disable LTO.")
+    else()
+        set(GCC_LTO FALSE)
+    endif()
 
-if(UNIX AND NOT APPLE AND NOT GCC_LTO)
-  find_program(LLVM_LINKER NAMES "ld.lld")
+    if(NOT GCC_LTO)
+      set(LINKER_FLAG "-fuse-ld=lld")
+      check_cxx_compiler_flag(${LINKER_FLAG} CXX_SUPPORTS_LLVM_LINKER)
 
-  if(LLVM_LINKER)
-    message(STATUS "Using LLVM linker: ${LLVM_LINKER}")
+      if(CXX_SUPPORTS_LLVM_LINKER)
+        find_program(LLVM_LINKER NAMES lld ld.lld)
+        message(STATUS "Using LLVM linker: ${LLVM_LINKER}")
 
-    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.29)
-      set(CMAKE_LINKER_TYPE "LLD" CACHE STRING "Linker type")
-    else()
-      set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=lld")
-      set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=lld")
-      set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -fuse-ld=lld")
+        if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.29)
+          set(CMAKE_LINKER_TYPE "LLD" CACHE STRING "Linker type")
+        else()
+          set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=lld")
+          set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -fuse-ld=lld")
+          set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -fuse-ld=lld")
+        endif()
+      else()
+        message(WARNING "Compiler does not support LLVM linker. Using default linker.")
+      endif()
     endif()
-
-  endif()
 endif()
+