[CMake]: Properly handle the LTO cache arguments for MinGW

[thieta]

Summary

There where a few problems with the handling originally discussed in this issue here: https://reviews.llvm.org/D80425

We want to make sure that LINKER_IS_LLD_LINK is properly set - in this case it shouldn't be set when building for MinGW.

Then we want to make the test for it correct and finally include the option to build with thinlto cache since the MinGW driver now supports that.

Note that this will break when building with LTO and a older lld than what ships before the addition of that option in the tree. We could add logic for checking if the linker flags are correct - but I think when using LTO multi-stage builds are not uncommon.

[mstorsjo]

LGTM

Note that this will break when building with LTO and a older lld than what ships before the addition of that option in the tree. We could add logic for checking if the linker flags are correct - but I think when using LTO multi-stage builds are not uncommon.

Well, wasn't it the case that lto mingw builds were broken to begin with? So either nobody did it, or they already patched around it (and will need to adjust their patch)?

llvm/cmake/modules/HandleLLVMOptions.cmake

959

I'd feel more comfortable with parentheses here

[mati865]

llvm/cmake/modules/HandleLLVMOptions.cmake

959

AND takes precedence over OR so this code is in fact:

elseif(UNIX OR (MINGW AND LLVM_USE_LINKER STREQUAL "lld"))

So parentheses around UNIX OR MINGW are necessary.

[thieta]

In D80493#2052698, @mstorsjo wrote

Well, wasn't it the case that lto mingw builds were broken to begin with? So either nobody did it, or they already patched around it (and will need to adjust their patch)?

Yes of course! Thanks for pointing that out.

[thieta]

llvm/cmake/modules/HandleLLVMOptions.cmake

959

I will fix this!

[thieta]

Updated with parenthesis - feel free to commit if it looks good to you. Same as before Tobias Hieta [e-mail].

llvm/cmake/modules/HandleLLVMOptions.cmake

 # This CMake module is responsible for interpreting the user defined LLVM_
 # options and executing the appropriate CMake commands to realize the users'
 # selections.
 
 # This is commonly needed so make sure it's defined before we include anything
 # else.
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 
 include(CheckCompilerVersion)
 include(HandleLLVMStdlib)
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 include(CheckSymbolExists)
 include(CMakeDependentOption)
 
-if(CMAKE_LINKER MATCHES "lld-link" OR (WIN32 AND LLVM_USE_LINKER STREQUAL "lld") OR LLVM_ENABLE_LLD)
+if(CMAKE_LINKER MATCHES "lld-link" OR (MSVC AND (LLVM_USE_LINKER STREQUAL "lld" OR LLVM_ENABLE_LLD)))
   set(LINKER_IS_LLD_LINK TRUE)
 else()
   set(LINKER_IS_LLD_LINK FALSE)
 endif()
 
 set(LLVM_ENABLE_LTO OFF CACHE STRING "Build LLVM with LTO. May be specified as Thin or Full to use a particular kind of LTO")
 string(TOUPPER "${LLVM_ENABLE_LTO}" uppercase_LLVM_ENABLE_LTO)
 
append_if(LLVM_BUILD_INSTRUMENTED_COVERAGE "-fprofile-instr-generate=\"${LLVM_PROFILE_FILE_PATTERN}\" -fcoverage-mapping"
   CMAKE_C_FLAGS
   CMAKE_EXE_LINKER_FLAGS
   CMAKE_SHARED_LINKER_FLAGS)
 
 if (LLVM_BUILD_INSTRUMENTED AND LLVM_BUILD_INSTRUMENTED_COVERAGE)
   message(FATAL_ERROR "LLVM_BUILD_INSTRUMENTED and LLVM_BUILD_INSTRUMENTED_COVERAGE cannot both be specified")
 endif()
 
-if(LLVM_ENABLE_LTO AND LLVM_ON_WIN32 AND NOT LINKER_IS_LLD_LINK)
+if(LLVM_ENABLE_LTO AND LLVM_ON_WIN32 AND NOT LINKER_IS_LLD_LINK AND NOT MINGW)
   message(FATAL_ERROR "When compiling for Windows, LLVM_ENABLE_LTO requires using lld as the linker (point CMAKE_LINKER at lld-link.exe)")
 endif()
 if(uppercase_LLVM_ENABLE_LTO STREQUAL "THIN")
   append("-flto=thin" CMAKE_CXX_FLAGS CMAKE_C_FLAGS)
   if(NOT LINKER_IS_LLD_LINK)
     append("-flto=thin" CMAKE_EXE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
   endif()
   # If the linker supports it, enable the lto cache. This improves initial build
   # time a little since we re-link a lot of the same objects, and significantly
   # improves incremental build time.
   # FIXME: We should move all this logic into the clang driver.
   if(APPLE)
     append("-Wl,-cache_path_lto,${PROJECT_BINARY_DIR}/lto.cache"
            CMAKE_EXE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
-  elseif(UNIX AND LLVM_USE_LINKER STREQUAL "lld")
+  elseif((UNIX OR MINGW) AND LLVM_USE_LINKER STREQUAL "lld")
     append("-Wl,--thinlto-cache-dir=${PROJECT_BINARY_DIR}/lto.cache"
            CMAKE_EXE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
   elseif(LLVM_USE_LINKER STREQUAL "gold")
     append("-Wl,--plugin-opt,cache-dir=${PROJECT_BINARY_DIR}/lto.cache"
            CMAKE_EXE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
   elseif(LINKER_IS_LLD_LINK)
     append("/lldltocache:${PROJECT_BINARY_DIR}/lto.cache"
            CMAKE_EXE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)