[clang] ad4ab81 - [clang][cmake] Force CMAKE_LINKER for multistage build in case of BOOTSTRAP_LLVM_ENABLE_LLD and MSVC

[Kristina Bessonova via cfe-commits]

Author: Kristina Bessonova
Date: 2020-07-28T10:11:52+02:00
New Revision: ad4ab81dccaa72d9b5137433a0923d325ff76135

URL: https://github.com/llvm/llvm-project/commit/ad4ab81dccaa72d9b5137433a0923d325ff76135
DIFF: https://github.com/llvm/llvm-project/commit/ad4ab81dccaa72d9b5137433a0923d325ff76135.diff

LOG: [clang][cmake] Force CMAKE_LINKER for multistage build in case of BOOTSTRAP_LLVM_ENABLE_LLD and MSVC

The issue with LLVM_ENABLE_LLD is that it just passes -fuse-ld=lld
to compiler/linker options which makes sense only for those platforms
where cmake invokes a compiler driver for linking. On Windows (MSVC) cmake
invokes the linker directly and requires CMAKE_LINKER to be specified
otherwise it defaults CMAKE_LINKER to be link.exe.

This patch allows BOOTSTRAP_LLVM_ENABLE_LLD to set CMAKE_LINKER in two cases:
* if building for host Windows,
* if crosscompiling for target Windows.

It also skips adding '-fuse-ld=lld' to make lld-link not warning
about 'unknown argument'.

This fixes build with `clang/cmake/caches/DistributionExample.cmake`
on Windows.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D80873

Added: 
    

Modified: 
    clang/CMakeLists.txt
    llvm/cmake/modules/HandleLLVMOptions.cmake

Removed: 
    


################################################################################
diff  --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index 1a6a20a271f3..0f08538495fc 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -753,6 +753,14 @@ if (CLANG_ENABLE_BOOTSTRAP)
     -DCMAKE_ASM_COMPILER=${LLVM_RUNTIME_OUTPUT_INTDIR}/${C_COMPILER}
     -DCMAKE_ASM_COMPILER_ID=Clang)
 
+  # cmake requires CMAKE_LINKER to be specified if the compiler is MSVC-like,
+  # otherwise it defaults the linker to be link.exe.
+  if(BOOTSTRAP_LLVM_ENABLE_LLD)
+    if((WIN32 AND NOT BOOTSTRAP_CMAKE_SYSTEM_NAME) OR BOOTSTRAP_CMAKE_SYSTEM_NAME STREQUAL "Windows")
+      set(${CLANG_STAGE}_LINKER -DCMAKE_LINKER=${LLVM_RUNTIME_OUTPUT_INTDIR}/lld-link${CMAKE_EXECUTABLE_SUFFIX})
+    endif()
+  endif()
+
   if(BOOTSTRAP_CMAKE_SYSTEM_NAME)
     set(${CLANG_STAGE}_CONFIG -DLLVM_CONFIG_PATH=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-config)
     set(${CLANG_STAGE}_TABLEGEN

diff  --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 62dd0ef79cf4..89f7016a7db4 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -261,7 +261,12 @@ if( LLVM_ENABLE_LLD )
   if ( LLVM_USE_LINKER )
     message(FATAL_ERROR "LLVM_ENABLE_LLD and LLVM_USE_LINKER can't be set at the same time")
   endif()
-  set(LLVM_USE_LINKER "lld")
+  # In case of MSVC cmake always invokes the linker directly, so the linker
+  # should be specified by CMAKE_LINKER cmake variable instead of by -fuse-ld
+  # compiler option.
+  if ( NOT MSVC )
+    set(LLVM_USE_LINKER "lld")
+  endif()
 endif()
 
 if( LLVM_USE_LINKER )