[compiler-rt] [compiler-rt] Fix linking a standalone libatomic for MinGW (PR #74668)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo created https://github.com/llvm/llvm-project/pull/74668

Whenever linking with -nodefaultlibs for a MinGW target, we manually need to specify a bunch of libraries - listed in ${MINGW_LIBRARIES}; the same is already done for sanitizers and libunwind/libcxxabi/libcxx.

Practically speaking, linking with -nodefaultlibs but manually passing the libraries in ${MINGW_LIBRARIES} restores most of the libraries that are linked by default, except for the potential compiler builtins and unwind library; i.e. it has essentially the same effect as linking with "--unwindlib=none -rtlib=none", except that -rtlib doesn't accept such a value.

When building only compiler-rt/lib/builtins, not all of compiler-rt, ${MINGW_LIBRARIES} is unset - set it manually here for that case. This matches what is set in
compiler-rt/cmake/config-ix.cmake, except that the builtins (libgcc or compiler-rt builtins) is omitted; the only use within lib/buitlins is for the standalone libatomic, which explicitly already links against the just-built builtins.

>From dd967ded2375dbff01f69293f832cbf88e12fd83 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin at martin.st>
Date: Tue, 5 Dec 2023 15:28:29 +0200
Subject: [PATCH] [compiler-rt] Fix linking a standalone libatomic for MinGW

Whenever linking with -nodefaultlibs for a MinGW target, we
manually need to specify a bunch of libraries - listed in
${MINGW_LIBRARIES}; the same is already done for sanitizers
and libunwind/libcxxabi/libcxx.

Practically speaking, linking with -nodefaultlibs but manually
passing the libraries in ${MINGW_LIBRARIES} restores most of
the libraries that are linked by default, except for the
potential compiler builtins and unwind library; i.e. it has
essentially the same effect as linking with "--unwindlib=none
-rtlib=none", except that -rtlib doesn't accept such a value.

When building only compiler-rt/lib/builtins, not all of
compiler-rt, ${MINGW_LIBRARIES} is unset - set it manually
here for that case. This matches what is set in
compiler-rt/cmake/config-ix.cmake, except that the builtins
(libgcc or compiler-rt builtins) is omitted; the only use
within lib/buitlins is for the standalone libatomic, which
explicitly already links against the just-built builtins.
---
 compiler-rt/lib/builtins/CMakeLists.txt | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
index 069d33bfd3d30..ea72c595a9b80 100644
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -38,6 +38,13 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     include(UseLibtool)
   endif()
   include(AddCompilerRT)
+
+  if(MINGW)
+    # Simplified version of what's set in cmake/config-ix.cmake; not including
+    # builtins, which are linked separately.
+    set(MINGW_LIBRARIES mingw32 moldname mingwex msvcrt advapi32 shell32
+                        user32 kernel32 mingw32 moldname mingwex msvcrt)
+   endif()
 endif()
 
 if (COMPILER_RT_STANDALONE_BUILD)
@@ -881,12 +888,14 @@ if(COMPILER_RT_BUILD_STANDALONE_LIBATOMIC)
   endif()
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if(CAN_TARGET_${arch})
+      list(APPEND COMPILER_RT_LIBATOMIC_LINK_LIBS_${arch} clang_rt.builtins-${arch})
+      append_list_if(MINGW "${MINGW_LIBRARIES}" COMPILER_RT_LIBATOMIC_LINK_LIBS_${arch})
       add_compiler_rt_runtime(clang_rt.atomic
                               ${BUILTIN_TYPE}
                               ARCHS ${arch}
                               SOURCES atomic.c
                               LINK_FLAGS ${COMPILER_RT_LIBATOMIC_LINK_FLAGS}
-                              LINK_LIBS clang_rt.builtins-${arch}
+                              LINK_LIBS ${COMPILER_RT_LIBATOMIC_LINK_LIBS_${arch}}
                               PARENT_TARGET builtins-standalone-atomic)
     endif()
   endforeach()