From fa4b5096f9a13224f1d5ce610739b7d206f97d67 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Miku=C5=82a?= <oss@mateuszmikula.dev>
Date: Mon, 30 Jun 2025 23:24:39 +0200
Subject: [PATCH] [LLVM][Cygwin] Enable dynamic linking of libLLVM

These changes allow to link everything* to shared LLVM library with MSYS2 "Cygwin" toolchain.

* `c-index-test` fails with ld.bfd with this error:
```
/usr/lib/gcc/x86_64-pc-cygwin/15.1.0/../../../../x86_64-pc-cygwin/bin/ld: lib/libclangSerialization.a(PCHContainerOperations.cpp.o):PCHContainerOperations.cpp:(.text+0xc0): multiple definition of `clang::PCHContainerOperations::PCHContainerOperations()'; lib/libclang.dll.a(msys_clang_21_0git_dll_d008967.o):(.text+0x0): first defined here
collect2: error: ld returned 1 exit status
```
Haven't tried with LLD.
---
 llvm/cmake/modules/AddLLVM.cmake           | 6 +++---
 llvm/cmake/modules/HandleLLVMOptions.cmake | 2 +-
 llvm/include/llvm/Support/Compiler.h       | 2 +-
 llvm/lib/Target/CMakeLists.txt             | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index 8d8a94d1cddc4..83772ed8d2b13 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -137,7 +137,7 @@ function(add_llvm_symbol_exports target_name export_file)
       set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                    LINK_FLAGS "  -Wl,--version-script,\"${CMAKE_CURRENT_BINARY_DIR}/${native_export_file}\"")
     endif()
-  elseif(WIN32)
+  elseif(WIN32 OR CYGWIN)
     set(native_export_file "${target_name}.def")
 
     add_custom_command(OUTPUT ${native_export_file}
@@ -153,7 +153,7 @@ function(add_llvm_symbol_exports target_name export_file)
     elseif(CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
       # clang in msvc mode, calling a link.exe/lld-link style linker
       set(export_file_linker_flag "-Wl,/DEF:${export_file_linker_flag}")
-    elseif(MINGW)
+    elseif(MINGW OR CYGWIN)
       # ${export_file_linker_flag}, which is the plain file name, works as is
       # when passed to the compiler driver, which then passes it on to the
       # linker as an input file.
@@ -666,7 +666,7 @@ function(llvm_add_library name)
     # When building shared objects for each target there are some internal APIs
     # that are used across shared objects which we can't hide.
     if (LLVM_BUILD_LLVM_DYLIB_VIS AND NOT BUILD_SHARED_LIBS AND NOT APPLE AND
-        (NOT (WIN32 OR CYGWIN) OR (MINGW AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
+        (NOT (WIN32 OR CYGWIN) OR ((MINGW OR CYGWIN) AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
         NOT (${CMAKE_SYSTEM_NAME} MATCHES "AIX") AND
         NOT DEFINED CMAKE_CXX_VISIBILITY_PRESET)
 
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 5aa047a33ba6a..c126b0d073322 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -465,7 +465,7 @@ if( LLVM_ENABLE_PIC )
 endif()
 
 if((NOT (${CMAKE_SYSTEM_NAME} MATCHES "AIX")) AND
-   (NOT (WIN32 OR CYGWIN) OR (MINGW AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")))
+   (NOT (WIN32 OR CYGWIN) OR ((MINGW OR CYGWIN) AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")))
   # GCC for MinGW does nothing about -fvisibility-inlines-hidden, but warns
   # about use of the attributes. As long as we don't use the attributes (to
   # override the default) we shouldn't set the command line options either.
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index f46a7aeccd0aa..f6d0d3591c33b 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -133,7 +133,7 @@
 #endif
 
 #if (!(defined(_WIN32) || defined(__CYGWIN__)) ||                              \
-     (defined(__MINGW32__) && defined(__clang__)))
+     ((defined(__MINGW32__) || defined(__CYGWIN__)) && defined(__clang__)))
 #define LLVM_LIBRARY_VISIBILITY LLVM_ATTRIBUTE_VISIBILITY_HIDDEN
 // Clang compilers older then 15 do not support gnu style attributes on
 // namespaces.
diff --git a/llvm/lib/Target/CMakeLists.txt b/llvm/lib/Target/CMakeLists.txt
index 9472288229cac..f5f6f5386f899 100644
--- a/llvm/lib/Target/CMakeLists.txt
+++ b/llvm/lib/Target/CMakeLists.txt
@@ -22,7 +22,7 @@ add_llvm_component_library(LLVMTarget
 # When building shared objects for each target there are some internal APIs
 # that are used across shared objects which we can't hide.
 if (NOT BUILD_SHARED_LIBS AND NOT APPLE AND
-    (NOT (WIN32 OR CYGWIN) OR (MINGW AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
+    (NOT (WIN32 OR CYGWIN) OR ((MINGW OR CYGWIN) AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")) AND
     NOT (${CMAKE_SYSTEM_NAME} MATCHES "AIX") AND
     NOT DEFINED CMAKE_CXX_VISIBILITY_PRESET)
   # Set default visibility to hidden, so we don't export all the Target classes