[llvm] Initial changes for llvm shared library build using explicit visibility annotations (PR #96630)

[Thomas Fransham via llvm-commits]

================
@@ -125,18 +126,79 @@
 #define LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
 #endif
 
-
-#if (!(defined(_WIN32) || defined(__CYGWIN__)) ||                              \
-     (defined(__MINGW32__) && defined(__clang__)))
-#define LLVM_LIBRARY_VISIBILITY LLVM_ATTRIBUTE_VISIBILITY_HIDDEN
 #if defined(LLVM_BUILD_LLVM_DYLIB) || defined(LLVM_BUILD_SHARED_LIBS)
 #define LLVM_EXTERNAL_VISIBILITY LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
 #else
 #define LLVM_EXTERNAL_VISIBILITY
 #endif
+
+#if (!(defined(_WIN32) || defined(__CYGWIN__)) ||                              \
+     (defined(__MINGW32__) && defined(__clang__)))
+#define LLVM_LIBRARY_VISIBILITY LLVM_ATTRIBUTE_VISIBILITY_HIDDEN
+#define LLVM_ALWAYS_EXPORT LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#elif defined(_WIN32)
+#define LLVM_ALWAYS_EXPORT __declspec(dllexport)
+#define LLVM_LIBRARY_VISIBILITY
 #else
 #define LLVM_LIBRARY_VISIBILITY
-#define LLVM_EXTERNAL_VISIBILITY
+#define LLVM_ALWAYS_EXPORT
+#endif
+
+/// LLVM_ABI is the main export/visibility macro to mark something as explicitly
+/// exported when llvm is built as a shared library with everything else that is
+/// unannotated will have internal visibility.
+///
+/// LLVM_EXPORT_TEMPLATE is used on explicit template instantiations in source
+/// files that were declared extern in a header. This macro is only set as a
+/// compiler export attribute on windows, on other platforms it does nothing.
+///
+/// LLVM_TEMPLATE_ABI is for annotating extern template declarations in headers
+/// for both functions and classes. On windows its turned in to dllimport for
+/// library consumers, for other platforms its a default visibility attribute.
+///
+/// LLVM_C_ABI is used to annotated functions and data that need to be exported
+/// for the libllvm-c API. This used both for the llvm-c headers and for the
+/// functions declared in the different Target's c++ source files that don't
+/// include the header forward declaring them.
+#ifndef LLVM_ABI_GENERATING_ANNOTATIONS
+// Marker to add to classes or functions in public headers that should not have
+// export macros added to them by the clang tool
+#define LLVM_ABI_NOT_EXPORTED
+#if defined(LLVM_BUILD_LLVM_DYLIB) || defined(LLVM_BUILD_SHARED_LIBS) ||       \
+    defined(LLVM_ENABLE_PLUGINS)
+// Some libraries like those for tablegen are linked in to tools that used
+// in the build so can't depend on the llvm shared library. If export macros
+// were left enabled when building these we would get duplicate or
+// missing symbol linker errors on windows.
+#if defined(LLVM_BUILD_STATIC)
+#define LLVM_ABI
+#define LLVM_TEMPLATE_ABI
+#define LLVM_EXPORT_TEMPLATE
+#elif defined(_WIN32)
+#if defined(LLVM_EXPORTS)
+#define LLVM_ABI __declspec(dllexport)
+#define LLVM_TEMPLATE_ABI
+#define LLVM_EXPORT_TEMPLATE __declspec(dllexport)
+#else
+#define LLVM_ABI __declspec(dllimport)
+#define LLVM_TEMPLATE_ABI __declspec(dllimport)
+#define LLVM_EXPORT_TEMPLATE
+#endif
+#elif defined(__ELF__)
+#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_TEMPLATE_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_EXPORT_TEMPLATE
+#elif defined(__MACH__) || defined(__WASM__)
+#define LLVM_ABI LLVM_ATTRIBUTE_VISIBILITY_DEFAULT
+#define LLVM_TEMPLATE_ABI
+#define LLVM_EXPORT_TEMPLATE
+#endif
+#else
+#define LLVM_ABI
+#define LLVM_TEMPLATE_ABI
+#define LLVM_EXPORT_TEMPLATE
+#endif
+#define LLVM_C_ABI LLVM_ABI
----------------
fsfod wrote:

The idea was it could maybe made separate later on for some kind of optimized llvmc only build. There also exported functions in Target libs like LLVMInitialize* that are used both in C and c++ API.

https://github.com/llvm/llvm-project/pull/96630