Initial changes for llvm shared library build using explicit visibility annotations

These are my initial build and code changes to supporting building llvm
as shared library/DLL on windows(without force exporting all symbols)
and making symbol visibility hidden by default on Linux which adding
explicit symbol visibility macros to the whole llvm codebase.

Updated cmake code to allow building llvm-shlib on windows by appending
/WHOLEARCHIVE:lib to the linker options.
Remove the hardcoded CMake error from using LLVM_BUILD_LLVM_DYLIB on
windows.
Updated CMake to define new macros to control conditional export macros
in llvm/Support/Compiler.h
Use /Zc:dllexportInlines- when compiling with clang-cl on windows with a
opt out CMake option to disable using it.
Replace some use of LLVM_EXTERNAL_VISIBILITY with new export macros.

Some of the cmake and code changes are based on @tstellar's earlier PR
#67502.

I have Windows building using clang-cl, while for MSVC its at-least able
to build libllvm, but some tests can't build because llvm iterator
template metaprogramming that doesn't work well with dllexport. Linux
should build without issue. My full branch is here
https://github.com/fsfod/llvm-project/tree/llvm-export-api-20.0 and
including all the auto generated export macros from clang tooling based
system.

Author: fsfod

llvm/CMakeLists.txt

@@ -2,6 +2,8 @@
 
 cmake_minimum_required(VERSION 3.20.0)
 
+include(CMakeDependentOption)
+
 set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
@@ -839,20 +841,40 @@ endif()
 
 if(MSVC)
   option(LLVM_BUILD_LLVM_C_DYLIB "Build LLVM-C.dll (Windows only)" ON)
-  # Set this variable to OFF here so it can't be set with a command-line
-  # argument.
-  set (LLVM_LINK_LLVM_DYLIB OFF)
   if (BUILD_SHARED_LIBS)
     message(FATAL_ERROR "BUILD_SHARED_LIBS options is not supported on Windows.")
   endif()
-else()
-  option(LLVM_LINK_LLVM_DYLIB "Link tools against the libllvm dynamic library" OFF)
+ else()
   option(LLVM_BUILD_LLVM_C_DYLIB "Build libllvm-c re-export library (Darwin only)" OFF)
-  set(LLVM_BUILD_LLVM_DYLIB_default OFF)
-  if(LLVM_LINK_LLVM_DYLIB OR LLVM_BUILD_LLVM_C_DYLIB)
-    set(LLVM_BUILD_LLVM_DYLIB_default ON)
-  endif()
-  option(LLVM_BUILD_LLVM_DYLIB "Build libllvm dynamic library" ${LLVM_BUILD_LLVM_DYLIB_default})
+endif()
+
+# Used to test building the llvm shared library with explicit symbol visibility on
+# Windows and Linux. For ELF platforms default symbols visibility is set to hidden.
+set(LLVM_BUILD_LLVM_DYLIB_VIS FALSE CACHE BOOL "")
+mark_as_advanced(LLVM_BUILD_LLVM_DYLIB_VIS)
+
+set(CAN_BUILD_LLVM_DYLIB OFF)
+if(NOT MSVC OR LLVM_BUILD_LLVM_DYLIB_VIS)
+  set(CAN_BUILD_LLVM_DYLIB ON)
+endif()
+
+cmake_dependent_option(LLVM_LINK_LLVM_DYLIB "Link tools against the libllvm dynamic library" OFF
+                       "CAN_BUILD_LLVM_DYLIB" OFF)
+
+set(LLVM_BUILD_LLVM_DYLIB_default OFF)
+if(LLVM_LINK_LLVM_DYLIB OR LLVM_BUILD_LLVM_C_DYLIB)
+  set(LLVM_BUILD_LLVM_DYLIB_default ON)
+endif()
+cmake_dependent_option(LLVM_BUILD_LLVM_DYLIB "Build libllvm dynamic library" ${LLVM_BUILD_LLVM_DYLIB_default}
+                       "CAN_BUILD_LLVM_DYLIB" OFF)
+
+cmake_dependent_option(LLVM_DYLIB_EXPORT_INLINES "Force inline members of classes to be DLL exported when
+                       building with clang-cl so the libllvm DLL is compatible with MSVC"
+                       OFF
+                       "MSVC;LLVM_BUILD_LLVM_DYLIB_VIS" OFF)
+
+if(LLVM_BUILD_LLVM_DYLIB_VIS)
+  set(LLVM_BUILD_LLVM_DYLIB ON)
 endif()
 
 if (LLVM_LINK_LLVM_DYLIB AND BUILD_SHARED_LIBS)

llvm/cmake/modules/AddLLVM.cmake

@@ -606,6 +606,10 @@ function(llvm_add_library name)
         endif()
       endforeach()
     endif()
+
+    if(ARG_DISABLE_LLVM_LINK_LLVM_DYLIB)
+      target_compile_definitions(${obj_name} PRIVATE LLVM_BUILD_STATIC)
+    endif()
   endif()
 
   if(ARG_SHARED AND ARG_STATIC)
@@ -641,8 +645,36 @@ function(llvm_add_library name)
   endif()
   set_target_properties(${name} PROPERTIES FOLDER "${subproject_title}/Libraries")
 
+  ## If were compiling with clang-cl use /Zc:dllexportInlines- to exclude inline 
+  ## class members from being dllexport'ed to reduce compile time.
+  ## This will also keep us below the 64k exported symbol limit
+  ## https://blog.llvm.org/2018/11/30-faster-windows-builds-with-clang-cl_14.html
+  if(LLVM_BUILD_LLVM_DYLIB AND NOT LLVM_DYLIB_EXPORT_INLINES AND 
+     MSVC AND CMAKE_CXX_COMPILER_ID MATCHES Clang)
+    target_compile_options(${name} PUBLIC /Zc:dllexportInlines-)
+    if(TARGET ${obj_name})
+      target_compile_options(${obj_name} PUBLIC /Zc:dllexportInlines-)
+    endif()
+  endif()
+
   if(ARG_COMPONENT_LIB)
     set_target_properties(${name} PROPERTIES LLVM_COMPONENT TRUE)
+    if(LLVM_BUILD_LLVM_DYLIB OR BUILD_SHARED_LIBS)
+      target_compile_definitions(${name} PRIVATE LLVM_EXPORTS)
+    endif()
+
+    # 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 (${CMAKE_SYSTEM_NAME} MATCHES "AIX") AND
+        NOT DEFINED CMAKE_CXX_VISIBILITY_PRESET)
+
+      set_target_properties(${name} PROPERTIES
+                            C_VISIBILITY_PRESET hidden
+                            CXX_VISIBILITY_PRESET hidden
+                            VISIBILITY_INLINES_HIDDEN YES)
+    endif()
     set_property(GLOBAL APPEND PROPERTY LLVM_COMPONENT_LIBS ${name})
   endif()
 
@@ -741,6 +773,9 @@ function(llvm_add_library name)
     if (LLVM_LINK_LLVM_DYLIB AND NOT ARG_DISABLE_LLVM_LINK_LLVM_DYLIB)
       set(llvm_libs LLVM)
     else()
+      if(ARG_DISABLE_LLVM_LINK_LLVM_DYLIB)
+        target_compile_definitions(${name} PRIVATE LLVM_BUILD_STATIC)
+      endif()
       llvm_map_components_to_libnames(llvm_libs
        ${ARG_LINK_COMPONENTS}
        ${LLVM_LINK_COMPONENTS}
@@ -1116,6 +1151,16 @@ macro(add_llvm_executable name)
   if (ARG_EXPORT_SYMBOLS)
     export_executable_symbols(${name})
   endif()
+
+  if(ARG_DISABLE_LLVM_LINK_LLVM_DYLIB OR NOT LLVM_LINK_LLVM_DYLIB)
+    target_compile_definitions(${name} PRIVATE LLVM_BUILD_STATIC)
+  endif()
+
+  if(LLVM_BUILD_LLVM_DYLIB_VIS AND NOT LLVM_DYLIB_EXPORT_INLINES AND
+     MSVC AND CMAKE_CXX_COMPILER_ID MATCHES Clang)
+    # This has to match how the libraries the executable is linked to are built or there be linker errors.
+    target_compile_options(${name} PRIVATE /Zc:dllexportInlines-)
+  endif()
 endmacro(add_llvm_executable name)
 
 # add_llvm_pass_plugin(name [NO_MODULE] ...)

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -754,6 +754,12 @@ if (MSVC)
       # any code that uses the LLVM_ALIGNAS macro), so this is must be disabled to
       # avoid unwanted alignment warnings.
       -wd4324 # Suppress 'structure was padded due to __declspec(align())'
+      # This is triggered for every variable that is a template type of a class even 
+      # if there private when the class is dllexport'ed
+      -wd4251 # Suppress 'needs to have dll-interface to be used by clients'
+      # We only putting dll export on classes with out of line members so this 
+      # warning gets triggered a lot for bases we haven't exported'
+      -wd4275 # non dll-interface class used as base for dll-interface class
 
       # Promoted warnings.
       -w14062 # Promote 'enumerator in switch of enum is not handled' to level 1 warning.

llvm/include/llvm/ADT/Any.h

@@ -25,7 +25,7 @@
 
 namespace llvm {
 
-class LLVM_EXTERNAL_VISIBILITY Any {
+class LLVM_ABI Any {
 
   // The `Typeid<T>::Id` static data member below is a globally unique
   // identifier for the type `T`. It is explicitly marked with default

llvm/include/llvm/Analysis/LazyCallGraph.h

@@ -412,7 +412,7 @@ class LazyCallGraph {
   /// outer structure. SCCs do not support mutation of the call graph, that
   /// must be done through the containing \c RefSCC in order to fully reason
   /// about the ordering and connections of the graph.
-  class LLVM_EXTERNAL_VISIBILITY SCC {
+  class LLVM_ABI SCC {
     friend class LazyCallGraph;
     friend class LazyCallGraph::Node;
 

llvm/include/llvm/Analysis/LoopInfo.h

@@ -36,7 +36,7 @@ extern template class LoopBase<BasicBlock, Loop>;
 
 /// Represents a single loop in the control flow graph.  Note that not all SCCs
 /// in the CFG are necessarily loops.
-class LLVM_EXTERNAL_VISIBILITY Loop : public LoopBase<BasicBlock, Loop> {
+class LLVM_ABI Loop : public LoopBase<BasicBlock, Loop> {
 public:
   /// A range representing the start and end location of a loop.
   class LocRange {

llvm/include/llvm/Analysis/LoopNestAnalysis.h

@@ -25,7 +25,7 @@ using LoopVectorTy = SmallVector<Loop *, 8>;
 class LPMUpdater;
 
 /// This class represents a loop nest and can be used to query its properties.
-class LLVM_EXTERNAL_VISIBILITY LoopNest {
+class LLVM_ABI LoopNest {
 public:
   using InstrVectorTy = SmallVector<const Instruction *>;
 

llvm/include/llvm/CodeGen/MachineFunction.h

@@ -254,7 +254,7 @@ struct LandingPadInfo {
       : LandingPadBlock(MBB) {}
 };
 
-class LLVM_EXTERNAL_VISIBILITY MachineFunction {
+class LLVM_ABI MachineFunction {
   Function &F;
   const LLVMTargetMachine &Target;
   const TargetSubtargetInfo *STI;

llvm/include/llvm/IR/Function.h

@@ -60,8 +60,7 @@ class User;
 class BranchProbabilityInfo;
 class BlockFrequencyInfo;
 
-class LLVM_EXTERNAL_VISIBILITY Function : public GlobalObject,
-                                          public ilist_node<Function> {
+class LLVM_ABI Function : public GlobalObject, public ilist_node<Function> {
 public:
   using BasicBlockListType = SymbolTableList<BasicBlock>;
 

llvm/include/llvm/IR/Module.h

@@ -62,7 +62,7 @@ class VersionTuple;
 /// constant references to global variables in the module.  When a global
 /// variable is destroyed, it should have no entries in the GlobalList.
 /// The main container class for the LLVM Intermediate Representation.
-class LLVM_EXTERNAL_VISIBILITY Module {
+class LLVM_ABI Module {
   /// @name Types And Enumerations
   /// @{
 public:

llvm/include/llvm/Support/Compiler.h

@@ -110,7 +110,8 @@
 /// this attribute will be made public and visible outside of any shared library
 /// they are linked in to.
 
-#if LLVM_HAS_CPP_ATTRIBUTE(gnu::visibility)
+#if LLVM_HAS_CPP_ATTRIBUTE(gnu::visibility) && defined(__GNUC__) &&            \
+    !defined(__clang__)
 #define LLVM_ATTRIBUTE_VISIBILITY_HIDDEN [[gnu::visibility("hidden")]]
 #define LLVM_ATTRIBUTE_VISIBILITY_DEFAULT [[gnu::visibility("default")]]
 #elif __has_attribute(visibility)
@@ -121,18 +122,79 @@
 #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) && !defined(__MINGW32__)
+#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__) || defined(__MINGW32__)
+#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
 #endif
 
 #if defined(__GNUC__)

llvm/tools/llvm-shlib/CMakeLists.txt

@@ -11,7 +11,7 @@ if(LLVM_LINK_LLVM_DYLIB AND LLVM_DYLIB_EXPORTED_SYMBOL_FILE)
 endif()
 
 if(LLVM_BUILD_LLVM_DYLIB)
-  if(MSVC)
+  if(MSVC AND NOT LLVM_BUILD_LLVM_DYLIB_VIS)
     message(FATAL_ERROR "Generating libLLVM is not supported on MSVC")
   endif()
   if(ZOS)
@@ -49,18 +49,25 @@ if(LLVM_BUILD_LLVM_DYLIB)
     ${CMAKE_CURRENT_SOURCE_DIR}/simple_version_script.map.in
     ${LLVM_LIBRARY_DIR}/tools/llvm-shlib/simple_version_script.map)
 
-    # GNU ld doesn't resolve symbols in the version script.
-    set(LIB_NAMES -Wl,--whole-archive ${LIB_NAMES} -Wl,--no-whole-archive)
-    if (NOT LLVM_LINKER_IS_SOLARISLD AND NOT MINGW)
-      # Solaris ld does not accept global: *; so there is no way to version *all* global symbols
-      set(LIB_NAMES -Wl,--version-script,${LLVM_LIBRARY_DIR}/tools/llvm-shlib/simple_version_script.map ${LIB_NAMES})
-    endif()
-    if (NOT MINGW AND NOT LLVM_LINKER_IS_SOLARISLD_ILLUMOS)
-      # Optimize function calls for default visibility definitions to avoid PLT and
-      # reduce dynamic relocations.
-      # Note: for -fno-pic default, the address of a function may be different from
-      # inside and outside libLLVM.so.
-      target_link_options(LLVM PRIVATE LINKER:-Bsymbolic-functions)
+    if(MSVC)
+      target_link_directories(LLVM PRIVATE ${LLVM_LIBRARY_DIR})
+      foreach(library ${LIB_NAMES})
+        target_link_options(LLVM PRIVATE /WHOLEARCHIVE:${library}.lib)
+      endforeach()
+    else()
+      # GNU ld doesn't resolve symbols in the version script.
+      set(LIB_NAMES -Wl,--whole-archive ${LIB_NAMES} -Wl,--no-whole-archive)
+      if (NOT LLVM_LINKER_IS_SOLARISLD AND NOT MINGW)
+        # Solaris ld does not accept global: *; so there is no way to version *all* global symbols
+        set(LIB_NAMES -Wl,--version-script,${LLVM_LIBRARY_DIR}/tools/llvm-shlib/simple_version_script.map ${LIB_NAMES})
+      endif()
+      if (NOT MINGW AND NOT LLVM_LINKER_IS_SOLARISLD_ILLUMOS)
+        # Optimize function calls for default visibility definitions to avoid PLT and
+        # reduce dynamic relocations.
+        # Note: for -fno-pic default, the address of a function may be different from
+        # inside and outside libLLVM.so.
+        target_link_options(LLVM PRIVATE LINKER:-Bsymbolic-functions)
+      endif()
     endif()
   endif()
 

llvm/utils/TableGen/Basic/CMakeLists.txt

@@ -8,7 +8,7 @@ set(LLVM_LINK_COMPONENTS
   TableGen
   )
 
-add_llvm_library(LLVMTableGenBasic OBJECT EXCLUDE_FROM_ALL
+add_llvm_library(LLVMTableGenBasic OBJECT EXCLUDE_FROM_ALL DISABLE_LLVM_LINK_LLVM_DYLIB
   CodeGenIntrinsics.cpp
   SDNodeProperties.cpp
 )

llvm/utils/TableGen/Common/CMakeLists.txt

@@ -10,7 +10,7 @@ set(LLVM_LINK_COMPONENTS
   TableGen
   )
 
-add_llvm_library(LLVMTableGenCommon STATIC OBJECT EXCLUDE_FROM_ALL
+add_llvm_library(LLVMTableGenCommon STATIC OBJECT EXCLUDE_FROM_ALL DISABLE_LLVM_LINK_LLVM_DYLIB
   GlobalISel/CodeExpander.cpp
   GlobalISel/CombinerUtils.cpp
   GlobalISel/CXXPredicates.cpp