[libc++] Replace LIBCXX_ENABLE_STATIC_ABI_LIBRARY & friends by a new LIBCXX_CXX_ABI choice

Instead of having complicated options like LIBCXX_ENABLE_STATIC_ABI_LIBRARY
and LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY, introduce a more general
mechanism to select the ABI library used by libc++. The new mechanism allows
specifying the ABI library for the static libc++ and the shared libc++
separately, and allows selecting a "merged" flavor of libc++ for both
the in-tree libc++abi and any external static ABI library.

As an example, one can now specify arbitrary combinations like
   -DLIBCXX_ABILIB_FOR_SHARED="shared-libcxxabi"
   -DLIBCXX_ABILIB_FOR_STATIC="merged-libcxxabi"

which would have been impossible or very brittle in the past. In theory,
one can even select an entirely different ABI library for the static and
the shared libc++ (e.g. libc++abi vs libsupc++), although supporting that
is not a primary goal of this patch but merely a result of the general
mechanism.

Closes #77655
Fixes #57759

Differential Revision: https://reviews.llvm.org/D125683

Author: ldionne

clang/cmake/caches/Android.cmake

@@ -21,8 +21,8 @@ if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
   list(APPEND EXTRA_ARGS -DLIBCXX_ENABLE_ABI_LINKER_SCRIPT=${LIBCXX_ENABLE_ABI_LINKER_SCRIPT})
 endif()
 
-if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
-  list(APPEND EXTRA_ARGS -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=${LIBCXX_ENABLE_STATIC_ABI_LIBRARY})
+if (LIBCXX_CXX_ABI)
+  list(APPEND EXTRA_ARGS -DLIBCXX_CXX_ABI=${LIBCXX_CXX_ABI})
 endif()
 
 if (LLVM_BUILD_EXTERNAL_COMPILER_RT)

clang/cmake/caches/CrossWinToARMLinux.cmake

@@ -215,10 +215,8 @@ set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_ENABLE_SHARED
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_USE_COMPILER_RT                    ON CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ENABLE_SHARED                      ${TOOLCHAIN_SHARED_LIBS} CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ABI_VERSION                        ${LIBCXX_ABI_VERSION} CACHE STRING "")
-set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_CXX_ABI                            "libcxxabi" CACHE STRING "")    #!!!
+set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_CXX_ABI                            "merged-libcxxabi" CACHE STRING "")    #!!!
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS      ON CACHE BOOL "")
-# Merge libc++ and libc++abi libraries into the single libc++ library file.
-set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY          ON CACHE BOOL "")
 
 # Avoid searching for the python3 interpreter during the runtimes configuration for the cross builds.
 # It starts searching the python3 package using the target's sysroot path, that usually is not compatible with the build host.

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -83,7 +83,7 @@ if(APPLE)
   set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
   set(LIBCXX_ABI_VERSION 2 CACHE STRING "")
   set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
-  set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
+  set(LIBCXX_CXX_ABI "merged-libcxxabi" CACHE STRING "")
   set(LIBCXX_HARDENING_MODE "none" CACHE STRING "")
   set(LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
   set(RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_DEPLOYMENT_TARGET=10.13;-DCMAKE_OSX_ARCHITECTURES=arm64|x86_64" CACHE STRING "")
@@ -180,9 +180,9 @@ foreach(target aarch64-unknown-linux-gnu;armv7-unknown-linux-gnueabihf;i386-unkn
     set(RUNTIMES_${target}_LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXXABI_INSTALL_LIBRARY OFF CACHE BOOL "")
+    set(RUNTIMES_${target}_LIBCXX_CXX_ABI "merged-libcxxabi" CACHE STRING "")
     set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
     set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}_SANITIZER_CXX_ABI "libc++" CACHE STRING "")
@@ -244,10 +244,10 @@ if(FUCHSIA_SDK)
     set(RUNTIMES_${target}_LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXXABI_INSTALL_STATIC_LIBRARY OFF CACHE BOOL "")
+    set(RUNTIMES_${target}_LIBCXX_ABILIB_FOR_STATIC "merged-libcxxabi" CACHE STRING "")
+    set(RUNTIMES_${target}_LIBCXX_ABILIB_FOR_SHARED "shared-libcxxabi" CACHE STRING "")
     set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
     set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")

clang/cmake/caches/Fuchsia.cmake

@@ -109,6 +109,7 @@ endif()
 
 if(WIN32)
   set(LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(LIBCXX_CXX_ABI "merged-libcxxabi" CACHE STRING "")
   set(LIBCXX_ENABLE_ABI_LINKER_SCRIPT OFF CACHE BOOL "")
   set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(BUILTINS_CMAKE_ARGS -DCMAKE_SYSTEM_NAME=Windows CACHE STRING "")
@@ -125,7 +126,6 @@ else()
   set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
   set(LIBCXX_ABI_VERSION 2 CACHE STRING "")
   set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
-  set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
   set(LIBCXX_HARDENING_MODE "none" CACHE STRING "")
   set(LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
   set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
@@ -155,8 +155,8 @@ if(BOOTSTRAP_CMAKE_SYSTEM_NAME)
     set(RUNTIMES_${target}_LIBCXXABI_INSTALL_LIBRARY OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+    set(RUNTIMES_${target}_LIBCXX_CXX_ABI "merged-libcxxabi" CACHE STRING "")
     set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
     set(RUNTIMES_${target}_SANITIZER_CXX_ABI "libc++" CACHE STRING "")

compiler-rt/cmake/Modules/AddCompilerRT.cmake

@@ -696,12 +696,11 @@ macro(add_custom_libcxx name prefix)
                -DLIBCXXABI_ENABLE_SHARED=OFF
                -DLIBCXXABI_HERMETIC_STATIC_LIBRARY=ON
                -DLIBCXXABI_INCLUDE_TESTS=OFF
-               -DLIBCXX_CXX_ABI=libcxxabi
+               -DLIBCXX_CXX_ABI="merged-libcxxabi"
                -DLIBCXX_ENABLE_SHARED=OFF
                -DLIBCXX_HERMETIC_STATIC_LIBRARY=ON
                -DLIBCXX_INCLUDE_BENCHMARKS=OFF
                -DLIBCXX_INCLUDE_TESTS=OFF
-               -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=ON
                ${LIBCXX_CMAKE_ARGS}
     INSTALL_COMMAND ""
     STEP_TARGETS configure build

libcxx/CMakeLists.txt

@@ -230,11 +230,22 @@ else()
 endif()
 
 set(LIBCXX_SUPPORTED_ABI_LIBRARIES none libcxxabi system-libcxxabi libcxxrt libstdc++ libsupc++ vcruntime)
-set(LIBCXX_CXX_ABI "${LIBCXX_DEFAULT_ABI_LIBRARY}" CACHE STRING "Specify C++ ABI library to use. Supported values are ${LIBCXX_SUPPORTED_ABI_LIBRARIES}.")
-if (NOT "${LIBCXX_CXX_ABI}" IN_LIST LIBCXX_SUPPORTED_ABI_LIBRARIES)
-  message(FATAL_ERROR "Unsupported C++ ABI library: '${LIBCXX_CXX_ABI}'. Supported values are ${LIBCXX_SUPPORTED_ABI_LIBRARIES}.")
-endif()
-
+set(LIBCXX_CXX_ABI "${LIBCXX_DEFAULT_ABI_LIBRARY}" CACHE STRING
+  "Specify the C++ ABI library to use for the shared and the static libc++ libraries. Supported values are ${LIBCXX_SUPPORTED_ABI_LIBRARIES}.
+   This CMake option also supports \"consumption specifiers\", which specify how the selected ABI library should be consumed by
+   libc++. The supported specifiers are:
+   - `shared`: The selected ABI library should be used as a shared library.
+   - `static`: The selected ABI library should be used as a static library.
+   - `merged`: The selected ABI library should be a static library whose object files will be merged directly into the produced libc++ library.
+
+   A consumption specifier is provided by appending it to the name of the library, such as `LIBCXX_CXX_ABI=merged-libcxxabi`.
+   If no consumption specifier is provided, the libc++ shared library will default to using a shared ABI library, and the
+   libc++ static library will default to using a static ABI library.")
+set(LIBCXX_ABILIB_FOR_SHARED "${LIBCXX_CXX_ABI}" CACHE STRING "C++ ABI library to use for the shared libc++ library.")
+set(LIBCXX_ABILIB_FOR_STATIC "${LIBCXX_CXX_ABI}" CACHE STRING "C++ ABI library to use for the static libc++ library.")
+
+#############################
+# TODO: Remove these options in LLVM 21.
 option(LIBCXX_ENABLE_STATIC_ABI_LIBRARY
   "Use a static copy of the ABI library when linking libc++.
    This option cannot be used with LIBCXX_ENABLE_ABI_LINKER_SCRIPT." OFF)
@@ -247,17 +258,34 @@ option(LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY
   "Statically link the ABI library to shared library"
   ${LIBCXX_ENABLE_STATIC_ABI_LIBRARY})
 
+if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY OR LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY OR LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY)
+  message(WARNING "The LIBCXX_ENABLE_STATIC_ABI_LIBRARY, LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY and "
+                  "LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY options have been deprecated in favor of "
+                  "using LIBCXX_CXX_ABI=merged-libcxxabi. This will become an error in LLVM 21.")
+endif()
+if (LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY)
+  set(LIBCXX_ABILIB_FOR_STATIC "merged-libcxxabi" CACHE STRING "" FORCE)
+endif()
+if (LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY)
+  set(LIBCXX_ABILIB_FOR_SHARED "merged-libcxxabi" CACHE STRING "" FORCE)
+endif()
+#############################
+
 # Generate and install a linker script inplace of libc++.so. The linker script
 # will link libc++ to the correct ABI library. This option is on by default
-# on UNIX platforms other than Apple, and on the Fuchsia platform unless we
-# statically link libc++abi inside libc++.so, we don't build libc++.so at all
-# or we don't have any ABI library.
-if (LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY
-    OR NOT LIBCXX_ENABLE_SHARED
-    OR LIBCXX_CXX_ABI STREQUAL "none")
-  set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
-elseif((UNIX OR FUCHSIA) AND NOT APPLE)
-  set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE ON)
+# on UNIX platforms other than Apple unless we are linking the ABI library as
+# an object library. This option is also disabled when the ABI library is not
+# specified or is specified to be "none".
+if(LIBCXX_ENABLE_SHARED)
+  if ((UNIX OR FUCHSIA) AND NOT APPLE)
+    if (LIBCXX_ABILIB_FOR_SHARED STREQUAL "merged-libcxxabi" OR LIBCXX_ABILIB_FOR_SHARED STREQUAL "none")
+      set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
+    else()
+      set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE ON)
+    endif()
+  else()
+    set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
+  endif()
 else()
   set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
 endif()
@@ -379,12 +407,6 @@ if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
     endif()
 endif()
 
-if (LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY AND LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
-    message(FATAL_ERROR "Conflicting options given.
-        LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY cannot be specified with
-        LIBCXX_ENABLE_ABI_LINKER_SCRIPT")
-endif()
-
 if (LIBCXX_ABI_FORCE_ITANIUM AND LIBCXX_ABI_FORCE_MICROSOFT)
   message(FATAL_ERROR "Only one of LIBCXX_ABI_FORCE_ITANIUM and LIBCXX_ABI_FORCE_MICROSOFT can be specified.")
 endif ()
@@ -481,10 +503,6 @@ include(config-ix)
 #===============================================================================
 # Setup Compiler Flags
 #===============================================================================
-
-include(HandleLibC) # Setup the C library flags
-include(HandleLibCXXABI) # Setup the ABI library flags
-
 # FIXME(EricWF): See the FIXME on LIBCXX_ENABLE_PEDANTIC.
 # Remove the -pedantic flag and -Wno-pedantic and -pedantic-errors
 # so they don't get transformed into -Wno and -errors respectively.
@@ -815,7 +833,7 @@ if (DEFINED WIN32 AND LIBCXX_ENABLE_STATIC AND NOT LIBCXX_ENABLE_SHARED)
   config_define(ON _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 endif()
 
-if (WIN32 AND LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
+if (WIN32 AND LIBCXX_CXX_ABI STREQUAL "merged-libcxxabi")
   # If linking libcxxabi statically into libcxx, skip the dllimport attributes
   # on symbols we refer to from libcxxabi.
   add_definitions(-D_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS)