[libc++abi] Introduce LIBCXXABI_ENABLE_DEMANGLER

[michael-kenzel]

This change introduces a LIBCXXABI_ENABLE_DEMANGLER CMake option that allows turning off the demangler API from being included in the build. This can be useful when trying to build a minimal version of libc++abi, e.g., for a baremetal target. The demangler is quite heavy in dependencies on libraries that are not easily available on such a target, and is not an essential component. As discussed in #72948, LIBCXXABI_NON_DEMANGLING_TERMINATE is removed, its functionality is now tied to the new LIBCXXABI_ENABLE_DEMANGLER option.

[michael-kenzel]

Note: this is the requested resubmission of #72948

[llvmbot]

@llvm/pr-subscribers-libcxxabi

Author: Michael Kenzel (michael-kenzel)

Changes

This change introduces a LIBCXXABI_ENABLE_DEMANGLER CMake option that allows turning off the demangler API from being included in the build. This can be useful when trying to build a minimal version of libc++abi, e.g., for a baremetal target. The demangler is quite heavy in dependencies on libraries that are not easily available on such a target, and is not an essential component. As discussed in #72948, LIBCXXABI_NON_DEMANGLING_TERMINATE is removed, its functionality is now tied to the new LIBCXXABI_ENABLE_DEMANGLER option.

---

Full diff: https://github.com/llvm/llvm-project/pull/132130.diff

2 Files Affected:

• (modified) libcxxabi/CMakeLists.txt (+4-3)
• (modified) libcxxabi/src/CMakeLists.txt (+6-1)

diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index 6dcfc51e55321..1c1247e165340 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -46,6 +46,9 @@ include(CMakeDependentOption)
 include(HandleCompilerRT)
 
 # Define options.
+option(LIBCXXABI_ENABLE_DEMANGLER
+  "Provide support for demangling in the runtime.
+   When disabled, libc++abi does not support the name demangler API." ON)
 option(LIBCXXABI_ENABLE_EXCEPTIONS
   "Provide support for exceptions in the runtime.
   When disabled, libc++abi does not support stack unwinding and other exceptions-related features." ON)
@@ -129,8 +132,6 @@ option(LIBCXXABI_BAREMETAL "Build libc++abi for baremetal targets." OFF)
 # The default terminate handler attempts to demangle uncaught exceptions, which
 # causes extra I/O and demangling code to be pulled in.
 option(LIBCXXABI_SILENT_TERMINATE "Set this to make the terminate handler default to a silent alternative" OFF)
-option(LIBCXXABI_NON_DEMANGLING_TERMINATE "Set this to make the terminate handler
-avoid demangling" OFF)
 
 if (NOT LIBCXXABI_ENABLE_SHARED AND NOT LIBCXXABI_ENABLE_STATIC)
   message(FATAL_ERROR "libc++abi must be built as either a shared or static library.")
@@ -431,7 +432,7 @@ if (LIBCXXABI_SILENT_TERMINATE)
   add_definitions(-DLIBCXXABI_SILENT_TERMINATE)
 endif()
 
-if (LIBCXXABI_NON_DEMANGLING_TERMINATE)
+if (NOT LIBCXXABI_ENABLE_DEMANGLER)
   add_definitions(-DLIBCXXABI_NON_DEMANGLING_TERMINATE)
 endif()
 
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index 0a6fc892a4f69..4167845c9713d 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -3,7 +3,6 @@ set(LIBCXXABI_SOURCES
   # C++ABI files
   cxa_aux_runtime.cpp
   cxa_default_handlers.cpp
-  cxa_demangle.cpp
   cxa_exception_storage.cpp
   cxa_guard.cpp
   cxa_handlers.cpp
@@ -19,6 +18,12 @@ set(LIBCXXABI_SOURCES
   private_typeinfo.cpp
 )
 
+if (LIBCXXABI_ENABLE_DEMANGLER)
+  list(APPEND LIBCXXABI_SOURCES
+    cxa_demangle.cpp
+  )
+endif()
+
 if (LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS)
   list(APPEND LIBCXXABI_SOURCES
     stdlib_new_delete.cpp

[ldionne]

CC @llvm/libcxx-vendors and in particular @DanAlbert in case any changes to downstream builds are needed.

@michael-kenzel Thinking about this again, can you please add this to the libc++ release notes under Build System Changes? And can you also make it an error to define LIBCXXABI_NON_DEMANGLING_TERMINATE with a TODO to remove it in LLVM 22? That way, anyone building with LIBCXXABI_NON_DEMANGLING_TERMINATE will be notified to migrate to the new spelling when the change lands. Otherwise it's a silent behavior change.