[libcxxabi] Don't process exceptions in cxa_handlers when they're disabled

When exceptions are disabled, avoid their processing altogether.
This avoids pulling in the depenency on demangler significantly
reducing binary size when statically linking against libc++abi
built without exception support.

Differential Revision: https://reviews.llvm.org/D64191

llvm-svn: 365944

Author: petrhosek

libcxxabi/CMakeLists.txt

@@ -43,7 +43,9 @@ include(CMakeDependentOption)
 include(HandleCompilerRT)
 
 # Define options.
-option(LIBCXXABI_ENABLE_EXCEPTIONS "Use exceptions." 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)
 option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 option(LIBCXXABI_ENABLE_PIC "Build Position-Independent Code, even in static library" ON)

libcxxabi/src/cxa_default_handlers.cpp

@@ -25,6 +25,7 @@ static const char* cause = "uncaught";
 __attribute__((noreturn))
 static void demangling_terminate_handler()
 {
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     // If there might be an uncaught exception
     using namespace __cxxabiv1;
     __cxa_eh_globals* globals = __cxa_get_globals_fast();
@@ -71,6 +72,7 @@ static void demangling_terminate_handler()
                 abort_message("terminating with %s foreign exception", cause);
         }
     }
+#endif
     // Else just note that we're terminating
     abort_message("terminating");
 }

libcxxabi/src/cxa_handlers.cpp

@@ -73,6 +73,7 @@ __attribute__((noreturn))
 void
 terminate() _NOEXCEPT
 {
+#ifndef _LIBCXXABI_NO_EXCEPTIONS
     // If there might be an uncaught exception
     using namespace __cxxabiv1;
     __cxa_eh_globals* globals = __cxa_get_globals_fast();
@@ -87,6 +88,7 @@ terminate() _NOEXCEPT
                 __terminate(exception_header->terminateHandler);
         }
     }
+#endif
     __terminate(get_terminate());
 }