Use protected visibility in llvm

[• espindola]

Summary

This should probably not be committed until it is easy to compile a program that uses a library with protected visibility.

This works for llvm's own programs because they are compiled with -fPIC.

On the particular machine I tested this in check-llvm wall time went from 58.32s to 51.30s. The task-clock reported by perf went from 1114528.526654 ms to 933402.530481ms, or about 3 minutes less.

cmake/modules/HandleLLVMOptions.cmake

else()
     add_flag_or_print_warning("-fPIC" FPIC)
   endif()
 endif()
 
 if(NOT WIN32 AND NOT CYGWIN)
   # MinGW warns if -fvisibility-inlines-hidden is used.
   check_cxx_compiler_flag("-fvisibility-inlines-hidden" SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
   append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
+
+  check_cxx_compiler_flag("-fvisibility=protected" SUPPORTS_FVISIBILITY_PROTECTED_FLAG)
+  append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility=protected" CMAKE_CXX_FLAGS)
 endif()
 
 if( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32 )
   # TODO: support other platforms and toolchains.
   if( LLVM_BUILD_32_BITS )
     message(STATUS "Building 32 bits executables and libraries.")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -m32")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -m32")

include/llvm/Support/Compiler.h

 /// LLVM_LIBRARY_VISIBILITY - If a class marked with this attribute is linked
 /// into a shared library, then the class should be private to the library and
 /// not accessible from outside it.  Can also be used to mark variables and
 /// functions, making them private to any shared library they are linked into.
 /// On PE/COFF targets, library visibility is the default, so this isn't needed.
 #if (__has_attribute(visibility) || LLVM_GNUC_PREREQ(4, 0, 0)) &&              \
     !defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32)
 #define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
+#define LLVM_PREEMPTIBLE_VISIBILITY __attribute__ ((visibility("default")))
 #else
 #define LLVM_LIBRARY_VISIBILITY
+#define LLVM_PREEMPTIBLE_VISIBILITY
 #endif
 
 #if defined(__GNUC__)
 #define LLVM_PREFETCH(addr, rw, locality) __builtin_prefetch(addr, rw, locality)
 #else
 #define LLVM_PREFETCH(addr, rw, locality)
 #endif
 

utils/unittest/UnitTestMain/TestMain.cpp

 # include <windows.h>
 # if defined(_MSC_VER)
 #   include <crtdbg.h>
 # endif
 #endif
 
 const char *TestMainArgv0;
 
-int main(int argc, char **argv) {
+LLVM_PREEMPTIBLE_VISIBILITY int main(int argc, char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0],
                                           true /* Disable crash reporting */);
 
   // Initialize both gmock and gtest.
   testing::InitGoogleMock(&argc, argv);
 
   llvm::cl::ParseCommandLineOptions(argc, argv);