Re-apply "Only define LLVM_EXTERNAL_VISIBILITY when building libLLVM dylib"

[benlangmuir]

Summary

With a fix for the MLIR test failure with BUILD_SHARED_LIBS.

Original commit message:

When building LLVM static libraries, we should not make symbols more
visible than CMAKE_CXX_VISIBILITY_PRESET, since the goal may be to have
a purely hidden llvm embedded in another library. Instead, we only
define LLVM_EXTERNAL_VISIBILITY for the dynamic library build (when
LLVM_BUILD_LLVM_DYLIB=YES).

[benlangmuir]

mlir/include/mlir/Support/TypeID.h

118 ↗

(On Diff #394643)

I'm not sure if matching the CAPI visibility is precisely what you want here, but it seems like a strict improvement over matching the LLVM visibility, which should be mostly orthogonal from what you do here.

[mehdi_amini]

mlir/include/mlir/Support/TypeID.h

118 ↗

(On Diff #394643)

Not really: if you look into mlir/tools/mlir-shlib/CMakeLists.txt we're creating libMLIR.dylib hand-in-hand with libLLVM.dylib ; this is what this mechanism is covering here.

(I need to go back to the original revision, I haven't followed exactly what the change is so far)

[mehdi_amini]

mlir/include/mlir/Support/TypeID.h

118 ↗

(On Diff #394643)

https://reviews.llvm.org/D113610 for the record

[benlangmuir]

Updated to enable the visibility macro when using BUILD_SHARED_LIBS and remove the MLIR-specific change, per review.

llvm/CMakeLists.txt

set(LLVM_ENUM_DISASSEMBLERS
       "${LLVM_ENUM_DISASSEMBLERS}LLVM_DISASSEMBLER(${t})\n")
   endif()
     if( EXISTS ${td}/MCA/CMakeLists.txt )
     set(LLVM_ENUM_TARGETMCAS
       "${LLVM_ENUM_TARGETMCAS}LLVM_TARGETMCA(${t})\n")
   endif()
 endforeach(t)
 
+# Provide an LLVM_ namespaced alias for use in #cmakedefine.
+set(LLVM_BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS})
+
 # Produce the target definition files, which provide a way for clients to easily
 # include various classes of targets.
 configure_file(
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Config/AsmPrinters.def.in
   ${LLVM_INCLUDE_DIR}/llvm/Config/AsmPrinters.def
   )
 configure_file(
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Config/AsmParsers.def.in

llvm/include/llvm/Config/llvm-config.h.cmake

 #cmakedefine HAVE_SYSEXITS_H ${HAVE_SYSEXITS_H}
 
 /* Define to 1 to enable the experimental new pass manager by default */
 #cmakedefine01 LLVM_ENABLE_NEW_PASS_MANAGER
 
 /* Define if the xar_open() function is supported on this platform. */
 #cmakedefine LLVM_HAVE_LIBXAR ${LLVM_HAVE_LIBXAR}
 
+/* Define if building libLLVM shared library */
+#cmakedefine LLVM_BUILD_LLVM_DYLIB
+
+/* Define if building LLVM with BUILD_SHARED_LIBS */
+#cmakedefine LLVM_BUILD_SHARED_LIBS
+
 #endif

llvm/include/llvm/Support/Compiler.h

 /// On PE/COFF targets, library visibility is the default, so this isn't needed.
 ///
 /// LLVM_EXTERNAL_VISIBILITY - classes, functions, and variables marked with
 /// this attribute will be made public and visible outside of any shared library
 /// they are linked in to.
 #if __has_attribute(visibility) && !defined(__MINGW32__) &&                    \
     !defined(__CYGWIN__) && !defined(_WIN32)
 #define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
-#define LLVM_EXTERNAL_VISIBILITY __attribute__ ((visibility("default")))
+#if defined(LLVM_BUILD_LLVM_DYLIB) || defined(LLVM_BUILD_SHARED_LIBS)
+#define LLVM_EXTERNAL_VISIBILITY __attribute__((visibility("default")))
 #else
+#define LLVM_EXTERNAL_VISIBILITY
+#endif
+#else
 #define LLVM_LIBRARY_VISIBILITY
 #define LLVM_EXTERNAL_VISIBILITY
 #endif
 
 #if defined(__GNUC__)
 #define LLVM_PREFETCH(addr, rw, locality) __builtin_prefetch(addr, rw, locality)
 #else
 #define LLVM_PREFETCH(addr, rw, locality)