CMake: Make most target symbols hidden by default

Summary:
For builds with LLVM_BUILD_LLVM_DYLIB=ON and BUILD_SHARED_LIBS=OFF
this change makes all symbols in the target specific libraries hidden
by default.

A new macro called LLVM_EXTERNAL_VISIBILITY has been added to mark symbols in these
libraries public, which is mainly needed for the definitions of the
LLVMInitialize* functions.

This patch reduces the number of public symbols in libLLVM.so by about
25%.  This should improve load times for the dynamic library and also
make abi checker tools, like abidiff require less memory when analyzing
libLLVM.so

One side-effect of this change is that for builds with
LLVM_BUILD_LLVM_DYLIB=ON and LLVM_LINK_LLVM_DYLIB=ON some unittests that
access symbols that are no longer public will need to be statically linked.

Before and after public symbol counts (using gcc 8.2.1, ld.bfd 2.31.1):
nm before/libLLVM-9svn.so | grep ' [A-Zuvw] ' | wc -l
36221
nm after/libLLVM-9svn.so | grep ' [A-Zuvw] ' | wc -l
26278

Reviewers: chandlerc, beanz, mgorny, rnk, hans

Reviewed By: rnk, hans

Subscribers: merge_guards_bot, luismarques, smeenai, ldionne, lenary, s.egerton, pzheng, sameer.abuasal, MaskRay, wuzish, echristo, Jim, hiraditya, michaelplatings, chapuni, jholewinski, arsenm, dschuff, jyknight, dylanmckay, sdardis, nemanjai, jvesely, javed.absar, sbc100, jgravelle-google, aheejin, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, zzheng, edward-jones, mgrang, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, PkmX, jocewei, kristina, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D54439

Author: tstellar

llvm/include/llvm/Support/Compiler.h

@@ -117,11 +117,17 @@
 /// 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.
+///
+/// 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) || LLVM_GNUC_PREREQ(4, 0, 0)) &&              \
     !defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(_WIN32)
 #define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
+#define LLVM_EXTERNAL_VISIBILITY __attribute__ ((visibility("default")))
 #else
 #define LLVM_LIBRARY_VISIBILITY
+#define LLVM_EXTERNAL_VISIBILITY
 #endif
 
 #if defined(__GNUC__)

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -1298,7 +1298,7 @@ void AArch64AsmPrinter::EmitInstruction(const MachineInstr *MI) {
 }
 
 // Force static initialization.
-extern "C" void LLVMInitializeAArch64AsmPrinter() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64AsmPrinter() {
   RegisterAsmPrinter<AArch64AsmPrinter> X(getTheAArch64leTarget());
   RegisterAsmPrinter<AArch64AsmPrinter> Y(getTheAArch64beTarget());
   RegisterAsmPrinter<AArch64AsmPrinter> Z(getTheARM64Target());

llvm/lib/Target/AArch64/AArch64TargetMachine.cpp

@@ -154,7 +154,7 @@ static cl::opt<bool>
                         cl::desc("Enable the AAcrh64 branch target pass"),
                         cl::init(true));
 
-extern "C" void LLVMInitializeAArch64Target() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64Target() {
   // Register the target.
   RegisterTargetMachine<AArch64leTargetMachine> X(getTheAArch64leTarget());
   RegisterTargetMachine<AArch64beTargetMachine> Y(getTheAArch64beTarget());

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -5515,7 +5515,7 @@ AArch64AsmParser::classifySymbolRef(const MCExpr *Expr,
 }
 
 /// Force static initialization.
-extern "C" void LLVMInitializeAArch64AsmParser() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64AsmParser() {
   RegisterMCAsmParser<AArch64AsmParser> X(getTheAArch64leTarget());
   RegisterMCAsmParser<AArch64AsmParser> Y(getTheAArch64beTarget());
   RegisterMCAsmParser<AArch64AsmParser> Z(getTheARM64Target());

llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp

@@ -277,7 +277,7 @@ createAArch64ExternalSymbolizer(const Triple &TT, LLVMOpInfoCallback GetOpInfo,
                                        SymbolLookUp, DisInfo);
 }
 
-extern "C" void LLVMInitializeAArch64Disassembler() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64Disassembler() {
   TargetRegistry::RegisterMCDisassembler(getTheAArch64leTarget(),
                                          createAArch64Disassembler);
   TargetRegistry::RegisterMCDisassembler(getTheAArch64beTarget(),

llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp

@@ -366,7 +366,7 @@ static MCInstrAnalysis *createAArch64InstrAnalysis(const MCInstrInfo *Info) {
 }
 
 // Force static initialization.
-extern "C" void LLVMInitializeAArch64TargetMC() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64TargetMC() {
   for (Target *T : {&getTheAArch64leTarget(), &getTheAArch64beTarget(),
                     &getTheAArch64_32Target(), &getTheARM64Target(),
                     &getTheARM64_32Target()}) {

llvm/lib/Target/AArch64/TargetInfo/AArch64TargetInfo.cpp

@@ -31,7 +31,7 @@ Target &llvm::getTheARM64_32Target() {
   return TheARM64_32Target;
 }
 
-extern "C" void LLVMInitializeAArch64TargetInfo() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64TargetInfo() {
   // Now register the "arm64" name for use with "-march". We don't want it to
   // take possession of the Triple::aarch64 tags though.
   TargetRegistry::RegisterTarget(getTheARM64Target(), "arm64",

llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp

@@ -90,7 +90,7 @@ createAMDGPUAsmPrinterPass(TargetMachine &tm,
   return new AMDGPUAsmPrinter(tm, std::move(Streamer));
 }
 
-extern "C" void LLVMInitializeAMDGPUAsmPrinter() {
+extern "C" void LLVM_EXTERNAL_VISIBILITY LLVMInitializeAMDGPUAsmPrinter() {
   TargetRegistry::RegisterAsmPrinter(getTheAMDGPUTarget(),
                                      llvm::createR600AsmPrinterPass);
   TargetRegistry::RegisterAsmPrinter(getTheGCNTarget(),

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -183,7 +183,7 @@ static cl::opt<bool> EnableScalarIRPasses(
   cl::init(true),
   cl::Hidden);
 
-extern "C" void LLVMInitializeAMDGPUTarget() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAMDGPUTarget() {
   // Register the target
   RegisterTargetMachine<R600TargetMachine> X(getTheAMDGPUTarget());
   RegisterTargetMachine<GCNTargetMachine> Y(getTheGCNTarget());

llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp

@@ -6980,7 +6980,7 @@ AMDGPUOperand::Ptr AMDGPUAsmParser::defaultABID() const {
 }
 
 /// Force static initialization.
-extern "C" void LLVMInitializeAMDGPUAsmParser() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAMDGPUAsmParser() {
   RegisterMCAsmParser<AMDGPUAsmParser> A(getTheAMDGPUTarget());
   RegisterMCAsmParser<AMDGPUAsmParser> B(getTheGCNTarget());
 }