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

6 files changed, 6 insertions, 6 deletions

diff --git a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
index 1dbfbcaa0d8..6f26ca127f9 100644
--- a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -2148,7 +2148,7 @@ void ARMAsmPrinter::EmitInstruction(const MachineInstr *MI) {
 //===----------------------------------------------------------------------===//
 
 // Force static initialization.
-extern "C" void LLVMInitializeARMAsmPrinter() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARMAsmPrinter() {
   RegisterAsmPrinter<ARMAsmPrinter> X(getTheARMLETarget());
   RegisterAsmPrinter<ARMAsmPrinter> Y(getTheARMBETarget());
   RegisterAsmPrinter<ARMAsmPrinter> A(getTheThumbLETarget());
diff --git a/llvm/lib/Target/ARM/ARMTargetMachine.cpp b/llvm/lib/Target/ARM/ARMTargetMachine.cpp
index a48f351f37a..84876eda33a 100644
--- a/llvm/lib/Target/ARM/ARMTargetMachine.cpp
+++ b/llvm/lib/Target/ARM/ARMTargetMachine.cpp
@@ -79,7 +79,7 @@ namespace llvm {
   void initializeARMExecutionDomainFixPass(PassRegistry&);
 }
 
-extern "C" void LLVMInitializeARMTarget() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARMTarget() {
   // Register the target.
   RegisterTargetMachine<ARMLETargetMachine> X(getTheARMLETarget());
   RegisterTargetMachine<ARMLETargetMachine> A(getTheThumbLETarget());
diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index cb07d17f194..f6d76ee0953 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -11546,7 +11546,7 @@ bool ARMAsmParser::parseDirectiveThumbSet(SMLoc L) {
 }
 
 /// Force static initialization.
-extern "C" void LLVMInitializeARMAsmParser() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARMAsmParser() {
   RegisterMCAsmParser<ARMAsmParser> X(getTheARMLETarget());
   RegisterMCAsmParser<ARMAsmParser> Y(getTheARMBETarget());
   RegisterMCAsmParser<ARMAsmParser> A(getTheThumbLETarget());
diff --git a/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index abfe47dbdea..d26b04556ab 100644
--- a/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -1099,7 +1099,7 @@ DecodeStatus ARMDisassembler::getThumbInstruction(MCInst &MI, uint64_t &Size,
   return MCDisassembler::Fail;
 }
 
-extern "C" void LLVMInitializeARMDisassembler() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARMDisassembler() {
   TargetRegistry::RegisterMCDisassembler(getTheARMLETarget(),
                                          createARMDisassembler);
   TargetRegistry::RegisterMCDisassembler(getTheARMBETarget(),
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
index 6c86550b1a4..9f60e70e0e0 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
@@ -317,7 +317,7 @@ static MCInstrAnalysis *createThumbMCInstrAnalysis(const MCInstrInfo *Info) {
 }
 
 // Force static initialization.
-extern "C" void LLVMInitializeARMTargetMC() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARMTargetMC() {
   for (Target *T : {&getTheARMLETarget(), &getTheARMBETarget(),
                     &getTheThumbLETarget(), &getTheThumbBETarget()}) {
     // Register the MC asm info.
diff --git a/llvm/lib/Target/ARM/TargetInfo/ARMTargetInfo.cpp b/llvm/lib/Target/ARM/TargetInfo/ARMTargetInfo.cpp
index 86cb907abfa..a7f7d75e356 100644
--- a/llvm/lib/Target/ARM/TargetInfo/ARMTargetInfo.cpp
+++ b/llvm/lib/Target/ARM/TargetInfo/ARMTargetInfo.cpp
@@ -27,7 +27,7 @@ Target &llvm::getTheThumbBETarget() {
   return TheThumbBETarget;
 }
 
-extern "C" void LLVMInitializeARMTargetInfo() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeARMTargetInfo() {
   RegisterTarget<Triple::arm, /*HasJIT=*/true> X(getTheARMLETarget(), "arm",
                                                  "ARM", "ARM");
   RegisterTarget<Triple::armeb, /*HasJIT=*/true> Y(getTheARMBETarget(), "armeb",