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/Mips/AsmParser/MipsAsmParser.cpp b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
index 34862bdadb9..e467ed36938 100644
--- a/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ b/llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -8645,7 +8645,7 @@ bool MipsAsmParser::parseInternalDirectiveReallowModule() {
   return false;
 }
 
-extern "C" void LLVMInitializeMipsAsmParser() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeMipsAsmParser() {
   RegisterMCAsmParser<MipsAsmParser> X(getTheMipsTarget());
   RegisterMCAsmParser<MipsAsmParser> Y(getTheMipselTarget());
   RegisterMCAsmParser<MipsAsmParser> A(getTheMips64Target());
diff --git a/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp b/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
index a858c6d1ca4..6f197e42456 100644
--- a/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
+++ b/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
@@ -563,7 +563,7 @@ static MCDisassembler *createMipselDisassembler(
   return new MipsDisassembler(STI, Ctx, false);
 }
 
-extern "C" void LLVMInitializeMipsDisassembler() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeMipsDisassembler() {
   // Register the disassembler.
   TargetRegistry::RegisterMCDisassembler(getTheMipsTarget(),
                                          createMipsDisassembler);
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
index d0b3c204730..de582bd60cb 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCTargetDesc.cpp
@@ -166,7 +166,7 @@ static MCInstrAnalysis *createMipsMCInstrAnalysis(const MCInstrInfo *Info) {
   return new MipsMCInstrAnalysis(Info);
 }
 
-extern "C" void LLVMInitializeMipsTargetMC() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeMipsTargetMC() {
   for (Target *T : {&getTheMipsTarget(), &getTheMipselTarget(),
                     &getTheMips64Target(), &getTheMips64elTarget()}) {
     // Register the MC asm info.
diff --git a/llvm/lib/Target/Mips/MipsAsmPrinter.cpp b/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
index be556cfba4d..8f75336dce5 100644
--- a/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
+++ b/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
@@ -1306,7 +1306,7 @@ bool MipsAsmPrinter::isLongBranchPseudo(int Opcode) const {
 }
 
 // Force static initialization.
-extern "C" void LLVMInitializeMipsAsmPrinter() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeMipsAsmPrinter() {
   RegisterAsmPrinter<MipsAsmPrinter> X(getTheMipsTarget());
   RegisterAsmPrinter<MipsAsmPrinter> Y(getTheMipselTarget());
   RegisterAsmPrinter<MipsAsmPrinter> A(getTheMips64Target());
diff --git a/llvm/lib/Target/Mips/MipsTargetMachine.cpp b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
index 66c20050c08..8fec6db00cb 100644
--- a/llvm/lib/Target/Mips/MipsTargetMachine.cpp
+++ b/llvm/lib/Target/Mips/MipsTargetMachine.cpp
@@ -45,7 +45,7 @@ using namespace llvm;
 
 #define DEBUG_TYPE "mips"
 
-extern "C" void LLVMInitializeMipsTarget() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeMipsTarget() {
   // Register the target.
   RegisterTargetMachine<MipsebTargetMachine> X(getTheMipsTarget());
   RegisterTargetMachine<MipselTargetMachine> Y(getTheMipselTarget());
diff --git a/llvm/lib/Target/Mips/TargetInfo/MipsTargetInfo.cpp b/llvm/lib/Target/Mips/TargetInfo/MipsTargetInfo.cpp
index 0082ca34cdb..44041987ec7 100644
--- a/llvm/lib/Target/Mips/TargetInfo/MipsTargetInfo.cpp
+++ b/llvm/lib/Target/Mips/TargetInfo/MipsTargetInfo.cpp
@@ -27,7 +27,7 @@ Target &llvm::getTheMips64elTarget() {
   return TheMips64elTarget;
 }
 
-extern "C" void LLVMInitializeMipsTargetInfo() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeMipsTargetInfo() {
   RegisterTarget<Triple::mips,
                  /*HasJIT=*/true>
       X(getTheMipsTarget(), "mips", "MIPS (32-bit big endian)", "Mips");