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

5 files changed, 5 insertions, 5 deletions

diff --git a/llvm/unittests/tools/llvm-exegesis/AArch64/CMakeLists.txt b/llvm/unittests/tools/llvm-exegesis/AArch64/CMakeLists.txt
index 392efce26c00..907de1119452 100644
--- a/llvm/unittests/tools/llvm-exegesis/AArch64/CMakeLists.txt
+++ b/llvm/unittests/tools/llvm-exegesis/AArch64/CMakeLists.txt
@@ -13,7 +13,7 @@ set(LLVM_LINK_COMPONENTS
   AArch64
   )
 
-add_llvm_unittest(LLVMExegesisAArch64Tests
+add_llvm_target_unittest(LLVMExegesisAArch64Tests
   TargetTest.cpp
   )
 target_link_libraries(LLVMExegesisAArch64Tests PRIVATE
diff --git a/llvm/unittests/tools/llvm-exegesis/ARM/CMakeLists.txt b/llvm/unittests/tools/llvm-exegesis/ARM/CMakeLists.txt
index b000974938f7..27ecff5f4ae9 100644
--- a/llvm/unittests/tools/llvm-exegesis/ARM/CMakeLists.txt
+++ b/llvm/unittests/tools/llvm-exegesis/ARM/CMakeLists.txt
@@ -13,7 +13,7 @@ set(LLVM_LINK_COMPONENTS
   ARM
   )
 
-add_llvm_unittest(LLVMExegesisARMTests
+add_llvm_target_unittest(LLVMExegesisARMTests
   AssemblerTest.cpp
   )
 target_link_libraries(LLVMExegesisARMTests PRIVATE LLVMExegesis)
diff --git a/llvm/unittests/tools/llvm-exegesis/Mips/CMakeLists.txt b/llvm/unittests/tools/llvm-exegesis/Mips/CMakeLists.txt
index 629fa0d3622c..4610dedb8f79 100644
--- a/llvm/unittests/tools/llvm-exegesis/Mips/CMakeLists.txt
+++ b/llvm/unittests/tools/llvm-exegesis/Mips/CMakeLists.txt
@@ -13,7 +13,7 @@ set(LLVM_LINK_COMPONENTS
   Mips
   )
 
-add_llvm_unittest(LLVMExegesisMipsTests
+add_llvm_target_unittest(LLVMExegesisMipsTests
   BenchmarkResultTest.cpp
   SnippetGeneratorTest.cpp
   TargetTest.cpp
diff --git a/llvm/unittests/tools/llvm-exegesis/PowerPC/CMakeLists.txt b/llvm/unittests/tools/llvm-exegesis/PowerPC/CMakeLists.txt
index e8a53e3692aa..6324ae652de0 100644
--- a/llvm/unittests/tools/llvm-exegesis/PowerPC/CMakeLists.txt
+++ b/llvm/unittests/tools/llvm-exegesis/PowerPC/CMakeLists.txt
@@ -13,7 +13,7 @@ set(LLVM_LINK_COMPONENTS
   PowerPC
   )
 
-add_llvm_unittest(LLVMExegesisPowerPCTests
+add_llvm_target_unittest(LLVMExegesisPowerPCTests
   AnalysisTest.cpp
   TargetTest.cpp
   )
diff --git a/llvm/unittests/tools/llvm-exegesis/X86/CMakeLists.txt b/llvm/unittests/tools/llvm-exegesis/X86/CMakeLists.txt
index c9de60d6c64b..52ca6680116c 100644
--- a/llvm/unittests/tools/llvm-exegesis/X86/CMakeLists.txt
+++ b/llvm/unittests/tools/llvm-exegesis/X86/CMakeLists.txt
@@ -13,7 +13,7 @@ set(LLVM_LINK_COMPONENTS
   X86
   )
 
-add_llvm_unittest(LLVMExegesisX86Tests
+add_llvm_target_unittest(LLVMExegesisX86Tests
   AssemblerTest.cpp
   BenchmarkResultTest.cpp
   RegisterAliasingTest.cpp