Explicit approach to controlling symbol visibility

[serge-sans-paille]

Summary

Setting -fvisibility=hidden when compiling Target libs has the advantage of
not being intrusive on the codebase, but it also sets the visibility of all
functions within header-only component like ADT. In the end, we endup with
some symbols with hidden visibility within llvm dylib (through the target libs),
and some with external visibility (through other libs). This paves the way for
subtle bugs like https://reviews.llvm.org/D101972

It's easier to reason on explicit, pin-point linkage as provided in this patch.
This also paves the way for a more visibility control in all components,
something -fvisibility=hidden doesn't help with.

[grandinj]

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.h

83

looks like the search and replace accidentally hit comments like these

[serge-sans-paille]

Don't modify the closing brace namespace comment

[jrtc27]

Is there a strategy for downstreams so that we don't have a weird mishmash of symbol visibilities, where files we've added have the old rules applied but files present upstream have the new rules? I don't particularly want to be trawling through both our modified backends trying to find every .h and .cpp file we've added, and people with complete out-of-tree backends will have even more of a hard time.

llvm/lib/Target/AArch64/AArch64.h

96

This has lost the actual namespace name

[serge-sans-paille]

In D108690#2968897, @jrtc27 wrote:

Is there a strategy for downstreams so that we don't have a weird mishmash of symbol visibilities, where files we've added have the old rules applied but files present upstream have the new rules?

I'm going to drop that patch, it's too intrusive. the alternative approach is to flag some classes used as parameter of llvm::Any as externally visible, I'm going to follow that way.

llvm/lib/Target/AArch64/AArch64.h

 #ifndef LLVM_LIB_TARGET_AARCH64_AARCH64_H
 #define LLVM_LIB_TARGET_AARCH64_AARCH64_H
 
 #include "MCTargetDesc/AArch64MCTargetDesc.h"
 #include "Utils/AArch64BaseInfo.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Target/TargetMachine.h"
 
-namespace llvm {
+namespace llvm LLVM_LIBRARY_VISIBILITY {
 
 class AArch64RegisterBankInfo;
 class AArch64Subtarget;
 class AArch64TargetMachine;
 class FunctionPass;
 class InstructionSelector;
 class MachineFunctionPass;
 

 void initializeAArch64RedundantCopyEliminationPass(PassRegistry&);
 void initializeAArch64StorePairSuppressPass(PassRegistry&);
 void initializeFalkorHWPFFixPass(PassRegistry&);
 void initializeFalkorMarkStridedAccessesLegacyPass(PassRegistry&);
 void initializeLDTLSCleanupPass(PassRegistry&);
 void initializeSVEIntrinsicOptsPass(PassRegistry&);
 void initializeAArch64StackTaggingPass(PassRegistry&);
 void initializeAArch64StackTaggingPreRAPass(PassRegistry&);
-} // end namespace llvm
+} // namespace LLVM_LIBRARY_VISIBILITY
 
 #endif

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.h

 #define LLVM_LIB_TARGET_AARCH64_AARCH64CALLLOWERING_H
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/CodeGen/GlobalISel/CallLowering.h"
 #include "llvm/IR/CallingConv.h"
 #include <cstdint>
 #include <functional>
 
-namespace llvm {
+namespace llvm LLVM_LIBRARY_VISIBILITY {
 
 class AArch64TargetLowering;
 class CCValAssign;
 class DataLayout;
 class MachineIRBuilder;
 class MachineRegisterInfo;
 class Type;
 
doCallerAndCalleePassArgsTheSameWay(CallLoweringInfo &Info,
                                       MachineFunction &MF,
                                       SmallVectorImpl<ArgInfo> &InArgs) const;
 
   bool
   areCalleeOutgoingArgsTailCallable(CallLoweringInfo &Info, MachineFunction &MF,
                                     SmallVectorImpl<ArgInfo> &OutArgs) const;
 };
 
-} // end namespace llvm
+} // namespace LLVM_LIBRARY_VISIBILITY
 
 #endif // LLVM_LIB_TARGET_AARCH64_AARCH64CALLLOWERING_H