[lto] Don't add variables with private linkage to the symbol table.

[silvas]

Summary

Do we need any other special handling for these?

This causes the issue in PR26872 to go away now that we aren't creating
symbols for the string literals, but that may just be concealing a
deeper problem, so best to keep that PR open.

In my testing, it seems that InternalLinkage also needs to be added to
this if condition (to avoid duplicate symbol errors for C/C++
"static") and also AppendingLinkage (to avoid duplicate symbols for
llvm.global_ctors).
Those will be in separate patches though.

[• rafael]

LGTM with nits.

ELF/InputFiles.cpp

447 ↗

(On Diff #50076)

Please move getFlags earlier and use

if (!(Fags & object::BasicSymbolRef::SF_Global))

continue;

test/ELF/lto/linkage.ll

4 ↗

(On Diff #50076)

Can you just pass %t1.o twice?

lld/trunk/ELF/InputFiles.cpp

for (const auto &P : M.getComdatSymbolTable()) {
     StringRef N = Saver.save(P.first());
     if (ComdatGroups.insert(N).second)
       KeptComdats.insert(&P.second);
   }
 
   for (const BasicSymbolRef &Sym : Obj->symbols()) {
     uint8_t Visibility = STV_DEFAULT;
     const GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
+    uint32_t Flags = Sym.getFlags();
     if (GV) {
       if (const Comdat *C = GV->getComdat())
         if (!KeptComdats.count(C))
           continue;
+      if (!(Flags & object::BasicSymbolRef::SF_Global))
+        continue;
       Visibility = getGvVisibility(GV);
     }
 
     SmallString<64> Name;
     raw_svector_ostream OS(Name);
     Sym.printName(OS);
     StringRef NameRef = Saver.save(StringRef(Name));
 
     SymbolBody *Body;
-    uint32_t Flags = Sym.getFlags();
     bool IsWeak = Flags & BasicSymbolRef::SF_Weak;
     if (Flags & BasicSymbolRef::SF_Undefined) {
       Body = new (Alloc) Undefined(NameRef, IsWeak, Visibility, false);
     } else if (Flags & BasicSymbolRef::SF_Common) {
       const DataLayout &DL = M.getDataLayout();
       uint64_t Size = DL.getTypeAllocSize(GV->getValueType());
       Body = new (Alloc)
           DefinedCommon(NameRef, Size, GV->getAlignment(), IsWeak, Visibility);

lld/trunk/test/ELF/lto/linkage.ll

+; REQUIRES: x86
+; RUN: llvm-as %s -o %t1.o
+; RUN: ld.lld -m elf_x86_64 %t1.o %t1.o -o %t.so -shared
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Should not encounter a duplicate symbol error for @.str
+@.str = private unnamed_addr constant [4 x i8] c"Hey\00", align 1