[lto] Make sure that ctors are added to the combined module.

Summary:
More generally, appending linkage is a special case that we don't want
to create a SymbolBody for.

Reviewers: rafael, ruiu

Subscribers: Bigcheese, llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D18012

llvm-svn: 263179

lld/ELF/InputFiles.cpp

@@ -450,8 +450,10 @@ void BitcodeFile::parse(DenseSet<StringRef> &ComdatGroups) {
         continue;
     if (!(Flags & BasicSymbolRef::SF_Global))
         continue;
-    if (Flags & BasicSymbolRef::SF_FormatSpecific)
+    if (GV->hasAppendingLinkage()) {
+      ExtraKeeps.push_back(GV->getName().copy(Alloc));
       continue;
+    }
     uint8_t Visibility = getGvVisibility(GV);
 
     SmallString<64> Name;

lld/ELF/InputFiles.h

@@ -185,9 +185,17 @@ public:
   static bool classof(const InputFile *F);
   void parse(llvm::DenseSet<StringRef> &ComdatGroups);
   ArrayRef<SymbolBody *> getSymbols() { return SymbolBodies; }
+  ArrayRef<StringRef> getExtraKeeps() { return ExtraKeeps; }
 
 private:
   std::vector<SymbolBody *> SymbolBodies;
+  // Some symbols like llvm.global_ctors are internal to the IR and so
+  // don't show up in SymbolBodies, but must be kept when creating the
+  // combined LTO module. We track them here.
+  // We currently use a different Module for creating SymbolBody's vs when
+  // we are creating the combined LTO module, and so we can't store IR
+  // pointers directly and must rely on the IR names.
+  std::vector<StringRef> ExtraKeeps;
   llvm::BumpPtrAllocator Alloc;
   llvm::StringSaver Saver{Alloc};
 };

lld/ELF/SymbolTable.cpp

@@ -155,6 +155,11 @@ static void addBitcodeFile(IRMover &Mover, BitcodeFile &F,
     assert(GV);
     Keep.push_back(GV);
   }
+  for (StringRef S : F.getExtraKeeps()) {
+    GlobalValue *GV = M->getNamedValue(S);
+    assert(GV);
+    Keep.push_back(GV);
+  }
   Mover.move(std::move(M), Keep, [](GlobalValue &, IRMover::ValueAdder) {});
 }
 

lld/test/ELF/lto/ctors.ll

@@ -0,0 +1,15 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+; RUN: ld.lld -m elf_x86_64 %t.o -o %t.so -shared
+; RUN: llvm-readobj -sections %t.so | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @ctor, i8* null }]
+define void @ctor() {
+  ret void
+}
+
+; The llvm.global_ctors should end up producing constructors.
+; CHECK: Name: .ctors