[LTO] Keep linkonce_odr symbols when appropriate.

Ensure we keep the symbol we need to before it reaches
the Writer (and hit an assertion), changing its linkage
from linkonce_odr to weak. For a more detailed description
of the problem, see PR19901 where a similar problem was
fixed for the gold plugin. Thanks to Rafael for providing
a testcase.

llvm-svn: 264111

3 files changed, 36 insertions, 1 deletions

diff --git a/lld/ELF/LTO.cpp b/lld/ELF/LTO.cpp
index cc570f1f82e..6d2be054813 100644
--- a/lld/ELF/LTO.cpp
+++ b/lld/ELF/LTO.cpp
@@ -82,10 +82,15 @@ void BitcodeCompiler::add(BitcodeFile &F) {
       Keep.push_back(GV);
       continue;
     }
-    if (!BitcodeFile::shouldSkip(Sym))
+    if (!BitcodeFile::shouldSkip(Sym)) {
+
+      if (GV->getLinkage() == llvm::GlobalValue::LinkOnceODRLinkage)
+        GV->setLinkage(GlobalValue::WeakODRLinkage);
+
       if (SymbolBody *B = Bodies[BodyIndex++])
         if (&B->repl() == B && isa<DefinedBitcode>(B))
           Keep.push_back(GV);
+    }
   }
 
   Mover.move(Obj->takeModule(), Keep,
diff --git a/lld/test/ELF/lto/Inputs/linkonce-odr.ll b/lld/test/ELF/lto/Inputs/linkonce-odr.ll
new file mode 100644
index 00000000000..0b3828846eb
--- /dev/null
+++ b/lld/test/ELF/lto/Inputs/linkonce-odr.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define linkonce_odr void @f() {
+  ret void
+}
diff --git a/lld/test/ELF/lto/linkonce-odr.ll b/lld/test/ELF/lto/linkonce-odr.ll
new file mode 100644
index 00000000000..470ae361db2
--- /dev/null
+++ b/lld/test/ELF/lto/linkonce-odr.ll
@@ -0,0 +1,24 @@
+; REQUIRES: x86
+; RUN: llvm-as %p/Inputs/linkonce-odr.ll -o %t1.o
+; RUN: llc %s -o %t2.o -filetype=obj
+; RUN: ld.lld %t1.o %t2.o -o %t.so -shared
+; RUN: llvm-readobj -t %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"
+declare void @f()
+
+define void @g() {
+  call void @f() ret void
+} 
+
+; Be sure that the linkonce_odr symbol 'f' is kept.
+; CHECK: Symbol {
+; CHECK:   Name: f
+; CHECK:   Value: 0x1010
+; CHECK:   Size: 1
+; CHECK:   Binding: Weak
+; CHECK:   Type: Function
+; CHECK:   Other: 0
+; CHECK:   Section: .text
+; CHECK: }