ThinLTO/ModuleLinker: add a flag to not always pull-in linkonce when performing importing

Summary:
The function importer already decided what symbols need to be pulled
in. Also these magically added ones will not be in the export list
for the source module, which can confuse the internalizer for
instance.

Reviewers: tejohnson, rafael

Subscribers: joker.eph, llvm-commits

Differential Revision: http://reviews.llvm.org/D19096

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 266948

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index cd3cd52f7ad..8ed885649ca 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -45,6 +45,9 @@ class ModuleLinker {
   /// to Add.
   void addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add);
 
+  bool shouldLinkReferencedLinkOnce() {
+    return !(Flags & Linker::DontForceLinkLinkonceODR);
+  }
   bool shouldOverrideFromSrc() { return Flags & Linker::OverrideFromSrc; }
   bool shouldLinkOnlyNeeded() { return Flags & Linker::LinkOnlyNeeded; }
   bool shouldInternalizeLinkedSymbols() {
@@ -413,6 +416,12 @@ bool ModuleLinker::linkIfNeeded(GlobalValue &GV) {
 }
 
 void ModuleLinker::addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add) {
+  if (!shouldLinkReferencedLinkOnce())
+    // For ThinLTO we don't import more than what was required.
+    // The client has to guarantee that the linkonce will be availabe at link
+    // time (by promoting it to weak for instance).
+    return;
+
   // Add these to the internalize list
   if (!GV.hasLinkOnceLinkage())
     return;