MergeFunc: preserve COMDAT information when creating a thunk

We would previously drop the COMDAT on the thunk we generated when replacing a
function body with the forwarding thunk. This would result in a function that
may have been multiply emitted and multiply merged to be emitted with the same
name without the COMDAT. This is a hard error with PE/COFF where the COMDAT is
used for the deduplication of Value Witness functions for Swift.

llvm-svn: 358728

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 1ca4ebecd08..d0c16138f9e 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -703,6 +703,7 @@ void MergeFunctions::writeThunk(Function *F, Function *G) {
   } else {
     NewG = Function::Create(G->getFunctionType(), G->getLinkage(),
                             G->getAddressSpace(), "", G->getParent());
+    NewG->setComdat(G->getComdat());
     BB = BasicBlock::Create(F->getContext(), "", NewG);
   }