From 667d4f41076c8eecf56aa6a4695575183948e116 Mon Sep 17 00:00:00 2001
From: Saleem Abdulrasool <compnerd@compnerd.org>
Date: Fri, 19 Apr 2019 01:48:36 +0000
Subject: [PATCH] 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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358728 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/IPO/MergeFunctions.cpp |  1 +
 test/Transforms/MergeFunc/comdat.ll   | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 test/Transforms/MergeFunc/comdat.ll

diff --git a/lib/Transforms/IPO/MergeFunctions.cpp b/lib/Transforms/IPO/MergeFunctions.cpp
index 1ca4ebecd08..d0c16138f9e 100644
--- a/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/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);
   }
 
diff --git a/test/Transforms/MergeFunc/comdat.ll b/test/Transforms/MergeFunc/comdat.ll
new file mode 100644
index 00000000000..ce289598fa1
--- /dev/null
+++ b/test/Transforms/MergeFunc/comdat.ll
@@ -0,0 +1,24 @@
+; RUN: opt -S -mergefunc %s | FileCheck %s
+
+@symbols = linkonce_odr global <{ i8*, i8* }> <{ i8* bitcast (i32 (i32, i32)* @f to i8*), i8* bitcast (i32 (i32, i32)* @g to i8*) }>
+
+$f = comdat any
+$g = comdat any
+
+define linkonce_odr hidden i32 @f(i32 %x, i32 %y) comdat {
+  %sum = add i32 %x, %y
+  %sum2 = add i32 %x, %sum
+  %sum3 = add i32 %x, %sum
+  ret i32 %sum3
+}
+
+define linkonce_odr hidden i32 @g(i32 %x, i32 %y) comdat {
+  %sum = add i32 %x, %y
+  %sum2 = add i32 %x, %sum
+  %sum3 = add i32 %x, %sum
+  ret i32 %sum3
+}
+
+; CHECK-DAG: define linkonce_odr hidden i32 @f(i32 %x, i32 %y) comdat
+; CHECK-DAG: define linkonce_odr hidden i32 @g(i32, i32) comdat
+
-- 
2.40.0