Index: llvm/trunk/include/llvm/Transforms/Utils/FunctionImportUtils.h
===================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/FunctionImportUtils.h
+++ llvm/trunk/include/llvm/Transforms/Utils/FunctionImportUtils.h
@@ -43,6 +43,11 @@
   /// to promote any non-renamable values.
   SmallPtrSet<GlobalValue *, 8> Used;
 
+  /// Keep track of any COMDATs that require renaming (because COMDAT
+  /// leader was promoted and renamed). Maps from original COMDAT to one
+  /// with new name.
+  DenseMap<const Comdat *, Comdat *> RenamedComdats;
+
   /// Check if we should promote the given local value to global scope.
   bool shouldPromoteLocalToGlobal(const GlobalValue *SGV);
 
Index: llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp
+++ llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp
@@ -248,6 +248,7 @@
   bool DoPromote = false;
   if (GV.hasLocalLinkage() &&
       ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
+    auto Name = GV.getName();
     // Once we change the name or linkage it is difficult to determine
     // again whether we should promote since shouldPromoteLocalToGlobal needs
     // to locate the summary (based on GUID from name and linkage). Therefore,
@@ -256,6 +257,12 @@
     GV.setLinkage(getLinkage(&GV, DoPromote));
     if (!GV.hasLocalLinkage())
       GV.setVisibility(GlobalValue::HiddenVisibility);
+
+    // If we are renaming a COMDAT leader, ensure that we record the COMDAT
+    // for later renaming as well. This is required for COFF.
+    if (const auto *C = GV.getComdat())
+      if (C->getName() == Name)
+        RenamedComdats.try_emplace(C, M.getOrInsertComdat(GV.getName()));
   } else
     GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));
 
@@ -280,6 +287,16 @@
     processGlobalForThinLTO(SF);
   for (GlobalAlias &GA : M.aliases())
     processGlobalForThinLTO(GA);
+
+  // Replace any COMDATS that required renaming (because the COMDAT leader was
+  // promoted and renamed).
+  if (!RenamedComdats.empty())
+    for (auto &GO : M.global_objects())
+      if (auto *C = GO.getComdat()) {
+        auto Replacement = RenamedComdats.find(C);
+        if (Replacement != RenamedComdats.end())
+          GO.setComdat(Replacement->second);
+      }
 }
 
 bool FunctionImportGlobalProcessing::run() {
Index: llvm/trunk/test/Transforms/FunctionImport/Inputs/comdat.ll
===================================================================
--- llvm/trunk/test/Transforms/FunctionImport/Inputs/comdat.ll
+++ llvm/trunk/test/Transforms/FunctionImport/Inputs/comdat.ll
@@ -0,0 +1,10 @@
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.24215"
+
+define void @main() {
+entry:
+  call i8* @lwt_fun()
+  ret void
+}
+
+declare i8* @lwt_fun()
Index: llvm/trunk/test/Transforms/FunctionImport/comdat.ll
===================================================================
--- llvm/trunk/test/Transforms/FunctionImport/comdat.ll
+++ llvm/trunk/test/Transforms/FunctionImport/comdat.ll
@@ -0,0 +1,32 @@
+; Test to ensure that comdat is renamed consistently when comdat leader is
+; promoted and renamed due to an import. Required by COFF.
+
+; REQUIRES: x86-registered-target
+
+; RUN: opt -thinlto-bc -o %t1.bc %s
+; RUN: opt -thinlto-bc -o %t2.bc %S/Inputs/comdat.ll
+; RUN: llvm-lto2 run -save-temps -o %t3 %t1.bc %t2.bc \
+; RUN:          -r %t1.bc,lwt_fun,plx \
+; RUN:          -r %t2.bc,main,plx \
+; RUN:          -r %t2.bc,lwt_fun,
+; RUN: llvm-dis -o - %t3.1.3.import.bc | FileCheck %s
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.24215"
+
+; CHECK: $lwt.llvm.[[HASH:[0-9]+]] = comdat any
+$lwt = comdat any
+
+; CHECK: @lwt_aliasee = private unnamed_addr global {{.*}}, comdat($lwt.llvm.[[HASH]])
+@lwt_aliasee = private unnamed_addr global [1 x i8*] [i8* null], comdat($lwt)
+
+; CHECK: @lwt.llvm.[[HASH]] = hidden unnamed_addr alias
+@lwt = internal unnamed_addr alias [1 x i8*], [1 x i8*]* @lwt_aliasee
+
+; Below function should get imported into other module, resulting in @lwt being
+; promoted and renamed.
+define i8* @lwt_fun() {
+  %1 = getelementptr inbounds [1 x i8*], [1 x i8*]* @lwt, i32 0, i32 0
+  %2 = load i8*, i8** %1
+  ret i8* %2
+}