Index: llvm/lib/Linker/IRMover.cpp
===================================================================
--- llvm/lib/Linker/IRMover.cpp
+++ llvm/lib/Linker/IRMover.cpp
@@ -1260,15 +1260,56 @@
       Flags[ID].first = SrcOp;
     };
 
+    // Check the input bitcode is swift generated bitcode.
+    auto isSwiftBitCode = [&](Module &M) {
+      SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
+      M.getModuleFlagsMetadata(ModuleFlags);
+      for (const auto &MFE: ModuleFlags) {
+        if (MFE.Behavior == Module::Require)
+          continue;
+        StringRef Key = MFE.Key->getString();
+        if (Key == "Swift Version")
+          return true;
+      }
+      return false;
+    };
+
     // If either flag has override behavior, handle it first.
     if (DstBehaviorValue == Module::Override) {
       // Diagnose inconsistent flags which both have override behavior.
       if (SrcBehaviorValue == Module::Override &&
-          SrcOp->getOperand(2) != DstOp->getOperand(2))
+          SrcOp->getOperand(2) != DstOp->getOperand(2)) {
+        if (ID->getString().equals("Objective-C Garbage Collection")) {
+
+          // Merge the value of metadata "Objective-C Garbage Collection"
+          // into one value by shifting. The purpose of this change is
+          // to support LTO in Swift and Objective-C mixed project.
+
+          auto Int32Ty = Type::getInt32Ty(DstM.getContext());
+          auto SrcMD = dyn_cast<ConstantAsMetadata>(SrcOp->getOperand(2));
+          auto DstMD = dyn_cast<ConstantAsMetadata>(DstOp->getOperand(2));
+          assert(SrcMD && DstMD);
+          unsigned SrcVal = SrcMD->getValue()->getUniqueInteger().getZExtValue();
+          unsigned DstVal = DstMD->getValue()->getUniqueInteger().getZExtValue();
+          if ((isSwiftBitCode(*SrcM) &&
+              (SrcVal & 0xffffffc0) == SrcVal &&
+              DstVal < 64) ||
+              (isSwiftBitCode(DstM) &&
+              (DstVal & 0xffffffc0) == DstVal &&
+              SrcVal < 64)) {
+            unsigned ResVal = SrcVal | DstVal;
+            SrcOp->replaceOperandWith(2,
+              ConstantAsMetadata::get(ConstantInt::get(Int32Ty,ResVal)));
+            DstOp->replaceOperandWith(2,
+              ConstantAsMetadata::get(ConstantInt::get(Int32Ty,ResVal)));
+            continue;
+          }
+        }
         return stringErr("linking module flags '" + ID->getString() +
                          "': IDs have conflicting override values in '" +
                          SrcM->getModuleIdentifier() + "' and '" +
                          DstM.getModuleIdentifier() + "'");
+      }
       continue;
     } else if (SrcBehaviorValue == Module::Override) {
       // Update the destination flag to that of the source.
Index: llvm/test/Linker/Inputs/empty-objc.ll
===================================================================
--- /dev/null
+++ llvm/test/Linker/Inputs/empty-objc.ll
@@ -0,0 +1,14 @@
+target triple = "x86_64-apple-macosx10.15.0"
+
+!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+
+!0 = !{i32 2, !"SDK Version", [2 x i32] [i32 10, i32 15]}
+!1 = !{i32 1, !"Objective-C Version", i32 2}
+!2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
+!3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
+!4 = !{i32 4, !"Objective-C Garbage Collection", i32 2}
+!5 = !{i32 1, !"Objective-C Class Properties", i32 64}
+!6 = !{i32 1, !"wchar_size", i32 4}
+!7 = !{i32 7, !"PIC Level", i32 2}
+!8 = !{!"Apple clang version 11.0.0 (clang-1100.0.33.12)"}
Index: llvm/test/Linker/empty-swift.ll
===================================================================
--- /dev/null
+++ llvm/test/Linker/empty-swift.ll
@@ -0,0 +1,37 @@
+; RUN: llvm-link %s %p/Inputs/empty-objc.ll -S | FileCheck %s
+
+; It tests whether Swift bitcode can be successfully with Objecitive-C bitcode.
+
+target triple = "x86_64-apple-macosx10.15.0"
+
+@__swift_reflection_version = linkonce_odr hidden constant i16 3
+@llvm.used = appending global [1 x i8*] [i8* bitcast (i16* @__swift_reflection_version to i8*)], section "llvm.metadata", align 8
+
+define i32 @main(i32 %0, i8** %1) #0 {
+  %3 = bitcast i8** %1 to i8*
+  ret i32 0
+}
+
+attributes #0 = { "frame-pointer"="all" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" }
+
+!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6, !7, !8}
+!swift.module.flags = !{!9}
+!llvm.linker.options = !{!10, !11, !12}
+!llvm.asan.globals = !{!13}
+
+!0 = !{i32 2, !"SDK Version", [2 x i32] [i32 10, i32 15]}
+!1 = !{i32 1, !"Objective-C Version", i32 2}
+!2 = !{i32 1, !"Objective-C Image Info Version", i32 0}
+!3 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
+!4 = !{i32 4, !"Objective-C Garbage Collection", i32 83953408}
+!5 = !{i32 1, !"Objective-C Class Properties", i32 64}
+!6 = !{i32 1, !"wchar_size", i32 4}
+!7 = !{i32 7, !"PIC Level", i32 2}
+!8 = !{i32 1, !"Swift Version", i32 7}
+!9 = !{!"standard-library", i1 false}
+!10 = !{!"-lswiftSwiftOnoneSupport"}
+!11 = !{!"-lswiftCore"}
+!12 = !{!"-lobjc"}
+!13 = !{[1 x i8*]* @llvm.used, null, null, i1 false, i1 true}
+
+; CHECK: !{{[0-9]}} = distinct !{i32 4, !"Objective-C Garbage Collection", i32 83953410}