Index: lib/Linker/IRMover.cpp
===================================================================
--- lib/Linker/IRMover.cpp
+++ lib/Linker/IRMover.cpp
@@ -954,7 +954,12 @@
     NewGV->setLinkage(GlobalValue::InternalLinkage);
 
   Constant *C = NewGV;
-  if (DGV)
+  // Only create a bitcast if necessary. In particular, with
+  // DebugTypeODRUniquing we may reach metadata in the destination module
+  // containing a GV from the source module, in which case SGV will be
+  // the same as DGV and NewGV, and TypeMap.get() will assert since it
+  // assumes it is being invoked on a type in the source module.
+  if (DGV && NewGV != SGV)
     C = ConstantExpr::getBitCast(NewGV, TypeMap.get(SGV->getType()));
 
   if (DGV && NewGV != DGV) {
Index: test/ThinLTO/X86/Inputs/dicompositetype-unique2.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/Inputs/dicompositetype-unique2.ll
@@ -0,0 +1,46 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-scei-ps4"
+
+%struct.CFVS = type { %struct.Vec }
+%struct.Vec = type { i8 }
+%struct.S = type { i8 }
+
+define void @_ZN4CFVSD2Ev(%struct.CFVS* %this) unnamed_addr align 2 !dbg !8 {
+entry:
+  %this.addr = alloca %struct.CFVS*, align 8
+  store %struct.CFVS* %this, %struct.CFVS** %this.addr, align 8
+  %this1 = load %struct.CFVS*, %struct.CFVS** %this.addr, align 8
+  %m_val = getelementptr inbounds %struct.CFVS, %struct.CFVS* %this1, i32 0, i32 0
+  ret void
+}
+
+declare dereferenceable(1) %struct.S* @_Z3Getv()
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 321360) (llvm/trunk 321359)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "bz188598-b.cpp", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!8 = distinct !DISubprogram(name: "~CFVS", linkageName: "_ZN4CFVSD2Ev", scope: !9, file: !1, line: 2, type: !28, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !27, variables: !2)
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "CFVS", file: !10, line: 7, size: 8, elements: !11, identifier: "_ZTS4CFVS")
+!10 = !DIFile(filename: "./bz188598.h", directory: "")
+!11 = !{!12, !27}
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "m_val", scope: !9, file: !10, line: 9, baseType: !13, size: 8)
+!13 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Vec<&Get>", file: !10, line: 4, size: 8, elements: !14, templateParams: !19, identifier: "_ZTS3VecIXadL_Z3GetvEEE")
+!14 = !{!35}
+!19 = !{!20}
+!20 = !DITemplateValueParameter(name: "F", type: !21, value: %struct.S* ()* @_Z3Getv)
+!21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !22, size: 64)
+!22 = !DIDerivedType(tag: DW_TAG_typedef, name: "Func", file: !10, line: 2, baseType: !23)
+!23 = !DISubroutineType(types: !24)
+!24 = !{!35}
+!27 = !DISubprogram(name: "~CFVS", scope: !9, file: !10, line: 8, type: !28, isLocal: false, isDefinition: false, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false)
+!28 = !DISubroutineType(types: !29)
+!29 = !{null, !30}
+!30 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!35 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
Index: test/ThinLTO/X86/dicompositetype-unique2.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/dicompositetype-unique2.ll
@@ -0,0 +1,69 @@
+; RUN: opt -module-summary -o %t1.bc %s
+; RUN: opt -module-summary -o %t2.bc %S/Inputs/dicompositetype-unique2.ll
+; RUN: llvm-lto --thinlto-action=run %t1.bc %t2.bc -thinlto-save-temps=%t3.
+; RUN: llvm-dis %t3.0.3.imported.bc -o - | FileCheck %s
+; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t --save-temps \
+; RUN: -r %t1.bc,_ZN1CD2Ev,pl \
+; RUN: -r %t1.bc,_ZN4CFVSD2Ev,l \
+; RUN: -r %t1.bc,_Z3Getv,l \
+; RUN: -r %t2.bc,_ZN4CFVSD2Ev,pl \
+; RUN: -r %t2.bc,_Z3Getv,l
+; RUN: llvm-dis %t.1.3.import.bc -o - | FileCheck %s
+
+; Only llvm-lto2 adds the dso_local keyword, hence the {{.*}}
+; CHECK: define available_externally{{.*}} void @_ZN4CFVSD2Ev
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-scei-ps4"
+
+%class.C = type <{ i32 (...)**, %class.A, %struct.CFVS, [6 x i8] }>
+%class.A = type { %struct.Vec }
+%struct.Vec = type { i8 }
+%struct.CFVS = type { %struct.Vec }
+%struct.S = type { i8 }
+
+define void @_ZN1CD2Ev(%class.C* %this) unnamed_addr align 2 !dbg !8 {
+entry:
+  %this.addr = alloca %class.C*, align 8
+  %this1 = load %class.C*, %class.C** %this.addr, align 8
+  %m = getelementptr inbounds %class.C, %class.C* %this1, i32 0, i32 2
+  call void @_ZN4CFVSD2Ev(%struct.CFVS* %m), !dbg !50
+  ret void
+}
+
+declare void @_ZN4CFVSD2Ev(%struct.CFVS*) unnamed_addr
+
+declare dereferenceable(1) %struct.S* @_Z3Getv()
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 321360) (llvm/trunk 321359)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "bz188598-a.cpp", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!8 = distinct !DISubprogram(name: "~C", linkageName: "_ZN1CD2Ev", scope: !9, file: !1, line: 9, type: !47, isLocal: false, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !46, variables: !2)
+!9 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "C", file: !1, line: 5, size: 128, elements: !10, vtableHolder: !9, identifier: "_ZTS1C")
+!10 = !{!38, !46}
+!15 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Vec<&Get>", file: !16, line: 4, size: 8, elements: !17, templateParams: !22, identifier: "_ZTS3VecIXadL_Z3GetvEEE")
+!16 = !DIFile(filename: "./bz188598.h", directory: ".")
+!17 = !{!55}
+!22 = !{!23}
+!23 = !DITemplateValueParameter(name: "F", type: !24, value: %struct.S* ()* @_Z3Getv)
+!24 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !25, size: 64)
+!25 = !DIDerivedType(tag: DW_TAG_typedef, name: "Func", file: !16, line: 2, baseType: !26)
+!26 = !DISubroutineType(types: !27)
+!27 = !{!55}
+!38 = !DIDerivedType(tag: DW_TAG_member, name: "m", scope: !9, file: !1, line: 7, baseType: !39, size: 8, offset: 72)
+!39 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "CFVS", file: !16, line: 7, size: 8, elements: !40, identifier: "_ZTS4CFVS")
+!40 = !{!41}
+!41 = !DIDerivedType(tag: DW_TAG_member, name: "m_val", scope: !39, file: !16, line: 9, baseType: !15, size: 8)
+!46 = !DISubprogram(name: "~C", scope: !9, file: !1, line: 6, type: !47, isLocal: false, isDefinition: false, scopeLine: 6, containingType: !9, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPrototyped, isOptimized: false)
+!47 = !DISubroutineType(types: !48)
+!48 = !{!55}
+!50 = !DILocation(line: 9, scope: !51)
+!51 = distinct !DILexicalBlock(scope: !8, file: !1, line: 9)
+!55 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)