Index: lib/Linker/IRMover.cpp
===================================================================
--- lib/Linker/IRMover.cpp
+++ lib/Linker/IRMover.cpp
@@ -392,7 +392,7 @@
   LocalValueMaterializer LValMaterializer;
 
   /// A metadata map that's shared between IRLinker instances.
-  MDMapT &SharedMDs;
+  MDMapT *SharedMDs;
 
   /// Mapping of values from what they used to be in Src, to what they are now
   /// in DstM.  ValueToValueMapTy is a ValueMap, which involves some overhead
@@ -509,7 +509,7 @@
            bool IsPerformingImport)
       : DstM(DstM), SrcM(std::move(SrcM)), AddLazyFor(std::move(AddLazyFor)),
         TypeMap(Set), GValMaterializer(*this), LValMaterializer(*this),
-        SharedMDs(SharedMDs), IsPerformingImport(IsPerformingImport),
+        SharedMDs(&SharedMDs), IsPerformingImport(IsPerformingImport),
         Mapper(ValueMap, RF_MoveDistinctMDs | RF_IgnoreMissingLocals, &TypeMap,
                &GValMaterializer),
         AliasMCID(Mapper.registerAlternateMappingContext(AliasValueMap,
@@ -520,7 +520,10 @@
     if (IsPerformingImport)
       prepareCompileUnitsForImport();
   }
-  ~IRLinker() { SharedMDs = std::move(*ValueMap.getMDMap()); }
+  ~IRLinker() {
+    if (SharedMDs)
+      *SharedMDs = std::move(*ValueMap.getMDMap());
+  }
 
   Error run();
   Value *materialize(Value *V, bool ForAlias);
@@ -561,6 +564,16 @@
   if (!SGV)
     return nullptr;
 
+  if (SGV->getParent() != SrcM.get()) {
+    // Import of some netadata node (like DITemplateValueParameter) made us
+    // materializing from a different source module. We can't do this because
+    // we might not have computed type mapping in this other module yet.
+    // Also we don't cache any MD nodes from current source module as this may
+    // cause broken metadata in the composite module.
+    SharedMDs = nullptr;
+    return nullptr;
+  }
+
   Expected<Constant *> NewProto = linkGlobalValueProto(SGV, ForAlias);
   if (!NewProto) {
     setError(NewProto.takeError());
Index: test/ThinLTO/X86/Inputs/fwd-decl.ll
===================================================================
--- test/ThinLTO/X86/Inputs/fwd-decl.ll
+++ test/ThinLTO/X86/Inputs/fwd-decl.ll
@@ -0,0 +1,29 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.TA = type opaque
+@gv = external dso_local global %struct.TA *
+
+define i1 @b(%struct.TA*) {
+  unreachable
+}
+
+define i1 @a(%struct.TA* %a) {
+  call i1 @b(%struct.TA* %a)
+  unreachable
+}
+
+!llvm.module.flags = !{!0, !1}
+!llvm.dbg.cu = !{!2}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = !{i32 1, !"ThinLTO", i32 0}
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, retainedTypes: !4)
+!3 = !DIFile(filename: "f1", directory: "")
+!4 = !{!5, !9}
+!5 = !DICompositeType(tag: DW_TAG_class_type, file: !3, templateParams: !6, scope: !8)
+!6 = !{!7}
+
+; The reference to @b and struct.TA.0 (renamed)  that will be loaded in %a.o
+!7 = !DITemplateValueParameter(value: i1 (%struct.TA*)* @b)
+!8 = distinct !DISubprogram(unit: !2)
+!9 = !DICompositeType(tag: DW_TAG_array_type, identifier: "SHARED", scope: !8)
Index: test/ThinLTO/X86/fwd-decl.ll
===================================================================
--- test/ThinLTO/X86/fwd-decl.ll
+++ test/ThinLTO/X86/fwd-decl.ll
@@ -0,0 +1,35 @@
+; Ensures IRMover only materializes values from current source module.
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/fwd-decl.ll -o %t2.bc
+; RUN: llvm-lto2 run -save-temps -o %t3.bc %t1.bc %t2.bc -r %t1.bc,c,px -r %t2.bc,a,px -r %t2.bc,b,px -r %t1.bc,gv -r %t2.bc,gv
+; RUN: llvm-dis %t3.bc.0.0.preopt.bc -o - | FileCheck %s
+
+; CHECK:        define i1 @a(%struct.TA* %a)
+; CHECK-NEXT:     %1 = call i1 @b(%struct.TA* %a)
+
+; Check that metadata was correctly imported.
+; CHECK:        !DITemplateValueParameter(value: i1 (%struct.TA*)* @b)
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.TA = type {}
+
+@gv = dso_local global %struct.TA * zeroinitializer
+
+define i32 @c() !dbg !6 {
+  bitcast %struct.TA ** @gv to i8*
+  unreachable
+}
+
+!llvm.module.flags = !{!0, !1}
+!llvm.dbg.cu = !{!2}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = !{i32 1, !"ThinLTO", i32 0}
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, retainedTypes: !4)
+!3 = !DIFile(filename: "f2", directory: "")
+!4 = !{!5}
+!5 = !DICompositeType(tag: DW_TAG_class_type, file: !3, flags: DIFlagFwdDecl, identifier: "SHARED")
+!6 = distinct !DISubprogram(unit: !2)
+
+