Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -4615,6 +4615,10 @@
     }
   }
 
+  // Resolve any forward refs found while loading the function.
+  if (MDLoader->hasFwdRefs())
+    MDLoader->finishFunctionMetadata();
+
   // Unexpected unresolved metadata about to be dropped.
   if (MDLoader->hasFwdRefs())
     return error("Invalid function metadata: outgoing forward refs");
Index: lib/Bitcode/Reader/MetadataLoader.h
===================================================================
--- lib/Bitcode/Reader/MetadataLoader.h
+++ lib/Bitcode/Reader/MetadataLoader.h
@@ -52,6 +52,9 @@
   // Parse a function metadata block
   Error parseFunctionMetadata() { return parseMetadata(false); }
 
+  // resolve any forward refs at the end of the parsing of a function.
+  void finishFunctionMetadata();
+
   /// Set the mode to strip TBAA metadata on load.
   void setStripTBAA(bool StripTBAA = true);
 
Index: lib/Bitcode/Reader/MetadataLoader.cpp
===================================================================
--- lib/Bitcode/Reader/MetadataLoader.cpp
+++ lib/Bitcode/Reader/MetadataLoader.cpp
@@ -634,6 +634,8 @@
 
   bool hasFwdRefs() const { return MetadataList.hasFwdRefs(); }
 
+  void finishFunctionMetadata();
+
   Metadata *getMetadataFwdRefOrLoad(unsigned ID) {
     if (ID < MDStringRef.size())
       return lazyLoadOneMDString(ID);
@@ -838,6 +840,14 @@
   }
 }
 
+// After reading a function body, resolve any forward refs.
+void MetadataLoader::MetadataLoaderImpl::finishFunctionMetadata()
+{
+  PlaceholderQueue Placeholders;
+  resolveForwardRefsAndPlaceholders(Placeholders);
+  upgradeDebugInfo();
+}
+
 /// Parse a METADATA_BLOCK. If ModuleLevel is true then we are parsing
 /// module level metadata.
 Error MetadataLoader::MetadataLoaderImpl::parseMetadata(bool ModuleLevel) {
@@ -1938,6 +1948,10 @@
   return Pimpl->parseMetadata(ModuleLevel);
 }
 
+void MetadataLoader::finishFunctionMetadata() {
+  Pimpl->finishFunctionMetadata();
+}
+
 bool MetadataLoader::hasFwdRefs() const { return Pimpl->hasFwdRefs(); }
 
 /// Return the given metadata, creating a replaceable forward reference if
Index: test/ThinLTO/X86/Inputs/pr35472-b.ll
===================================================================
--- test/ThinLTO/X86/Inputs/pr35472-b.ll
+++ test/ThinLTO/X86/Inputs/pr35472-b.ll
@@ -0,0 +1,33 @@
+; ModuleID = 'b.cpp'
+source_filename = "b.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline optnone uwtable
+define void @_Z5Alphav() #0 !dbg !7 {
+entry:
+  call void @_Z5Bravov(), !dbg !10
+  ret void, !dbg !11
+}
+
+declare void @_Z5Bravov() #1
+
+attributes #0 = { noinline optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 321056)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "b.cpp", directory: "/home/sunil/185335/302")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 (trunk 321056)"}
+!7 = distinct !DISubprogram(name: "Alpha", linkageName: "_Z5Alphav", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 3, column: 16, scope: !7)
+!11 = !DILocation(line: 3, column: 25, scope: !7)
Index: test/ThinLTO/X86/pr35472-a.ll
===================================================================
--- test/ThinLTO/X86/pr35472-a.ll
+++ test/ThinLTO/X86/pr35472-a.ll
@@ -0,0 +1,117 @@
+; RUN: opt -module-hash -module-summary %s -o %t1.bc
+; RUN: opt -module-hash -module-summary %p/Inputs/pr35472-b.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=run %t1.bc %t2.bc
+; RUN: llvm-nm %t1.bc.thinlto.o | FileCheck %s -check-prefix=ThinLTOa
+; RUN: llvm-nm %t2.bc.thinlto.o | FileCheck %s -check-prefix=ThinLTOb
+
+; ThinLTOa-DAG: T _Z5Bravov
+; ThinLTOa-DAG: W _ZN4EchoD2Ev
+; ThinLTOb-DAG: T _Z5Alphav
+; ThinLTOb-DAG: U _Z5Bravov
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+%struct.Delta = type { %struct.Charlie }
+%struct.Charlie = type { i32 }
+%struct.Echo = type { %struct.Charlie }
+$_ZN4EchoD2Ev = comdat any
+$_ZN5DeltaD2Ev = comdat any
+define void @_Z5Bravov() #0 !dbg !7 {
+  %Hotel = alloca %struct.Delta, align 4
+  %India = alloca %struct.Echo, align 4
+  call void @llvm.dbg.declare(metadata %struct.Delta* %Hotel, metadata !10, metadata !DIExpression()), !dbg !22
+  call void @_ZN4EchoD2Ev(%struct.Echo* %India) #2, !dbg !28
+  ret void, !dbg !28
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+
+define linkonce_odr void @_ZN4EchoD2Ev(%struct.Echo* %this) unnamed_addr #0 comdat align 2 {
+  %this.addr.i = alloca %struct.Charlie*, align 8
+  call void @llvm.dbg.declare(metadata %struct.Charlie** %this.addr.i, metadata !29, metadata !DIExpression()), !dbg !32
+  %this1.i = load %struct.Charlie*, %struct.Charlie** %this.addr.i, align 8
+  %Golf.i = getelementptr inbounds %struct.Charlie, %struct.Charlie* %this1.i, i32 0, i32 0, !dbg !33
+  ret void
+}
+
+
+define linkonce_odr void @_ZN5DeltaD2Ev(%struct.Delta* %this) unnamed_addr #0 comdat align 2 !dbg !36 {
+  %this.addr.i = alloca %struct.Charlie*, align 8
+  call void @llvm.dbg.declare(metadata %struct.Charlie** %this.addr.i, metadata !29, metadata !DIExpression()), !dbg !41
+  %this1.i = load %struct.Charlie*, %struct.Charlie** %this.addr.i, align 8
+  %Golf.i = getelementptr inbounds %struct.Charlie, %struct.Charlie* %this1.i, i32 0, i32 0, !dbg !48
+  ret void
+}
+
+
+!llvm.module.flags = !{!3, !4, !5}
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 321056)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "a.cpp", directory: "/home/sunil/185335/302")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!7 = distinct !DISubprogram(name: "Bravo", linkageName: "_Z5Bravov", scope: !1, file: !1, line: 17, type: !8, isLocal: false, isDefinition: true, scopeLine: 17, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocalVariable(name: "Hotel", scope: !7, file: !1, line: 18, type: !11)
+!11 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Delta", file: !1, line: 6, size: 32, elements: !12, identifier: "_ZTS5Delta")
+!12 = !{!13}
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "Foxtrot", scope: !11, file: !1, line: 7, baseType: !14, size: 32)
+!14 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Charlie", file: !1, line: 1, size: 32, elements: !15, identifier: "_ZTS7Charlie")
+!15 = !{!16, !18}
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "Golf", scope: !14, file: !1, line: 3, baseType: !17, size: 32)
+!17 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!18 = !DISubprogram(name: "~Charlie", scope: !14, file: !1, line: 2, type: !19, isLocal: false, isDefinition: false, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false)
+!19 = !DISubroutineType(types: !20)
+!20 = !{null, !21}
+!21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!22 = !DILocation(line: 18, column: 11, scope: !7)
+!24 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Echo", file: !1, line: 10, size: 32, elements: !25, identifier: "_ZTS4Echo")
+!25 = !{!26}
+!26 = !DIDerivedType(tag: DW_TAG_member, name: "Foxtrot", scope: !24, file: !1, line: 11, baseType: !14, size: 32)
+!28 = !DILocation(line: 20, column: 1, scope: !7)
+!29 = !DILocalVariable(name: "this", arg: 1, scope: !30, type: !31, flags: DIFlagArtificial | DIFlagObjectPointer)
+!30 = distinct !DISubprogram(name: "~Charlie", linkageName: "_ZN7CharlieD2Ev", scope: !14, file: !1, line: 2, type: !19, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !18, variables: !2)
+!31 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64)
+!32 = !DILocation(line: 0, scope: !30)
+!33 = !DILocation(line: 2, column: 53, scope: !34)
+!34 = distinct !DILexicalBlock(scope: !30, file: !1, line: 2, column: 51)
+!36 = distinct !DISubprogram(name: "~Delta", linkageName: "_ZN5DeltaD2Ev", scope: !11, file: !1, line: 6, type: !37, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !40, variables: !2)
+!37 = !DISubroutineType(types: !38)
+!38 = !{null, !39}
+!39 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!40 = !DISubprogram(name: "~Delta", scope: !11, type: !37, isLocal: false, isDefinition: false, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false)
+!41 = !DILocation(line: 0, scope: !30, inlinedAt: !42)
+!42 = distinct !DILocation(line: 6, column: 8, scope: !43)
+!43 = distinct !DILexicalBlock(scope: !36, file: !1, line: 6, column: 8)
+!48 = !DILocation(line: 2, column: 53, scope: !34, inlinedAt: !42)
+
+;----------------------------------------------------------------------------------------------
+; Compiled from following two source files with 'clang++ -S --std=c++11 -O0 -g -flto=thin' 
+; struct Charlie {
+;     __attribute__((__always_inline__)) ~Charlie() { Golf = 0; }
+;     int Golf;
+; };
+; 
+; struct Delta {
+;     Charlie Foxtrot;
+; };
+; 
+; struct Echo {
+;     Charlie Foxtrot;
+;     __attribute__((nodebug)) ~Echo() = default;
+; };
+; 
+; extern void Bravo();
+; 
+; void Bravo() {
+;     Delta Hotel;
+;     Echo India;
+; }
+; -----------------------------
+; extern void Bravo();
+; extern void Alpha();
+; void Alpha() { Bravo(); }
+