Index: lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -420,6 +420,8 @@
   assert(Scope->getScopeNode());
   auto *DS = Scope->getScopeNode();
   auto *InlinedSP = getDISubprogram(DS);
+  if (InlinedSP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug)
+    return nullptr;
   // Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
   // was inlined from another compile unit.
   DIE *OriginDIE = DU->getAbstractSPDies()[InlinedSP];
Index: lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -366,6 +366,9 @@
 
   auto *SP = cast<DISubprogram>(Scope->getScopeNode());
 
+  if (SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug)
+    return;
+
   ProcessedSPNodes.insert(SP);
 
   // Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
Index: test/ThinLTO/X86/Inputs/nodebug_import.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/Inputs/nodebug_import.ll
@@ -0,0 +1,33 @@
+; ModuleID = 'nodebug_import2.c'
+source_filename = "nodebug_import2.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@.str = private unnamed_addr constant [6 x i8] c"hello\00", align 1
+
+; Function Attrs: nounwind uwtable
+define void @foo() #0 !dbg !6 {
+entry:
+  %call = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str, i32 0, i32 0)), !dbg !8
+  ret void, !dbg !9
+}
+
+declare i32 @printf(i8*, ...) #1
+
+attributes #0 = { nounwind 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}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.0 (trunk 293911) (llvm/trunk 293920)", isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug, enums: !2)
+!1 = !DIFile(filename: "nodebug_import2.c", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 5.0.0 (trunk 293911) (llvm/trunk 293920)"}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 3, column: 1, scope: !6)
+!9 = !DILocation(line: 4, column: 1, scope: !6)
Index: test/ThinLTO/X86/nodebug_import.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/nodebug_import.ll
@@ -0,0 +1,57 @@
+; Test to ensure that a link or import of a NoDebug CU into one with debug is
+; handled correctly.
+
+; Test in regular LTO mode
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/nodebug_import.ll -o %t2.bc
+; RUN: llvm-lto2 %t1.bc %t2.bc -o %t.o -save-temps \
+; RUN:     -r=%t1.bc,main,plx \
+; RUN:     -r=%t1.bc,foo,lx \
+; RUN:     -r=%t2.bc,foo,plx \
+; RUN:     -r=%t2.bc,printf,
+; RUN: llvm-nm %t.o.0 | FileCheck  %s --check-prefix=NM0
+
+; Test in ThinLTO mode
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/nodebug_import.ll -o %t2.bc
+; RUN: llvm-lto2 %t1.bc %t2.bc -o %t.o -save-temps \
+; RUN:     -r=%t1.bc,main,plx \
+; RUN:     -r=%t1.bc,foo,lx \
+; RUN:     -r=%t2.bc,foo,plx \
+; RUN:     -r=%t2.bc,printf,
+; RUN: llvm-nm %t.o.0 | FileCheck  %s --check-prefix=NM0
+
+; Make sure we imported foo (leaving behind printf reference)
+; NM0-DAG: U printf
+
+; ModuleID = 'nodebug_import.c'
+source_filename = "nodebug_import.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define i32 @main() #0 !dbg !6 {
+entry:
+  call void (...) @foo(), !dbg !8
+  ret i32 0, !dbg !9
+}
+
+declare void @foo(...) #1
+
+attributes #0 = { nounwind 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}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.0 (trunk 293911) (llvm/trunk 293920)", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "nodebug_import.c", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 5.0.0 (trunk 293911) (llvm/trunk 293920)"}
+!6 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 2, column: 14, scope: !6)
+!9 = !DILocation(line: 2, column: 21, scope: !6)