Index: llvm/trunk/include/llvm/CodeGen/LexicalScopes.h
===================================================================
--- llvm/trunk/include/llvm/CodeGen/LexicalScopes.h
+++ llvm/trunk/include/llvm/CodeGen/LexicalScopes.h
@@ -49,7 +49,11 @@
                bool A)
       : Parent(P), Desc(D), InlinedAtLocation(I), AbstractScope(A),
         LastInsn(nullptr), FirstInsn(nullptr), DFSIn(0), DFSOut(0) {
-    assert((!D || D->isResolved()) && "Expected resolved node");
+    assert(D);
+    assert(D->getSubprogram()->getUnit()->getEmissionKind() !=
+           DICompileUnit::NoDebug &&
+           "Don't build lexical scopes for non-debug locations");
+    assert(D->isResolved() && "Expected resolved node");
     assert((!I || I->isResolved()) && "Expected resolved node");
     if (Parent)
       Parent->addChild(this);
Index: llvm/trunk/lib/CodeGen/LexicalScopes.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/LexicalScopes.cpp
+++ llvm/trunk/lib/CodeGen/LexicalScopes.cpp
@@ -38,6 +38,10 @@
 
 /// initialize - Scan machine function and constuct lexical scope nest.
 void LexicalScopes::initialize(const MachineFunction &Fn) {
+  // Don't attempt any lexical scope creation for a NoDebug compile unit.
+  if (Fn.getFunction()->getSubprogram()->getUnit()->getEmissionKind() ==
+      DICompileUnit::NoDebug)
+    return;
   reset();
   MF = &Fn;
   SmallVector<InsnRange, 4> MIRanges;
@@ -127,6 +131,10 @@
 LexicalScope *LexicalScopes::getOrCreateLexicalScope(const DILocalScope *Scope,
                                                      const DILocation *IA) {
   if (IA) {
+    // Skip scopes inlined from a NoDebug compile unit.
+    if (Scope->getSubprogram()->getUnit()->getEmissionKind() ==
+        DICompileUnit::NoDebug)
+      return getOrCreateLexicalScope(IA);
     // Create an abstract scope for inlined function.
     getOrCreateAbstractScope(Scope);
     // Create an inlined scope for inlined function.
Index: llvm/trunk/test/DebugInfo/Generic/debug_and_nodebug_CUs.ll
===================================================================
--- llvm/trunk/test/DebugInfo/Generic/debug_and_nodebug_CUs.ll
+++ llvm/trunk/test/DebugInfo/Generic/debug_and_nodebug_CUs.ll
@@ -0,0 +1,82 @@
+; Test to ensure that a module containing both a NoDebug CU and one with
+; debug is handled correctly.
+
+; LLVM IR was generated the following way:
+; $ cat a.cpp
+; void f1();
+; __attribute__((always_inline)) void f2() {
+;     f1();
+; }
+; void f3();
+; void f4() {
+;     f3();
+; }
+; $ cat b.cpp
+; void f2();
+; __attribute__((always_inline)) void f3() {
+;     f2();
+; }
+; $ clang++ -flto a.cpp -g -c
+; $ clang++ -flto b.cpp -Rpass=inline -c
+; $ llvm-link {a,b}.o -o - | opt -O2 - -o ab.bc
+; $ llvm-dis ab.bc
+
+; Ensure we can successfully generate assembly, and check that neither
+; "b.cpp" nor "f3" strings show up (which would be in the .debug_str
+; section if we had generated any lexical scopes and debug for them).
+; RUN: llc %s -o - | FileCheck %s
+; CHECK-NOT: .asciz  "b.cpp"
+; CHECK-NOT: .asciz  "f3"
+
+; ModuleID = 'debug_and_nodebug_CUs.bc'
+source_filename = "debug_and_nodebug_CUs.ll"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @_Z2f2v() local_unnamed_addr !dbg !8 {
+entry:
+  tail call void @_Z2f1v(), !dbg !11
+  ret void, !dbg !12
+}
+
+declare void @_Z2f1v() local_unnamed_addr
+
+define void @_Z2f4v() local_unnamed_addr !dbg !13 {
+entry:
+  tail call void @_Z2f1v(), !dbg !14
+  ret void, !dbg !19
+}
+
+define void @_Z2f3v() local_unnamed_addr !dbg !16 {
+entry:
+  tail call void @_Z2f1v(), !dbg !20
+  ret void, !dbg !22
+}
+
+!llvm.dbg.cu = !{!0, !3}
+!llvm.ident = !{!5, !5}
+!llvm.module.flags = !{!6, !7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 294362) (llvm/trunk 294367)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "a.cpp", directory: ".")
+!2 = !{}
+!3 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4, producer: "clang version 5.0.0 (trunk 294362) (llvm/trunk 294367)", isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug, enums: !2)
+!4 = !DIFile(filename: "b.cpp", directory: ".")
+!5 = !{!"clang version 5.0.0 (trunk 294362) (llvm/trunk 294367)"}
+!6 = !{i32 2, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DISubprogram(name: "f2", linkageName: "_Z2f2v", scope: !1, file: !1, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !DILocation(line: 3, column: 3, scope: !8)
+!12 = !DILocation(line: 4, column: 1, scope: !8)
+!13 = distinct !DISubprogram(name: "f4", linkageName: "_Z2f4v", scope: !1, file: !1, line: 6, type: !9, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!14 = !DILocation(line: 3, column: 3, scope: !8, inlinedAt: !15)
+!15 = distinct !DILocation(line: 3, column: 3, scope: !16, inlinedAt: !18)
+!16 = distinct !DISubprogram(name: "f3", scope: !4, file: !4, line: 2, type: !17, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !3, variables: !2)
+!17 = !DISubroutineType(types: !2)
+!18 = distinct !DILocation(line: 7, column: 3, scope: !13)
+!19 = !DILocation(line: 8, column: 1, scope: !13)
+!20 = !DILocation(line: 3, column: 3, scope: !8, inlinedAt: !21)
+!21 = distinct !DILocation(line: 3, column: 3, scope: !16)
+!22 = !DILocation(line: 4, column: 1, scope: !16)