Index: lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1217,7 +1217,6 @@
       TheCU.getCUNode()->getEmissionKind() == DICompileUnit::LineTablesOnly &&
       LScopes.getAbstractScopesList().empty() && !IsDarwin) {
     assert(InfoHolder.getScopeVariables().empty());
-    assert(DbgValues.empty());
     // FIXME: This wouldn't be true in LTO with a -g (with inlining) CU followed
     // by a -gmlt CU. Add a test and remove this assertion.
     assert(AbstractVariables.empty());
Index: test/DebugInfo/X86/dbg-value-g-gmlt.ll
===================================================================
--- test/DebugInfo/X86/dbg-value-g-gmlt.ll
+++ test/DebugInfo/X86/dbg-value-g-gmlt.ll
@@ -0,0 +1,100 @@
+; RUN: llc < %s -filetype=obj | llvm-dwarfdump - -debug-dump=info | FileCheck %s
+;
+; IR module created as follows:
+;   clang -emit-llvm -S -O2 foo.cpp -o foo.ll -g
+;   clang -emit-llvm -S -O2 bar.cpp -o bar.ll -gmlt
+;   llvm-link foo.ll bar.ll -S -o linked.ll
+;   opt -std-link-opts linked.ll -S -o opt.ll
+; --- foo.cpp ---
+; void f();
+; void foo(int param) {
+;   if (param) f();
+; }
+; --- bar.cpp ---
+; void foo(int);
+; void bar() {
+;   foo(0);
+; }
+; ---
+; The point is that bar() is compiled -gmlt and calls foo() with a constant 0.
+; foo() is compiled -g and gets inlined into bar(); foo's body is then
+; optimized away, leaving only a dbg.value call describing the inlined copy
+; of 'param', which should be benign.
+; That is, the compile-unit for bar.cpp should have nothing in it.
+; PR31437.
+
+; foo.cpp's unit comes first; skip past it, second unit should be empty.
+; CHECK:     DW_TAG_compile_unit
+; CHECK-NOT: {{DW_TAG|NULL}}
+; CHECK:     DW_AT_name {{.*}} "foo.cpp"
+; CHECK:     DW_TAG_compile_unit
+; CHECK-NOT: DW_TAG
+
+; ModuleID = 'linked.ll'
+source_filename = "llvm-link"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: uwtable
+define void @_Z3fooi(i32 %param) local_unnamed_addr #0 !dbg !8 {
+entry:
+  tail call void @llvm.dbg.value(metadata i32 %param, i64 0, metadata !13, metadata !14), !dbg !15
+  %tobool = icmp eq i32 %param, 0, !dbg !16
+  br i1 %tobool, label %if.end, label %if.then, !dbg !18
+
+if.then:                                          ; preds = %entry
+  tail call void @_Z1fv(), !dbg !19
+  br label %if.end, !dbg !19
+
+if.end:                                           ; preds = %if.then, %entry
+  ret void, !dbg !21
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #1
+
+declare void @_Z1fv() local_unnamed_addr #2
+
+; Function Attrs: nounwind readnone uwtable
+define void @_Z3barv() local_unnamed_addr #3 !dbg !22 {
+entry:
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !13, metadata !14), !dbg !24
+  ret void, !dbg !26
+}
+
+attributes #0 = { uwtable }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone uwtable }
+
+!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 293745)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "foo.cpp", directory: "/home/probinson/projects/scratch/pr31437")
+!2 = !{}
+!3 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4, producer: "clang version 5.0.0 (trunk 293745)", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!4 = !DIFile(filename: "bar.cpp", directory: "/home/probinson/projects/scratch/pr31437")
+!5 = !{!"clang version 5.0.0 (trunk 293745)"}
+!6 = !{i32 2, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooi", scope: !1, file: !1, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !12)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null, !11}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !{!13}
+!13 = !DILocalVariable(name: "param", arg: 1, scope: !8, file: !1, line: 2, type: !11)
+!14 = !DIExpression()
+!15 = !DILocation(line: 2, column: 14, scope: !8)
+!16 = !DILocation(line: 3, column: 7, scope: !17)
+!17 = distinct !DILexicalBlock(scope: !8, file: !1, line: 3, column: 7)
+!18 = !DILocation(line: 3, column: 7, scope: !8)
+!19 = !DILocation(line: 3, column: 14, scope: !20)
+!20 = !DILexicalBlockFile(scope: !17, file: !1, discriminator: 1)
+!21 = !DILocation(line: 4, column: 1, scope: !8)
+!22 = distinct !DISubprogram(name: "bar", scope: !4, file: !4, line: 2, type: !23, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !3, variables: !2)
+!23 = !DISubroutineType(types: !2)
+!24 = !DILocation(line: 2, column: 14, scope: !8, inlinedAt: !25)
+!25 = distinct !DILocation(line: 3, column: 3, scope: !22)
+!26 = !DILocation(line: 4, column: 1, scope: !22)