Index: lib/IR/AsmWriter.cpp
===================================================================
--- lib/IR/AsmWriter.cpp
+++ lib/IR/AsmWriter.cpp
@@ -3148,13 +3148,13 @@
   if (MDs.empty())
     return;
 
-  if (MDNames.empty())
+  if (TheModule && MDNames.empty())
     TheModule->getMDKindNames(MDNames);
 
   for (const auto &I : MDs) {
     unsigned Kind = I.first;
     Out << Separator;
-    if (Kind < MDNames.size()) {
+    if (TheModule && Kind < MDNames.size()) {
       Out << "!";
       printMetadataIdentifier(MDNames[Kind], Out);
     } else
Index: test/Transforms/InstCombine/crash-with-debug.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/crash-with-debug.ll
@@ -0,0 +1,78 @@
+; RUN: opt < %s -instcombine -debug -S
+; ModuleID = 'stack-dce.bc'
+
+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 @_Z6ifthenii(i32 %x, i32 %y) #0 !dbg !4 {
+entry:
+  %retval = alloca i32, align 4
+  %x.addr = alloca i32, align 4
+  %y.addr = alloca i32, align 4
+  store i32 %x, i32* %x.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %x.addr, metadata !11, metadata !12), !dbg !13
+  store i32 %y, i32* %y.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %y.addr, metadata !14, metadata !12), !dbg !15
+  %0 = load i32, i32* %x.addr, align 4, !dbg !16
+  %and = and i32 %0, 1, !dbg !18
+  %tobool = icmp ne i32 %and, 0, !dbg !16
+  br i1 %tobool, label %if.then, label %if.end, !dbg !19
+
+if.then:                                          ; preds = %entry
+  %1 = load i32, i32* %x.addr, align 4, !dbg !20
+  %neg = xor i32 %1, -1, !dbg !22
+  %add = add nsw i32 %neg, 9, !dbg !23
+  store i32 %add, i32* %retval, align 4, !dbg !24
+  br label %return, !dbg !24
+
+if.end:                                           ; preds = %entry
+  %2 = load i32, i32* %x.addr, align 4, !dbg !25
+  %add1 = add nsw i32 %2, 2, !dbg !26
+  store i32 %add1, i32* %retval, align 4, !dbg !27
+  br label %return, !dbg !27
+
+return:                                           ; preds = %if.end, %if.then
+  %3 = load i32, i32* %retval, align 4, !dbg !28
+  ret i32 %3, !dbg !28
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable "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" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.8.0 (http://llvm.org/git/clang.git 449c5870aca4e5f2a35b20ac859fca3b8d3699de) (http://llvm.org/git/llvm.git 24a3d0e0ad16e91eac0511689f0166c4123f83ee)", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "stack-dce.cc", directory: "/usr/local/google/home/thanm/stack-layout")
+!2 = !{}
+!3 = !{!4}
+!4 = distinct !DISubprogram(name: "ifthen", linkageName: "_Z6ifthenii", scope: !1, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !7, !7}
+!7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!8 = !{i32 2, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{!"clang version 3.8.0 (http://llvm.org/git/clang.git 449c5870aca4e5f2a35b20ac859fca3b8d3699de) (http://llvm.org/git/llvm.git 24a3d0e0ad16e91eac0511689f0166c4123f83ee)"}
+!11 = !DILocalVariable(name: "x", arg: 1, scope: !4, file: !1, line: 2, type: !7)
+!12 = !DIExpression()
+!13 = !DILocation(line: 2, column: 16, scope: !4)
+!14 = !DILocalVariable(name: "y", arg: 2, scope: !4, file: !1, line: 2, type: !7)
+!15 = !DILocation(line: 2, column: 23, scope: !4)
+!16 = !DILocation(line: 4, column: 7, scope: !17)
+!17 = distinct !DILexicalBlock(scope: !4, file: !1, line: 4, column: 7)
+!18 = !DILocation(line: 4, column: 9, scope: !17)
+!19 = !DILocation(line: 4, column: 7, scope: !4)
+!20 = !DILocation(line: 5, column: 13, scope: !21)
+!21 = distinct !DILexicalBlock(scope: !17, file: !1, line: 4, column: 14)
+!22 = !DILocation(line: 5, column: 12, scope: !21)
+!23 = !DILocation(line: 5, column: 14, scope: !21)
+!24 = !DILocation(line: 5, column: 5, scope: !21)
+!25 = !DILocation(line: 7, column: 10, scope: !4)
+!26 = !DILocation(line: 7, column: 11, scope: !4)
+!27 = !DILocation(line: 7, column: 3, scope: !4)
+!28 = !DILocation(line: 9, column: 1, scope: !4)