Index: lib/DebugInfo/DWARF/DWARFContext.cpp
===================================================================
--- lib/DebugInfo/DWARF/DWARFContext.cpp
+++ lib/DebugInfo/DWARF/DWARFContext.cpp
@@ -692,9 +692,10 @@
 
   LocDWO.reset(new DWARFDebugLocDWO());
   // Assume all compile units have the same address byte size.
-  if (getNumCompileUnits()) {
-    DataExtractor LocData(DObj->getLocDWOSection().Data, isLittleEndian(),
-                          getUnitAtIndex(0)->getAddressByteSize());
+  if (getNumDWOCompileUnits()) {
+    // FIXME: We don't need AddressSize for split DWARF since relocatable
+    // addresses cannot appear there. At the moment DWARFExpression requires it.
+    DataExtractor LocData(DObj->getLocDWOSection().Data, isLittleEndian(), 4);
     LocDWO->parse(LocData);
   }
   return LocDWO.get();
Index: test/tools/llvm-dwarfdump/X86/debug_loc_dwo.ll
===================================================================
--- test/tools/llvm-dwarfdump/X86/debug_loc_dwo.ll
+++ test/tools/llvm-dwarfdump/X86/debug_loc_dwo.ll
@@ -0,0 +1,52 @@
+; RUN: llc -filetype=obj -o %t.o -split-dwarf-file=%t.dwo %s
+; RUN: llvm-objcopy --split-dwo=%t.dwo %t.o
+; RUN: llvm-dwarfdump --debug-loc %t.dwo | FileCheck %s
+
+; Make sure llvm-dwarfdump can display a location list in a split dwarf context
+; (i.e. in the .debug_loc.dwo section).
+;
+; Generated from the following source with 
+; clang -emit-llvm -S -O2 -gsplit-dwarf from:
+;
+; void y();
+; void a(int i) {
+;   y();
+;   asm("" : : : "rdi");
+; }
+;
+; CHECK:      .debug_loc.dwo contents:
+; CHECK-NEXT: 0x00000000:
+; CHECK-NEXT: Addr idx 0 (w/ length 6): DW_OP_reg5 RDI
+
+define dso_local void @_Z1ai(i32 %i) local_unnamed_addr !dbg !6 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %i, metadata !11, metadata !DIExpression()), !dbg !12
+  tail call void @_Z1yv(), !dbg !13
+  tail call void asm sideeffect "", "~{rdi},~{dirflag},~{fpsr},~{flags}"(), !dbg !14, !srcloc !15
+  ret void, !dbg !16
+}
+
+declare dso_local void @_Z1yv() local_unnamed_addr
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 342698)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: GNU)
+!1 = !DIFile(filename: "a.cpp", directory: "/home/test/Bugzillas/PR38990")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{!"clang version 8.0.0 (trunk 342698)"}
+!6 = distinct !DISubprogram(name: "a", linkageName: "_Z1ai", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !10)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null, !9}
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !{!11}
+!11 = !DILocalVariable(name: "i", arg: 1, scope: !6, file: !1, line: 2, type: !9)
+!12 = !DILocation(line: 2, column: 12, scope: !6)
+!13 = !DILocation(line: 3, column: 3, scope: !6)
+!14 = !DILocation(line: 4, column: 3, scope: !6)
+!15 = !{i32 41}
+!16 = !DILocation(line: 5, column: 1, scope: !6)