Index: llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
+++ llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
@@ -341,7 +341,8 @@
            MI != ME; ++MI)
         if (canTransferMetadata(MI->first))
           New->setMetadata(MI->first, MI->second);
-      New->setDebugLoc(Op->getDebugLoc());
+      if (Op->getDebugLoc() && !New->getDebugLoc())
+        New->setDebugLoc(Op->getDebugLoc());
     }
   }
 }
Index: llvm/trunk/test/Transforms/Scalarizer/dbgloc-bug.ll
===================================================================
--- llvm/trunk/test/Transforms/Scalarizer/dbgloc-bug.ll
+++ llvm/trunk/test/Transforms/Scalarizer/dbgloc-bug.ll
@@ -0,0 +1,43 @@
+; RUN: opt -S -march=x86 -scalarizer %s | FileCheck %s
+
+; Reproducer for pr27938
+; https://llvm.org/bugs/show_bug.cgi?id=27938
+
+define i16 @f1() !dbg !5 {
+  ret i16 undef, !dbg !9
+}
+
+define void @f2() !dbg !10 {
+bb1:
+  %_tmp7 = tail call i16 @f1(), !dbg !13
+; CHECK: call i16 @f1(), !dbg !13
+  %broadcast.splatinsert5 = insertelement <4 x i16> undef, i16 %_tmp7, i32 0
+  %broadcast.splat6 = shufflevector <4 x i16> %broadcast.splatinsert5, <4 x i16> undef, <4 x i32> zeroinitializer
+  br label %vector.body
+
+vector.body:
+  br i1 undef, label %middle.block, label %vector.body
+
+middle.block:
+  ret void, !dbg !15
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, retainedTypes: !2)
+!1 = !DIFile(filename: "dbgloc-bug.c", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "f1", scope: !1, file: !1, line: 9, type: !6, isLocal: false, isDefinition: true, scopeLine: 10, isOptimized: true, unit: !0, variables: !2)
+!6 = !DISubroutineType(types: !7)
+!7 = !{!8}
+!8 = !DIBasicType(name: "short", size: 16, align: 16, encoding: DW_ATE_signed)
+!9 = !DILocation(line: 11, column: 5, scope: !5)
+!10 = distinct !DISubprogram(name: "f2", scope: !1, file: !1, line: 14, type: !11, isLocal: false, isDefinition: true, scopeLine: 15, isOptimized: true, unit: !0, variables: !2)
+!11 = !DISubroutineType(types: !12)
+!12 = !{null}
+!13 = !DILocation(line: 24, column: 9, scope: !14)
+!14 = !DILexicalBlock(scope: !10, file: !1, line: 17, column: 5)
+!15 = !DILocation(line: 28, column: 1, scope: !10)