Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -985,8 +985,9 @@
     // that this code is not reachable.  We do this instead of inserting
     // an unreachable instruction directly because we cannot modify the
     // CFG.
-    new StoreInst(UndefValue::get(LI.getType()),
-                  Constant::getNullValue(Op->getType()), &LI);
+    StoreInst *SI = new StoreInst(UndefValue::get(LI.getType()),
+                                  Constant::getNullValue(Op->getType()), &LI);
+    SI->setDebugLoc(LI.getDebugLoc());
     return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
   }
 
Index: lib/Transforms/Scalar/GVN.cpp
===================================================================
--- lib/Transforms/Scalar/GVN.cpp
+++ lib/Transforms/Scalar/GVN.cpp
@@ -1168,6 +1168,7 @@
                                  LI->isVolatile(), LI->getAlignment(),
                                  LI->getOrdering(), LI->getSynchScope(),
                                  UnavailablePred->getTerminator());
+    NewLoad->setDebugLoc(LI->getDebugLoc());
 
     // Transfer the old load's AA tags to the new load.
     AAMDNodes Tags;
Index: test/Transforms/GVN/PRE/2017-06-28-pre-load-dbgloc.ll
===================================================================
--- /dev/null
+++ test/Transforms/GVN/PRE/2017-06-28-pre-load-dbgloc.ll
@@ -0,0 +1,123 @@
+; This test checks if debug loc is propagated to load/store created by GVN/Instcombine.
+; RUN: opt < %s -gvn -S | FileCheck %s --check-prefixes=ALL,GVN
+; RUN: opt < %s -gvn -instcombine -S | FileCheck %s --check-prefixes=ALL,INSTCOMBINE
+
+; struct node {
+;  int  *v;
+; struct desc *descs;
+; };
+
+; struct desc {
+;  struct node *node;
+; };
+
+; extern int bar(void *v, void* n);
+
+; int test(struct desc *desc)
+; {
+;  void *v, *n;
+;  v = !desc ? ((void *)0) : desc->node->v;
+;  n = &desc->node->descs[0];
+;  return bar(v, n);
+; }
+
+; dbg !30 is:
+; v = !desc ? ((void *)0) : desc->node->v;
+;                                 ^
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux-gnu"
+
+%struct.desc = type { %struct.node* }
+%struct.node = type { i32*, %struct.desc* }
+
+define i32 @test(%struct.desc* readonly %desc) local_unnamed_addr #0 !dbg !7 {
+entry:
+  tail call void @llvm.dbg.value(metadata %struct.desc* %desc, i64 0, metadata !22, metadata !26), !dbg !27
+  %tobool = icmp eq %struct.desc* %desc, null, !dbg !28
+  br i1 %tobool, label %cond.end, label %cond.false, !dbg !29
+; ALL: br i1 %tobool, label %entry.cond.end_crit_edge, label %cond.false, !dbg !29
+; ALL: entry.cond.end_crit_edge:
+; GVN: %.pre = load %struct.node*, %struct.node** null, align 8, !dbg !30
+; INSTCOMBINE:store %struct.node* undef, %struct.node** null, align 536870912, !dbg !30
+
+cond.false:                                       ; preds = %entry
+  %0 = bitcast %struct.desc* %desc to i8***, !dbg !30
+  %1 = load i8**, i8*** %0, align 8, !dbg !30, !tbaa !31
+  %2 = load i8*, i8** %1, align 8, !dbg !36, !tbaa !37
+  br label %cond.end, !dbg !29
+
+cond.end:                                         ; preds = %entry, %cond.false
+  %3 = phi i8* [ %2, %cond.false ], [ null, %entry ], !dbg !29
+  tail call void @llvm.dbg.value(metadata i8* %3, i64 0, metadata !23, metadata !26), !dbg !39
+  %node2 = getelementptr inbounds %struct.desc, %struct.desc* %desc, i64 0, i32 0, !dbg !40
+  %4 = load %struct.node*, %struct.node** %node2, align 8, !dbg !40, !tbaa !31
+  %descs = getelementptr inbounds %struct.node, %struct.node* %4, i64 0, i32 1, !dbg !41
+  %5 = bitcast %struct.desc** %descs to i8**, !dbg !41
+  %6 = load i8*, i8** %5, align 8, !dbg !41, !tbaa !42
+  tail call void @llvm.dbg.value(metadata i8* %6, i64 0, metadata !25, metadata !26), !dbg !43
+  %call = tail call i32 @bar(i8* %3, i8* %6) #3, !dbg !44
+  ret i32 %call, !dbg !45
+}
+
+declare i32 @bar(i8*, i8*) local_unnamed_addr #1
+
+;  Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "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-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+neon" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "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" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+neon" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind readnone speculatable }
+attributes #3 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "/prj/llvm-arm/home/weimingz/llvm_tests/undefined_opt")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 5.0.0 "}
+!7 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 12, type: !8, isLocal: false, isDefinition: true, scopeLine: 13, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !21)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !11}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "desc", file: !1, line: 6, size: 64, elements: !13)
+!13 = !{!14}
+!14 = !DIDerivedType(tag: DW_TAG_member, name: "node", scope: !12, file: !1, line: 7, baseType: !15, size: 64)
+!15 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
+!16 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "node", file: !1, line: 1, size: 128, elements: !17)
+!17 = !{!18, !20}
+!18 = !DIDerivedType(tag: DW_TAG_member, name: "v", scope: !16, file: !1, line: 2, baseType: !19, size: 64)
+!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64)
+!20 = !DIDerivedType(tag: DW_TAG_member, name: "descs", scope: !16, file: !1, line: 3, baseType: !11, size: 64, offset: 64)
+!21 = !{!22, !23, !25}
+!22 = !DILocalVariable(name: "desc", arg: 1, scope: !7, file: !1, line: 12, type: !11)
+!23 = !DILocalVariable(name: "v", scope: !7, file: !1, line: 14, type: !24)
+!24 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!25 = !DILocalVariable(name: "n", scope: !7, file: !1, line: 14, type: !24)
+!26 = !DIExpression()
+!27 = !DILocation(line: 12, column: 23, scope: !7)
+!28 = !DILocation(line: 15, column: 7, scope: !7)
+!29 = !DILocation(line: 15, column: 6, scope: !7)
+!30 = !DILocation(line: 15, column: 34, scope: !7)
+!31 = !{!32, !33, i64 0}
+!32 = !{!"desc", !33, i64 0}
+!33 = !{!"any pointer", !34, i64 0}
+!34 = !{!"omnipotent char", !35, i64 0}
+!35 = !{!"Simple C/C++ TBAA"}
+!36 = !DILocation(line: 15, column: 40, scope: !7)
+!37 = !{!38, !33, i64 0}
+!38 = !{!"node", !33, i64 0, !33, i64 8}
+!39 = !DILocation(line: 14, column: 8, scope: !7)
+!40 = !DILocation(line: 16, column: 13, scope: !7)
+!41 = !DILocation(line: 16, column: 19, scope: !7)
+!42 = !{!38, !33, i64 8}
+!43 = !DILocation(line: 14, column: 12, scope: !7)
+!44 = !DILocation(line: 17, column: 9, scope: !7)
+!45 = !DILocation(line: 17, column: 2, scope: !7)
+
Index: test/Transforms/GVN/PRE/phi-translate.ll
===================================================================
--- test/Transforms/GVN/PRE/phi-translate.ll
+++ test/Transforms/GVN/PRE/phi-translate.ll
@@ -6,12 +6,12 @@
 ; CHECK: entry.end_crit_edge:
 ; CHECK: %[[INDEX:[a-z0-9.]+]] = sext i32 %x to i64{{$}}
 ; CHECK: %[[ADDRESS:[a-z0-9.]+]] = getelementptr [100 x i32], [100 x i32]* @G, i64 0, i64 %[[INDEX]]{{$}}
-; CHECK:   %n.pre = load i32, i32* %[[ADDRESS]]{{$}}
+; CHECK:   %n.pre = load i32, i32* %[[ADDRESS]], !dbg [[N_LOC:![0-9]+]]
 ; CHECK: br label %end
 ; CHECK: then:
 ; CHECK:   store i32 %z
 ; CHECK: end:
-; CHECK:   %n = phi i32 [ %n.pre, %entry.end_crit_edge ], [ %z, %then ], !dbg [[N_LOC:![0-9]+]]
+; CHECK:   %n = phi i32 [ %n.pre, %entry.end_crit_edge ], [ %z, %then ], !dbg [[N_LOC]]
 ; CHECK:   ret i32 %n
 
 ; CHECK: [[N_LOC]] = !DILocation(line: 47, column: 1, scope: !{{.*}})