Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -54,6 +54,7 @@
 #include "llvm/IR/Type.h"
 #include "llvm/IR/User.h"
 #include "llvm/IR/Value.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -1573,12 +1574,19 @@
     I0->getOperandUse(O).set(NewOperands[O]);
   I0->moveBefore(&*BBEnd->getFirstInsertionPt());
 
-  // Update metadata and IR flags.
+  // The debug location for the "common" instruction is the merged locations of
+  // all the commoned instructions.  We start with the original location of the
+  // "common" instruction and iteratively merge each location in the loop below.
+  DILocation *Loc = I0->getDebugLoc();
+
+  // Update metadata and IR flags, and merge debug locations.
   for (auto *I : Insts)
     if (I != I0) {
+      Loc = DILocation::getMergedLocation(Loc, I->getDebugLoc());
       combineMetadataForCSE(I0, I);
       I0->andIRFlags(I);
     }
+  I0->setDebugLoc(Loc);
 
   if (!isa<StoreInst>(I0)) {
     // canSinkLastInstruction checked that all instructions were used by
Index: test/DebugInfo/Generic/simplifycfg_sink_last_inst.ll
===================================================================
--- test/DebugInfo/Generic/simplifycfg_sink_last_inst.ll
+++ test/DebugInfo/Generic/simplifycfg_sink_last_inst.ll
@@ -0,0 +1,70 @@
+; RUN: opt -simplifycfg -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Simplify CFG will try to sink the last instruction in a series of basic
+; blocks, creating a "common" instruction in the successor block.  If the
+; debug locations of the commoned instructions have different file/line
+; numbers the debug location of the common instruction should not be set.
+
+; Generated from source:
+
+; extern int foo(void);
+; extern int bar(void);
+; 
+; int test(int a, int b) {
+;   if(a)
+;     b -= foo();
+;   else
+;     b -= bar();
+;   return b;
+; }
+
+; CHECK: define i32 @test
+; CHECK-LABEL: if.end:
+; CHECK: %[[PHI:.*]] = phi i32 [ %call1, %if.else ], [ %call, %if.then ]
+; CHECK: sub nsw i32 %b, %[[PHI]]
+; CHECK-NOT: !dbg
+; CHECK: ret i32
+
+define i32 @test(i32 %a, i32 %b) !dbg !6 {
+entry:
+  %tobool = icmp ne i32 %a, 0, !dbg !8
+  br i1 %tobool, label %if.then, label %if.else, !dbg !8
+
+if.then:                                          ; preds = %entry
+  %call = call i32 @foo(), !dbg !9
+  %sub = sub nsw i32 %b, %call, !dbg !10
+  br label %if.end, !dbg !11
+
+if.else:                                          ; preds = %entry
+  %call1 = call i32 @bar(), !dbg !12
+  %sub2 = sub nsw i32 %b, %call1, !dbg !13
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %b.addr.0 = phi i32 [ %sub, %if.then ], [ %sub2, %if.else ]
+  ret i32 %b.addr.0, !dbg !14
+}
+
+declare i32 @foo()
+declare i32 @bar()
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 8, type: !7, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 9, column: 6, scope: !6)
+!9 = !DILocation(line: 10, column: 10, scope: !6)
+!10 = !DILocation(line: 10, column: 7, scope: !6)
+!11 = !DILocation(line: 10, column: 5, scope: !6)
+!12 = !DILocation(line: 12, column: 10, scope: !6)
+!13 = !DILocation(line: 12, column: 7, scope: !6)
+!14 = !DILocation(line: 13, column: 3, scope: !6)