Index: lib/Transforms/Utils/AddDiscriminators.cpp
===================================================================
--- lib/Transforms/Utils/AddDiscriminators.cpp
+++ lib/Transforms/Utils/AddDiscriminators.cpp
@@ -70,14 +70,14 @@
 #define DEBUG_TYPE "add-discriminators"
 
 namespace {
-  struct AddDiscriminators : public FunctionPass {
-    static char ID; // Pass identification, replacement for typeid
-    AddDiscriminators() : FunctionPass(ID) {
-      initializeAddDiscriminatorsPass(*PassRegistry::getPassRegistry());
-    }
+struct AddDiscriminators : public FunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+  AddDiscriminators() : FunctionPass(ID) {
+    initializeAddDiscriminatorsPass(*PassRegistry::getPassRegistry());
+  }
 
-    bool runOnFunction(Function &F) override;
-  };
+  bool runOnFunction(Function &F) override;
+};
 }
 
 char AddDiscriminators::ID = 0;
@@ -89,9 +89,9 @@
 // Command line option to disable discriminator generation even in the
 // presence of debug information. This is only needed when debugging
 // debug info generation issues.
-static cl::opt<bool>
-NoDiscriminators("no-discriminators", cl::init(false),
-                 cl::desc("Disable generation of discriminator information."));
+static cl::opt<bool> NoDiscriminators(
+    "no-discriminators", cl::init(false),
+    cl::desc("Disable generation of discriminator information."));
 
 FunctionPass *llvm::createAddDiscriminatorsPass() {
   return new AddDiscriminators();
@@ -159,8 +159,7 @@
   // Simlarly, if the function has no debug info, do nothing.
   // Finally, if this module is built with dwarf versions earlier than 4,
   // do nothing (discriminator support is a DWARF 4 feature).
-  if (NoDiscriminators ||
-      !hasDebugInfo(F) ||
+  if (NoDiscriminators || !hasDebugInfo(F) ||
       F.getParent()->getDwarfVersion() < 4)
     return false;
 
@@ -181,7 +180,7 @@
       BasicBlock *Succ = Last->getSuccessor(I);
       Instruction *First = Succ->getFirstNonPHIOrDbgOrLifetime();
       const DILocation *FirstDIL = First->getDebugLoc();
-      if (!FirstDIL)
+      if (!FirstDIL || FirstDIL->getDiscriminator())
         continue;
 
       // If the first instruction (First) of Succ is at the same file
@@ -212,12 +211,17 @@
         // instruction following First that shares the same location.
         for (BasicBlock::iterator I1(*First), E1 = Succ->end(); I1 != E1;
              ++I1) {
-          if (I1->getDebugLoc().get() != FirstDIL)
-            break;
-          I1->setDebugLoc(newDebugLoc);
-          DEBUG(dbgs() << NewDIL->getFilename() << ":" << NewDIL->getLine()
-                       << ":" << NewDIL->getColumn() << ":"
-                       << NewDIL->getDiscriminator() << *I1 << "\n");
+          const DILocation *CurrentDIL = I1->getDebugLoc();
+          if (CurrentDIL && CurrentDIL->getLine() == FirstDIL->getLine() &&
+              CurrentDIL->getFilename() == FirstDIL->getFilename()) {
+            I1->setDebugLoc(DILocation::get(Ctx, CurrentDIL->getLine(),
+                                            CurrentDIL->getColumn(), NewScope,
+                                            CurrentDIL->getInlinedAt()));
+            DEBUG(dbgs() << CurrentDIL->getFilename() << ":"
+                         << CurrentDIL->getLine() << ":"
+                         << CurrentDIL->getColumn() << ":"
+                         << NewDIL->getDiscriminator() << *I1 << "\n");
+          }
         }
         DEBUG(dbgs() << "\n");
         Changed = true;
Index: test/Transforms/AddDiscriminators/oneline.ll
===================================================================
--- /dev/null
+++ test/Transforms/AddDiscriminators/oneline.ll
@@ -0,0 +1,88 @@
+; RUN: opt < %s -add-discriminators -S | FileCheck %s
+
+define i32 @_Z3fooi(i32 %i) #0 {
+  %1 = alloca i32, align 4
+  %2 = alloca i32, align 4
+  store i32 %i, i32* %2, align 4, !tbaa !13
+  call void @llvm.dbg.declare(metadata i32* %2, metadata !9, metadata !17), !dbg !18
+  %3 = load i32, i32* %2, align 4, !dbg !19, !tbaa !13
+  %4 = icmp eq i32 %3, 3, !dbg !21
+  br i1 %4, label %8, label %5, !dbg !22
+
+; <label>:5                                       ; preds = %0
+  %6 = load i32, i32* %2, align 4, !dbg !23, !tbaa !13
+; CHECK:  %6 = load i32, i32* %2, align 4, !dbg ![[THEN1:[0-9]+]],{{.*}}
+
+  %7 = icmp eq i32 %6, 5, !dbg !24
+; CHECK:  %7 = icmp eq i32 %6, 5, !dbg ![[THEN2:[0-9]+]]
+
+  br i1 %7, label %8, label %9, !dbg !25
+; CHECK:  br i1 %7, label %8, label %9, !dbg ![[THEN3:[0-9]+]]
+
+; <label>:8                                       ; preds = %5, %0
+  store i32 100, i32* %1, align 4, !dbg !26
+; CHECK: store i32 100, i32* %1, align 4, !dbg ![[ELSE:[0-9]+]]
+
+  br label %10, !dbg !26
+; CHECK: br label %10, !dbg ![[ELSE]]
+
+; <label>:9                                       ; preds = %5
+  store i32 99, i32* %1, align 4, !dbg !27
+; CHECK: store i32 99, i32* %1, align 4, !dbg ![[COMBINE:[0-9]+]]
+
+  br label %10, !dbg !27
+; CHECK: br label %10, !dbg ![[COMBINE]]
+
+; <label>:10                                      ; preds = %9, %8
+  %11 = load i32, i32* %1, align 4, !dbg !28
+  ret i32 %11, !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"="false" "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 = !{!10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.8.0 (trunk 250915)", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "a.cc", directory: "/usr/local/google/home/dehao/discr")
+!2 = !{}
+!3 = !{!4}
+!4 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooi", scope: !1, file: !1, line: 1, type: !5, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, function: i32 (i32)* @_Z3fooi, variables: !8)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !7}
+!7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!8 = !{!9}
+!9 = !DILocalVariable(name: "i", arg: 1, scope: !4, file: !1, line: 1, type: !7)
+!10 = !{i32 2, !"Dwarf Version", i32 4}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{!"clang version 3.8.0 (trunk 250915)"}
+!13 = !{!14, !14, i64 0}
+!14 = !{!"int", !15, i64 0}
+!15 = !{!"omnipotent char", !16, i64 0}
+!16 = !{!"Simple C/C++ TBAA"}
+!17 = !DIExpression()
+!18 = !DILocation(line: 1, column: 13, scope: !4)
+!19 = !DILocation(line: 2, column: 7, scope: !20)
+!20 = distinct !DILexicalBlock(scope: !4, file: !1, line: 2, column: 7)
+!21 = !DILocation(line: 2, column: 9, scope: !20)
+!22 = !DILocation(line: 2, column: 14, scope: !20)
+!23 = !DILocation(line: 2, column: 17, scope: !20)
+!24 = !DILocation(line: 2, column: 19, scope: !20)
+!25 = !DILocation(line: 2, column: 7, scope: !4)
+!26 = !DILocation(line: 2, column: 25, scope: !20)
+!27 = !DILocation(line: 2, column: 42, scope: !20)
+!28 = !DILocation(line: 3, column: 1, scope: !4)
+
+; CHECK: ![[THEN1]] = !DILocation(line: 2, column: 17, scope: ![[THENBLOCK:[0-9]+]])
+; CHECK: ![[THENBLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 2)
+; CHECK: ![[THEN2]] = !DILocation(line: 2, column: 19, scope: ![[THENBLOCK]])
+; CHECK: ![[THEN3]] = !DILocation(line: 2, column: 7, scope: ![[THENBLOCK]])
+; CHECK: ![[ELSE]] = !DILocation(line: 2, column: 25, scope: ![[ELSEBLOCK:[0-9]+]])
+; CHECK: ![[ELSEBLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 1)
+; CHECK: ![[COMBINE]] = !DILocation(line: 2, column: 42, scope: ![[COMBINEBLOCK:[0-9]+]])
+; CHECK: ![[COMBINEBLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 3)