Index: lib/IR/DebugInfoMetadata.cpp
===================================================================
--- lib/IR/DebugInfoMetadata.cpp
+++ lib/IR/DebugInfoMetadata.cpp
@@ -80,17 +80,47 @@
   if (!dyn_cast_or_null<CallInst>(ForInst))
     return nullptr;
 
+  // Find closest common scope for LocA and LocB.
+  DIScope *CommonScope = nullptr;
+  SmallPtrSet<DIScope *, 5> ScopesA;
+  for (DIScope *S = LocA->getScope(); S; S = S->getScope().resolve())
+    ScopesA.insert(S);
+  for (DIScope *S = LocB->getScope(); S; S = S->getScope().resolve())
+    if (ScopesA.count(S)) {
+      CommonScope = S;
+      break;
+    }
+
+  // If no common scope exists, make up a new compiler-generated location.
+  // At this point the inlinedAt field will be meaningless as well.
+  if (!CommonScope)
+    return DILocation::get(LocA->getContext(),
+                           0, 0, LocA->getInlinedAtScope());
+
+  // If either LocA or LocB is not inlined, the merged location does not
+  // need to be inlined either.
+  if (LocA->getInlinedAt() == nullptr || LocB->getInlinedAt() == nullptr)
+    return DILocation::get(LocA->getContext(), 0, 0, CommonScope);
+
+  // Otherwise find the closest common inlined-at location for LocA and LocB.
+  DILocation *CommonInlinedAt = nullptr;
   SmallPtrSet<DILocation *, 5> InlinedLocationsA;
   for (DILocation *L = LocA->getInlinedAt(); L; L = L->getInlinedAt())
     InlinedLocationsA.insert(L);
-  const DILocation *Result = LocB;
-  for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt()) {
-    Result = L;
-    if (InlinedLocationsA.count(L))
+  for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt())
+    if (InlinedLocationsA.count(L)) {
+      CommonInlinedAt = L;
       break;
-  }
-  return DILocation::get(Result->getContext(), 0, 0, Result->getScope(),
-                         Result->getInlinedAt());
+    }
+
+  // If no common inlined-at location exists, mark as inlined at a
+  // compiler-generated location in the current function.
+  if (!CommonInlinedAt)
+    CommonInlinedAt = DILocation::get(LocA->getContext(),
+                                      0, 0, LocA->getInlinedAtScope());
+
+  return DILocation::get(LocA->getContext(),
+                         0, 0, CommonScope, CommonInlinedAt);
 }
 
 DINode::DIFlags DINode::getFlag(StringRef Flag) {
Index: test/Transforms/SimplifyCFG/hoist-dbgvalue-inlined.ll
===================================================================
--- test/Transforms/SimplifyCFG/hoist-dbgvalue-inlined.ll
+++ test/Transforms/SimplifyCFG/hoist-dbgvalue-inlined.ll
@@ -0,0 +1,47 @@
+; RUN: opt -simplifycfg -S < %s | FileCheck %s
+; Verify that we don't crash due an invalid !dbg location on the hoisted llvm.dbg.value
+
+define i64 @caller(i64* %ptr, i64 %flag) !dbg !10 {
+; CHECK: llvm.dbg.value
+init:
+  %v9 = icmp eq i64 %flag, 0
+  br i1 %v9, label %a, label %b
+
+a:                                              ; preds = %init
+  %vala = load i64, i64* %ptr, align 8
+  call void @llvm.dbg.value(metadata i64 %vala, metadata !8, metadata !DIExpression()), !dbg !12
+  br label %test.exit
+
+b:                                              ; preds = %init
+  %valb = load i64, i64* %ptr, align 8
+  call void @llvm.dbg.value(metadata i64 %valb, metadata !8, metadata !DIExpression()), !dbg !13
+  %valbmasked = and i64 %valb, 1
+  br label %test.exit
+
+test.exit:                                      ; preds = %a, %b
+  %retv = phi i64 [ %vala, %a ], [ %valbmasked, %b ]
+  ret i64 %retv
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+
+attributes #0 = { nounwind readnone speculatable }
+
+!llvm.module.flags = !{!0}
+!llvm.dbg.cu = !{!1}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !2, isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !3)
+!2 = !DIFile(filename: "optbug", directory: "")
+!3 = !{}
+!4 = distinct !DISubprogram(name: "callee", scope: !2, file: !2, line: 1, type: !5, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: false, unit: !1, variables: !7)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null}
+!7 = !{!8}
+!8 = !DILocalVariable(name: "var", scope: !4, file: !2, type: !9)
+!9 = !DIBasicType(name: "var_t", size: 64, encoding: DW_ATE_unsigned)
+!10 = distinct !DISubprogram(name: "caller", scope: !2, file: !2, line: 5, type: !5, isLocal: false, isDefinition: true, scopeLine: 5, isOptimized: false, unit: !1, variables: !3)
+!11 = distinct !DILocation(line: 6, scope: !10)
+!12 = !DILocation(line: 2, scope: !4, inlinedAt: !11)
+!13 = !DILocation(line: 3, scope: !4, inlinedAt: !11)
Index: unittests/IR/MetadataTest.cpp
===================================================================
--- unittests/IR/MetadataTest.cpp
+++ unittests/IR/MetadataTest.cpp
@@ -883,6 +883,81 @@
   EXPECT_TRUE(L2->isTemporary());
 }
 
+TEST_F(DILocationTest, getMergedLocation) {
+  FunctionType *FT = FunctionType::get(Type::getVoidTy(Context), false);
+  auto *F = Function::Create(FT, GlobalValue::ExternalLinkage);
+  const CallInst *Call = CallInst::Create(F, None);
+
+  // Merging two identical locations should result in the same location.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 2, 7, Prg);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, nullptr);
+    EXPECT_EQ(2u, L->getLine());
+    EXPECT_EQ(7u, L->getColumn());
+    EXPECT_EQ(Prg, L->getScope());
+  }
+  // If the two locations are incompatible, there should be a null result.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 3, 7, Prg);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, nullptr);
+    EXPECT_EQ(nullptr, L);
+  }
+  // Unless we are merging locations for a call instruction.  If the
+  // scopes agree, the result should be a compiler-generated location
+  // in that same scope.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 3, 7, Prg);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+  }
+  // Likewise if the one scope is a sub-scope of the other.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILexicalBlock *B = DILexicalBlock::get(Context, Prg, getFile(), 5, 7);
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 3, 7, B);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+  }
+  // Even if the calls were inlined (possibly into different places),
+  // if they originate from the same scope, the result should also be
+  // a compiler-generated location in that same scope.
+  {
+    DISubprogram *IPrg = getSubprogram();
+    DILocation *I1 = DILocation::get(Context, 10, 7, IPrg);
+    DILocation *I2 = DILocation::get(Context, 11, 7, IPrg);
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg, I1);
+    DILocation *L2 = DILocation::get(Context, 3, 7, Prg, I2);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+    EXPECT_NE(nullptr, L->getInlinedAt());
+  }
+  // Likewise if the one scope is a sub-scope of the other.
+  {
+    DISubprogram *IPrg = getSubprogram();
+    DILocation *I1 = DILocation::get(Context, 10, 7, IPrg);
+    DILocation *I2 = DILocation::get(Context, 11, 7, IPrg);
+    DISubprogram *Prg = getSubprogram();
+    DILexicalBlock *B = DILexicalBlock::get(Context, Prg, getFile(), 5, 7);
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg, I1);
+    DILocation *L2 = DILocation::get(Context, 3, 7, B, I2);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+    EXPECT_NE(nullptr, L->getInlinedAt());
+  }
+}
+
 typedef MetadataTest GenericDINodeTest;
 
 TEST_F(GenericDINodeTest, get) {