Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1920,6 +1920,8 @@
   // - All of their uses are in CondBB.
   SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
 
+  SmallVector<Instruction *, 4> SpeculatedDbgIntrinsics;
+
   unsigned SpeculationCost = 0;
   Value *SpeculatedStoreValue = nullptr;
   StoreInst *SpeculatedStore = nullptr;
@@ -1928,8 +1930,10 @@
        BBI != BBE; ++BBI) {
     Instruction *I = &*BBI;
     // Skip debug info.
-    if (isa<DbgInfoIntrinsic>(I))
+    if (isa<DbgInfoIntrinsic>(I)) {
+      SpeculatedDbgIntrinsics.push_back(I);
       continue;
+    }
 
     // Only speculatively execute a single instruction (not counting the
     // terminator) for now.
@@ -2074,6 +2078,12 @@
     PN->setIncomingValue(ThenI, V);
   }
 
+  // Remove speculated dbg intrinsics.
+  // FIXME: Is it possible to do this in a more elegant way? Moving/merging the
+  // dbg value for the different flows and inserting it after the select.
+  for (Instruction *I : SpeculatedDbgIntrinsics)
+    I->eraseFromParent();
+
   ++NumSpeculations;
   return true;
 }
Index: test/Transforms/SimplifyCFG/speculate-dbgvalue.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/speculate-dbgvalue.ll
@@ -0,0 +1,83 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -simplifycfg | FileCheck %s
+
+; This test case was generated from speculate-dbgvalue.c:
+;
+;   int test1(int getdirt, int dirt) {
+;     int result = 100;
+;     if (getdirt != 0)
+;       result = dirt;
+;     return result;
+;   }
+;
+; using
+;   clang speculate-dbgvalue.c -S -emit-llvm -g -O3 -mllvm -disable-llvm-optzns -o - | opt -mem2reg -S
+
+
+; Function Attrs: nounwind uwtable
+define i32 @test1(i32 %getdirt, i32 %dirt) #0 !dbg !7 {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[GETDIRT:%.*]], metadata !12, metadata !DIExpression()), !dbg !15
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[DIRT:%.*]], metadata !13, metadata !DIExpression()), !dbg !16
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 100, metadata !14, metadata !DIExpression()), !dbg !17
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[GETDIRT]], 0, !dbg !18
+; *** We used to get an incorrect "call void @llvm.dbg.value(metadata i32 [[DIRT]], metadata !14, metadata !DIExpression()), !dbg !17" here, before the select. ***
+; CHECK-NOT:     call void @llvm.dbg.value(metadata i32 [[DIRT]], metadata !14
+; CHECK-NEXT:    [[RESULT:%.*]] = select i1 [[CMP]], i32 [[DIRT]], i32 100, !dbg !20
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[RESULT]], metadata !14, metadata !DIExpression()), !dbg !17
+; CHECK-NEXT:    ret i32 [[RESULT]], !dbg !21
+; CHECK: !12 = !DILocalVariable(name: "getdirt"
+; CHECK: !13 = !DILocalVariable(name: "dirt"
+; CHECK: !14 = !DILocalVariable(name: "result"
+;
+entry:
+  call void @llvm.dbg.value(metadata i32 %getdirt, metadata !12, metadata !DIExpression()), !dbg !15
+  call void @llvm.dbg.value(metadata i32 %dirt, metadata !13, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i32 100, metadata !14, metadata !DIExpression()), !dbg !17
+  %cmp = icmp ne i32 %getdirt, 0, !dbg !18
+  br i1 %cmp, label %if.then, label %if.end, !dbg !20
+
+if.then:                                          ; preds = %entry
+  call void @llvm.dbg.value(metadata i32 %dirt, metadata !14, metadata !DIExpression()), !dbg !17
+  br label %if.end, !dbg !21
+
+if.end:                                           ; preds = %if.then, %entry
+  %result.0 = phi i32 [ %dirt, %if.then ], [ 100, %entry ]
+  call void @llvm.dbg.value(metadata i32 %result.0, metadata !14, metadata !DIExpression()), !dbg !17
+  ret i32 %result.0, !dbg !22
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable }
+attributes #1 = { nounwind readnone speculatable }
+
+!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 6.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "speculate-dbgvalue.c", directory: "/foo")
+!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 6.0.0"}
+!7 = distinct !DISubprogram(name: "test1", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12, !13, !14}
+!12 = !DILocalVariable(name: "getdirt", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = !DILocalVariable(name: "dirt", arg: 2, scope: !7, file: !1, line: 1, type: !10)
+!14 = !DILocalVariable(name: "result", scope: !7, file: !1, line: 2, type: !10)
+!15 = !DILocation(line: 1, column: 15, scope: !7)
+!16 = !DILocation(line: 1, column: 28, scope: !7)
+!17 = !DILocation(line: 2, column: 7, scope: !7)
+!18 = !DILocation(line: 3, column: 15, scope: !19)
+!19 = distinct !DILexicalBlock(scope: !7, file: !1, line: 3, column: 7)
+!20 = !DILocation(line: 3, column: 7, scope: !7)
+!21 = !DILocation(line: 4, column: 5, scope: !19)
+!22 = !DILocation(line: 5, column: 3, scope: !7)