Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -37,6 +37,7 @@
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
@@ -1395,7 +1396,11 @@
   // are created from any PHI nodes, will take its debug location, giving
   // the impression that those 'select' instructions are in the true branch,
   // causing incorrect stepping, affecting the debug experience.
-  NT->setDebugLoc(InsertPt ? InsertPt->getDebugLoc() : DebugLoc());
+  // If there are no earlier locations, either adopt from the merged insns
+  // or produce an unknown location.
+  NT->setDebugLoc(InsertPt ? InsertPt->getDebugLoc().get()
+                           : DILocation::getMergedLocation(I1->getDebugLoc(),
+                                                           I2->getDebugLoc()));
 
   IRBuilder<NoFolder> Builder(NT);
   // Hoisting one of the terminators from our successor is a great thing.
Index: test/Transforms/SimplifyCFG/pr39807.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/pr39807.ll
@@ -0,0 +1,43 @@
+; RUN: opt -S -simplifycfg < %s | FileCheck %s
+
+declare void @personality()
+
+define void @test(i1 %b) personality void()* @personality !dbg !1 {
+; CHECK:      invoke void @inlinable()
+; CHECK-NEXT:    to label %success unwind label %failure, !dbg ![[DBGLOC:[0-9]+]]
+    br i1 %b, label %if, label %else
+
+if:
+    invoke void @inlinable()
+        to label %success unwind label %failure, !dbg !2
+
+else:
+    invoke void @inlinable()
+        to label %success unwind label %failure, !dbg !8
+
+success:
+    ret void
+
+failure:
+    landingpad {}
+        cleanup
+    ret void
+}
+
+define internal void @inlinable() !dbg !7 {
+    ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!4, !5, !6}
+
+; CHECK: ![[DBGLOC]] = !DILocation(line: 0
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, runtimeVersion: 0, file: !3)
+!1 = distinct !DISubprogram(name: "test", unit: !0)
+!2 = !DILocation(line: 2, scope: !1)
+!3 = !DIFile(filename: "foo", directory: ".")
+!4 = !{i32 2, !"Dwarf Version", i32 4}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = !{i32 1, !"wchar_size", i32 4}
+!7 = distinct !DISubprogram(name: "inlinable", unit: !0)
+!8 = !DILocation(line: 3, scope: !1)