Index: lib/LTO/ThinLTOCodeGenerator.cpp
===================================================================
--- lib/LTO/ThinLTOCodeGenerator.cpp
+++ lib/LTO/ThinLTOCodeGenerator.cpp
@@ -25,9 +25,11 @@
 #include "llvm/Bitcode/BitcodeWriterPass.h"
 #include "llvm/ExecutionEngine/ObjectMemoryBuffer.h"
 #include "llvm/IR/DiagnosticPrinter.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Mangler.h"
+#include "llvm/IR/Verifier.h"
 #include "llvm/IRReader/IRReader.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/Linker/Linker.h"
@@ -50,6 +52,7 @@
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
+#include "llvm/Transforms/ObjCARC.h"
 
 #include <numeric>
 
@@ -62,6 +65,7 @@
 extern cl::opt<bool> LTODiscardValueNames;
 extern cl::opt<std::string> LTORemarksFilename;
 extern cl::opt<bool> LTOPassRemarksWithHotness;
+extern cl::opt<bool> LTOStripInvalidDebugInfo;
 }
 
 namespace {
@@ -195,7 +199,8 @@
   PMB.OptLevel = OptLevel;
   PMB.LoopVectorize = true;
   PMB.SLPVectorize = true;
-  PMB.VerifyInput = true;
+  // Already did this in verifyMergedModule().
+  PMB.VerifyInput = false;
   PMB.VerifyOutput = false;
 
   legacy::PassManager PM;
@@ -224,6 +229,30 @@
   return GUIDPreservedSymbols;
 }
 
+namespace {
+class ThinLTODiagnosticInfo : public DiagnosticInfo {
+  const Twine &Msg;
+public:
+  ThinLTODiagnosticInfo(const Twine &DiagMsg,
+                        DiagnosticSeverity Severity = DS_Error)
+      : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
+  void print(DiagnosticPrinter &DP) const override { DP << Msg; }
+};
+}
+
+/// Verify the module and strip broken debug info.
+static void verifyMergedModule(Module &TheModule) {
+  bool BrokenDebugInfo = false;
+  if (verifyModule(TheModule, &dbgs(),
+                   LTOStripInvalidDebugInfo ? &BrokenDebugInfo : nullptr))
+    report_fatal_error("Broken module found, compilation aborted!");
+  if (BrokenDebugInfo) {
+    TheModule.getContext().diagnose(ThinLTODiagnosticInfo(
+        "Invalid debug info found, debug info will be stripped", DS_Warning));
+    StripDebugInfo(TheModule);
+  }
+}
+
 std::unique_ptr<MemoryBuffer> codegenModule(Module &TheModule,
                                             TargetMachine &TM) {
   SmallVector<char, 128> OutputBuffer;
@@ -408,6 +437,7 @@
 
   // "Benchmark"-like optimization: single-source case
   bool SingleModule = (ModuleMap.size() == 1);
+  verifyMergedModule(TheModule);
 
   if (!SingleModule) {
     promoteModule(TheModule, Index);
@@ -436,6 +466,8 @@
     saveTempBitcode(TheModule, SaveTempsDir, count, ".3.imported.bc");
   }
 
+  // Verify again to catch all cross-imports.
+  verifyMergedModule(TheModule);
   optimizeModule(TheModule, TM, OptLevel, Freestanding);
 
   saveTempBitcode(TheModule, SaveTempsDir, count, ".4.opt.bc");
@@ -762,6 +794,7 @@
  * Perform ThinLTO CodeGen.
  */
 std::unique_ptr<MemoryBuffer> ThinLTOCodeGenerator::codegen(Module &TheModule) {
+  verifyMergedModule(TheModule);
   initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
   return codegenModule(TheModule, *TMBuilder.create());
 }
Index: test/LTO/X86/strip-debug-info.ll
===================================================================
--- test/LTO/X86/strip-debug-info.ll
+++ test/LTO/X86/strip-debug-info.ll
@@ -6,10 +6,30 @@
 ; RUN:     -o %t.o %S/Inputs/strip-debug-info.bc 2>&1 | \
 ; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-WARN
 ; RUN: llvm-nm %t.o | FileCheck %s 
+; RUN: not llvm-lto -thinlto -thinlto-action=codegen \
+; RUN:     -lto-strip-invalid-debug-info=false \
+; RUN:     %S/Inputs/strip-debug-info.bc -disable-verify 2>&1 | \
+; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-ERR
+; RUN: llvm-lto -thinlto -thinlto-action=codegen \
+; RUN:     -lto-strip-invalid-debug-info=true \
+; RUN:     %S/Inputs/strip-debug-info.bc -disable-verify 2>&1 | \
+; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-WARN
+; RUN: not llvm-lto -thinlto -thinlto-action=run \
+; RUN:     -lto-strip-invalid-debug-info=false \
+; RUN:     %S/Inputs/strip-debug-info.bc -disable-verify 2>&1 | \
+; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-ERR
+; RUN: llvm-lto -thinlto -thinlto-action=run \
+; RUN:     -lto-strip-invalid-debug-info=true \
+; RUN:     %S/Inputs/strip-debug-info.bc -disable-verify 2>&1 | \
+; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-WARN
 
 ; CHECK-ERR: Broken module found, compilation aborted
 ; CHECK-WARN: Invalid debug info found, debug info will be stripped
+; CHECK-WARN-NOT: Broken module found
 ; CHECK: foo
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.12"
+
 define void @foo() {
   ret void
 }