diff --git a/llvm/lib/IR/AutoUpgrade.cpp b/llvm/lib/IR/AutoUpgrade.cpp
--- a/llvm/lib/IR/AutoUpgrade.cpp
+++ b/llvm/lib/IR/AutoUpgrade.cpp
@@ -29,12 +29,19 @@
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Regex.h"
 #include "llvm/TargetParser/Triple.h"
 #include <cstring>
+
 using namespace llvm;
 
+static cl::opt<bool>
+    DisableAutoUpgrade("disable-auto-upgrade",
+                       cl::desc("Assume that input bitcode needs no upgrading, "
+                                "skipping any auto-upgrading"));
+
 static void rename(GlobalValue *GV) { GV->setName(GV->getName() + ".old"); }
 
 // Upgrade the declarations of the SSE4.1 ptest intrinsics whose arguments have
@@ -1173,6 +1180,9 @@
 }
 
 bool llvm::UpgradeIntrinsicFunction(Function *F, Function *&NewFn) {
+  if (DisableAutoUpgrade)
+    return false;
+
   NewFn = nullptr;
   bool Upgraded = UpgradeIntrinsicFunction1(F, NewFn);
   assert(F != NewFn && "Intrinsic function upgraded to the same function");
@@ -1186,6 +1196,9 @@
 }
 
 GlobalVariable *llvm::UpgradeGlobalVariable(GlobalVariable *GV) {
+  if (DisableAutoUpgrade)
+    return nullptr;
+
   if (!(GV->hasName() && (GV->getName() == "llvm.global_ctors" ||
                           GV->getName() == "llvm.global_dtors")) ||
       !GV->hasInitializer())
@@ -1968,6 +1981,9 @@
 /// Upgrade comment in call to inline asm that represents an objc retain release
 /// marker.
 void llvm::UpgradeInlineAsmString(std::string *AsmStr) {
+  if (DisableAutoUpgrade)
+    return;
+
   size_t Pos;
   if (AsmStr->find("mov\tfp") == 0 &&
       AsmStr->find("objc_retainAutoreleaseReturnValue") != std::string::npos &&
@@ -2073,6 +2089,9 @@
 /// Upgrade a call to an old intrinsic. All argument and return casting must be
 /// provided to seamlessly integrate with existing context.
 void llvm::UpgradeIntrinsicCall(CallBase *CI, Function *NewFn) {
+  if (DisableAutoUpgrade)
+    return;
+
   // Note dyn_cast to Function is not quite the same as getCalledFunction, which
   // checks the callee's function type matches. It's likely we need to handle
   // type changes here.
@@ -4374,6 +4393,9 @@
 }
 
 void llvm::UpgradeCallsToIntrinsic(Function *F) {
+  if (DisableAutoUpgrade)
+    return;
+
   assert(F && "Illegal attempt to upgrade a non-existent intrinsic.");
 
   // Check if this function should be upgraded and get the replacement function
@@ -4392,6 +4414,9 @@
 }
 
 MDNode *llvm::UpgradeTBAANode(MDNode &MD) {
+  if (DisableAutoUpgrade)
+    return &MD;
+
   // Check if the tag uses struct-path aware TBAA format.
   if (isa<MDNode>(MD.getOperand(0)) && MD.getNumOperands() >= 3)
     return &MD;
@@ -4415,6 +4440,9 @@
 
 Instruction *llvm::UpgradeBitCastInst(unsigned Opc, Value *V, Type *DestTy,
                                       Instruction *&Temp) {
+  if (DisableAutoUpgrade)
+    return nullptr;
+
   if (Opc != Instruction::BitCast)
     return nullptr;
 
@@ -4436,6 +4464,9 @@
 }
 
 Constant *llvm::UpgradeBitCastExpr(unsigned Opc, Constant *C, Type *DestTy) {
+  if (DisableAutoUpgrade)
+    return nullptr;
+
   if (Opc != Instruction::BitCast)
     return nullptr;
 
@@ -4458,6 +4489,9 @@
 /// Check the debug info version number, if it is out-dated, drop the debug
 /// info. Return true if module is modified.
 bool llvm::UpgradeDebugInfo(Module &M) {
+  if (DisableAutoUpgrade)
+    return false;
+
   unsigned Version = getDebugMetadataVersionFromModule(M);
   if (Version == DEBUG_METADATA_VERSION) {
     bool BrokenDebugInfo = false;
@@ -4508,6 +4542,9 @@
 }
 
 void llvm::UpgradeARCRuntime(Module &M) {
+  if (DisableAutoUpgrade)
+    return;
+
   // This lambda converts normal function calls to ARC runtime functions to
   // intrinsic calls.
   auto UpgradeToIntrinsic = [&](const char *OldFunc,
@@ -4629,6 +4666,9 @@
 }
 
 bool llvm::UpgradeModuleFlags(Module &M) {
+  if (DisableAutoUpgrade)
+    return false;
+
   NamedMDNode *ModFlags = M.getModuleFlagsMetadata();
   if (!ModFlags)
     return false;
@@ -4763,6 +4803,9 @@
 }
 
 void llvm::UpgradeSectionAttributes(Module &M) {
+  if (DisableAutoUpgrade)
+    return;
+
   auto TrimSpaces = [](StringRef Section) -> std::string {
     SmallVector<StringRef, 5> Components;
     Section.split(Components, ',');
@@ -4820,6 +4863,9 @@
 } // namespace
 
 void llvm::UpgradeFunctionAttributes(Function &F) {
+  if (DisableAutoUpgrade)
+    return;
+
   // If a function definition doesn't have the strictfp attribute,
   // convert any callsite strictfp attributes to nobuiltin.
   if (!F.isDeclaration() && !F.hasFnAttribute(Attribute::StrictFP)) {
@@ -4880,6 +4926,9 @@
 }
 
 MDNode *llvm::upgradeInstructionLoopAttachment(MDNode &N) {
+  if (DisableAutoUpgrade)
+    return &N;
+
   auto *T = dyn_cast<MDTuple>(&N);
   if (!T)
     return &N;
@@ -4896,6 +4945,9 @@
 }
 
 std::string llvm::UpgradeDataLayoutString(StringRef DL, StringRef TT) {
+  if (DisableAutoUpgrade)
+    return DL.str();
+
   Triple T(TT);
   // For AMDGPU we uprgrade older DataLayouts to include the default globals
   // address space of 1.
@@ -4939,6 +4991,9 @@
 }
 
 void llvm::UpgradeAttributes(AttrBuilder &B) {
+  if (DisableAutoUpgrade)
+    return;
+
   StringRef FramePointer;
   Attribute A = B.getAttribute("no-frame-pointer-elim");
   if (A.isValid()) {
@@ -4966,6 +5021,8 @@
 }
 
 void llvm::UpgradeOperandBundles(std::vector<OperandBundleDef> &Bundles) {
+  if (DisableAutoUpgrade)
+    return;
 
   // clang.arc.attachedcall bundles are now required to have an operand.
   // If they don't, it's okay to drop them entirely: when there is an operand,
diff --git a/llvm/test/LTO/X86/strip-debug-info.ll b/llvm/test/LTO/X86/strip-debug-info.ll
--- a/llvm/test/LTO/X86/strip-debug-info.ll
+++ b/llvm/test/LTO/X86/strip-debug-info.ll
@@ -24,10 +24,18 @@
 ; RUN:     -exported-symbol foo -exported-symbol _foo \
 ; RUN:     %t-stripped.bc -disable-verify 2>&1 | \
 ; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-WARN
+; ---- Thin LTO (optimize, don't strip imported file)
+; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t-stripped.bc %t2.bc
+; RUN: llvm-lto -thinlto -thinlto-action=import -disable-auto-upgrade \
+; RUN:     -thinlto-index=%t.index.bc \
+; RUN:     -exported-symbol foo -exported-symbol _foo \
+; RUN:     %t-stripped.bc -disable-verify 2>&1 | \
+; RUN:     FileCheck %s -allow-empty -check-prefix=CHECK-NO-WARN
 
 ; CHECK-WARN: warning{{.*}} ignoring invalid debug info
 ; CHECK-WARN-NOT: Broken module found
 ; CHECK: foo
+; CHECK-NO-WARN-NOT: ignoring invalid debug info
 target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.12"