Index: include/llvm/LTO/LTO.h
===================================================================
--- include/llvm/LTO/LTO.h
+++ include/llvm/LTO/LTO.h
@@ -325,6 +325,7 @@
     bool HasModule = false;
     std::unique_ptr<Module> CombinedModule;
     std::unique_ptr<IRMover> Mover;
+    StringSet<> AsmUndefinedRefs;
   } RegularLTO;
 
   struct ThinLTOState {
Index: include/llvm/LTO/LTOBackend.h
===================================================================
--- include/llvm/LTO/LTOBackend.h
+++ include/llvm/LTO/LTOBackend.h
@@ -18,6 +18,7 @@
 #define LLVM_LTO_LTOBACKEND_H
 
 #include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/ModuleSummaryIndex.h"
 #include "llvm/LTO/Config.h"
@@ -36,7 +37,7 @@
 /// Runs a regular LTO backend.
 Error backend(Config &C, AddOutputFn AddStream,
               unsigned ParallelCodeGenParallelismLevel,
-              std::unique_ptr<Module> M);
+              std::unique_ptr<Module> M, StringSet<> AsmUndefinedRefs);
 
 /// Runs a ThinLTO backend.
 Error thinBackend(Config &C, unsigned Task, AddOutputFn AddStream, Module &M,
Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -301,6 +301,18 @@
     return addRegularLTO(std::move(Input), Res);
 }
 
+static void handleUndefinedAsmRefs(const InputFile::Symbol &Sym, GlobalValue *GV,
+                                   StringSet<> &AsmUndefinedRefs) {
+  // GV associated => not an assembly symbol, bail out.
+  if (GV)
+    return;
+
+  // This is an undefined reference to a symbol in asm. We put that in
+  // compiler.used, so that we can preserve it from being dropped from
+  // the output, without necessarily preventing its internalization.
+  AsmUndefinedRefs.insert(Sym.getName().str());
+}
+
 // Add a regular LTO object to the link.
 Error LTO::addRegularLTO(std::unique_ptr<InputFile> Input,
                          ArrayRef<SymbolResolution> Res) {
@@ -337,8 +349,10 @@
     addSymbolToGlobalRes(Obj.get(), Used, Sym, Res, 0);
 
     GlobalValue *GV = Obj->getSymbolGV(Sym.I->getRawDataRefImpl());
-    if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined)
+    if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined) {
+			handleUndefinedAsmRefs(Sym, GV, RegularLTO.AsmUndefinedRefs);
       continue;
+		}
     if (Res.Prevailing && GV) {
       Keep.push_back(GV);
       switch (GV->getLinkage()) {
@@ -475,7 +489,7 @@
       return Error();
   }
   return backend(Conf, AddOutput, RegularLTO.ParallelCodeGenParallelismLevel,
-                 std::move(RegularLTO.CombinedModule));
+                 std::move(RegularLTO.CombinedModule), RegularLTO.AsmUndefinedRefs);
 }
 
 /// This class defines the interface to the ThinLTO backend.
Index: lib/LTO/LTOBackend.cpp
===================================================================
--- lib/LTO/LTOBackend.cpp
+++ lib/LTO/LTOBackend.cpp
@@ -24,6 +24,7 @@
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/Verifier.h"
+#include "llvm/LTO/legacy/UpdateCompilerUsed.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Passes/PassBuilder.h"
@@ -277,7 +278,7 @@
 
 Error lto::backend(Config &C, AddOutputFn AddOutput,
                    unsigned ParallelCodeGenParallelismLevel,
-                   std::unique_ptr<Module> Mod) {
+                   std::unique_ptr<Module> Mod, StringSet<> AsmUndefinedRefs) {
   Expected<const Target *> TOrErr = initAndLookupTarget(C, *Mod);
   if (!TOrErr)
     return TOrErr.takeError();
@@ -285,6 +286,10 @@
   std::unique_ptr<TargetMachine> TM =
       createTargetMachine(C, Mod->getTargetTriple(), *TOrErr);
 
+  // Update llvm.compiler.used to that optimizations won't strip
+  // off asm undefined references.
+  updateCompilerUsed(*Mod, *TM, AsmUndefinedRefs);
+
   if (!C.CodeGenOnly)
     if (!opt(C, TM.get(), 0, *Mod, /*IsThinLto=*/false))
       return Error();