Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -433,6 +433,7 @@
 class BitcodeReader : public BitcodeReaderBase, public GVMaterializer {
   LLVMContext &Context;
   Module *TheModule = nullptr;
+  Triple TargetTriple;
   // Next offset to start scanning for lazy parsing of function bodies.
   uint64_t NextUnreadBit = 0;
   // Last function offset found in the VST.
@@ -650,7 +651,7 @@
   Error parseOperandBundleTags();
 
   Expected<Value *> recordValue(SmallVectorImpl<uint64_t> &Record,
-                                unsigned NameIndex, Triple &TT);
+                                unsigned NameIndex);
   void setDeferredFunctionInfo(unsigned FuncBitcodeOffsetDelta, Function *F,
                                ArrayRef<uint64_t> Record);
   Error parseValueSymbolTable(uint64_t Offset = 0);
@@ -761,7 +762,7 @@
                              StringRef ProducerIdentification,
                              LLVMContext &Context)
     : BitcodeReaderBase(std::move(Stream), Strtab), Context(Context),
-      ValueList(Context) {
+      TargetTriple(), ValueList(Context) {
   this->ProducerIdentification = ProducerIdentification;
 }
 
@@ -1747,7 +1748,7 @@
 
 /// Associate a value with its name from the given index in the provided record.
 Expected<Value *> BitcodeReader::recordValue(SmallVectorImpl<uint64_t> &Record,
-                                             unsigned NameIndex, Triple &TT) {
+                                             unsigned NameIndex) {
   SmallString<128> ValueName;
   if (convertToString(Record, NameIndex, ValueName))
     return error("Invalid record");
@@ -1763,7 +1764,7 @@
   auto *GO = dyn_cast<GlobalObject>(V);
   if (GO) {
     if (GO->getComdat() == reinterpret_cast<Comdat *>(1)) {
-      if (TT.isOSBinFormatMachO())
+      if (TargetTriple.isOSBinFormatMachO())
         GO->setComdat(nullptr);
       else
         GO->setComdat(TheModule->getOrInsertComdat(V->getName()));
@@ -1880,8 +1881,6 @@
 
   SmallVector<uint64_t, 64> Record;
 
-  Triple TT(TheModule->getTargetTriple());
-
   // Read all the records for this value table.
   SmallString<128> ValueName;
 
@@ -1907,7 +1906,7 @@
     default:  // Default behavior: unknown type.
       break;
     case bitc::VST_CODE_ENTRY: {  // VST_CODE_ENTRY: [valueid, namechar x N]
-      Expected<Value *> ValOrErr = recordValue(Record, 1, TT);
+      Expected<Value *> ValOrErr = recordValue(Record, 1);
       if (Error Err = ValOrErr.takeError())
         return Err;
       ValOrErr.get();
@@ -1915,7 +1914,7 @@
     }
     case bitc::VST_CODE_FNENTRY: {
       // VST_CODE_FNENTRY: [valueid, offset, namechar x N]
-      Expected<Value *> ValOrErr = recordValue(Record, 2, TT);
+      Expected<Value *> ValOrErr = recordValue(Record, 2);
       if (Error Err = ValOrErr.takeError())
         return Err;
       Value *V = ValOrErr.get();
@@ -2656,6 +2655,7 @@
 
   // Look for intrinsic functions which need to be upgraded at some point
   for (Function &F : *TheModule) {
+    MDLoader->upgradeThumbMode(F);
     MDLoader->upgradeDebugIntrinsics(F);
     Function *NewFn;
     if (UpgradeIntrinsicFunction(&F, NewFn))
@@ -3156,6 +3156,7 @@
       if (convertToString(Record, 0, S))
         return error("Invalid record");
       TheModule->setTargetTriple(S);
+      TargetTriple = Triple(S);
       break;
     }
     case bitc::MODULE_CODE_DATALAYOUT: {  // DATALAYOUT: [strchr x N]
@@ -3240,7 +3241,7 @@
 Error BitcodeReader::parseBitcodeInto(Module *M, bool ShouldLazyLoadMetadata,
                                       bool IsImporting) {
   TheModule = M;
-  MDLoader = MetadataLoader(Stream, *M, ValueList, IsImporting,
+  MDLoader = MetadataLoader(Stream, *M, TargetTriple, ValueList, IsImporting,
                             [&](unsigned ID) { return getTypeByID(ID); });
   return parseModule(0, ShouldLazyLoadMetadata);
 }
Index: lib/Bitcode/Reader/MetadataLoader.h
===================================================================
--- lib/Bitcode/Reader/MetadataLoader.h
+++ lib/Bitcode/Reader/MetadataLoader.h
@@ -15,6 +15,7 @@
 #define LLVM_LIB_BITCODE_READER_METADATALOADER_H
 
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/Support/Error.h"
 
 #include <functional>
@@ -40,7 +41,7 @@
 
 public:
   ~MetadataLoader();
-  MetadataLoader(BitstreamCursor &Stream, Module &TheModule,
+  MetadataLoader(BitstreamCursor &Stream, Module &TheModule, Triple &TT,
                  BitcodeReaderValueList &ValueList, bool IsImporting,
                  std::function<Type *(unsigned)> getTypeByID);
   MetadataLoader &operator=(MetadataLoader &&);
@@ -82,6 +83,9 @@
 
   /// Perform bitcode upgrades on llvm.dbg.* calls.
   void upgradeDebugIntrinsics(Function &F);
+
+  /// Add thumb-mode target-feature for arm and thumb triples.
+  void upgradeThumbMode(Function &F);
 };
 }
 
Index: lib/Bitcode/Reader/MetadataLoader.cpp
===================================================================
--- lib/Bitcode/Reader/MetadataLoader.cpp
+++ lib/Bitcode/Reader/MetadataLoader.cpp
@@ -21,7 +21,6 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/Bitcode/BitstreamReader.h"
@@ -418,6 +417,7 @@
   BitstreamCursor &Stream;
   LLVMContext &Context;
   Module &TheModule;
+  Triple &TargetTriple;
   std::function<Type *(unsigned)> getTypeByID;
 
   /// Cursor associated with the lazy-loading of Metadata. This is the easy way
@@ -626,13 +626,15 @@
   }
 
 public:
-  MetadataLoaderImpl(BitstreamCursor &Stream, Module &TheModule,
+  MetadataLoaderImpl(BitstreamCursor &Stream, Module &TheModule, Triple &TT,
                      BitcodeReaderValueList &ValueList,
                      std::function<Type *(unsigned)> getTypeByID,
                      bool IsImporting)
       : MetadataList(TheModule.getContext()), ValueList(ValueList),
         Stream(Stream), Context(TheModule.getContext()), TheModule(TheModule),
-        getTypeByID(std::move(getTypeByID)), IsImporting(IsImporting) {}
+        TargetTriple(TT), getTypeByID(std::move(getTypeByID)),
+        IsImporting(IsImporting) {}
+
 
   Error parseMetadata(bool ModuleLevel);
 
@@ -675,6 +677,32 @@
   unsigned size() const { return MetadataList.size(); }
   void shrinkTo(unsigned N) { MetadataList.shrinkTo(N); }
   void upgradeDebugIntrinsics(Function &F) { upgradeDeclareExpressions(F); }
+
+  void upgradeThumbMode(Function &F) {
+    bool isArm = TargetTriple.getArch() == Triple::arm ||
+                 TargetTriple.getArch() == Triple::armeb;
+
+    if (TargetTriple.getArch() != Triple::thumb &&
+        TargetTriple.getArch() != Triple::thumbeb && !isArm)
+      return;
+
+    std::string TargetFeatures =
+      F.getFnAttribute("target-features").getValueAsString();
+
+    // Check that the target features do not already contain the thumb-mode
+    // feature.
+    auto Start = TargetFeatures.find("thumb-mode");
+    auto End = Start + std::string("thumb-mode").size();
+    if (Start != std::string::npos &&
+        (TargetFeatures[Start-1] == '-' || TargetFeatures[Start-1] == '+') &&
+        (End == TargetFeatures.size() || TargetFeatures[End] == ','))
+      return;
+
+    TargetFeatures += TargetFeatures.empty() ? "" : ",";
+    TargetFeatures += isArm ? "-" : "+";
+    TargetFeatures += "thumb-mode";
+    F.addFnAttr("target-features", TargetFeatures);
+  }
 };
 
 Expected<bool>
@@ -1925,11 +1953,12 @@
 
 MetadataLoader::~MetadataLoader() = default;
 MetadataLoader::MetadataLoader(BitstreamCursor &Stream, Module &TheModule,
-                               BitcodeReaderValueList &ValueList,
+                               Triple &TT, BitcodeReaderValueList &ValueList,
                                bool IsImporting,
                                std::function<Type *(unsigned)> getTypeByID)
     : Pimpl(llvm::make_unique<MetadataLoaderImpl>(
-          Stream, TheModule, ValueList, std::move(getTypeByID), IsImporting)) {}
+          Stream, TheModule, TT, ValueList, std::move(getTypeByID),
+          IsImporting)) {}
 
 Error MetadataLoader::parseMetadata(bool ModuleLevel) {
   return Pimpl->parseMetadata(ModuleLevel);
@@ -1972,3 +2001,7 @@
 void MetadataLoader::upgradeDebugIntrinsics(Function &F) {
   return Pimpl->upgradeDebugIntrinsics(F);
 }
+
+void MetadataLoader::upgradeThumbMode(Function &F) {
+  return Pimpl->upgradeThumbMode(F);
+}
Index: test/Bitcode/thumb-mode-upgrade-arm.ll
===================================================================
--- /dev/null
+++ test/Bitcode/thumb-mode-upgrade-arm.ll
@@ -0,0 +1,24 @@
+; RUN: llvm-dis -o - %s.bc | FileCheck %s
+
+target triple = "arm-apple-ios"
+
+define void @foo() #0 {
+  ret void
+}
+define void @zar() #1 {
+  ret void
+}
+define void @bar() {
+  ret void
+}
+
+attributes #0 = { "target-features"="+thumb-mode" }
+attributes #1 = { "target-features"="+thumb-mode,+vfp3" }
+
+; CHECK: void @foo() [[ThumbModeAttr1:#[0-7]]]
+; CHECK: void @zar() [[ThumbModeAttr2:#[0-7]]]
+; CHECK: void @bar() [[NoThumbModeAttr:#[0-7]]]
+
+; CHECK: attributes [[ThumbModeAttr1]] = { "target-features"="+thumb-mode" }
+; CHECK: attributes [[ThumbModeAttr2]] = { "target-features"="+thumb-mode,+vfp3" }
+; CHECK: attributes [[NoThumbModeAttr]] = { "target-features"="-thumb-mode" }
Index: test/Bitcode/thumb-mode-upgrade-thumb.ll
===================================================================
--- /dev/null
+++ test/Bitcode/thumb-mode-upgrade-thumb.ll
@@ -0,0 +1,24 @@
+; RUN: llvm-dis -o - %s.bc | FileCheck %s
+
+target triple = "thumb-apple-ios"
+
+define void @foo() #0 {
+  ret void
+}
+define void @zar() #1 {
+  ret void
+}
+define void @bar() {
+  ret void
+}
+
+attributes #0 = { "target-features"="-thumb-mode" }
+attributes #1 = { "target-features"="-thumb-mode,+vfp3" }
+
+; CHECK: void @foo() [[NoThumbModeAttr1:#[0-7]]]
+; CHECK: void @zar() [[NoThumbModeAttr2:#[0-7]]]
+; CHECK: void @bar() [[ThumbModeAttr:#[0-7]]]
+
+; CHECK: attributes [[NoThumbModeAttr1]] = { "target-features"="-thumb-mode" }
+; CHECK: attributes [[NoThumbModeAttr2]] = { "target-features"="-thumb-mode,+vfp3" }
+; CHECK: attributes [[ThumbModeAttr]] = { "target-features"="+thumb-mode" }
Index: test/Linker/link-arm-and-thumb.ll
===================================================================
--- test/Linker/link-arm-and-thumb.ll
+++ test/Linker/link-arm-and-thumb.ll
@@ -13,7 +13,7 @@
   ret i32 %add
 }
 
-; CHECK: define i32 @main() {
+; CHECK: define i32 @main() [[ARM_ATTRS:#[0-9]+]]
 ; CHECK: define i32 @foo(i32 %a, i32 %b) [[ARM_ATTRS:#[0-9]+]]
 ; CHECK: define i32 @bar(i32 %a, i32 %b) [[THUMB_ATTRS:#[0-9]+]]