Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2646,6 +2646,7 @@
 
   // 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))
Index: lib/Bitcode/Reader/MetadataLoader.h
===================================================================
--- lib/Bitcode/Reader/MetadataLoader.h
+++ lib/Bitcode/Reader/MetadataLoader.h
@@ -82,6 +82,9 @@
 
   /// 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
@@ -588,6 +588,25 @@
   unsigned size() const { return MetadataList.size(); }
   void shrinkTo(unsigned N) { MetadataList.shrinkTo(N); }
   void upgradeDebugIntrinsics(Function &F) { upgradeDeclareExpressions(F); }
+
+  void upgradeThumbMode(Function &F) {
+    const Triple TT(TheModule.getTargetTriple());
+    if (TT.getArch() != Triple::thumb && TT.getArch() != Triple::thumbeb &&
+        TT.getArch() != Triple::arm && TT.getArch() != Triple::armeb)
+      return;
+
+    std::string TargetFeatures;
+    if (F.hasFnAttribute("target-features"))
+      TargetFeatures = F.getFnAttribute("target-features").getValueAsString();
+    if (TargetFeatures.find("thumb-mode") != std::string::npos)
+      return;
+
+    bool isArm = TT.getArch() == Triple::arm || TT.getArch() == Triple::armeb;
+    TargetFeatures += TargetFeatures.empty() ? "" : ",";
+    TargetFeatures += isArm ? "-" : "+";
+    TargetFeatures += "thumb-mode";
+    F.addFnAttr("target-features", TargetFeatures);
+  }
 };
 
 static Error error(const Twine &Message) {
@@ -1911,3 +1930,7 @@
 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 +1,18 @@
+; RUN: llvm-dis -o - %s.bc | FileCheck %s
+
+target triple = "arm-apple-ios"
+
+define void @foo() #0 {
+  ret void
+}
+define void @bar() {
+  ret void
+}
+
+attributes #0 = { "target-features"="+thumb-mode" }
+
+; CHECK: void @foo() [[ThumbModeAttr:#[0-7]]]
+; CHECK: void @bar() [[NoThumbModeAttr:#[0-7]]]
+
+; CHECK: attributes [[ThumbModeAttr]] = { "target-features"="+thumb-mode" }
+; 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 +1,18 @@
+; RUN: llvm-dis -o - %s.bc | FileCheck %s
+
+target triple = "thumb-apple-ios"
+
+define void @foo() #0 {
+  ret void
+}
+define void @bar() {
+  ret void
+}
+
+attributes #0 = { "target-features"="-thumb-mode" }
+
+; CHECK: void @foo() [[NoThumbModeAttr:#[0-7]]]
+; CHECK: void @bar() [[ThumbModeAttr:#[0-7]]]
+
+; CHECK: attributes [[NoThumbModeAttr]] = { "target-features"="-thumb-mode" }
+; CHECK: attributes [[ThumbModeAttr]] = { "target-features"="+thumb-mode" }