Revert "[ADT] Make Twine's copy constructor private."

This reverts commit 4e4ee1c507e2707bb3c208e1e1b6551c3015cbf5.

This is failing due to some code that isn't built on MSVC
so I didn't catch.  Not immediately obvious how to fix this
at first glance, so I'm reverting for now.

llvm-svn: 315536

24 files changed, 110 insertions, 129 deletions

diff --git a/clang/include/clang/Tooling/CompilationDatabase.h b/clang/include/clang/Tooling/CompilationDatabase.h
index d63afef1217..28af33a407d 100644
--- a/clang/include/clang/Tooling/CompilationDatabase.h
+++ b/clang/include/clang/Tooling/CompilationDatabase.h
@@ -42,10 +42,12 @@ namespace tooling {
 /// \brief Specifies the working directory and command of a compilation.
 struct CompileCommand {
   CompileCommand() {}
-  CompileCommand(const Twine &Directory, const Twine &Filename,
-                 std::vector<std::string> CommandLine, const Twine &Output)
-      : Directory(Directory.str()), Filename(Filename.str()),
-        CommandLine(std::move(CommandLine)), Output(Output.str()) {}
+  CompileCommand(Twine Directory, Twine Filename,
+                 std::vector<std::string> CommandLine, Twine Output)
+      : Directory(Directory.str()),
+        Filename(Filename.str()),
+        CommandLine(std::move(CommandLine)),
+        Output(Output.str()){}
 
   /// \brief The working directory the command was executed from.
   std::string Directory;
@@ -176,14 +178,13 @@ public:
   /// \param Argv Points to the command line arguments.
   /// \param ErrorMsg Contains error text if the function returns null pointer.
   /// \param Directory The base directory used in the FixedCompilationDatabase.
-  static std::unique_ptr<FixedCompilationDatabase>
-  loadFromCommandLine(int &Argc, const char *const *Argv, std::string &ErrorMsg,
-                      const Twine &Directory = ".");
+  static std::unique_ptr<FixedCompilationDatabase> loadFromCommandLine(
+      int &Argc, const char *const *Argv, std::string &ErrorMsg,
+      Twine Directory = ".");
 
   /// \brief Constructs a compilation data base from a specified directory
   /// and command line.
-  FixedCompilationDatabase(const Twine &Directory,
-                           ArrayRef<std::string> CommandLine);
+  FixedCompilationDatabase(Twine Directory, ArrayRef<std::string> CommandLine);
 
   /// \brief Returns the given compile command.
   ///
diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index 97a337a96fb..98435fefbd2 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -981,17 +981,17 @@ protected:
 
   /// EmitPropertyList - Emit the given property list. The return
   /// value has type PropertyListPtrTy.
-  llvm::Constant *EmitPropertyList(const Twine &Name, const Decl *Container,
+  llvm::Constant *EmitPropertyList(Twine Name,
+                                   const Decl *Container,
                                    const ObjCContainerDecl *OCD,
                                    const ObjCCommonTypesHelper &ObjCTypes,
                                    bool IsClassProperty);
 
   /// EmitProtocolMethodTypes - Generate the array of extended method type 
   /// strings. The return value has type Int8PtrPtrTy.
-  llvm::Constant *
-  EmitProtocolMethodTypes(const Twine &Name,
-                          ArrayRef<llvm::Constant *> MethodTypes,
-                          const ObjCCommonTypesHelper &ObjCTypes);
+  llvm::Constant *EmitProtocolMethodTypes(Twine Name, 
+                                          ArrayRef<llvm::Constant*> MethodTypes,
+                                       const ObjCCommonTypesHelper &ObjCTypes);
 
   /// GetProtocolRef - Return a reference to the internal protocol
   /// description, creating an empty one if it has not been
@@ -1021,11 +1021,11 @@ public:
   /// \param Align - The alignment for the variable, or 0.
   /// \param AddToUsed - Whether the variable should be added to
   ///   "llvm.used".
-  llvm::GlobalVariable *CreateMetadataVar(const Twine &Name,
+  llvm::GlobalVariable *CreateMetadataVar(Twine Name,
                                           ConstantStructBuilder &Init,
                                           StringRef Section, CharUnits Align,
                                           bool AddToUsed);
-  llvm::GlobalVariable *CreateMetadataVar(const Twine &Name,
+  llvm::GlobalVariable *CreateMetadataVar(Twine Name,
                                           llvm::Constant *Init,
                                           StringRef Section, CharUnits Align,
                                           bool AddToUsed);
@@ -1241,7 +1241,7 @@ private:
 
   /// EmitMethodList - Emit the method list for the given
   /// implementation. The return value has type MethodListPtrTy.
-  llvm::Constant *emitMethodList(const Twine &Name, MethodListType MLT,
+  llvm::Constant *emitMethodList(Twine Name, MethodListType MLT,
                                  ArrayRef<const ObjCMethodDecl *> Methods);
 
   /// GetOrEmitProtocol - Get the protocol object for the given
@@ -1265,7 +1265,7 @@ private:
 
   /// EmitProtocolList - Generate the list of referenced
   /// protocols. The return value has type ProtocolListPtrTy.
-  llvm::Constant *EmitProtocolList(const Twine &Name,
+  llvm::Constant *EmitProtocolList(Twine Name,
                                    ObjCProtocolDecl::protocol_iterator begin,
                                    ObjCProtocolDecl::protocol_iterator end);
 
@@ -1413,7 +1413,7 @@ private:
 
   /// Emit the method list for the given implementation. The return value
   /// has type MethodListnfABITy.
-  llvm::Constant *emitMethodList(const Twine &Name, MethodListType MLT,
+  llvm::Constant *emitMethodList(Twine Name, MethodListType MLT,
                                  ArrayRef<const ObjCMethodDecl *> Methods);
 
   /// EmitIvarList - Emit the ivar list for the given
@@ -1440,7 +1440,7 @@ private:
 
   /// EmitProtocolList - Generate the list of referenced
   /// protocols. The return value has type ProtocolListPtrTy.
-  llvm::Constant *EmitProtocolList(const Twine &Name,
+  llvm::Constant *EmitProtocolList(Twine Name,
                                    ObjCProtocolDecl::protocol_iterator begin,
                                    ObjCProtocolDecl::protocol_iterator end);
 
@@ -3057,7 +3057,7 @@ CGObjCMac::EmitProtocolExtension(const ObjCProtocolDecl *PD,
   };
 */
 llvm::Constant *
-CGObjCMac::EmitProtocolList(const Twine &Name,
+CGObjCMac::EmitProtocolList(Twine name,
                             ObjCProtocolDecl::protocol_iterator begin,
                             ObjCProtocolDecl::protocol_iterator end) {
   // Just return null for empty protocol lists
@@ -3090,7 +3090,7 @@ CGObjCMac::EmitProtocolList(const Twine &Name,
     section = "__OBJC,__cat_cls_meth,regular,no_dead_strip";
 
   llvm::GlobalVariable *GV =
-      CreateMetadataVar(Name, values, section, CGM.getPointerAlign(), false);
+      CreateMetadataVar(name, values, section, CGM.getPointerAlign(), false);
   return llvm::ConstantExpr::getBitCast(GV, ObjCTypes.ProtocolListPtrTy);
 }
 
@@ -3123,9 +3123,11 @@ PushProtocolProperties(llvm::SmallPtrSet<const IdentifierInfo*,16> &PropertySet,
     struct _objc_property[prop_count];
   };
 */
-llvm::Constant *CGObjCCommonMac::EmitPropertyList(
-    const Twine &Name, const Decl *Container, const ObjCContainerDecl *OCD,
-    const ObjCCommonTypesHelper &ObjCTypes, bool IsClassProperty) {
+llvm::Constant *CGObjCCommonMac::EmitPropertyList(Twine Name,
+                                       const Decl *Container,
+                                       const ObjCContainerDecl *OCD,
+                                       const ObjCCommonTypesHelper &ObjCTypes,
+                                       bool IsClassProperty) {
   if (IsClassProperty) {
     // Make this entry NULL for OS X with deployment target < 10.11, for iOS
     // with deployment target < 9.0.
@@ -3196,9 +3198,10 @@ llvm::Constant *CGObjCCommonMac::EmitPropertyList(
   return llvm::ConstantExpr::getBitCast(GV, ObjCTypes.PropertyListPtrTy);
 }
 
-llvm::Constant *CGObjCCommonMac::EmitProtocolMethodTypes(
-    const Twine &Name, ArrayRef<llvm::Constant *> MethodTypes,
-    const ObjCCommonTypesHelper &ObjCTypes) {
+llvm::Constant *
+CGObjCCommonMac::EmitProtocolMethodTypes(Twine Name,
+                                         ArrayRef<llvm::Constant*> MethodTypes,
+                                         const ObjCCommonTypesHelper &ObjCTypes) {
   // Return null for empty list.
   if (MethodTypes.empty())
     return llvm::Constant::getNullValue(ObjCTypes.Int8PtrPtrTy);
@@ -3759,9 +3762,8 @@ void CGObjCMac::emitMethodConstant(ConstantArrayBuilder &builder,
 ///   int count;
 ///   struct objc_method_description list[count];
 /// };
-llvm::Constant *
-CGObjCMac::emitMethodList(const Twine &Name, MethodListType MLT,
-                          ArrayRef<const ObjCMethodDecl *> methods) {
+llvm::Constant *CGObjCMac::emitMethodList(Twine name, MethodListType MLT,
+                                 ArrayRef<const ObjCMethodDecl *> methods) {
   StringRef prefix;
   StringRef section;
   bool forProtocol = false;
@@ -3826,7 +3828,7 @@ CGObjCMac::emitMethodList(const Twine &Name, MethodListType MLT,
     }
     methodArray.finishAndAddTo(values);
 
-    llvm::GlobalVariable *GV = CreateMetadataVar(prefix + Name, values, section,
+    llvm::GlobalVariable *GV = CreateMetadataVar(prefix + name, values, section,
                                                  CGM.getPointerAlign(), true);
     return llvm::ConstantExpr::getBitCast(GV,
                                           ObjCTypes.MethodDescriptionListPtrTy);
@@ -3843,7 +3845,7 @@ CGObjCMac::emitMethodList(const Twine &Name, MethodListType MLT,
   }
   methodArray.finishAndAddTo(values);
 
-  llvm::GlobalVariable *GV = CreateMetadataVar(prefix + Name, values, section,
+  llvm::GlobalVariable *GV = CreateMetadataVar(prefix + name, values, section,
                                                CGM.getPointerAlign(), true);
   return llvm::ConstantExpr::getBitCast(GV, ObjCTypes.MethodListPtrTy);
 }
@@ -3866,9 +3868,11 @@ llvm::Function *CGObjCCommonMac::GenerateMethod(const ObjCMethodDecl *OMD,
   return Method;
 }
 
-llvm::GlobalVariable *CGObjCCommonMac::CreateMetadataVar(
-    const Twine &Name, ConstantStructBuilder &Init, StringRef Section,
-    CharUnits Align, bool AddToUsed) {
+llvm::GlobalVariable *CGObjCCommonMac::CreateMetadataVar(Twine Name,
+                                               ConstantStructBuilder &Init,
+                                                         StringRef Section,
+                                                         CharUnits Align,
+                                                         bool AddToUsed) {
   llvm::GlobalVariable *GV =
     Init.finishAndCreateGlobal(Name, Align, /*constant*/ false,
                                llvm::GlobalValue::PrivateLinkage);
@@ -3879,7 +3883,7 @@ llvm::GlobalVariable *CGObjCCommonMac::CreateMetadataVar(
   return GV;
 }
 
-llvm::GlobalVariable *CGObjCCommonMac::CreateMetadataVar(const Twine &Name,
+llvm::GlobalVariable *CGObjCCommonMac::CreateMetadataVar(Twine Name,
                                                          llvm::Constant *Init,
                                                          StringRef Section,
                                                          CharUnits Align,
@@ -6522,9 +6526,9 @@ void CGObjCNonFragileABIMac::emitMethodConstant(ConstantArrayBuilder &builder,
 ///   struct _objc_method method_list[method_count];
 /// }
 ///
-llvm::Constant *CGObjCNonFragileABIMac::emitMethodList(
-    const Twine &Name, MethodListType kind,
-    ArrayRef<const ObjCMethodDecl *> methods) {
+llvm::Constant *
+CGObjCNonFragileABIMac::emitMethodList(Twine name, MethodListType kind,
+                              ArrayRef<const ObjCMethodDecl *> methods) {
   // Return null for empty list.
   if (methods.empty())
     return llvm::Constant::getNullValue(ObjCTypes.MethodListnfABIPtrTy);
@@ -6581,7 +6585,7 @@ llvm::Constant *CGObjCNonFragileABIMac::emitMethodList(
   }
   methodArray.finishAndAddTo(values);
 
-  auto *GV = values.finishAndCreateGlobal(prefix + Name, CGM.getPointerAlign(),
+  auto *GV = values.finishAndCreateGlobal(prefix + name, CGM.getPointerAlign(),
                                           /*constant*/ false,
                                           llvm::GlobalValue::PrivateLinkage);
   if (CGM.getTriple().isOSBinFormatMachO())
@@ -6868,9 +6872,10 @@ llvm::Constant *CGObjCNonFragileABIMac::GetOrEmitProtocol(
 /// }
 /// @endcode
 ///
-llvm::Constant *CGObjCNonFragileABIMac::EmitProtocolList(
-    const Twine &Name, ObjCProtocolDecl::protocol_iterator begin,
-    ObjCProtocolDecl::protocol_iterator end) {
+llvm::Constant *
+CGObjCNonFragileABIMac::EmitProtocolList(Twine Name,
+                                      ObjCProtocolDecl::protocol_iterator begin,
+                                      ObjCProtocolDecl::protocol_iterator end) {
   SmallVector<llvm::Constant *, 16> ProtocolRefs;
 
   // Just return null for empty protocol lists
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index cdaa1fd42ac..7f9c3771f14 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -586,7 +586,7 @@ void BackendConsumer::UnsupportedDiagHandler(
   FullSourceLoc Loc =
       getBestLocationFromDebugLoc(D, BadDebugInfo, Filename, Line, Column);
 
-  Diags.Report(Loc, diag::err_fe_backend_unsupported) << D.getMessage();
+  Diags.Report(Loc, diag::err_fe_backend_unsupported) << D.getMessage().str();
 
   if (BadDebugInfo)
     // If we were not able to translate the file:line:col information
diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
index b0e2a7605eb..ae41ee9e22c 100644
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -369,7 +369,7 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
     SmallString<128> ImplibName(Output.getFilename());
     llvm::sys::path::replace_extension(ImplibName, "lib");
-    CmdArgs.push_back(Args.MakeArgString(Twine("-implib:") + ImplibName));
+    CmdArgs.push_back(Args.MakeArgString(std::string("-implib:") + ImplibName));
   }
 
   if (TC.getSanitizerArgs().needsAsanRt()) {
diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
index 72a0ac4cf90..660b0c798ec 100644
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -479,7 +479,7 @@ void toolchains::MinGW::AddClangCXXStdlibIncludeArgs(
     for (auto &CppIncludeBase : CppIncludeBases) {
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase);
       CppIncludeBase += llvm::sys::path::get_separator();
-      addSystemInclude(DriverArgs, CC1Args, Twine(CppIncludeBase) + Arch);
+      addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + Arch);
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase + "backward");
     }
     break;
diff --git a/clang/lib/Tooling/CompilationDatabase.cpp b/clang/lib/Tooling/CompilationDatabase.cpp
index 121e0014499..0e835579e04 100644
--- a/clang/lib/Tooling/CompilationDatabase.cpp
+++ b/clang/lib/Tooling/CompilationDatabase.cpp
@@ -289,7 +289,7 @@ std::unique_ptr<FixedCompilationDatabase>
 FixedCompilationDatabase::loadFromCommandLine(int &Argc,
                                               const char *const *Argv,
                                               std::string &ErrorMsg,
-                                              const Twine &Directory) {
+                                              Twine Directory) {
   ErrorMsg.clear();
   if (Argc == 0)
     return nullptr;
@@ -306,8 +306,8 @@ FixedCompilationDatabase::loadFromCommandLine(int &Argc,
       new FixedCompilationDatabase(Directory, StrippedArgs));
 }
 
-FixedCompilationDatabase::FixedCompilationDatabase(
-    const Twine &Directory, ArrayRef<std::string> CommandLine) {
+FixedCompilationDatabase::
+FixedCompilationDatabase(Twine Directory, ArrayRef<std::string> CommandLine) {
   std::vector<std::string> ToolCommandLine(1, "clang-tool");
   ToolCommandLine.insert(ToolCommandLine.end(),
                          CommandLine.begin(), CommandLine.end());
diff --git a/clang/unittests/Tooling/TestVisitor.h b/clang/unittests/Tooling/TestVisitor.h
index a3a50cf0d49..fb6a76ccadd 100644
--- a/clang/unittests/Tooling/TestVisitor.h
+++ b/clang/unittests/Tooling/TestVisitor.h
@@ -128,7 +128,7 @@ public:
   /// \brief Expect 'Match' *not* to occur at the given 'Line' and 'Column'.
   ///
   /// Any number of matches can be disallowed.
-  void DisallowMatch(const Twine &Match, unsigned Line, unsigned Column) {
+  void DisallowMatch(Twine Match, unsigned Line, unsigned Column) {
     DisallowedMatches.push_back(MatchCandidate(Match, Line, Column));
   }
 
@@ -138,7 +138,7 @@ public:
   /// Each is expected to be matched 'Times' number of times. (This is useful in
   /// cases in which different AST nodes can match at the same source code
   /// location.)
-  void ExpectMatch(const Twine &Match, unsigned Line, unsigned Column,
+  void ExpectMatch(Twine Match, unsigned Line, unsigned Column,
                    unsigned Times = 1) {
     ExpectedMatches.push_back(ExpectedMatch(Match, Line, Column, Times));
   }
@@ -180,10 +180,10 @@ protected:
     unsigned LineNumber;
     unsigned ColumnNumber;
 
-    MatchCandidate(const Twine &Name, unsigned LineNumber,
-                   unsigned ColumnNumber)
-        : ExpectedName(Name.str()), LineNumber(LineNumber),
-          ColumnNumber(ColumnNumber) {}
+    MatchCandidate(Twine Name, unsigned LineNumber, unsigned ColumnNumber)
+      : ExpectedName(Name.str()), LineNumber(LineNumber),
+        ColumnNumber(ColumnNumber) {
+    }
 
     bool Matches(StringRef Name, FullSourceLoc const &Location) const {
       return MatchesName(Name) && MatchesLocation(Location);
@@ -211,7 +211,7 @@ protected:
   };
 
   struct ExpectedMatch {
-    ExpectedMatch(const Twine &Name, unsigned LineNumber, unsigned ColumnNumber,
+    ExpectedMatch(Twine Name, unsigned LineNumber, unsigned ColumnNumber,
                   unsigned Times)
         : Candidate(Name, LineNumber, ColumnNumber), TimesExpected(Times),
           TimesSeen(0) {}
diff --git a/llvm/include/llvm/ADT/Twine.h b/llvm/include/llvm/ADT/Twine.h
index c9cefa982d6..f5f00dcfafe 100644
--- a/llvm/include/llvm/ADT/Twine.h
+++ b/llvm/include/llvm/ADT/Twine.h
@@ -79,10 +79,6 @@ namespace llvm {
   /// overloads) to guarantee that particularly important cases (cstring plus
   /// StringRef) codegen as desired.
   class Twine {
-    friend Twine operator+(const char *LHS, const StringRef &RHS);
-    friend Twine operator+(const StringRef &LHS, const char *RHS);
-    friend Twine operator+(const StringRef &LHS, const StringRef &RHS);
-
     /// NodeKind - Represent the type of an argument.
     enum NodeKind : unsigned char {
       /// An empty string; the result of concatenating anything with it is also
@@ -173,12 +169,6 @@ namespace llvm {
       assert(isNullary() && "Invalid kind!");
     }
 
-    // While there are some valid use cases for copying Twines, most of them
-    // are confined to the implementation of Twine itself, and Twine itself is
-    // not intended to be publicly copyable since it can very easily lead to
-    // dangling pointers / references.
-    Twine(const Twine &) = default;
-
     /// Construct a binary twine.
     explicit Twine(const Twine &LHS, const Twine &RHS)
         : LHSKind(TwineKind), RHSKind(TwineKind) {
@@ -266,6 +256,8 @@ namespace llvm {
       assert(isValid() && "Invalid twine!");
     }
 
+    Twine(const Twine &) = default;
+
     /// Construct from a C string.
     ///
     /// We take care here to optimize "" into the empty twine -- this will be
@@ -282,8 +274,6 @@ namespace llvm {
       assert(isValid() && "Invalid twine!");
     }
 
-    Twine(Twine &&Other) = default;
-
     /// Construct from an std::string.
     /*implicit*/ Twine(const std::string &Str)
       : LHSKind(StdStringKind), RHSKind(EmptyKind) {
@@ -387,14 +377,6 @@ namespace llvm {
       assert(isValid() && "Invalid twine!");
     }
 
-    /// Construct as the concatenation of two StringRefs.
-    /*implicit*/ Twine(const StringRef &LHS, const StringRef &RHS)
-        : LHSKind(StringRefKind), RHSKind(StringRefKind) {
-      this->LHS.stringRef = &LHS;
-      this->RHS.stringRef = &RHS;
-      assert(isValid() && "Invalid twine!");
-    }
-
     /// Since the intended use of twines is as temporary objects, assignments
     /// when concatenating might cause undefined behavior or stack corruptions
     Twine &operator=(const Twine &) = delete;
@@ -505,10 +487,6 @@ namespace llvm {
     /// Dump the representation of this twine to stderr.
     void dumpRepr() const;
 
-    friend inline Twine operator+(const Twine &LHS, const Twine &RHS) {
-      return LHS.concat(RHS);
-    }
-
     /// @}
   };
 
@@ -544,6 +522,10 @@ namespace llvm {
     return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
   }
 
+  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
+    return LHS.concat(RHS);
+  }
+
   /// Additional overload to guarantee simplified codegen; this is equivalent to
   /// concat().
 
@@ -551,11 +533,10 @@ namespace llvm {
     return Twine(LHS, RHS);
   }
 
-  inline Twine operator+(const StringRef &LHS, const char *RHS) {
-    return Twine(LHS, RHS);
-  }
+  /// Additional overload to guarantee simplified codegen; this is equivalent to
+  /// concat().
 
-  inline Twine operator+(const StringRef &LHS, const StringRef &RHS) {
+  inline Twine operator+(const StringRef &LHS, const char *RHS) {
     return Twine(LHS, RHS);
   }
 
diff --git a/llvm/include/llvm/IR/DiagnosticInfo.h b/llvm/include/llvm/IR/DiagnosticInfo.h
index 0ce9c2f9b11..020b67d6b71 100644
--- a/llvm/include/llvm/IR/DiagnosticInfo.h
+++ b/llvm/include/llvm/IR/DiagnosticInfo.h
@@ -962,7 +962,7 @@ public:
 /// Diagnostic information for unsupported feature in backend.
 class DiagnosticInfoUnsupported : public DiagnosticInfoWithLocationBase {
 private:
-  std::string Msg;
+  Twine Msg;
 
 public:
   /// \p Fn is the function where the diagnostic is being emitted. \p Loc is
@@ -976,13 +976,13 @@ public:
       const DiagnosticLocation &Loc = DiagnosticLocation(),
       DiagnosticSeverity Severity = DS_Error)
       : DiagnosticInfoWithLocationBase(DK_Unsupported, Severity, Fn, Loc),
-        Msg(Msg.str()) {}
+        Msg(Msg) {}
 
   static bool classof(const DiagnosticInfo *DI) {
     return DI->getKind() == DK_Unsupported;
   }
 
-  StringRef getMessage() const { return Msg; }
+  const Twine &getMessage() const { return Msg; }
 
   void print(DiagnosticPrinter &DP) const override;
 };
diff --git a/llvm/include/llvm/Object/Error.h b/llvm/include/llvm/Object/Error.h
index ef820bdba31..eb938338715 100644
--- a/llvm/include/llvm/Object/Error.h
+++ b/llvm/include/llvm/Object/Error.h
@@ -65,8 +65,8 @@ public:
 class GenericBinaryError : public ErrorInfo<GenericBinaryError, BinaryError> {
 public:
   static char ID;
-  GenericBinaryError(const Twine &Msg);
-  GenericBinaryError(const Twine &Msg, object_error ECOverride);
+  GenericBinaryError(Twine Msg);
+  GenericBinaryError(Twine Msg, object_error ECOverride);
   const std::string &getMessage() const { return Msg; }
   void log(raw_ostream &OS) const override;
 private:
diff --git a/llvm/include/llvm/Object/WindowsResource.h b/llvm/include/llvm/Object/WindowsResource.h
index bf17ad3f8a8..05fe10a770e 100644
--- a/llvm/include/llvm/Object/WindowsResource.h
+++ b/llvm/include/llvm/Object/WindowsResource.h
@@ -87,7 +87,7 @@ struct WinResHeaderSuffix {
 
 class EmptyResError : public GenericBinaryError {
 public:
-  EmptyResError(const Twine &Msg, object_error ECOverride)
+  EmptyResError(Twine Msg, object_error ECOverride)
       : GenericBinaryError(Msg, ECOverride) {}
 };
 
diff --git a/llvm/include/llvm/Support/Error.h b/llvm/include/llvm/Support/Error.h
index 63d441fa58e..bb40dbee053 100644
--- a/llvm/include/llvm/Support/Error.h
+++ b/llvm/include/llvm/Support/Error.h
@@ -931,7 +931,7 @@ Expected<T> handleExpected(Expected<T> ValOrErr, RecoveryFtor &&RecoveryPath,
 /// This is useful in the base level of your program to allow clean termination
 /// (allowing clean deallocation of resources, etc.), while reporting error
 /// information to the user.
-void logAllUnhandledErrors(Error E, raw_ostream &OS, const Twine &ErrorBanner);
+void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner);
 
 /// Write all error messages (if any) in E to a string. The newline character
 /// is used to separate error messages.
diff --git a/llvm/include/llvm/Support/FormatVariadicDetails.h b/llvm/include/llvm/Support/FormatVariadicDetails.h
index 9aa60089a80..b4a564ffc26 100644
--- a/llvm/include/llvm/Support/FormatVariadicDetails.h
+++ b/llvm/include/llvm/Support/FormatVariadicDetails.h
@@ -28,7 +28,7 @@ public:
 };
 
 template <typename T> class provider_format_adapter : public format_adapter {
-  T &Item;
+  T Item;
 
 public:
   explicit provider_format_adapter(T &&Item) : Item(Item) {}
diff --git a/llvm/lib/Object/Error.cpp b/llvm/lib/Object/Error.cpp
index d4ab9163886..7d43a84f3e0 100644
--- a/llvm/lib/Object/Error.cpp
+++ b/llvm/lib/Object/Error.cpp
@@ -60,10 +60,9 @@ std::string _object_error_category::message(int EV) const {
 char BinaryError::ID = 0;
 char GenericBinaryError::ID = 0;
 
-GenericBinaryError::GenericBinaryError(const Twine &Msg) : Msg(Msg.str()) {}
+GenericBinaryError::GenericBinaryError(Twine Msg) : Msg(Msg.str()) {}
 
-GenericBinaryError::GenericBinaryError(const Twine &Msg,
-                                       object_error ECOverride)
+GenericBinaryError::GenericBinaryError(Twine Msg, object_error ECOverride)
     : Msg(Msg.str()) {
   setErrorCode(make_error_code(ECOverride));
 }
diff --git a/llvm/lib/Support/Error.cpp b/llvm/lib/Support/Error.cpp
index fe8ffd817f4..bb02c03ff2b 100644
--- a/llvm/lib/Support/Error.cpp
+++ b/llvm/lib/Support/Error.cpp
@@ -54,7 +54,7 @@ char ErrorList::ID = 0;
 char ECError::ID = 0;
 char StringError::ID = 0;
 
-void logAllUnhandledErrors(Error E, raw_ostream &OS, const Twine &ErrorBanner) {
+void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner) {
   if (!E)
     return;
   OS << ErrorBanner;
diff --git a/llvm/lib/Support/Twine.cpp b/llvm/lib/Support/Twine.cpp
index bf434f34e43..d17cd4e6643 100644
--- a/llvm/lib/Support/Twine.cpp
+++ b/llvm/lib/Support/Twine.cpp
@@ -120,10 +120,12 @@ void Twine::printOneChildRepr(raw_ostream &OS, Child Ptr,
        << Ptr.cString << "\"";
     break;
   case Twine::StdStringKind:
-    OS << "std::string:\"" << *Ptr.stdString << "\"";
+    OS << "std::string:\""
+       << Ptr.stdString << "\"";
     break;
   case Twine::StringRefKind:
-    OS << "stringref:\"" << *Ptr.stringRef << "\"";
+    OS << "stringref:\""
+       << Ptr.stringRef << "\"";
     break;
   case Twine::SmallStringKind:
     OS << "smallstring:\"" << *Ptr.smallString << "\"";
diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index c64c0408758..b968cb8c892 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -130,15 +130,18 @@ namespace {
 class IRBuilderPrefixedInserter : public IRBuilderDefaultInserter {
   std::string Prefix;
 
+  const Twine getNameWithPrefix(const Twine &Name) const {
+    return Name.isTriviallyEmpty() ? Name : Prefix + Name;
+  }
+
 public:
   void SetNamePrefix(const Twine &P) { Prefix = P.str(); }
 
 protected:
   void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB,
                     BasicBlock::iterator InsertPt) const {
-    const Twine &Prefixed = Prefix + Name;
-    IRBuilderDefaultInserter::InsertHelper(
-        I, Name.isTriviallyEmpty() ? Name : Prefixed, BB, InsertPt);
+    IRBuilderDefaultInserter::InsertHelper(I, getNameWithPrefix(Name), BB,
+                                           InsertPt);
   }
 };
 
@@ -1352,8 +1355,7 @@ static void speculateSelectInstLoads(SelectInst &SI) {
 /// This will return the BasePtr if that is valid, or build a new GEP
 /// instruction using the IRBuilder if GEP-ing is needed.
 static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
-                       SmallVectorImpl<Value *> &Indices,
-                       const Twine &NamePrefix) {
+                       SmallVectorImpl<Value *> &Indices, Twine NamePrefix) {
   if (Indices.empty())
     return BasePtr;
 
@@ -1378,7 +1380,7 @@ static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
 static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
                                     Value *BasePtr, Type *Ty, Type *TargetTy,
                                     SmallVectorImpl<Value *> &Indices,
-                                    const Twine &NamePrefix) {
+                                    Twine NamePrefix) {
   if (Ty == TargetTy)
     return buildGEP(IRB, BasePtr, Indices, NamePrefix);
 
@@ -1423,7 +1425,7 @@ static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
                                        Value *Ptr, Type *Ty, APInt &Offset,
                                        Type *TargetTy,
                                        SmallVectorImpl<Value *> &Indices,
-                                       const Twine &NamePrefix) {
+                                       Twine NamePrefix) {
   if (Offset == 0)
     return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices,
                                  NamePrefix);
@@ -1496,7 +1498,7 @@ static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
 static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
                                       Value *Ptr, APInt Offset, Type *TargetTy,
                                       SmallVectorImpl<Value *> &Indices,
-                                      const Twine &NamePrefix) {
+                                      Twine NamePrefix) {
   PointerType *Ty = cast<PointerType>(Ptr->getType());
 
   // Don't consider any GEPs through an i8* as natural unless the TargetTy is
@@ -1534,8 +1536,7 @@ static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
 /// a single GEP as possible, thus making each GEP more independent of the
 /// surrounding code.
 static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr,
-                             APInt Offset, Type *PointerTy,
-                             const Twine &NamePrefix) {
+                             APInt Offset, Type *PointerTy, Twine NamePrefix) {
   // Even though we don't look through PHI nodes, we could be called on an
   // instruction in an unreachable block, which may be on a cycle.
   SmallPtrSet<Value *, 4> Visited;
diff --git a/llvm/tools/llvm-nm/llvm-nm.cpp b/llvm/tools/llvm-nm/llvm-nm.cpp
index 6b9ae463979..4ad0d95d67f 100644
--- a/llvm/tools/llvm-nm/llvm-nm.cpp
+++ b/llvm/tools/llvm-nm/llvm-nm.cpp
@@ -195,12 +195,12 @@ bool HadError = false;
 std::string ToolName;
 } // anonymous namespace
 
-static void error(const Twine &Message, const Twine &Path = Twine()) {
+static void error(Twine Message, Twine Path = Twine()) {
   HadError = true;
   errs() << ToolName << ": " << Path << ": " << Message << ".\n";
 }
 
-static bool error(std::error_code EC, const Twine &Path = Twine()) {
+static bool error(std::error_code EC, Twine Path = Twine()) {
   if (EC) {
     error(EC.message(), Path);
     return true;
diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
index f4c159cd1cb..f9acf001ae9 100644
--- a/llvm/tools/llvm-objcopy/Object.cpp
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -428,15 +428,15 @@ void initRelocations(RelocationSection<ELFT> *Relocs,
   }
 }
 
-SectionBase *SectionTableRef::getSection(uint16_t Index, const Twine &ErrMsg) {
+SectionBase *SectionTableRef::getSection(uint16_t Index, Twine ErrMsg) {
   if (Index == SHN_UNDEF || Index > Sections.size())
     error(ErrMsg);
   return Sections[Index - 1].get();
 }
 
 template <class T>
-T *SectionTableRef::getSectionOfType(uint16_t Index, const Twine &IndexErrMsg,
-                                     const Twine &TypeErrMsg) {
+T *SectionTableRef::getSectionOfType(uint16_t Index, Twine IndexErrMsg,
+                                     Twine TypeErrMsg) {
   if (T *Sec = llvm::dyn_cast<T>(getSection(Index, IndexErrMsg)))
     return Sec;
   error(TypeErrMsg);
diff --git a/llvm/tools/llvm-objcopy/Object.h b/llvm/tools/llvm-objcopy/Object.h
index d266912db0b..f6088434805 100644
--- a/llvm/tools/llvm-objcopy/Object.h
+++ b/llvm/tools/llvm-objcopy/Object.h
@@ -29,11 +29,11 @@ public:
       : Sections(Secs) {}
   SectionTableRef(const SectionTableRef &) = default;
 
-  SectionBase *getSection(uint16_t Index, const llvm::Twine &ErrMsg);
+  SectionBase *getSection(uint16_t Index, llvm::Twine ErrMsg);
 
   template <class T>
-  T *getSectionOfType(uint16_t Index, const llvm::Twine &IndexErrMsg,
-                      const llvm::Twine &TypeErrMsg);
+  T *getSectionOfType(uint16_t Index, llvm::Twine IndexErrMsg,
+                      llvm::Twine TypeErrMsg);
 };
 
 class SectionBase {
diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
index 9fc2897959c..7f55a434b33 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -27,7 +27,7 @@ static StringRef ToolName;
 
 namespace llvm {
 
-LLVM_ATTRIBUTE_NORETURN void error(const Twine &Message) {
+LLVM_ATTRIBUTE_NORETURN void error(Twine Message) {
   errs() << ToolName << ": " << Message << ".\n";
   errs().flush();
   exit(1);
diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.h b/llvm/tools/llvm-objcopy/llvm-objcopy.h
index d30b43a46a4..de7bf367ac8 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.h
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.h
@@ -14,7 +14,7 @@
 
 namespace llvm {
 
-LLVM_ATTRIBUTE_NORETURN extern void error(const Twine &Message);
+LLVM_ATTRIBUTE_NORETURN extern void error(Twine Message);
 
 // This is taken from llvm-readobj.
 // [see here](llvm/tools/llvm-readobj/llvm-readobj.h:38)
diff --git a/llvm/unittests/ADT/TwineTest.cpp b/llvm/unittests/ADT/TwineTest.cpp
index ebe06917cee..950eda2b058 100644
--- a/llvm/unittests/ADT/TwineTest.cpp
+++ b/llvm/unittests/ADT/TwineTest.cpp
@@ -88,14 +88,6 @@ TEST(TwineTest, Concat) {
             repr(Twine("a").concat(Twine(SmallString<3>("b")).concat(Twine("c")))));
 }
 
-TEST(TwineTest, Operators) {
-  EXPECT_EQ(R"((Twine cstring:"a" stringref:"b"))", repr("a" + StringRef("b")));
-
-  EXPECT_EQ(R"((Twine stringref:"a" cstring:"b"))", repr(StringRef("a") + "b"));
-  EXPECT_EQ(R"((Twine stringref:"a" stringref:"b"))",
-            repr(StringRef("a") + StringRef("b")));
-}
-
 TEST(TwineTest, toNullTerminatedStringRef) {
   SmallString<8> storage;
   EXPECT_EQ(0, *Twine("hello").toNullTerminatedStringRef(storage).end());
diff --git a/llvm/utils/TableGen/RegisterBankEmitter.cpp b/llvm/utils/TableGen/RegisterBankEmitter.cpp
index 36f66f4fe8b..293933ffb8d 100644
--- a/llvm/utils/TableGen/RegisterBankEmitter.cpp
+++ b/llvm/utils/TableGen/RegisterBankEmitter.cpp
@@ -169,7 +169,7 @@ void RegisterBankEmitter::emitBaseClassDefinition(
 ///                to the class.
 static void visitRegisterBankClasses(
     CodeGenRegBank &RegisterClassHierarchy, const CodeGenRegisterClass *RC,
-    const Twine &Kind,
+    const Twine Kind,
     std::function<void(const CodeGenRegisterClass *, StringRef)> VisitFn,
     SmallPtrSetImpl<const CodeGenRegisterClass *> &VisitedRCs) {
 
@@ -183,7 +183,7 @@ static void visitRegisterBankClasses(
 
   for (const auto &PossibleSubclass : RegisterClassHierarchy.getRegClasses()) {
     std::string TmpKind =
-        (Kind + " (" + PossibleSubclass.getName() + ")").str();
+        (Twine(Kind) + " (" + PossibleSubclass.getName() + ")").str();
 
     // Visit each subclass of an explicitly named class.
     if (RC != &PossibleSubclass && RC->hasSubClass(&PossibleSubclass))