Apply most suggestions of clang-tidy's performance-unnecessary-value-param

Avoids unnecessary copies. All changes audited & pass tests with asan.
No functional change intended.

llvm-svn: 272190

48 files changed, 108 insertions, 108 deletions

diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
index cdb72b95ad7..bde05ff973e 100644
--- a/llvm/include/llvm/ADT/APInt.h
+++ b/llvm/include/llvm/ADT/APInt.h
@@ -177,7 +177,7 @@ class APInt {
   /// provides a more convenient form of divide for internal use since KnuthDiv
   /// has specific constraints on its inputs. If those constraints are not met
   /// then it provides a simpler form of divide.
-  static void divide(const APInt LHS, unsigned lhsWords, const APInt &RHS,
+  static void divide(const APInt &LHS, unsigned lhsWords, const APInt &RHS,
                      unsigned rhsWords, APInt *Quotient, APInt *Remainder);
 
   /// out-of-line slow case for inline constructor
diff --git a/llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h b/llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h
index 5724a11e601..bc6fb578f1f 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h
@@ -335,8 +335,8 @@ namespace llvm {
     /// where the value is not in the condition, thus computing the
     /// exit count.  If the iteration count can't be computed, an
     /// instance of SCEVCouldNotCompute is returned.
-    const SCEV *getNumIterationsInRange(ConstantRange Range,
-                                       ScalarEvolution &SE) const;
+    const SCEV *getNumIterationsInRange(const ConstantRange &Range,
+                                        ScalarEvolution &SE) const;
 
     /// Return an expression representing the value of this expression
     /// one iteration of the loop ahead.
diff --git a/llvm/include/llvm/Analysis/TargetLibraryInfo.h b/llvm/include/llvm/Analysis/TargetLibraryInfo.h
index a28e0fa739d..afe6d8b0377 100644
--- a/llvm/include/llvm/Analysis/TargetLibraryInfo.h
+++ b/llvm/include/llvm/Analysis/TargetLibraryInfo.h
@@ -315,7 +315,7 @@ private:
 
   StringMap<std::unique_ptr<TargetLibraryInfoImpl>> Impls;
 
-  TargetLibraryInfoImpl &lookupInfoImpl(Triple T);
+  TargetLibraryInfoImpl &lookupInfoImpl(const Triple &T);
 };
 
 class TargetLibraryInfoWrapperPass : public ImmutablePass {
diff --git a/llvm/include/llvm/DebugInfo/Symbolize/DIPrinter.h b/llvm/include/llvm/DebugInfo/Symbolize/DIPrinter.h
index 3098199bb4d..49f86eae01c 100644
--- a/llvm/include/llvm/DebugInfo/Symbolize/DIPrinter.h
+++ b/llvm/include/llvm/DebugInfo/Symbolize/DIPrinter.h
@@ -31,7 +31,7 @@ class DIPrinter {
   int PrintSourceContext;
 
   void print(const DILineInfo &Info, bool Inlined);
-  void printContext(std::string FileName, int64_t Line);
+  void printContext(const std::string &FileName, int64_t Line);
 
 public:
   DIPrinter(raw_ostream &OS, bool PrintFunctionNames = true,
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/IndirectionUtils.h b/llvm/include/llvm/ExecutionEngine/Orc/IndirectionUtils.h
index fe7a85ba020..51172c51e13 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/IndirectionUtils.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/IndirectionUtils.h
@@ -334,13 +334,14 @@ private:
 /// ErrorHandlerAddress will be used by the resulting compile callback
 /// manager if a compile callback fails.
 std::unique_ptr<JITCompileCallbackManager>
-createLocalCompileCallbackManager(Triple T, TargetAddress ErrorHandlerAddress);
+createLocalCompileCallbackManager(const Triple &T,
+                                  TargetAddress ErrorHandlerAddress);
 
 /// @brief Create a local indriect stubs manager builder.
 ///
 /// The given target triple will determine the ABI.
 std::function<std::unique_ptr<IndirectStubsManager>()>
-createLocalIndirectStubsManagerBuilder(Triple T);
+createLocalIndirectStubsManagerBuilder(const Triple &T);
 
 /// @brief Build a function pointer of FunctionType with the given constant
 ///        address.
diff --git a/llvm/include/llvm/LTO/LTOCodeGenerator.h b/llvm/include/llvm/LTO/LTOCodeGenerator.h
index e6a9fb1813f..d083e37d75b 100644
--- a/llvm/include/llvm/LTO/LTOCodeGenerator.h
+++ b/llvm/include/llvm/LTO/LTOCodeGenerator.h
@@ -77,7 +77,7 @@ struct LTOCodeGenerator {
   /// Resets \a HasVerifiedInput.
   void setModule(std::unique_ptr<LTOModule> M);
 
-  void setTargetOptions(TargetOptions Options);
+  void setTargetOptions(const TargetOptions &Options);
   void setDebugInfo(lto_debug_model);
   void setCodePICModel(Optional<Reloc::Model> Model) { RelocModel = Model; }
 
diff --git a/llvm/include/llvm/LTO/LTOModule.h b/llvm/include/llvm/LTO/LTOModule.h
index 0d89d819c50..2e46219be19 100644
--- a/llvm/include/llvm/LTO/LTOModule.h
+++ b/llvm/include/llvm/LTO/LTOModule.h
@@ -91,19 +91,22 @@ public:
   /// InitializeAllAsmPrinters();
   /// InitializeAllAsmParsers();
   static ErrorOr<std::unique_ptr<LTOModule>>
-  createFromFile(LLVMContext &Context, const char *path, TargetOptions options);
+  createFromFile(LLVMContext &Context, const char *path,
+                 const TargetOptions &options);
   static ErrorOr<std::unique_ptr<LTOModule>>
   createFromOpenFile(LLVMContext &Context, int fd, const char *path,
-                     size_t size, TargetOptions options);
+                     size_t size, const TargetOptions &options);
   static ErrorOr<std::unique_ptr<LTOModule>>
   createFromOpenFileSlice(LLVMContext &Context, int fd, const char *path,
-                          size_t map_size, off_t offset, TargetOptions options);
+                          size_t map_size, off_t offset,
+                          const TargetOptions &options);
   static ErrorOr<std::unique_ptr<LTOModule>>
   createFromBuffer(LLVMContext &Context, const void *mem, size_t length,
-                   TargetOptions options, StringRef path = "");
+                   const TargetOptions &options, StringRef path = "");
   static ErrorOr<std::unique_ptr<LTOModule>>
   createInLocalContext(std::unique_ptr<LLVMContext> Context, const void *mem,
-                       size_t length, TargetOptions options, StringRef path);
+                       size_t length, const TargetOptions &options,
+                       StringRef path);
 
   const Module &getModule() const {
     return const_cast<LTOModule*>(this)->getModule();
@@ -202,7 +205,7 @@ private:
 
   /// Create an LTOModule (private version).
   static ErrorOr<std::unique_ptr<LTOModule>>
-  makeLTOModule(MemoryBufferRef Buffer, TargetOptions options,
+  makeLTOModule(MemoryBufferRef Buffer, const TargetOptions &options,
                 LLVMContext &Context, bool ShouldBeLazy);
 };
 }
diff --git a/llvm/include/llvm/MC/MCObjectFileInfo.h b/llvm/include/llvm/MC/MCObjectFileInfo.h
index 0b1ec32bd1a..cef4e5b3eb9 100644
--- a/llvm/include/llvm/MC/MCObjectFileInfo.h
+++ b/llvm/include/llvm/MC/MCObjectFileInfo.h
@@ -356,9 +356,9 @@ private:
   MCContext *Ctx;
   Triple TT;
 
-  void initMachOMCObjectFileInfo(Triple T);
-  void initELFMCObjectFileInfo(Triple T);
-  void initCOFFMCObjectFileInfo(Triple T);
+  void initMachOMCObjectFileInfo(const Triple &T);
+  void initELFMCObjectFileInfo(const Triple &T);
+  void initCOFFMCObjectFileInfo(const Triple &T);
 
 public:
   const Triple &getTargetTriple() const { return TT; }
diff --git a/llvm/include/llvm/ProfileData/SampleProf.h b/llvm/include/llvm/ProfileData/SampleProf.h
index d731dec1c1c..9fefefa627b 100644
--- a/llvm/include/llvm/ProfileData/SampleProf.h
+++ b/llvm/include/llvm/ProfileData/SampleProf.h
@@ -204,8 +204,8 @@ public:
   }
   sampleprof_error addCalledTargetSamples(uint32_t LineOffset,
                                           uint32_t Discriminator,
-                                          std::string FName, uint64_t Num,
-                                          uint64_t Weight = 1) {
+                                          const std::string &FName,
+                                          uint64_t Num, uint64_t Weight = 1) {
     return BodySamples[LineLocation(LineOffset, Discriminator)].addCalledTarget(
         FName, Num, Weight);
   }
diff --git a/llvm/include/llvm/Support/CommandLine.h b/llvm/include/llvm/Support/CommandLine.h
index 943d2df3770..432ae267478 100644
--- a/llvm/include/llvm/Support/CommandLine.h
+++ b/llvm/include/llvm/Support/CommandLine.h
@@ -946,7 +946,7 @@ public:
   // getValueName - Overload in subclass to provide a better default value.
   const char *getValueName() const override { return "string"; }
 
-  void printOptionDiff(const Option &O, StringRef V, OptVal Default,
+  void printOptionDiff(const Option &O, StringRef V, const OptVal &Default,
                        size_t GlobalWidth) const;
 
   // An out-of-line virtual method to provide a 'home' for this class.
diff --git a/llvm/include/llvm/Support/ScopedPrinter.h b/llvm/include/llvm/Support/ScopedPrinter.h
index b9d8a8db1b6..a2f2e098543 100644
--- a/llvm/include/llvm/Support/ScopedPrinter.h
+++ b/llvm/include/llvm/Support/ScopedPrinter.h
@@ -190,7 +190,7 @@ public:
     startLine() << Label << ": " << int(Value) << "\n";
   }
 
-  void printNumber(StringRef Label, APSInt Value) {
+  void printNumber(StringRef Label, const APSInt &Value) {
     startLine() << Label << ": " << Value << "\n";
   }
 
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 3342bdffa39..796c872f014 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -1326,9 +1326,8 @@ bool DependenceInfo::weakCrossingSIVtest(
 // Computes the GCD of AM and BM.
 // Also finds a solution to the equation ax - by = gcd(a, b).
 // Returns true if dependence disproved; i.e., gcd does not divide Delta.
-static
-bool findGCD(unsigned Bits, APInt AM, APInt BM, APInt Delta,
-             APInt &G, APInt &X, APInt &Y) {
+static bool findGCD(unsigned Bits, const APInt &AM, const APInt &BM,
+                    const APInt &Delta, APInt &G, APInt &X, APInt &Y) {
   APInt A0(Bits, 1, true), A1(Bits, 0, true);
   APInt B0(Bits, 0, true), B1(Bits, 1, true);
   APInt G0 = AM.abs();
@@ -1357,9 +1356,7 @@ bool findGCD(unsigned Bits, APInt AM, APInt BM, APInt Delta,
   return false;
 }
 
-
-static
-APInt floorOfQuotient(APInt A, APInt B) {
+static APInt floorOfQuotient(const APInt &A, const APInt &B) {
   APInt Q = A; // these need to be initialized
   APInt R = A;
   APInt::sdivrem(A, B, Q, R);
@@ -1372,9 +1369,7 @@ APInt floorOfQuotient(APInt A, APInt B) {
     return Q - 1;
 }
 
-
-static
-APInt ceilingOfQuotient(APInt A, APInt B) {
+static APInt ceilingOfQuotient(const APInt &A, const APInt &B) {
   APInt Q = A; // these need to be initialized
   APInt R = A;
   APInt::sdivrem(A, B, Q, R);
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 041481411a4..c8568452d5a 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -297,7 +297,7 @@ raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
 /// Returns true if this lattice value represents at most one possible value.
 /// This is as precise as any lattice value can get while still representing
 /// reachable code.
-static bool hasSingleValue(LVILatticeVal Val) {
+static bool hasSingleValue(const LVILatticeVal &Val) {
   if (Val.isConstantRange() &&
       Val.getConstantRange().isSingleElement())
     // Integer constants are single element ranges
diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index a687eccf3e9..dce243ca673 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -25,7 +25,7 @@
 
 using namespace llvm;
 
-static bool isAligned(const Value *Base, APInt Offset, unsigned Align,
+static bool isAligned(const Value *Base, const APInt &Offset, unsigned Align,
                       const DataLayout &DL) {
   APInt BaseAlign(Offset.getBitWidth(), Base->getPointerAlignment(DL));
 
@@ -52,7 +52,7 @@ static bool isAligned(const Value *Base, unsigned Align, const DataLayout &DL) {
 /// Test if V is always a pointer to allocated and suitably aligned memory for
 /// a simple load or store.
 static bool isDereferenceableAndAlignedPointer(
-    const Value *V, unsigned Align, APInt Size, const DataLayout &DL,
+    const Value *V, unsigned Align, const APInt &Size, const DataLayout &DL,
     const Instruction *CtxI, const DominatorTree *DT,
     const TargetLibraryInfo *TLI, SmallPtrSetImpl<const Value *> &Visited) {
   // Note that it is not safe to speculate into a malloc'd region because
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index b3d98d8ff55..7a6bc3a7637 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8811,7 +8811,7 @@ ScalarEvolution::howManyGreaterThans(const SCEV *LHS, const SCEV *RHS,
   return ExitLimit(BECount, MaxBECount, P);
 }
 
-const SCEV *SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range,
+const SCEV *SCEVAddRecExpr::getNumIterationsInRange(const ConstantRange &Range,
                                                     ScalarEvolution &SE) const {
   if (Range.isFullSet())  // Infinite loop.
     return SE.getCouldNotCompute();
diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp
index 925e7ce2d0d..68b0764c62d 100644
--- a/llvm/lib/Analysis/TargetLibraryInfo.cpp
+++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp
@@ -1133,7 +1133,7 @@ TargetLibraryInfo TargetLibraryAnalysis::run(Function &F) {
       lookupInfoImpl(Triple(F.getParent()->getTargetTriple())));
 }
 
-TargetLibraryInfoImpl &TargetLibraryAnalysis::lookupInfoImpl(Triple T) {
+TargetLibraryInfoImpl &TargetLibraryAnalysis::lookupInfoImpl(const Triple &T) {
   std::unique_ptr<TargetLibraryInfoImpl> &Impl =
       Impls[T.normalize()];
   if (!Impl)
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index d614dfd6fc8..b66084be821 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -178,7 +178,7 @@ void DwarfExpression::AddUnsignedConstant(unsigned Value) {
   AddStackValue();
 }
 
-void DwarfExpression::AddUnsignedConstant(APInt Value) {
+void DwarfExpression::AddUnsignedConstant(const APInt &Value) {
   unsigned Size = Value.getBitWidth();
   const uint64_t *Data = Value.getRawData();
 
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
index 318d8d3d765..e8a8025add9 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -100,7 +100,7 @@ public:
   /// Emit an unsigned constant.
   void AddUnsignedConstant(unsigned Value);
   /// Emit an unsigned constant.
-  void AddUnsignedConstant(APInt Value);
+  void AddUnsignedConstant(const APInt &Value);
 
   /// \brief Emit an entire expression on top of a machine register location.
   ///
diff --git a/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp b/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
index 3eb9ffc17f1..be5c603a38e 100644
--- a/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
+++ b/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
@@ -36,7 +36,7 @@ static const char kDILineInfoBadString[] = "<invalid>";
 static const char kBadString[] = "??";
 
 // Prints source code around in the FileName the Line.
-void DIPrinter::printContext(std::string FileName, int64_t Line) {
+void DIPrinter::printContext(const std::string &FileName, int64_t Line) {
   if (PrintSourceContext <= 0)
     return;
 
diff --git a/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp b/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
index 34a0ddf00c8..c7b97865ab7 100644
--- a/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
@@ -23,7 +23,8 @@ void JITCompileCallbackManager::anchor() {}
 void IndirectStubsManager::anchor() {}
 
 std::unique_ptr<JITCompileCallbackManager>
-createLocalCompileCallbackManager(Triple T, TargetAddress ErrorHandlerAddress) {
+createLocalCompileCallbackManager(const Triple &T,
+                                  TargetAddress ErrorHandlerAddress) {
   switch (T.getArch()) {
     default: return nullptr;
 
@@ -45,7 +46,7 @@ createLocalCompileCallbackManager(Triple T, TargetAddress ErrorHandlerAddress) {
 }
 
 std::function<std::unique_ptr<IndirectStubsManager>()>
-createLocalIndirectStubsManagerBuilder(Triple T) {
+createLocalIndirectStubsManagerBuilder(const Triple &T) {
   switch (T.getArch()) {
     default: return nullptr;
 
diff --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
index 0e1c46cff27..52634652932 100644
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -165,7 +165,7 @@ void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
   HasVerifiedInput = false;
 }
 
-void LTOCodeGenerator::setTargetOptions(TargetOptions Options) {
+void LTOCodeGenerator::setTargetOptions(const TargetOptions &Options) {
   this->Options = Options;
 }
 
diff --git a/llvm/lib/LTO/LTOModule.cpp b/llvm/lib/LTO/LTOModule.cpp
index 7e826779870..fca6ca8011f 100644
--- a/llvm/lib/LTO/LTOModule.cpp
+++ b/llvm/lib/LTO/LTOModule.cpp
@@ -108,7 +108,7 @@ std::string LTOModule::getProducerString(MemoryBuffer *Buffer) {
 
 ErrorOr<std::unique_ptr<LTOModule>>
 LTOModule::createFromFile(LLVMContext &Context, const char *path,
-                          TargetOptions options) {
+                          const TargetOptions &options) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
       MemoryBuffer::getFile(path);
   if (std::error_code EC = BufferOrErr.getError()) {
@@ -122,14 +122,14 @@ LTOModule::createFromFile(LLVMContext &Context, const char *path,
 
 ErrorOr<std::unique_ptr<LTOModule>>
 LTOModule::createFromOpenFile(LLVMContext &Context, int fd, const char *path,
-                              size_t size, TargetOptions options) {
+                              size_t size, const TargetOptions &options) {
   return createFromOpenFileSlice(Context, fd, path, size, 0, options);
 }
 
 ErrorOr<std::unique_ptr<LTOModule>>
 LTOModule::createFromOpenFileSlice(LLVMContext &Context, int fd,
                                    const char *path, size_t map_size,
-                                   off_t offset, TargetOptions options) {
+                                   off_t offset, const TargetOptions &options) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
       MemoryBuffer::getOpenFileSlice(fd, path, map_size, offset);
   if (std::error_code EC = BufferOrErr.getError()) {
@@ -143,7 +143,7 @@ LTOModule::createFromOpenFileSlice(LLVMContext &Context, int fd,
 
 ErrorOr<std::unique_ptr<LTOModule>>
 LTOModule::createFromBuffer(LLVMContext &Context, const void *mem,
-                            size_t length, TargetOptions options,
+                            size_t length, const TargetOptions &options,
                             StringRef path) {
   StringRef Data((const char *)mem, length);
   MemoryBufferRef Buffer(Data, path);
@@ -153,7 +153,7 @@ LTOModule::createFromBuffer(LLVMContext &Context, const void *mem,
 ErrorOr<std::unique_ptr<LTOModule>>
 LTOModule::createInLocalContext(std::unique_ptr<LLVMContext> Context,
                                 const void *mem, size_t length,
-                                TargetOptions options, StringRef path) {
+                                const TargetOptions &options, StringRef path) {
   StringRef Data((const char *)mem, length);
   MemoryBufferRef Buffer(Data, path);
   // If we own a context, we know this is being used only for symbol extraction,
@@ -196,7 +196,7 @@ parseBitcodeFileImpl(MemoryBufferRef Buffer, LLVMContext &Context,
 }
 
 ErrorOr<std::unique_ptr<LTOModule>>
-LTOModule::makeLTOModule(MemoryBufferRef Buffer, TargetOptions options,
+LTOModule::makeLTOModule(MemoryBufferRef Buffer, const TargetOptions &options,
                          LLVMContext &Context, bool ShouldBeLazy) {
   ErrorOr<std::unique_ptr<Module>> MOrErr =
       parseBitcodeFileImpl(Buffer, Context, ShouldBeLazy);
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 8baab57a796..4758ef8ba9f 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -335,7 +335,7 @@ ProcessThinLTOModule(Module &TheModule, ModuleSummaryIndex &Index,
                      const FunctionImporter::ExportSetTy &ExportList,
                      const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
                      const GVSummaryMapTy &DefinedGlobals,
-                     ThinLTOCodeGenerator::CachingOptions CacheOptions,
+                     const ThinLTOCodeGenerator::CachingOptions &CacheOptions,
                      bool DisableCodeGen, StringRef SaveTempsDir,
                      unsigned count) {
 
diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index 14a25612259..ff36f90b53f 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -44,7 +44,7 @@ class ModuleLinker {
   /// The mover has just hit GV and we have to decide if it, and other members
   /// of the same comdat, should be linked. Every member to be linked is passed
   /// to Add.
-  void addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add);
+  void addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add);
 
   bool shouldLinkReferencedLinkOnce() {
     return !(Flags & Linker::DontForceLinkLinkonceODR);
@@ -416,7 +416,7 @@ bool ModuleLinker::linkIfNeeded(GlobalValue &GV) {
   return false;
 }
 
-void ModuleLinker::addLazyFor(GlobalValue &GV, IRMover::ValueAdder Add) {
+void ModuleLinker::addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add) {
   if (!shouldLinkReferencedLinkOnce())
     // For ThinLTO we don't import more than what was required.
     // The client has to guarantee that the linkonce will be availabe at link
diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index 059dcf2477e..5bbc8d5c5a9 100644
--- a/llvm/lib/MC/MCObjectFileInfo.cpp
+++ b/llvm/lib/MC/MCObjectFileInfo.cpp
@@ -45,7 +45,7 @@ static bool useCompactUnwind(const Triple &T) {
   return false;
 }
 
-void MCObjectFileInfo::initMachOMCObjectFileInfo(Triple T) {
+void MCObjectFileInfo::initMachOMCObjectFileInfo(const Triple &T) {
   // MachO
   SupportsWeakOmittedEHFrame = false;
 
@@ -283,7 +283,7 @@ void MCObjectFileInfo::initMachOMCObjectFileInfo(Triple T) {
   TLSExtraDataSection = TLSTLVSection;
 }
 
-void MCObjectFileInfo::initELFMCObjectFileInfo(Triple T) {
+void MCObjectFileInfo::initELFMCObjectFileInfo(const Triple &T) {
   switch (T.getArch()) {
   case Triple::mips:
   case Triple::mipsel:
@@ -589,7 +589,7 @@ void MCObjectFileInfo::initELFMCObjectFileInfo(Triple T) {
       Ctx->getELFSection(".eh_frame", EHSectionType, EHSectionFlags);
 }
 
-void MCObjectFileInfo::initCOFFMCObjectFileInfo(Triple T) {
+void MCObjectFileInfo::initCOFFMCObjectFileInfo(const Triple &T) {
   EHFrameSection = Ctx->getCOFFSection(
       ".eh_frame", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                        COFF::IMAGE_SCN_MEM_READ | COFF::IMAGE_SCN_MEM_WRITE,
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 8aec54730ca..cd7b9a9980d 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -1664,10 +1664,8 @@ static void KnuthDiv(unsigned *u, unsigned *v, unsigned *q, unsigned* r,
   DEBUG(dbgs() << '\n');
 }
 
-void APInt::divide(const APInt LHS, unsigned lhsWords,
-                   const APInt &RHS, unsigned rhsWords,
-                   APInt *Quotient, APInt *Remainder)
-{
+void APInt::divide(const APInt &LHS, unsigned lhsWords, const APInt &RHS,
+                   unsigned rhsWords, APInt *Quotient, APInt *Remainder) {
   assert(lhsWords >= rhsWords && "Fractional result");
 
   // First, compose the values into an array of 32-bit words instead of
diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index 54756fb85a9..aed42b25e64 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -1432,7 +1432,7 @@ PRINT_OPT_DIFF(float)
 PRINT_OPT_DIFF(char)
 
 void parser<std::string>::printOptionDiff(const Option &O, StringRef V,
-                                          OptionValue<std::string> D,
+                                          const OptionValue<std::string> &D,
                                           size_t GlobalWidth) const {
   printOptionName(O, GlobalWidth);
   outs() << "= " << V;
diff --git a/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp b/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
index dfa391916d5..5a11fe66b75 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
@@ -1748,7 +1748,7 @@ bool AArch64DAGToDAGISel::tryBitfieldExtractOp(SDNode *N) {
 /// BitsToBeInserted, suitable for use in a BFI instruction. Roughly speaking,
 /// this asks whether DstMask zeroes precisely those bits that will be set by
 /// the other half.
-static bool isBitfieldDstMask(uint64_t DstMask, APInt BitsToBeInserted,
+static bool isBitfieldDstMask(uint64_t DstMask, const APInt &BitsToBeInserted,
                               unsigned NumberOfIgnoredHighBits, EVT VT) {
   assert((VT == MVT::i32 || VT == MVT::i64) &&
          "i32 or i64 mask type expected!");
diff --git a/llvm/lib/Target/AArch64/Utils/AArch64BaseInfo.h b/llvm/lib/Target/AArch64/Utils/AArch64BaseInfo.h
index 98eaa388024..f4676e48c0c 100644
--- a/llvm/lib/Target/AArch64/Utils/AArch64BaseInfo.h
+++ b/llvm/lib/Target/AArch64/Utils/AArch64BaseInfo.h
@@ -285,8 +285,8 @@ struct AArch64NamedImmMapper {
     // Zero value of FeatureBitSet means the mapping is always available
     FeatureBitset FeatureBitSet;
 
-    bool isNameEqual(std::string Other,
-                     const FeatureBitset& FeatureBits) const {
+    bool isNameEqual(const std::string &Other,
+                     const FeatureBitset &FeatureBits) const {
       if (FeatureBitSet.any() &&
           (FeatureBitSet & FeatureBits).none())
         return false;
diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index ec53f0f1b6d..660016bfcd0 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -2341,7 +2341,7 @@ void NVPTXAsmPrinter::emitSrcInText(StringRef filename, unsigned line) {
   this->OutStreamer->EmitRawText(temp.str());
 }
 
-LineReader *NVPTXAsmPrinter::getReader(std::string filename) {
+LineReader *NVPTXAsmPrinter::getReader(const std::string &filename) {
   if (!reader) {
     reader = new LineReader(filename);
   }
diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h
index 9f6a6353649..85660fbdb26 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h
@@ -293,7 +293,7 @@ private:
   bool isLoopHeaderOfNoUnroll(const MachineBasicBlock &MBB) const;
 
   LineReader *reader;
-  LineReader *getReader(std::string);
+  LineReader *getReader(const std::string &);
 
   // Used to control the need to emit .generic() in the initializer of
   // module scope variables.
diff --git a/llvm/lib/Target/NVPTX/NVPTXMCExpr.cpp b/llvm/lib/Target/NVPTX/NVPTXMCExpr.cpp
index 3c98b9febf8..84d5239ec09 100644
--- a/llvm/lib/Target/NVPTX/NVPTXMCExpr.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXMCExpr.cpp
@@ -15,8 +15,8 @@ using namespace llvm;
 
 #define DEBUG_TYPE "nvptx-mcexpr"
 
-const NVPTXFloatMCExpr*
-NVPTXFloatMCExpr::create(VariantKind Kind, APFloat Flt, MCContext &Ctx) {
+const NVPTXFloatMCExpr *
+NVPTXFloatMCExpr::create(VariantKind Kind, const APFloat &Flt, MCContext &Ctx) {
   return new (Ctx) NVPTXFloatMCExpr(Kind, Flt);
 }
 
diff --git a/llvm/lib/Target/NVPTX/NVPTXMCExpr.h b/llvm/lib/Target/NVPTX/NVPTXMCExpr.h
index 7661c10fde4..7f833c42fa8 100644
--- a/llvm/lib/Target/NVPTX/NVPTXMCExpr.h
+++ b/llvm/lib/Target/NVPTX/NVPTXMCExpr.h
@@ -37,15 +37,15 @@ public:
   /// @name Construction
   /// @{
 
-  static const NVPTXFloatMCExpr *create(VariantKind Kind, APFloat Flt,
+  static const NVPTXFloatMCExpr *create(VariantKind Kind, const APFloat &Flt,
                                         MCContext &Ctx);
 
-  static const NVPTXFloatMCExpr *createConstantFPSingle(APFloat Flt,
+  static const NVPTXFloatMCExpr *createConstantFPSingle(const APFloat &Flt,
                                                         MCContext &Ctx) {
     return create(VK_NVPTX_SINGLE_PREC_FLOAT, Flt, Ctx);
   }
 
-  static const NVPTXFloatMCExpr *createConstantFPDouble(APFloat Flt,
+  static const NVPTXFloatMCExpr *createConstantFPDouble(const APFloat &Flt,
                                                         MCContext &Ctx) {
     return create(VK_NVPTX_DOUBLE_PREC_FLOAT, Flt, Ctx);
   }
diff --git a/llvm/lib/Target/NVPTX/NVPTXUtilities.cpp b/llvm/lib/Target/NVPTX/NVPTXUtilities.cpp
index 578b466568a..835e4b44203 100644
--- a/llvm/lib/Target/NVPTX/NVPTXUtilities.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXUtilities.cpp
@@ -99,7 +99,7 @@ static void cacheAnnotationFromMD(const Module *m, const GlobalValue *gv) {
   }
 }
 
-bool llvm::findOneNVVMAnnotation(const GlobalValue *gv, std::string prop,
+bool llvm::findOneNVVMAnnotation(const GlobalValue *gv, const std::string &prop,
                                  unsigned &retval) {
   MutexGuard Guard(Lock);
   const Module *m = gv->getParent();
@@ -113,7 +113,7 @@ bool llvm::findOneNVVMAnnotation(const GlobalValue *gv, std::string prop,
   return true;
 }
 
-bool llvm::findAllNVVMAnnotation(const GlobalValue *gv, std::string prop,
+bool llvm::findAllNVVMAnnotation(const GlobalValue *gv, const std::string &prop,
                                  std::vector<unsigned> &retval) {
   MutexGuard Guard(Lock);
   const Module *m = gv->getParent();
diff --git a/llvm/lib/Target/NVPTX/NVPTXUtilities.h b/llvm/lib/Target/NVPTX/NVPTXUtilities.h
index a5262cb7412..ec5bfc17afc 100644
--- a/llvm/lib/Target/NVPTX/NVPTXUtilities.h
+++ b/llvm/lib/Target/NVPTX/NVPTXUtilities.h
@@ -30,8 +30,9 @@ namespace llvm {
 
 void clearAnnotationCache(const llvm::Module *);
 
-bool findOneNVVMAnnotation(const llvm::GlobalValue *, std::string, unsigned &);
-bool findAllNVVMAnnotation(const llvm::GlobalValue *, std::string,
+bool findOneNVVMAnnotation(const llvm::GlobalValue *, const std::string &,
+                           unsigned &);
+bool findAllNVVMAnnotation(const llvm::GlobalValue *, const std::string &,
                            std::vector<unsigned> &);
 
 bool isTexture(const llvm::Value &);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 326029d8187..0f1121aef94 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -522,12 +522,12 @@ private:
   Value *SimplifyDemandedUseBits(Value *V, APInt DemandedMask, APInt &KnownZero,
                                  APInt &KnownOne, unsigned Depth,
                                  Instruction *CxtI);
-  bool SimplifyDemandedBits(Use &U, APInt DemandedMask, APInt &KnownZero,
+  bool SimplifyDemandedBits(Use &U, const APInt &DemandedMask, APInt &KnownZero,
                             APInt &KnownOne, unsigned Depth = 0);
   /// Helper routine of SimplifyDemandedUseBits. It tries to simplify demanded
   /// bit for "r1 = shr x, c1; r2 = shl r1, c2" instruction sequence.
   Value *SimplifyShrShlDemandedBits(Instruction *Lsr, Instruction *Sftl,
-                                    APInt DemandedMask, APInt &KnownZero,
+                                    const APInt &DemandedMask, APInt &KnownZero,
                                     APInt &KnownOne);
 
   /// \brief Tries to simplify operands to an integer instruction based on its
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index adc433c4b70..6d06c0a6a8c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -68,7 +68,7 @@ bool InstCombiner::SimplifyDemandedInstructionBits(Instruction &Inst) {
 /// SimplifyDemandedBits - This form of SimplifyDemandedBits simplifies the
 /// specified instruction operand if possible, updating it in place.  It returns
 /// true if it made any change and false otherwise.
-bool InstCombiner::SimplifyDemandedBits(Use &U, APInt DemandedMask,
+bool InstCombiner::SimplifyDemandedBits(Use &U, const APInt &DemandedMask,
                                         APInt &KnownZero, APInt &KnownOne,
                                         unsigned Depth) {
   auto *UserI = dyn_cast<Instruction>(U.getUser());
@@ -830,7 +830,10 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
 /// As with SimplifyDemandedUseBits, it returns NULL if the simplification was
 /// not successful.
 Value *InstCombiner::SimplifyShrShlDemandedBits(Instruction *Shr,
-  Instruction *Shl, APInt DemandedMask, APInt &KnownZero, APInt &KnownOne) {
+                                                Instruction *Shl,
+                                                const APInt &DemandedMask,
+                                                APInt &KnownZero,
+                                                APInt &KnownOne) {
 
   const APInt &ShlOp1 = cast<ConstantInt>(Shl->getOperand(1))->getValue();
   const APInt &ShrOp1 = cast<ConstantInt>(Shr->getOperand(1))->getValue();
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index 806c101e462..05d187f7795 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -493,7 +493,7 @@ struct LoopInterchange : public FunctionPass {
     return true;
   }
 
-  unsigned selectLoopForInterchange(LoopVector LoopList) {
+  unsigned selectLoopForInterchange(const LoopVector &LoopList) {
     // TODO: Add a better heuristic to select the loop to be interchanged based
     // on the dependence matrix. Currently we select the innermost loop.
     return LoopList.size() - 1;
diff --git a/llvm/tools/bugpoint/BugDriver.h b/llvm/tools/bugpoint/BugDriver.h
index 20efff3fda5..56ed8ab712e 100644
--- a/llvm/tools/bugpoint/BugDriver.h
+++ b/llvm/tools/bugpoint/BugDriver.h
@@ -76,7 +76,7 @@ public:
   // command line arguments into instance variables of BugDriver.
   //
   bool addSources(const std::vector<std::string> &FileNames);
-  void addPass(std::string p) { PassesToRun.push_back(p); }
+  void addPass(std::string p) { PassesToRun.push_back(std::move(p)); }
   void setPassesToRun(const std::vector<std::string> &PTR) {
     PassesToRun = PTR;
   }
@@ -183,7 +183,7 @@ public:
   /// Error.
   ///
   std::string executeProgramSafely(const Module *Program,
-                                   std::string OutputFile,
+                                   const std::string &OutputFile,
                                    std::string *Error) const;
 
   /// createReferenceFile - calls compileProgram and then records the output
diff --git a/llvm/tools/bugpoint/ExecutionDriver.cpp b/llvm/tools/bugpoint/ExecutionDriver.cpp
index 41b8ccc18e8..ab9c05fa924 100644
--- a/llvm/tools/bugpoint/ExecutionDriver.cpp
+++ b/llvm/tools/bugpoint/ExecutionDriver.cpp
@@ -384,7 +384,7 @@ std::string BugDriver::executeProgram(const Module *Program,
 /// backend, if reference output is not provided.
 ///
 std::string BugDriver::executeProgramSafely(const Module *Program,
-                                            std::string OutputFile,
+                                            const std::string &OutputFile,
                                             std::string *Error) const {
   return executeProgram(Program, OutputFile, "", "", SafeInterpreter, Error);
 }
diff --git a/llvm/tools/dsymutil/DwarfLinker.cpp b/llvm/tools/dsymutil/DwarfLinker.cpp
index 3a5718b2b20..bea30ded591 100644
--- a/llvm/tools/dsymutil/DwarfLinker.cpp
+++ b/llvm/tools/dsymutil/DwarfLinker.cpp
@@ -531,7 +531,7 @@ public:
   /// original \p Entries.
   void emitRangesEntries(
       int64_t UnitPcOffset, uint64_t OrigLowPc,
-      FunctionIntervals::const_iterator FuncRange,
+      const FunctionIntervals::const_iterator &FuncRange,
       const std::vector<DWARFDebugRangeList::RangeListEntry> &Entries,
       unsigned AddressSize);
 
@@ -715,7 +715,7 @@ void DwarfStreamer::emitStrings(const NonRelocatableStringpool &Pool) {
 /// sized addresses describing the ranges.
 void DwarfStreamer::emitRangesEntries(
     int64_t UnitPcOffset, uint64_t OrigLowPc,
-    FunctionIntervals::const_iterator FuncRange,
+    const FunctionIntervals::const_iterator &FuncRange,
     const std::vector<DWARFDebugRangeList::RangeListEntry> &Entries,
     unsigned AddressSize) {
   MS->SwitchSection(MC->getObjectFileInfo()->getDwarfRangesSection());
@@ -1416,7 +1416,7 @@ private:
   /// \defgroup Helpers Various helper methods.
   ///
   /// @{
-  bool createStreamer(Triple TheTriple, StringRef OutputFilename);
+  bool createStreamer(const Triple &TheTriple, StringRef OutputFilename);
 
   /// \brief Attempt to load a debug object from disk.
   ErrorOr<const object::ObjectFile &> loadObject(BinaryHolder &BinaryHolder,
@@ -1744,7 +1744,8 @@ void DwarfLinker::reportWarning(const Twine &Warning, const DWARFUnit *Unit,
             6 /* Indent */);
 }
 
-bool DwarfLinker::createStreamer(Triple TheTriple, StringRef OutputFilename) {
+bool DwarfLinker::createStreamer(const Triple &TheTriple,
+                                 StringRef OutputFilename) {
   if (Options.NoOutput)
     return true;
 
diff --git a/llvm/tools/llvm-cov/CodeCoverage.cpp b/llvm/tools/llvm-cov/CodeCoverage.cpp
index cd786edc25d..1d40a28e286 100644
--- a/llvm/tools/llvm-cov/CodeCoverage.cpp
+++ b/llvm/tools/llvm-cov/CodeCoverage.cpp
@@ -72,7 +72,7 @@ public:
 
   int run(Command Cmd, int argc, const char **argv);
 
-  typedef std::function<int(int, const char **)> CommandLineParserType;
+  typedef llvm::function_ref<int(int, const char **)> CommandLineParserType;
 
   int show(int argc, const char **argv,
            CommandLineParserType commandLineParser);
diff --git a/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp b/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp
index b0facfb294d..7079ed215c0 100644
--- a/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp
+++ b/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp
@@ -114,7 +114,7 @@ static void DumpInput(StringRef Filename) {
 /// If the input path is a .dSYM bundle (as created by the dsymutil tool),
 /// replace it with individual entries for each of the object files inside the
 /// bundle otherwise return the input path.
-static std::vector<std::string> expandBundle(std::string InputPath) {
+static std::vector<std::string> expandBundle(const std::string &InputPath) {
   std::vector<std::string> BundlePaths;
   SmallString<256> BundlePath(InputPath);
   // Manually open up the bundle to avoid introducing additional dependencies.
diff --git a/llvm/tools/llvm-nm/llvm-nm.cpp b/llvm/tools/llvm-nm/llvm-nm.cpp
index d838ad870ba..1e4a7eee373 100644
--- a/llvm/tools/llvm-nm/llvm-nm.cpp
+++ b/llvm/tools/llvm-nm/llvm-nm.cpp
@@ -597,8 +597,8 @@ static void darwinPrintStab(MachOObjectFile *MachO, SymbolListT::iterator I) {
 }
 
 static void sortAndPrintSymbolList(SymbolicFile &Obj, bool printName,
-                                   std::string ArchiveName,
-                                   std::string ArchitectureName) {
+                                   const std::string &ArchiveName,
+                                   const std::string &ArchitectureName) {
   if (!NoSort) {
     std::function<bool(const NMSymbol &, const NMSymbol &)> Cmp;
     if (NumericSort)
@@ -963,10 +963,10 @@ static unsigned getNsectInMachO(MachOObjectFile &Obj, BasicSymbolRef Sym) {
   return (STE.n_type & MachO::N_TYPE) == MachO::N_SECT ? STE.n_sect : 0;
 }
 
-static void dumpSymbolNamesFromObject(SymbolicFile &Obj, bool printName,
-                                      std::string ArchiveName = std::string(),
-                                      std::string ArchitectureName =
-                                        std::string()) {
+static void
+dumpSymbolNamesFromObject(SymbolicFile &Obj, bool printName,
+                          const std::string &ArchiveName = std::string(),
+                          const std::string &ArchitectureName = std::string()) {
   auto Symbols = Obj.symbols();
   if (DynamicSyms) {
     const auto *E = dyn_cast<ELFObjectFileBase>(&Obj);
diff --git a/llvm/utils/TableGen/DAGISelMatcherGen.cpp b/llvm/utils/TableGen/DAGISelMatcherGen.cpp
index 04d8ff0b8e6..4110e9725b5 100644
--- a/llvm/utils/TableGen/DAGISelMatcherGen.cpp
+++ b/llvm/utils/TableGen/DAGISelMatcherGen.cpp
@@ -116,7 +116,7 @@ namespace {
     /// If this is the first time a node with unique identifier Name has been
     /// seen, record it. Otherwise, emit a check to make sure this is the same
     /// node. Returns true if this is the first encounter.
-    bool recordUniqueNode(std::string Name);
+    bool recordUniqueNode(const std::string &Name);
 
     // Result Code Generation.
     unsigned getNamedArgumentSlot(StringRef Name) {
@@ -438,7 +438,7 @@ void MatcherGen::EmitOperatorMatchCode(const TreePatternNode *N,
   }
 }
 
-bool MatcherGen::recordUniqueNode(std::string Name) {
+bool MatcherGen::recordUniqueNode(const std::string &Name) {
   unsigned &VarMapEntry = VariableMap[Name];
   if (VarMapEntry == 0) {
     // If it is a named node, we must emit a 'Record' opcode.
diff --git a/llvm/utils/TableGen/DisassemblerEmitter.cpp b/llvm/utils/TableGen/DisassemblerEmitter.cpp
index b6a2b1c7f5d..44815b05f27 100644
--- a/llvm/utils/TableGen/DisassemblerEmitter.cpp
+++ b/llvm/utils/TableGen/DisassemblerEmitter.cpp
@@ -96,12 +96,11 @@ using namespace llvm::X86Disassembler;
 namespace llvm {
 
 extern void EmitFixedLenDecoder(RecordKeeper &RK, raw_ostream &OS,
-                                std::string PredicateNamespace,
-                                std::string GPrefix,
-                                std::string GPostfix,
-                                std::string ROK,
-                                std::string RFail,
-                                std::string L);
+                                const std::string &PredicateNamespace,
+                                const std::string &GPrefix,
+                                const std::string &GPostfix,
+                                const std::string &ROK,
+                                const std::string &RFail, const std::string &L);
 
 void EmitDisassembler(RecordKeeper &Records, raw_ostream &OS) {
   CodeGenTarget Target(Records);
diff --git a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp b/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
index 51f1971258f..ca6fe501f73 100644
--- a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
+++ b/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -2324,12 +2324,10 @@ void FixedLenDecoderEmitter::run(raw_ostream &o) {
 namespace llvm {
 
 void EmitFixedLenDecoder(RecordKeeper &RK, raw_ostream &OS,
-                         std::string PredicateNamespace,
-                         std::string GPrefix,
-                         std::string GPostfix,
-                         std::string ROK,
-                         std::string RFail,
-                         std::string L) {
+                         const std::string &PredicateNamespace,
+                         const std::string &GPrefix,
+                         const std::string &GPostfix, const std::string &ROK,
+                         const std::string &RFail, const std::string &L) {
   FixedLenDecoderEmitter(RK, PredicateNamespace, GPrefix, GPostfix,
                          ROK, RFail, L).run(OS);
 }
diff --git a/llvm/utils/TableGen/SubtargetEmitter.cpp b/llvm/utils/TableGen/SubtargetEmitter.cpp
index c69fcdc25b4..228882177bd 100644
--- a/llvm/utils/TableGen/SubtargetEmitter.cpp
+++ b/llvm/utils/TableGen/SubtargetEmitter.cpp
@@ -101,7 +101,7 @@ class SubtargetEmitter {
   void EmitSchedClassTables(SchedClassTables &SchedTables, raw_ostream &OS);
   void EmitProcessorModels(raw_ostream &OS);
   void EmitProcessorLookup(raw_ostream &OS);
-  void EmitSchedModelHelpers(std::string ClassName, raw_ostream &OS);
+  void EmitSchedModelHelpers(const std::string &ClassName, raw_ostream &OS);
   void EmitSchedModel(raw_ostream &OS);
   void ParseFeaturesFunction(raw_ostream &OS, unsigned NumFeatures,
                              unsigned NumProcs);
@@ -1268,7 +1268,7 @@ void SubtargetEmitter::EmitSchedModel(raw_ostream &OS) {
   OS << "#undef DBGFIELD";
 }
 
-void SubtargetEmitter::EmitSchedModelHelpers(std::string ClassName,
+void SubtargetEmitter::EmitSchedModelHelpers(const std::string &ClassName,
                                              raw_ostream &OS) {
   OS << "unsigned " << ClassName
      << "\n::resolveSchedClass(unsigned SchedClass, const MachineInstr *MI,"