Remove unneccessary string copies from method invocations.

[hctim]

Summary

Change string parameter 'File' to be passed by const-reference to
reduce copies.

[vlad.tsyrklevich]

Do you need me to commit on your behalf?

[Eugene.Zelenko]

Will be good idea to also run Clang-tidy modernize-* over this code.

tools/llvm-objdump/llvm-objdump.cpp

432

Please use = default and move it after constructors.

433

Please use default member initialization and = default;

[hctim]

Added = default for trivial constructors/destructors.

[hctim]

Made a mistake in last diff, SourcePrinter() is now correctly default-member initialised (note that the unique_ptr is already nullptr-initialised on construction).

tools/llvm-objdump/llvm-objdump.cpp

protected:
   const ObjectFile *Obj;
   std::unique_ptr<symbolize::LLVMSymbolizer> Symbolizer;
   // File name to file contents of source
   std::unordered_map<std::string, std::unique_ptr<MemoryBuffer>> SourceCache;
   // Mark the line endings of the cached source
   std::unordered_map<std::string, std::vector<StringRef>> LineCache;
 
 private:
-  bool cacheSource(std::string File);
+  bool cacheSource(const std::string& File);
 
 public:
   virtual ~SourcePrinter() {}
   SourcePrinter() : Obj(nullptr), Symbolizer(nullptr) {}
   SourcePrinter(const ObjectFile *Obj, StringRef DefaultArch) : Obj(Obj) {
     symbolize::LLVMSymbolizer::Options SymbolizerOpts(
         DILineInfoSpecifier::FunctionNameKind::None, true, false, false,
         DefaultArch);
     Symbolizer.reset(new symbolize::LLVMSymbolizer(SymbolizerOpts));
   }
   virtual void printSourceLine(raw_ostream &OS, uint64_t Address,
                                StringRef Delimiter = "; ");
 };
 
-bool SourcePrinter::cacheSource(std::string File) {
+bool SourcePrinter::cacheSource(const std::string& File) {
   auto BufferOrError = MemoryBuffer::getFile(File);
   if (!BufferOrError)
     return false;
   // Chomp the file to get lines
   size_t BufferSize = (*BufferOrError)->getBufferSize();
   const char *BufferStart = (*BufferOrError)->getBufferStart();
   for (const char *Start = BufferStart, *End = BufferStart;
        End < BufferStart + BufferSize; End++)