Frontend: Simplify handling of non-seeking streams in CompilerInstance, NFC

[dexonsmith]

Summary

Add a new raw_pwrite_ostream variant, buffer_unique_ostream, which
is like buffer_ostream but with unique ownership of the stream it's
wrapping. Use this in CompilerInstance to simplify the ownership of
non-seeking output streams, avoiding logic sprawled around to deal with
them specially.

This also simplifies future work to encapsulate output files in a
different class.

[dexonsmith]

Ping!

[erik.pilkington]

LGTM

clang/include/clang/Frontend/CompilerInstance.h

struct OutputFile {
     std::string Filename;
     std::string TempFilename;
 
     OutputFile(std::string filename, std::string tempFilename)
         : Filename(std::move(filename)), TempFilename(std::move(tempFilename)) {
     }
   };
 
-  /// If the output doesn't support seeking (terminal, pipe). we switch
-  /// the stream to a buffer_ostream. These are the buffer and the original
-  /// stream.
-  std::unique_ptr<llvm::raw_fd_ostream> NonSeekStream;
-
   /// The list of active output files.
   std::list<OutputFile> OutputFiles;
 
   /// Force an output buffer.
   std::unique_ptr<llvm::raw_pwrite_stream> OutputStream;
 
   CompilerInstance(const CompilerInstance &) = delete;
   void operator=(const CompilerInstance &) = delete;

clang/lib/Frontend/CompilerInstance.cpp

if (!OF.TempFilename.empty()) {
       llvm::sys::fs::remove(OF.Filename);
   }
   OutputFiles.clear();
   if (DeleteBuiltModules) {
     for (auto &Module : BuiltModules)
       llvm::sys::fs::remove(Module.second);
     BuiltModules.clear();
   }
-  NonSeekStream.reset();
 }
 
 std::unique_ptr<raw_pwrite_stream>
 CompilerInstance::createDefaultOutputFile(bool Binary, StringRef InFile,
                                           StringRef Extension) {
   return createOutputFile(getFrontendOpts().OutputFile, Binary,
                           /*RemoveFileOnSignal=*/true, InFile, Extension,
                           getFrontendOpts().UseTemporary);
std::unique_ptr<llvm::raw_pwrite_stream> CompilerInstance::createOutputFile(
   if (ResultPathName)
     *ResultPathName = OutFile;
   if (TempPathName)
     *TempPathName = TempFile;
 
   if (!Binary || OS->supportsSeeking())
     return std::move(OS);
 
-  auto B = std::make_unique<llvm::buffer_ostream>(*OS);
-  assert(!NonSeekStream);
-  NonSeekStream = std::move(OS);
-  return std::move(B);
+  return std::make_unique<llvm::buffer_unique_ostream>(std::move(OS));
 }
 
 // Initialization Utilities
 
 bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input){
   return InitializeSourceManager(Input, getDiagnostics(), getFileManager(),
                                  getSourceManager());
 }

llvm/include/llvm/Support/raw_ostream.h

class buffer_ostream : public raw_svector_ostream {
 
   virtual void anchor() override;
 
 public:
   buffer_ostream(raw_ostream &OS) : raw_svector_ostream(Buffer), OS(OS) {}
   ~buffer_ostream() override { OS << str(); }
 };
 
+class buffer_unique_ostream : public raw_svector_ostream {
+  std::unique_ptr<raw_ostream> OS;
+  SmallVector<char, 0> Buffer;
+
+  virtual void anchor() override;
+
+public:
+  buffer_unique_ostream(std::unique_ptr<raw_ostream> OS)
+      : raw_svector_ostream(Buffer), OS(std::move(OS)) {}
+  ~buffer_unique_ostream() override { *OS << str(); }
+};
+
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_RAW_OSTREAM_H

llvm/lib/Support/raw_ostream.cpp

 }
 
 void raw_null_ostream::pwrite_impl(const char *Ptr, size_t Size,
                                    uint64_t Offset) {}
 
 void raw_pwrite_stream::anchor() {}
 
 void buffer_ostream::anchor() {}
+
+void buffer_unique_ostream::anchor() {}