1 files changed, 30 insertions, 13 deletions
diff --git a/lib/Support/FileOutputBuffer.cpp b/lib/Support/FileOutputBuffer.cpp
index c4ff563e5f44..1214b5a0ba1f 100644
--- a/lib/Support/FileOutputBuffer.cpp
+++ b/lib/Support/FileOutputBuffer.cpp
@@ -82,9 +82,11 @@ public:
   size_t getBufferSize() const override { return Buffer.size(); }
 
   Error commit() override {
+    using namespace sys::fs;
     int FD;
     std::error_code EC;
-    if (auto EC = openFileForWrite(FinalPath, FD, fs::F_None, Mode))
+    if (auto EC =
+            openFileForWrite(FinalPath, FD, CD_CreateAlways, OF_None, Mode))
       return errorCodeToError(EC);
     raw_fd_ostream OS(FD, /*shouldClose=*/true, /*unbuffered=*/true);
     OS << StringRef((const char *)Buffer.base(), Buffer.size());
@@ -108,24 +110,30 @@ createInMemoryBuffer(StringRef Path, size_t Size, unsigned Mode) {
 }
 
 static Expected<std::unique_ptr<OnDiskBuffer>>
-createOnDiskBuffer(StringRef Path, size_t Size, unsigned Mode) {
+createOnDiskBuffer(StringRef Path, size_t Size, bool InitExisting,
+                   unsigned Mode) {
   Expected<fs::TempFile> FileOrErr =
       fs::TempFile::create(Path + ".tmp%%%%%%%", Mode);
   if (!FileOrErr)
     return FileOrErr.takeError();
   fs::TempFile File = std::move(*FileOrErr);
 
-#ifndef LLVM_ON_WIN32
-  // On Windows, CreateFileMapping (the mmap function on Windows)
-  // automatically extends the underlying file. We don't need to
-  // extend the file beforehand. _chsize (ftruncate on Windows) is
-  // pretty slow just like it writes specified amount of bytes,
-  // so we should avoid calling that function.
-  if (auto EC = fs::resize_file(File.FD, Size)) {
-    consumeError(File.discard());
-    return errorCodeToError(EC);
-  }
+  if (InitExisting) {
+    if (auto EC = sys::fs::copy_file(Path, File.FD))
+      return errorCodeToError(EC);
+  } else {
+#ifndef _WIN32
+    // On Windows, CreateFileMapping (the mmap function on Windows)
+    // automatically extends the underlying file. We don't need to
+    // extend the file beforehand. _chsize (ftruncate on Windows) is
+    // pretty slow just like it writes specified amount of bytes,
+    // so we should avoid calling that function.
+    if (auto EC = fs::resize_file(File.FD, Size)) {
+      consumeError(File.discard());
+      return errorCodeToError(EC);
+    }
 #endif
+  }
 
   // Mmap it.
   std::error_code EC;
@@ -149,6 +157,15 @@ FileOutputBuffer::create(StringRef Path, size_t Size, unsigned Flags) {
   fs::file_status Stat;
   fs::status(Path, Stat);
 
+  if ((Flags & F_modify) && Size == size_t(-1)) {
+    if (Stat.type() == fs::file_type::regular_file)
+      Size = Stat.getSize();
+    else if (Stat.type() == fs::file_type::file_not_found)
+      return errorCodeToError(errc::no_such_file_or_directory);
+    else
+      return errorCodeToError(errc::invalid_argument);
+  }
+
   // Usually, we want to create OnDiskBuffer to create a temporary file in
   // the same directory as the destination file and atomically replaces it
   // by rename(2).
@@ -163,7 +180,7 @@ FileOutputBuffer::create(StringRef Path, size_t Size, unsigned Flags) {
   case fs::file_type::regular_file:
   case fs::file_type::file_not_found:
   case fs::file_type::status_error:
-    return createOnDiskBuffer(Path, Size, Mode);
+    return createOnDiskBuffer(Path, Size, !!(Flags & F_modify), Mode);
   default:
     return createInMemoryBuffer(Path, Size, Mode);
   }