Support,lld: Rename misnamed F_no_mmap to F_mmap

`F_no_mmap` introduced by https://reviews.llvm.org/D69294 is misnamed.
It oughts to be `F_mmap`

When the output is a regular file or do not exist,
`--no-mmap-output-file` is the default. Relands #134787 by fixing the
lld option default. Note: changing the default to --map-output-file
would likely fail on llvm-clang-x86_64-sie-win
(https://lab.llvm.org/buildbot/#/builders/46/builds/14847)

Pull Request: #139836

Author: MaskRay

lld/ELF/Arch/ARM.cpp

@@ -1489,7 +1489,7 @@ template <typename ELFT> void elf::writeARMCmseImportLib(Ctx &ctx) {
   const uint64_t fileSize =
       sectionHeaderOff + shnum * sizeof(typename ELFT::Shdr);
   const unsigned flags =
-      ctx.arg.mmapOutputFile ? 0 : (unsigned)FileOutputBuffer::F_no_mmap;
+      ctx.arg.mmapOutputFile ? (unsigned)FileOutputBuffer::F_mmap : 0;
   unlinkAsync(ctx.arg.cmseOutputLib);
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(ctx.arg.cmseOutputLib, fileSize, flags);

lld/ELF/Driver.cpp

@@ -1421,7 +1421,7 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
   ctx.arg.mergeArmExidx =
       args.hasFlag(OPT_merge_exidx_entries, OPT_no_merge_exidx_entries, true);
   ctx.arg.mmapOutputFile =
-      args.hasFlag(OPT_mmap_output_file, OPT_no_mmap_output_file, true);
+      args.hasFlag(OPT_mmap_output_file, OPT_no_mmap_output_file, false);
   ctx.arg.nmagic = args.hasFlag(OPT_nmagic, OPT_no_nmagic, false);
   ctx.arg.noinhibitExec = args.hasArg(OPT_noinhibit_exec);
   ctx.arg.nostdlib = args.hasArg(OPT_nostdlib);

lld/ELF/Writer.cpp

@@ -2908,8 +2908,8 @@ template <class ELFT> void Writer<ELFT>::openFile() {
   unsigned flags = 0;
   if (!ctx.arg.relocatable)
     flags |= FileOutputBuffer::F_executable;
-  if (!ctx.arg.mmapOutputFile)
-    flags |= FileOutputBuffer::F_no_mmap;
+  if (ctx.arg.mmapOutputFile)
+    flags |= FileOutputBuffer::F_mmap;
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(ctx.arg.outputFile, fileSize, flags);
 

llvm/include/llvm/Support/FileOutputBuffer.h

@@ -32,9 +32,8 @@ class FileOutputBuffer {
     /// Set the 'x' bit on the resulting file.
     F_executable = 1,
 
-    /// Don't use mmap and instead write an in-memory buffer to a file when this
-    /// buffer is closed.
-    F_no_mmap = 2,
+    /// Use mmap for in-memory file buffer.
+    F_mmap = 2,
   };
 
   /// Factory method to create an OutputBuffer object which manages a read/write

llvm/lib/Support/FileOutputBuffer.cpp

@@ -186,7 +186,7 @@ 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:
-    if (Flags & F_no_mmap)
+    if (Flags & F_mmap)
       return createInMemoryBuffer(Path, Size, Mode);
     else
       return createOnDiskBuffer(Path, Size, Mode);

llvm/unittests/Support/FileOutputBufferTest.cpp

@@ -123,7 +123,7 @@ TEST(FileOutputBuffer, Test) {
   File5.append("/file5");
   {
     Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
-        FileOutputBuffer::create(File5, 8000, FileOutputBuffer::F_no_mmap);
+        FileOutputBuffer::create(File5, 8000, FileOutputBuffer::F_mmap);
     ASSERT_NO_ERROR(errorToErrorCode(BufferOrErr.takeError()));
     std::unique_ptr<FileOutputBuffer> &Buffer = *BufferOrErr;
     // Start buffer with special header.