[lld] [llvm] Revert "Rename `F_no_mmap` to `F_mmap`" (PR #134924)

[via llvm-commits]

https://github.com/dgg5503 created https://github.com/llvm/llvm-project/pull/134924

Reverts llvm/llvm-project#134787

Causes the LIT test `lld\test\ELF\link-open-file.test` to fail on the `llvm-clang-x86_64-sie-win` Build Bot. First instance of the failure observed in: https://lab.llvm.org/buildbot/#/builders/46/builds/14847

>From 06ef32e84b7de9498678576f67b9bdaec24d4dcc Mon Sep 17 00:00:00 2001
From: Douglas <Douglas.Gliner at gmail.com>
Date: Tue, 8 Apr 2025 13:08:47 -0700
Subject: [PATCH] Revert "Rename `F_no_mmap` to `F_mmap` (#134787)"

This reverts commit d6c8e8908d421979a428ede9f9a630dac8576c5b.
---
 lld/ELF/Arch/ARM.cpp                            | 2 +-
 lld/ELF/Writer.cpp                              | 4 ++--
 llvm/include/llvm/Support/FileOutputBuffer.h    | 5 +++--
 llvm/lib/Support/FileOutputBuffer.cpp           | 2 +-
 llvm/unittests/Support/FileOutputBufferTest.cpp | 2 +-
 5 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/lld/ELF/Arch/ARM.cpp b/lld/ELF/Arch/ARM.cpp
index e45dd4d354afb..e667fdc0633c5 100644
--- a/lld/ELF/Arch/ARM.cpp
+++ b/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 ? (unsigned)FileOutputBuffer::F_mmap : 0;
+      ctx.arg.mmapOutputFile ? 0 : (unsigned)FileOutputBuffer::F_no_mmap;
   unlinkAsync(ctx.arg.cmseOutputLib);
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(ctx.arg.cmseOutputLib, fileSize, flags);
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index cc1538cc76c3c..28b24f90716b8 100644
--- a/lld/ELF/Writer.cpp
+++ b/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_mmap;
+  if (!ctx.arg.mmapOutputFile)
+    flags |= FileOutputBuffer::F_no_mmap;
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(ctx.arg.outputFile, fileSize, flags);
 
diff --git a/llvm/include/llvm/Support/FileOutputBuffer.h b/llvm/include/llvm/Support/FileOutputBuffer.h
index f98e7a5470b55..d4b73522115db 100644
--- a/llvm/include/llvm/Support/FileOutputBuffer.h
+++ b/llvm/include/llvm/Support/FileOutputBuffer.h
@@ -31,8 +31,9 @@ class FileOutputBuffer {
     /// Set the 'x' bit on the resulting file.
     F_executable = 1,
 
-    /// Use mmap for in-memory file buffer.
-    F_mmap = 2,
+    /// Don't use mmap and instead write an in-memory buffer to a file when this
+    /// buffer is closed.
+    F_no_mmap = 2,
   };
 
   /// Factory method to create an OutputBuffer object which manages a read/write
diff --git a/llvm/lib/Support/FileOutputBuffer.cpp b/llvm/lib/Support/FileOutputBuffer.cpp
index a2396d7629488..58a06a34e8cf3 100644
--- a/llvm/lib/Support/FileOutputBuffer.cpp
+++ b/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_mmap)
+    if (Flags & F_no_mmap)
       return createInMemoryBuffer(Path, Size, Mode);
     else
       return createOnDiskBuffer(Path, Size, Mode);
diff --git a/llvm/unittests/Support/FileOutputBufferTest.cpp b/llvm/unittests/Support/FileOutputBufferTest.cpp
index 423a6e12240c0..f7bb0833e5a0e 100644
--- a/llvm/unittests/Support/FileOutputBufferTest.cpp
+++ b/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_mmap);
+        FileOutputBuffer::create(File5, 8000, FileOutputBuffer::F_no_mmap);
     ASSERT_NO_ERROR(errorToErrorCode(BufferOrErr.takeError()));
     std::unique_ptr<FileOutputBuffer> &Buffer = *BufferOrErr;
     // Start buffer with special header.