[Support] Use outs() in ToolOutputFile

Summary:
If the output filename was specified as "-", the ToolOutputFile class
would create a brand new raw_ostream object referring to the stdout.
This patch changes it to reuse the llvm::outs() singleton.

At the moment, this change should be "NFC", but it does enable other
enhancements, like the automatic stdout/stderr synchronization as
discussed on D80803.

I've checked the history, and I did not find any indication that this
class *has* to use a brand new stream object instead of outs() --
indeed, it is special-casing "-" in a number of places already, so this
change fits the pattern pretty well. I suspect the main reason for the
current state of affairs is that the class was originally introduced
(r111595, in 2010) as a raw_fd_ostream subclass, which made any other
solution impossible.

Another potential benefit of this patch is that it makes it possible to
move the raw_ostream class out of the business of special-casing "-" for
stdout handling. That state of affairs does not seem appropriate because
"-" is a valid filename (albeit hard to access with a lot of command
line tools) on most systems. Handling "-" in ToolOutputFile seems more
appropriate.

To make this possible, this patch changes the return type of
llvm::outs() and errs() to raw_fd_ostream&. Previously the functions
were constructing objects of that type, but returning a generic
raw_ostream reference. This makes it possible for new ToolOutputFile and
other code to use raw_fd_ostream methods like error() on the outs()
object. This does not seem like a bad thing (since stdout is a file
descriptor which can be redirected to anywhere, it makes sense to ask it
whether the writing was successful or if it supports seeking), and
indeed a lot of code was already depending on this fact via the
ToolOutputFile "back door".

Reviewers: dblaikie, JDevlieghere, MaskRay, jhenderson

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D81078

1 files changed, 20 insertions, 6 deletions

diff --git a/llvm/lib/Support/ToolOutputFile.cpp b/llvm/lib/Support/ToolOutputFile.cpp
index 1051af3..c2ca97a 100644
--- a/llvm/lib/Support/ToolOutputFile.cpp
+++ b/llvm/lib/Support/ToolOutputFile.cpp
@@ -15,31 +15,45 @@
 #include "llvm/Support/Signals.h"
 using namespace llvm;
 
+static bool isStdout(StringRef Filename) { return Filename == "-"; }
+
 ToolOutputFile::CleanupInstaller::CleanupInstaller(StringRef Filename)
     : Filename(std::string(Filename)), Keep(false) {
   // Arrange for the file to be deleted if the process is killed.
-  if (Filename != "-")
+  if (!isStdout(Filename))
     sys::RemoveFileOnSignal(Filename);
 }
 
 ToolOutputFile::CleanupInstaller::~CleanupInstaller() {
+  if (isStdout(Filename))
+    return;
+
   // Delete the file if the client hasn't told us not to.
-  if (!Keep && Filename != "-")
+  if (!Keep)
     sys::fs::remove(Filename);
 
   // Ok, the file is successfully written and closed, or deleted. There's no
   // further need to clean it up on signals.
-  if (Filename != "-")
-    sys::DontRemoveFileOnSignal(Filename);
+  sys::DontRemoveFileOnSignal(Filename);
 }
 
 ToolOutputFile::ToolOutputFile(StringRef Filename, std::error_code &EC,
                                sys::fs::OpenFlags Flags)
-    : Installer(Filename), OS(Filename, EC, Flags) {
+    : Installer(Filename) {
+  if (isStdout(Filename)) {
+    OS = &outs();
+    EC = std::error_code();
+    return;
+  }
+  OSHolder.emplace(Filename, EC, Flags);
+  OS = OSHolder.getPointer();
   // If open fails, no cleanup is needed.
   if (EC)
     Installer.Keep = true;
 }
 
 ToolOutputFile::ToolOutputFile(StringRef Filename, int FD)
-    : Installer(Filename), OS(FD, true) {}
+    : Installer(Filename) {
+  OSHolder.emplace(FD, true);
+  OS = OSHolder.getPointer();
+}