[llvm] 0308975 - [Support] Don't tie errs() to outs() by default

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2020-06-11T15:19:56-07:00
New Revision: 030897523d43e3296f69d25a71a140d9e5793c6a

URL: https://github.com/llvm/llvm-project/commit/030897523d43e3296f69d25a71a140d9e5793c6a
DIFF: https://github.com/llvm/llvm-project/commit/030897523d43e3296f69d25a71a140d9e5793c6a.diff

LOG: [Support] Don't tie errs() to outs() by default

This reverts part of D81156.

Accessing errs() concurrently was safe before and racy after D81156.
(`errs() << 'a'` is always racy)

Accessing outs() and errs() concurrently was safe before and racy after D81156.

Don't tie errs() to outs() by default to fix the fallout.
llvm-dwarfdump is single-threaded and opting in the tie behavior is safe.

Added: 
    

Modified: 
    llvm/lib/Support/raw_ostream.cpp
    llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Support/raw_ostream.cpp b/llvm/lib/Support/raw_ostream.cpp
index c06ea55afcfd..f2d78d773239 100644
--- a/llvm/lib/Support/raw_ostream.cpp
+++ b/llvm/lib/Support/raw_ostream.cpp
@@ -878,7 +878,6 @@ raw_fd_ostream &llvm::outs() {
 raw_fd_ostream &llvm::errs() {
   // Set standard error to be unbuffered and tied to outs() by default.
   static raw_fd_ostream S(STDERR_FILENO, false, true);
-  S.tie(&outs());
   return S;
 }
 

diff  --git a/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp b/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp
index d9e348e92282..47e426b2561b 100644
--- a/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp
+++ b/llvm/tools/llvm-dwarfdump/llvm-dwarfdump.cpp
@@ -606,6 +606,10 @@ static std::vector<std::string> expandBundle(const std::string &InputPath) {
 int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
 
+  // Flush outs() when printing to errs(). This avoids interleaving output
+  // between the two.
+  errs().tie(&outs());
+
   llvm::InitializeAllTargetInfos();
   llvm::InitializeAllTargetMCs();