Add support for tsan annotations (thread sanitizer, a valgrind-based tool).

These annotations are disabled entirely when either ENABLE_THREADS is off, or
building a release build. When enabled, they add calls to functions with no
statements to ManagedStatic's getters.

Use these annotations to inform tsan that the race used inside ManagedStatic
initialization is actually benign. Thanks to Kostya Serebryany for helping
write this patch!

llvm-svn: 144567

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/Support/ManagedStatic.cpp b/llvm/lib/Support/ManagedStatic.cpp
index c767c15e71c..098cccb68df 100644
--- a/llvm/lib/Support/ManagedStatic.cpp
+++ b/llvm/lib/Support/ManagedStatic.cpp
@@ -27,8 +27,15 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
     if (Ptr == 0) {
       void* tmp = Creator ? Creator() : 0;
 
+      TsanHappensBefore(this);
       sys::MemoryFence();
+
+      // This write is racy against the first read in the ManagedStatic
+      // accessors. The race is benign because it does a second read after a
+      // memory fence, at which point it isn't possible to get a partial value.
+      TsanIgnoreWritesBegin();
       Ptr = tmp;
+      TsanIgnoreWritesEnd();
       DeleterFn = Deleter;
       
       // Add to list of managed statics.
@@ -72,4 +79,3 @@ void llvm::llvm_shutdown() {
 
   if (llvm_is_multithreaded()) llvm_stop_multithreaded();
 }
-