[-cxx-abi microsoft] Add commentary for mangleStaticGuardVariable

We will need to do some work here if we want to play nice with MSVC2013.
Add a TODO indicating what changed and why this matters.

llvm-svn: 197193

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index 24eac84cdd2..8a2357d057b 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -2048,6 +2048,15 @@ void MicrosoftMangleContextImpl::mangleReferenceTemporary(const VarDecl *VD,
 
 void MicrosoftMangleContextImpl::mangleStaticGuardVariable(const VarDecl *VD,
                                                            raw_ostream &Out) {
+  // TODO: This is not correct, especially with respect to MSVC2013.  MSVC2013
+  // utilizes thread local variables to implement thread safe, re-entrant
+  // initialization for statics.  They no longer differentiate between an
+  // externally visible and non-externally visible static with respect to
+  // mangling, they all get $TSS <number>.
+  //
+  // N.B. This means that they can get more than 32 static variable guards in a
+  // scope.  It also means that they broke compatibility with their own ABI.
+
   // <guard-name> ::= ?_B <postfix> @51
   //              ::= ?$S <guard-num> @ <postfix> @4IA