[ms-cxxabi] Implement guard variables for static initialization

Static locals requiring initialization are not thread safe on Windows.
Unfortunately, it's possible to create static locals that are actually
externally visible with inline functions and templates.  As a result, we
have to implement an initialization guard scheme that is compatible with
TUs built by MSVC, which makes thread safety prohibitively difficult.

MSVC's scheme is that every function that requires a guard gets an i32
bitfield.  Each static local is assigned a bit that indicates if it has
been initialized, up to 32 bits, at which point a new bitfield is
created.  MSVC rejects inline functions with more than 32 static locals,
and the externally visible mangling (?_B) only allows for one guard
variable per function.

On Eli's recommendation, I used MangleNumberingContext to track which
bit each static corresponds to.

Implements PR16888.

Reviewers: rjmccall, eli.friedman

Differential Revision: http://llvm-reviews.chandlerc.com/D1416

llvm-svn: 190427

1 files changed, 3 insertions, 2 deletions

diff --git a/clang/include/clang/AST/MangleNumberingContext.h b/clang/include/clang/AST/MangleNumberingContext.h
index 4f81e0c5548..5a227f201fb 100644
--- a/clang/include/clang/AST/MangleNumberingContext.h
+++ b/clang/include/clang/AST/MangleNumberingContext.h
@@ -33,10 +33,11 @@ class VarDecl;
 class MangleNumberingContext 
     : public RefCountedBase<MangleNumberingContext> {
   llvm::DenseMap<const Type *, unsigned> ManglingNumbers;
-  llvm::DenseMap<IdentifierInfo*, unsigned> VarManglingNumbers;
   llvm::DenseMap<IdentifierInfo*, unsigned> TagManglingNumbers;
 
 public:
+  virtual ~MangleNumberingContext() {}
+
   /// \brief Retrieve the mangling number of a new lambda expression with the
   /// given call operator within this context.
   unsigned getManglingNumber(const CXXMethodDecl *CallOperator);
@@ -47,7 +48,7 @@ public:
 
   /// \brief Retrieve the mangling number of a static local variable within
   /// this context.
-  unsigned getManglingNumber(const VarDecl *VD);
+  virtual unsigned getManglingNumber(const VarDecl *VD) = 0;
 
   /// \brief Retrieve the mangling number of a static local variable within
   /// this context.