[PATCH] [ms-cxxabi] Implement guard variables for static initialization

[Eli Friedman]

class MicrosoftFunctionState : public CXXABIFunctionState {
public:
  MicrosoftFunctionState() : NumGuardedInitsEmitted(0), GuardGV(0) {}
  int NumGuardedInitsEmitted;
  llvm::GlobalVariable *GuardGV;
};

This is very suspicious.  For the Itanium ABI, to get this right, we have
to track it in the AST.  (See clang::MangleNumberingContext etc.)  A
testcase (which we messed up with the Itanium ABI until quite recently):

int foo();
inline void f() {
  if (0) {
    static int x = foo();
  }
  static int x = foo();
}
void g() { f(); }


-Eli

On Thu, Aug 15, 2013 at 4:59 PM, Reid Kleckner <rnk at google.com> wrote:

> Hi rjmccall,
>
> 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.
>
> Implements PR16888.
>
> http://llvm-reviews.chandlerc.com/D1416
>
> Files:
>   include/clang/AST/Mangle.h
>   lib/AST/ItaniumMangle.cpp
>   lib/AST/MicrosoftMangle.cpp
>   lib/CodeGen/CGCXXABI.cpp
>   lib/CodeGen/CGCXXABI.h
>   lib/CodeGen/CGDeclCXX.cpp
>   lib/CodeGen/CodeGenFunction.cpp
>   lib/CodeGen/CodeGenFunction.h
>   lib/CodeGen/ItaniumCXXABI.cpp
>   lib/CodeGen/MicrosoftCXXABI.cpp
>   test/CodeGenCXX/microsoft-abi-static-initializers.cpp
>
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>
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