[PATCH] Fix IRGen for referencing a static local before emitting its decl

[Richard Smith]

================
Comment at: lib/CodeGen/CGDecl.cpp:174
@@ -173,4 +173,3 @@
 
-llvm::Constant *
-CodeGenFunction::CreateStaticVarDecl(const VarDecl &D,
-                                     llvm::GlobalValue::LinkageTypes Linkage) {
+llvm::Constant *CodeGenFunction::getOrCreateStaticVarDecl(
+    const VarDecl &D, llvm::GlobalValue::LinkageTypes Linkage) {
----------------
Does it still make sense for this to be on `CodeGenFunction` since it can now be called while emitting the "wrong" function? It seems to risk using local state of the `CodeGenFunction` object, which would be bad.

================
Comment at: lib/CodeGen/CGDecl.cpp:191
@@ -184,3 +190,3 @@
   else
     Name = GetStaticDeclName(*this, D);
 
----------------
Case in point: this will presumably produce the wrong mangled name if the static local's emission is triggered by a function other than the containing one.

================
Comment at: lib/CodeGen/CGDecl.cpp:199
@@ -192,3 +198,3 @@
                              Ty.isConstant(getContext()), Linkage,
                              CGM.EmitNullConstant(D.getType()), Name, nullptr,
                              llvm::GlobalVariable::NotThreadLocal,
----------------
This doesn't look right. If the static local has a constant initializer, you need to emit it here, not as part of emitting the surrounding function. Given:

  static auto f() {
    static int n = 1;
    struct S { int &operator()() { return n; } };
    return S();
  }

  int main() { return decltype(f())()(); }

... `main` should return 1, and I think with this patch it returns 0.

http://reviews.llvm.org/D4787