[Sema] Mark a virtual CXXMethodDecl as used if a call to it can be

devirtualized.

The code to detect devirtualized calls is already in IRGen, so move the
code to lib/AST and make it a shared utility between Sema and IRGen.

This commit fixes a linkage error I was seeing when compiling the
following code:

$ cat test1.cpp
struct Base {
  virtual void operator()() {}
};

template<class T>
struct Derived final : Base {
  void operator()() override {}
};

Derived<int> *d;

int main() {
  if (d)
    (*d)();
  return 0;
}

rdar://problem/33195657

Differential Revision: https://reviews.llvm.org/D34301

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@307883 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 14 insertions, 1 deletions

diff --git a/include/clang/AST/DeclCXX.h b/include/clang/AST/DeclCXX.h
index 6965e8143f..9d64f0244e 100644
--- a/include/clang/AST/DeclCXX.h
+++ b/include/clang/AST/DeclCXX.h
@@ -1886,6 +1886,19 @@ public:
     return (CD->begin_overridden_methods() != CD->end_overridden_methods());
   }
 
+  /// If it's possible to devirtualize a call to this method, return the called
+  /// function. Otherwise, return null.
+
+  /// \param Base The object on which this virtual function is called.
+  /// \param IsAppleKext True if we are compiling for Apple kext.
+  CXXMethodDecl *getDevirtualizedMethod(const Expr *Base, bool IsAppleKext);
+
+  const CXXMethodDecl *getDevirtualizedMethod(const Expr *Base,
+                                              bool IsAppleKext) const {
+    return const_cast<CXXMethodDecl *>(this)->getDevirtualizedMethod(
+        Base, IsAppleKext);
+  }
+
   /// \brief Determine whether this is a usual deallocation function
   /// (C++ [basic.stc.dynamic.deallocation]p2), which is an overloaded
   /// delete or delete[] operator with a particular signature.
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index 31728a9f23..95629a2591 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -3944,7 +3944,7 @@ public:
   void MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
                               bool MightBeOdrUse = true);
   void MarkVariableReferenced(SourceLocation Loc, VarDecl *Var);
-  void MarkDeclRefReferenced(DeclRefExpr *E);
+  void MarkDeclRefReferenced(DeclRefExpr *E, const Expr *Base = nullptr);
   void MarkMemberReferenced(MemberExpr *E);
 
   void UpdateMarkingForLValueToRValue(Expr *E);