[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

llvm-svn: 307883

3 files changed, 2 insertions, 88 deletions

diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 127d7df348e..50d702c6226 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2716,88 +2716,6 @@ llvm::Value *CodeGenFunction::EmitVTableTypeCheckedLoad(
       cast<llvm::PointerType>(VTable->getType())->getElementType());
 }
 
-bool
-CodeGenFunction::CanDevirtualizeMemberFunctionCall(const Expr *Base,
-                                                   const CXXMethodDecl *MD) {
-  // When building with -fapple-kext, all calls must go through the vtable since
-  // the kernel linker can do runtime patching of vtables.
-  if (getLangOpts().AppleKext)
-    return false;
-
-  // If the member function is marked 'final', we know that it can't be
-  // overridden and can therefore devirtualize it unless it's pure virtual.
-  if (MD->hasAttr<FinalAttr>())
-    return !MD->isPure();
-
-  // If the base expression (after skipping derived-to-base conversions) is a
-  // class prvalue, then we can devirtualize.
-  Base = Base->getBestDynamicClassTypeExpr();
-  if (Base->isRValue() && Base->getType()->isRecordType())
-    return true;
-
-  // If we don't even know what we would call, we can't devirtualize.
-  const CXXRecordDecl *BestDynamicDecl = Base->getBestDynamicClassType();
-  if (!BestDynamicDecl)
-    return false;
-
-  // There may be a method corresponding to MD in a derived class.
-  const CXXMethodDecl *DevirtualizedMethod =
-      MD->getCorrespondingMethodInClass(BestDynamicDecl);
-
-  // If that method is pure virtual, we can't devirtualize. If this code is
-  // reached, the result would be UB, not a direct call to the derived class
-  // function, and we can't assume the derived class function is defined.
-  if (DevirtualizedMethod->isPure())
-    return false;
-
-  // If that method is marked final, we can devirtualize it.
-  if (DevirtualizedMethod->hasAttr<FinalAttr>())
-    return true;
-
-  // Similarly, if the class itself is marked 'final' it can't be overridden
-  // and we can therefore devirtualize the member function call.
-  if (BestDynamicDecl->hasAttr<FinalAttr>())
-    return true;
-
-  if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Base)) {
-    if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
-      // This is a record decl. We know the type and can devirtualize it.
-      return VD->getType()->isRecordType();
-    }
-
-    return false;
-  }
-
-  // We can devirtualize calls on an object accessed by a class member access
-  // expression, since by C++11 [basic.life]p6 we know that it can't refer to
-  // a derived class object constructed in the same location. However, we avoid
-  // devirtualizing a call to a template function that we could instantiate
-  // implicitly, but have not decided to do so. This is needed because if this
-  // function does not get instantiated, the devirtualization will create a
-  // direct call to a function whose body may not exist. In contrast, calls to
-  // template functions that are not defined in this TU are allowed to be 
-  // devirtualized under assumption that it is user responsibility to
-  // instantiate them in some other TU.
-  if (const MemberExpr *ME = dyn_cast<MemberExpr>(Base))
-    if (const ValueDecl *VD = dyn_cast<ValueDecl>(ME->getMemberDecl()))
-      return VD->getType()->isRecordType() && 
-             (MD->instantiationIsPending() || MD->isDefined() ||
-               !MD->isImplicitlyInstantiable());
-
-  // Likewise for calls on an object accessed by a (non-reference) pointer to
-  // member access.
-  if (auto *BO = dyn_cast<BinaryOperator>(Base)) {
-    if (BO->isPtrMemOp()) {
-      auto *MPT = BO->getRHS()->getType()->castAs<MemberPointerType>();
-      if (MPT->getPointeeType()->isRecordType())
-        return true;
-    }
-  }
-
-  // We can't devirtualize the call.
-  return false;
-}
-
 void CodeGenFunction::EmitForwardingCallToLambda(
                                       const CXXMethodDecl *callOperator,
                                       CallArgList &callArgs) {
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index a9865f3703d..ab170245284 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -199,7 +199,8 @@ RValue CodeGenFunction::EmitCXXMemberOrOperatorMemberCallExpr(
   bool CanUseVirtualCall = MD->isVirtual() && !HasQualifier;
 
   const CXXMethodDecl *DevirtualizedMethod = nullptr;
-  if (CanUseVirtualCall && CanDevirtualizeMemberFunctionCall(Base, MD)) {
+  if (CanUseVirtualCall &&
+      MD->getDevirtualizedMethod(Base, getLangOpts().AppleKext)) {
     const CXXRecordDecl *BestDynamicDecl = Base->getBestDynamicClassType();
     DevirtualizedMethod = MD->getCorrespondingMethodInClass(BestDynamicDecl);
     assert(DevirtualizedMethod);
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 85aa5d4c022..5933e029be8 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1752,11 +1752,6 @@ public:
   llvm::Value *EmitVTableTypeCheckedLoad(const CXXRecordDecl *RD, llvm::Value *VTable,
                                          uint64_t VTableByteOffset);
 
-  /// CanDevirtualizeMemberFunctionCalls - Checks whether virtual calls on given
-  /// expr can be devirtualized.
-  bool CanDevirtualizeMemberFunctionCall(const Expr *Base,
-                                         const CXXMethodDecl *MD);
-
   /// EnterDtorCleanups - Enter the cleanups necessary to complete the
   /// given phase of destruction for a destructor.  The end result
   /// should call destructors on members and base classes in reverse