Move code to emit the callee of an CXXOperatorCallExpr out into a separate function in CGClass.cpp

llvm-svn: 131075

clang/lib/CodeGen/CGClass.cpp

@@ -1521,3 +1521,136 @@ llvm::Value *CodeGenFunction::GetVTablePtr(llvm::Value *This,
   llvm::Value *VTablePtrSrc = Builder.CreateBitCast(This, Ty->getPointerTo());
   return Builder.CreateLoad(VTablePtrSrc, "vtable");
 }
+
+static const CXXRecordDecl *getMostDerivedClassDecl(const Expr *Base) {
+  const Expr *E = Base;
+  
+  while (true) {
+    E = E->IgnoreParens();
+    if (const CastExpr *CE = dyn_cast<CastExpr>(E)) {
+      if (CE->getCastKind() == CK_DerivedToBase || 
+          CE->getCastKind() == CK_UncheckedDerivedToBase ||
+          CE->getCastKind() == CK_NoOp) {
+        E = CE->getSubExpr();
+        continue;
+      }
+    }
+
+    break;
+  }
+
+  QualType DerivedType = E->getType();
+  if (const PointerType *PTy = DerivedType->getAs<PointerType>())
+    DerivedType = PTy->getPointeeType();
+
+  return cast<CXXRecordDecl>(DerivedType->castAs<RecordType>()->getDecl());
+}
+
+// FIXME: Ideally Expr::IgnoreParenNoopCasts should do this, but it doesn't do
+// quite what we want.
+static const Expr *skipNoOpCastsAndParens(const Expr *E) {
+  while (true) {
+    if (const ParenExpr *PE = dyn_cast<ParenExpr>(E)) {
+      E = PE->getSubExpr();
+      continue;
+    }
+
+    if (const CastExpr *CE = dyn_cast<CastExpr>(E)) {
+      if (CE->getCastKind() == CK_NoOp) {
+        E = CE->getSubExpr();
+        continue;
+      }
+    }
+    if (const UnaryOperator *UO = dyn_cast<UnaryOperator>(E)) {
+      if (UO->getOpcode() == UO_Extension) {
+        E = UO->getSubExpr();
+        continue;
+      }
+    }
+    return E;
+  }
+}
+
+/// canDevirtualizeMemberFunctionCall - Checks whether the given virtual member
+/// function call on the given expr can be devirtualized.
+/// expr can be devirtualized.
+static bool canDevirtualizeMemberFunctionCall(const Expr *Base, 
+                                              const CXXMethodDecl *MD) {
+  // If the most derived class is marked final, we know that no subclass can
+  // override this member function and so we can devirtualize it. For example:
+  //
+  // struct A { virtual void f(); }
+  // struct B final : A { };
+  //
+  // void f(B *b) {
+  //   b->f();
+  // }
+  //
+  const CXXRecordDecl *MostDerivedClassDecl = getMostDerivedClassDecl(Base);
+  if (MostDerivedClassDecl->hasAttr<FinalAttr>())
+    return true;
+
+  // If the member function is marked 'final', we know that it can't be
+  // overridden and can therefore devirtualize it.
+  if (MD->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 (MD->getParent()->hasAttr<FinalAttr>())
+    return true;
+
+  Base = skipNoOpCastsAndParens(Base);
+  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 always devirtualize calls on temporary object expressions.
+  if (isa<CXXConstructExpr>(Base))
+    return true;
+  
+  // And calls on bound temporaries.
+  if (isa<CXXBindTemporaryExpr>(Base))
+    return true;
+  
+  // Check if this is a call expr that returns a record type.
+  if (const CallExpr *CE = dyn_cast<CallExpr>(Base))
+    return CE->getCallReturnType()->isRecordType();
+
+  // We can't devirtualize the call.
+  return false;
+}
+
+static bool UseVirtualCall(ASTContext &Context,
+                           const CXXOperatorCallExpr *CE,
+                           const CXXMethodDecl *MD) {
+  if (!MD->isVirtual())
+    return false;
+  
+  // When building with -fapple-kext, all calls must go through the vtable since
+  // the kernel linker can do runtime patching of vtables.
+  if (Context.getLangOptions().AppleKext)
+    return true;
+
+  return !canDevirtualizeMemberFunctionCall(CE->getArg(0), MD);
+}
+
+llvm::Value *
+CodeGenFunction::EmitCXXOperatorMemberCallee(const CXXOperatorCallExpr *E,
+                                             const CXXMethodDecl *MD,
+                                             llvm::Value *This) {
+  const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
+  const llvm::Type *Ty =
+    CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(MD),
+                                   FPT->isVariadic());
+
+  if (UseVirtualCall(getContext(), E, MD))
+    return BuildVirtualCall(MD, This, Ty);
+
+  return CGM.GetAddrOfFunction(MD, Ty);
+}

clang/lib/CodeGen/CGExprCXX.cpp

@@ -345,18 +345,7 @@ CodeGenFunction::EmitCXXOperatorMemberCallExpr(const CXXOperatorCallExpr *E,
     }
   }
 
-  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
-  const llvm::Type *Ty =
-    CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(MD),
-                                   FPT->isVariadic());
-  llvm::Value *Callee;
-  if (MD->isVirtual() && 
-      !canDevirtualizeMemberFunctionCalls(getContext(),
-                                           E->getArg(0), MD))
-    Callee = BuildVirtualCall(MD, This, Ty);
-  else
-    Callee = CGM.GetAddrOfFunction(MD, Ty);
-
+  llvm::Value *Callee = EmitCXXOperatorMemberCallee(E, MD, This);
   return EmitCXXMemberCall(MD, Callee, ReturnValue, This, /*VTT=*/0,
                            E->arg_begin() + 1, E->arg_end());
 }

clang/lib/CodeGen/CodeGenFunction.h

@@ -1918,6 +1918,9 @@ public:
   RValue EmitCXXMemberPointerCallExpr(const CXXMemberCallExpr *E,
                                       ReturnValueSlot ReturnValue);
 
+  llvm::Value *EmitCXXOperatorMemberCallee(const CXXOperatorCallExpr *E,
+                                           const CXXMethodDecl *MD,
+                                           llvm::Value *This);
   RValue EmitCXXOperatorMemberCallExpr(const CXXOperatorCallExpr *E,
                                        const CXXMethodDecl *MD,
                                        ReturnValueSlot ReturnValue);