[CIR][CIRGen] Support pure and deleted virtual functions (llvm#823)

This is a straightforward adaption of existing CodeGen logic. While I'm
here, move block comments inside their blocks, so that they look nicer.

Author: smeenai

clang/lib/CIR/CodeGen/CIRGenCXXABI.h

@@ -235,6 +235,12 @@ class CIRGenCXXABI {
                                   BaseSubobject Base,
                                   const CXXRecordDecl *NearestVBase) = 0;
 
+  /// Gets the pure virtual member call function.
+  virtual StringRef getPureVirtualCallName() = 0;
+
+  /// Gets the deleted virtual member call name.
+  virtual StringRef getDeletedVirtualCallName() = 0;
+
   /// Specify how one should pass an argument of a record type.
   enum class RecordArgABI {
     /// Pass it using the normal C aggregate rules for the ABI, potentially

clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp

@@ -215,6 +215,11 @@ class CIRGenItaniumCXXABI : public cir::CIRGenCXXABI {
     return false;
   }
 
+  StringRef getPureVirtualCallName() override { return "__cxa_pure_virtual"; }
+  StringRef getDeletedVirtualCallName() override {
+    return "__cxa_deleted_virtual";
+  }
+
   /// TODO(cir): seems like could be shared between LLVM IR and CIR codegen.
   bool mayNeedDestruction(const VarDecl *VD) const {
     if (VD->needsDestruction(getContext()))

clang/lib/CIR/CodeGen/CIRGenVTables.cpp

@@ -217,8 +217,7 @@ void CIRGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
       llvm_unreachable("NYI");
     }
 
-    [[maybe_unused]] auto getSpecialVirtualFn =
-        [&](StringRef name) -> mlir::Attribute {
+    auto getSpecialVirtualFn = [&](StringRef name) -> mlir::cir::FuncOp {
       // FIXME(PR43094): When merging comdat groups, lld can select a local
       // symbol as the signature symbol even though it cannot be accessed
       // outside that symbol's TU. The relative vtables ABI would make
@@ -235,45 +234,41 @@ void CIRGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
           CGM.getTriple().isNVPTX())
         llvm_unreachable("NYI");
 
-      llvm_unreachable("NYI");
-      // llvm::FunctionType *fnTy =
-      //     llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
-      // llvm::Constant *fn = cast<llvm::Constant>(
-      //     CGM.CreateRuntimeFunction(fnTy, name).getCallee());
-      // if (auto f = dyn_cast<llvm::Function>(fn))
-      //   f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
-      // return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
+      mlir::cir::FuncType fnTy =
+          CGM.getBuilder().getFuncType({}, CGM.getBuilder().getVoidTy());
+      mlir::cir::FuncOp fnPtr = CGM.createRuntimeFunction(fnTy, name);
+      // LLVM codegen handles unnamedAddr
+      assert(!MissingFeatures::unnamedAddr());
+      return fnPtr;
     };
 
     mlir::cir::FuncOp fnPtr;
-    // Pure virtual member functions.
     if (cast<CXXMethodDecl>(GD.getDecl())->isPureVirtual()) {
-      llvm_unreachable("NYI");
-      // if (!PureVirtualFn)
-      //   PureVirtualFn =
-      //       getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
-      // fnPtr = PureVirtualFn;
+      // Pure virtual member functions.
+      if (!PureVirtualFn)
+        PureVirtualFn =
+            getSpecialVirtualFn(CGM.getCXXABI().getPureVirtualCallName());
+      fnPtr = PureVirtualFn;
 
-      // Deleted virtual member functions.
     } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
-      llvm_unreachable("NYI");
-      // if (!DeletedVirtualFn)
-      //   DeletedVirtualFn =
-      //       getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
-      // fnPtr = DeletedVirtualFn;
+      // Deleted virtual member functions.
+      if (!DeletedVirtualFn)
+        DeletedVirtualFn =
+            getSpecialVirtualFn(CGM.getCXXABI().getDeletedVirtualCallName());
+      fnPtr = DeletedVirtualFn;
 
-      // Thunks.
     } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
                layout.vtable_thunks()[nextVTableThunkIndex].first ==
                    componentIndex) {
+      // Thunks.
       llvm_unreachable("NYI");
       // auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
 
       // nextVTableThunkIndex++;
       // fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
 
-      // Otherwise we can use the method definition directly.
     } else {
+      // Otherwise we can use the method definition directly.
       auto fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
       fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
     }

clang/lib/CIR/CodeGen/CIRGenVTables.h

@@ -19,6 +19,7 @@
 #include "clang/AST/GlobalDecl.h"
 #include "clang/AST/VTableBuilder.h"
 #include "clang/Basic/ABI.h"
+#include "clang/CIR/Dialect/IR/CIRDialect.h"
 #include "llvm/ADT/DenseMap.h"
 
 namespace clang {
@@ -52,11 +53,11 @@ class CIRGenVTables {
   /// indices.
   SecondaryVirtualPointerIndicesMapTy SecondaryVirtualPointerIndices;
 
-  //   /// Cache for the pure virtual member call function.
-  //   llvm::Constant *PureVirtualFn = nullptr;
+  /// Cache for the pure virtual member call function.
+  mlir::cir::FuncOp PureVirtualFn = nullptr;
 
-  //   /// Cache for the deleted virtual member call function.
-  //   llvm::Constant *DeletedVirtualFn = nullptr;
+  /// Cache for the deleted virtual member call function.
+  mlir::cir::FuncOp DeletedVirtualFn = nullptr;
 
   //   /// Get the address of a thunk and emit it if necessary.
   //   llvm::Constant *maybeEmitThunk(GlobalDecl GD,

clang/test/CIR/CodeGen/special-virtual-func.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s
+
+// Check that pure and deleted virtual functions are correctly emitted in the
+// vtable.
+class A {
+  A();
+  virtual void pure() = 0;
+  virtual void deleted() = delete;
+};
+
+A::A() = default;
+
+// CHECK: @_ZTV1A = #cir.vtable<{#cir.const_array<[#cir.ptr<null> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1A> : !cir.ptr<!u8i>, #cir.global_view<@__cxa_pure_virtual> : !cir.ptr<!u8i>, #cir.global_view<@__cxa_deleted_virtual> : !cir.ptr<!u8i>]>
+// CHECK: cir.func private @__cxa_pure_virtual()
+// CHECK: cir.func private @__cxa_deleted_virtual()