[CIR] Add lowering for the cir.vtable.address_point operation

This adds support for lowering the cir.vtable.address_point
operation to the LLVM dialect, as well as type converter support
for the cir.vptr type.

Author: andykaylor

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -2083,6 +2083,10 @@ static void prepareTypeConverter(mlir::LLVMTypeConverter &converter,
 
     return mlir::LLVM::LLVMPointerType::get(type.getContext(), targetAS);
   });
+  converter.addConversion([&](cir::VPtrType type) -> mlir::Type {
+    assert(!cir::MissingFeatures::addressSpace());
+    return mlir::LLVM::LLVMPointerType::get(type.getContext());
+  });
   converter.addConversion([&](cir::ArrayType type) -> mlir::Type {
     mlir::Type ty =
         convertTypeForMemory(converter, dataLayout, type.getElementType());
@@ -2314,6 +2318,7 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                CIRToLLVMSwitchFlatOpLowering,
                CIRToLLVMTrapOpLowering,
                CIRToLLVMUnaryOpLowering,
+               CIRToLLVMUnreachableOpLowering,
                CIRToLLVMVecCmpOpLowering,
                CIRToLLVMVecCreateOpLowering,
                CIRToLLVMVecExtractOpLowering,
@@ -2322,7 +2327,8 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                CIRToLLVMVecShuffleOpLowering,
                CIRToLLVMVecSplatOpLowering,
                CIRToLLVMVecTernaryOpLowering,
-               CIRToLLVMUnreachableOpLowering
+               CIRToLLVMVTableAddrPointOpLowering
+      // clang-format on
       >(converter, patterns.getContext());
 
   processCIRAttrs(module);
@@ -2400,6 +2406,45 @@ mlir::LogicalResult CIRToLLVMTrapOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+static mlir::Value
+getValueForVTableSymbol(mlir::Operation *op,
+                        mlir::ConversionPatternRewriter &rewriter,
+                        const mlir::TypeConverter *converter,
+                        mlir::FlatSymbolRefAttr nameAttr, mlir::Type &eltType) {
+  auto module = op->getParentOfType<mlir::ModuleOp>();
+  mlir::Operation *symbol = mlir::SymbolTable::lookupSymbolIn(module, nameAttr);
+  if (auto llvmSymbol = mlir::dyn_cast<mlir::LLVM::GlobalOp>(symbol))
+    eltType = llvmSymbol.getType();
+  else if (auto cirSymbol = mlir::dyn_cast<cir::GlobalOp>(symbol))
+    eltType = converter->convertType(cirSymbol.getSymType());
+
+  return mlir::LLVM::AddressOfOp::create(
+      rewriter, op->getLoc(),
+      mlir::LLVM::LLVMPointerType::get(op->getContext()), nameAttr.getValue());
+}
+
+mlir::LogicalResult CIRToLLVMVTableAddrPointOpLowering::matchAndRewrite(
+    cir::VTableAddrPointOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  const mlir::TypeConverter *converter = getTypeConverter();
+  mlir::Type targetType = converter->convertType(op.getType());
+  llvm::SmallVector<mlir::LLVM::GEPArg> offsets;
+  mlir::Type eltType;
+  mlir::Value symAddr = getValueForVTableSymbol(op, rewriter, converter,
+                                                op.getNameAttr(), eltType);
+  offsets = llvm::SmallVector<mlir::LLVM::GEPArg>{
+      0, op.getAddressPointAttr().getIndex(),
+      op.getAddressPointAttr().getOffset()};
+
+  assert(eltType && "Shouldn't ever be missing an eltType here");
+  mlir::LLVM::GEPNoWrapFlags inboundsNuw =
+      mlir::LLVM::GEPNoWrapFlags::inbounds | mlir::LLVM::GEPNoWrapFlags::nuw;
+  rewriter.replaceOpWithNewOp<mlir::LLVM::GEPOp>(op, targetType, eltType,
+                                                 symAddr, offsets, inboundsNuw);
+
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRToLLVMStackSaveOpLowering::matchAndRewrite(
     cir::StackSaveOp op, OpAdaptor adaptor,
     mlir::ConversionPatternRewriter &rewriter) const {

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h

@@ -457,6 +457,16 @@ class CIRToLLVMBaseClassAddrOpLowering
                   mlir::ConversionPatternRewriter &) const override;
 };
 
+class CIRToLLVMVTableAddrPointOpLowering
+    : public mlir::OpConversionPattern<cir::VTableAddrPointOp> {
+public:
+  using mlir::OpConversionPattern<cir::VTableAddrPointOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::VTableAddrPointOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
 class CIRToLLVMStackSaveOpLowering
     : public mlir::OpConversionPattern<cir::StackSaveOp> {
 public:

clang/test/CIR/CodeGen/virtual-function-calls.cpp

@@ -1,5 +1,9 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -mconstructor-aliases -fclangir -emit-cir %s -o %t.cir
 // RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -mconstructor-aliases -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -mconstructor-aliases -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
 
 struct A {
   A();
@@ -14,11 +18,31 @@ A::A() {}
 
 // CIR: cir.global "private" external @_ZTV1A : !rec_anon_struct
 
-// CIR: cir.func dso_local @_ZN1AC2Ev(%arg0: !cir.ptr<!rec_A> {{.*}})
+// LLVM: @_ZTV1A = external global { [3 x ptr] }
+
+// OGCG: @_ZTV1A = external unnamed_addr constant { [3 x ptr] }
+
+// CIR: cir.func{{.*}} @_ZN1AC2Ev(%arg0: !cir.ptr<!rec_A> {{.*}})
 // CIR:    %[[THIS_ADDR:.*]] = cir.alloca !cir.ptr<!rec_A>, !cir.ptr<!cir.ptr<!rec_A>>, ["this", init]
 // CIR:    cir.store %arg0, %[[THIS_ADDR]] : !cir.ptr<!rec_A>, !cir.ptr<!cir.ptr<!rec_A>>
 // CIR:    %[[THIS:.*]] = cir.load %[[THIS_ADDR]] : !cir.ptr<!cir.ptr<!rec_A>>, !cir.ptr<!rec_A>
 // CIR:    %[[VPTR:.*]] = cir.vtable.address_point(@_ZTV1A, address_point = <index = 0, offset = 2>) : !cir.vptr
 // CIR:    %[[THIS_VPTR_PTR:.*]] = cir.cast(bitcast, %[[THIS]] : !cir.ptr<!rec_A>), !cir.ptr<!cir.vptr>
 // CIR:    cir.store align(8) %[[VPTR]], %[[THIS_VPTR_PTR]] : !cir.vptr, !cir.ptr<!cir.vptr>
 // CIR:    cir.return
+
+// LLVM: define{{.*}} void @_ZN1AC2Ev(ptr %[[ARG0:.*]])
+// LLVM:   %[[THIS_ADDR:.*]] = alloca ptr
+// LLVM:   store ptr %[[ARG0]], ptr %[[THIS_ADDR]]
+// LLVM:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// LLVM:   store ptr getelementptr inbounds nuw (i8, ptr @_ZTV1A, i64 16), ptr %[[THIS]]
+
+// OGCG: define{{.*}} void @_ZN1AC2Ev(ptr {{.*}} %[[ARG0:.*]])
+// OGCG:   %[[THIS_ADDR:.*]] = alloca ptr
+// OGCG:   store ptr %[[ARG0]], ptr %[[THIS_ADDR]]
+// OGCG:   %[[THIS:.*]] = load ptr, ptr %[[THIS_ADDR]]
+// OGCG:   store ptr getelementptr inbounds inrange(-16, 8) ({ [3 x ptr] }, ptr @_ZTV1A, i32 0, i32 0, i32 2), ptr %[[THIS]]
+
+// NOTE: The GEP in OGCG looks very different from the one generated with CIR,
+//       but it is equivalent. The OGCG GEP indexes by base pointer, then
+//       structure, then array, whereas the CIR GEP indexes by byte offset.