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[CIR] Add lowering for the cir.vtable.address_point operation #153243

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merged 2 commits into from
Aug 14, 2025
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[CIR] Add lowering for the cir.vtable.address_point operation #153243

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[CIR] Add lowering for the cir.vtable.address_point operation
andykaylor Aug 8, 2025
7ac51e7
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andykaylor Aug 13, 2025
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53 changes: 52 additions & 1 deletion clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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());
Expand Down Expand Up @@ -2314,6 +2318,7 @@ void ConvertCIRToLLVMPass::runOnOperation() {
CIRToLLVMSwitchFlatOpLowering,
CIRToLLVMTrapOpLowering,
CIRToLLVMUnaryOpLowering,
CIRToLLVMUnreachableOpLowering,
CIRToLLVMVecCmpOpLowering,
CIRToLLVMVecCreateOpLowering,
CIRToLLVMVecExtractOpLowering,
Expand All @@ -2322,7 +2327,8 @@ void ConvertCIRToLLVMPass::runOnOperation() {
CIRToLLVMVecShuffleOpLowering,
CIRToLLVMVecSplatOpLowering,
CIRToLLVMVecTernaryOpLowering,
CIRToLLVMUnreachableOpLowering
CIRToLLVMVTableAddrPointOpLowering
// clang-format on
>(converter, patterns.getContext());

processCIRAttrs(module);
Expand Down Expand Up @@ -2400,6 +2406,51 @@ 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());
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Looks like we are relying on this function clients to check if eltType is filled in (same in incubator), should we just do it here as a final else?

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I'm not sure what else this would be if it isn't a cir::GlobalOp or LLVM::GlobalOp. Maybe the else should call op.emitError()?

} else {
op->emitError() << "unexpected symbol type for " << symbol;
return {};
}

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);
if (!symAddr)
return op.emitError() << "Unable to get value for vtable symbol";

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 {
Expand Down
10 changes: 10 additions & 0 deletions clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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:
Expand Down
26 changes: 25 additions & 1 deletion clang/test/CIR/CodeGen/virtual-function-calls.cpp
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Original file line number Diff line number Diff line change
@@ -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();
Expand All @@ -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.