Author: Akimasa Watanuki Date: 2026-01-09T09:52:30-08:00 New Revision: e927f4bbf4800fe9b68fc32b935799d5136925fb
URL: https://github.com/llvm/llvm-project/commit/e927f4bbf4800fe9b68fc32b935799d5136925fb DIFF: https://github.com/llvm/llvm-project/commit/e927f4bbf4800fe9b68fc32b935799d5136925fb.diff LOG: [CIR] Handle empty unions in record lowering and LLVM conversion (#172666) Handle empty unions in CIR record lowering and LLVM conversion by emitting padding when needed, guarding `getLargestMember` for empty/padded unions, and lowering to empty or padded LLVM structs based on language rules. Added regression tests for C and C++ empty union lowering in `clang/test/CIR/CodeGen/empty-union.c` and `empty-union.cpp`. Added: clang/test/CIR/CodeGen/empty-union.c clang/test/CIR/CodeGen/empty-union.cpp Modified: clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp clang/lib/CIR/Dialect/IR/CIRTypes.cpp clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp Removed: ################################################################################ diff --git a/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp b/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp index 87f23409e8e4b..29eda175c208c 100644 --- a/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp +++ b/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp @@ -811,9 +811,10 @@ void CIRRecordLowering::lowerUnion() { fieldTypes.push_back(fieldType); } - if (!storageType) - cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(), - "No-storage Union NYI"); + if (!storageType) { + appendPaddingBytes(layoutSize); + return; + } if (layoutSize < getSize(storageType)) storageType = getByteArrayType(layoutSize); diff --git a/clang/lib/CIR/Dialect/IR/CIRTypes.cpp b/clang/lib/CIR/Dialect/IR/CIRTypes.cpp index f72eae94e2e5d..43853b6696a94 100644 --- a/clang/lib/CIR/Dialect/IR/CIRTypes.cpp +++ b/clang/lib/CIR/Dialect/IR/CIRTypes.cpp @@ -297,11 +297,16 @@ void RecordType::complete(ArrayRef<Type> members, bool packed, bool padded) { Type RecordType::getLargestMember(const ::mlir::DataLayout &dataLayout) const { assert(isUnion() && "Only call getLargestMember on unions"); llvm::ArrayRef<Type> members = getMembers(); + if (members.empty()) + return {}; + // If the union is padded, we need to ignore the last member, // which is the padding. + auto endIt = getPadded() ? std::prev(members.end()) : members.end(); + if (endIt == members.begin()) + return {}; return *std::max_element( - members.begin(), getPadded() ? members.end() - 1 : members.end(), - [&](Type lhs, Type rhs) { + members.begin(), endIt, [&](Type lhs, Type rhs) { return dataLayout.getTypeABIAlignment(lhs) < dataLayout.getTypeABIAlignment(rhs) || (dataLayout.getTypeABIAlignment(lhs) == diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp index 914233d8f6b8f..d0fa8bae545be 100644 --- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp +++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp @@ -3010,6 +3010,8 @@ static void prepareTypeConverter(mlir::LLVMTypeConverter &converter, break; // Unions are lowered as only the largest member. case cir::RecordType::Union: + if (type.getMembers().empty()) + break; if (auto largestMember = type.getLargestMember(dataLayout)) llvmMembers.push_back( convertTypeForMemory(converter, dataLayout, largestMember)); diff --git a/clang/test/CIR/CodeGen/empty-union.c b/clang/test/CIR/CodeGen/empty-union.c new file mode 100644 index 0000000000000..87cc012706160 --- /dev/null +++ b/clang/test/CIR/CodeGen/empty-union.c @@ -0,0 +1,35 @@ +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o - | FileCheck %s --check-prefix=CIR +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o - | FileCheck %s --check-prefix=LLVM +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=OGCG + +// Empty union (no padding, size 0 in CIR) +union Empty {}; +// CIR: !rec_Empty = !cir.record<union "Empty" {}> +// LLVM: %union.Empty = type {} +// OGCG: %union.Empty = type {} + +// Aligned empty union (size 0, alignment 16) +union EmptyAligned {} __attribute__((aligned(16))); +// CIR: !rec_EmptyAligned = !cir.record<union "EmptyAligned" {}> +// LLVM: %union.EmptyAligned = type {} +// OGCG: %union.EmptyAligned = type {} + +void useEmpty() { + union Empty e; +} +// CIR: cir.func {{.*}}@useEmpty() +// CIR: cir.alloca !rec_Empty, !cir.ptr<!rec_Empty>, ["e"] {alignment = 1 : i64} +// LLVM: define {{.*}} void @useEmpty() +// LLVM: alloca %union.Empty, i64 1, align 1 +// OGCG: define {{.*}} void @useEmpty() +// OGCG: alloca %union.Empty, align 1 + +void useEmptyAligned() { + union EmptyAligned e; +} +// CIR: cir.func {{.*}}@useEmptyAligned() +// CIR: cir.alloca !rec_EmptyAligned, !cir.ptr<!rec_EmptyAligned>, ["e"] {alignment = 16 : i64} +// LLVM: define {{.*}} void @useEmptyAligned() +// LLVM: alloca %union.EmptyAligned, i64 1, align 16 +// OGCG: define {{.*}} void @useEmptyAligned() +// OGCG: alloca %union.EmptyAligned, align 16 diff --git a/clang/test/CIR/CodeGen/empty-union.cpp b/clang/test/CIR/CodeGen/empty-union.cpp new file mode 100644 index 0000000000000..e1d7e793cac39 --- /dev/null +++ b/clang/test/CIR/CodeGen/empty-union.cpp @@ -0,0 +1,35 @@ +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o - | FileCheck %s --check-prefix=CIR +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o - | FileCheck %s --check-prefix=LLVM +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=OGCG + +// Empty union (should be padded to size 1) +union Empty {}; +// CIR: !rec_Empty = !cir.record<union "Empty" padded {!u8i}> +// LLVM: %union.Empty = type { i8 } +// OGCG: %union.Empty = type { i8 } + +// Aligned empty union (should have aligned integer member in CIR) +union alignas(16) EmptyAligned {}; +// CIR: !rec_EmptyAligned = !cir.record<union "EmptyAligned" padded {!cir.array<!u8i x 16>}> +// LLVM: %union.EmptyAligned = type { [16 x i8] } +// OGCG: %union.EmptyAligned = type { [16 x i8] } + +void useEmpty() { + Empty e; +} +// CIR: cir.func {{.*}}@_Z8useEmptyv() +// CIR: cir.alloca !rec_Empty, !cir.ptr<!rec_Empty>, ["e"] {alignment = 1 : i64} +// LLVM: define {{.*}} void @_Z8useEmptyv() +// LLVM: alloca %union.Empty, i64 1, align 1 +// OGCG: define {{.*}} void @_Z8useEmptyv() +// OGCG: alloca %union.Empty, align 1 + +void useEmptyAligned() { + EmptyAligned e; +} +// CIR: cir.func {{.*}}@_Z15useEmptyAlignedv() +// CIR: cir.alloca !rec_EmptyAligned, !cir.ptr<!rec_EmptyAligned>, ["e"] {alignment = 16 : i64} +// LLVM: define {{.*}} void @_Z15useEmptyAlignedv() +// LLVM: alloca %union.EmptyAligned, i64 1, align 16 +// OGCG: define {{.*}} void @_Z15useEmptyAlignedv() +// OGCG: alloca %union.EmptyAligned, align 16 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
