| //===--- CGRecordLayout.h - LLVM Record Layout Information ------*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_CLANG_LIB_CODEGEN_CGRECORDLAYOUT_H |
| #define LLVM_CLANG_LIB_CODEGEN_CGRECORDLAYOUT_H |
| |
| #include "clang/AST/CharUnits.h" |
| #include "clang/AST/DeclCXX.h" |
| #include "clang/Basic/LLVM.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/IR/DerivedTypes.h" |
| |
| namespace llvm { |
| class StructType; |
| } |
| |
| namespace clang { |
| namespace CodeGen { |
| |
| /// Structure with information about how a bitfield should be accessed. |
| /// |
| /// Often we layout a sequence of bitfields as a contiguous sequence of bits. |
| /// When the AST record layout does this, we represent it in the LLVM IR's type |
| /// as either a sequence of i8 members or a byte array to reserve the number of |
| /// bytes touched without forcing any particular alignment beyond the basic |
| /// character alignment. |
| /// |
| /// Then accessing a particular bitfield involves converting this byte array |
| /// into a single integer of that size (i24 or i40 -- may not be power-of-two |
| /// size), loading it, and shifting and masking to extract the particular |
| /// subsequence of bits which make up that particular bitfield. This structure |
| /// encodes the information used to construct the extraction code sequences. |
| /// The CGRecordLayout also has a field index which encodes which byte-sequence |
| /// this bitfield falls within. Let's assume the following C struct: |
| /// |
| /// struct S { |
| /// char a, b, c; |
| /// unsigned bits : 3; |
| /// unsigned more_bits : 4; |
| /// unsigned still_more_bits : 7; |
| /// }; |
| /// |
| /// This will end up as the following LLVM type. The first array is the |
| /// bitfield, and the second is the padding out to a 4-byte alignmnet. |
| /// |
| /// %t = type { i8, i8, i8, i8, i8, [3 x i8] } |
| /// |
| /// When generating code to access more_bits, we'll generate something |
| /// essentially like this: |
| /// |
| /// define i32 @foo(%t* %base) { |
| /// %0 = gep %t* %base, i32 0, i32 3 |
| /// %2 = load i8* %1 |
| /// %3 = lshr i8 %2, 3 |
| /// %4 = and i8 %3, 15 |
| /// %5 = zext i8 %4 to i32 |
| /// ret i32 %i |
| /// } |
| /// |
| struct CGBitFieldInfo { |
| /// The offset within a contiguous run of bitfields that are represented as |
| /// a single "field" within the LLVM struct type. This offset is in bits. |
| unsigned Offset : 16; |
| |
| /// The total size of the bit-field, in bits. |
| unsigned Size : 15; |
| |
| /// Whether the bit-field is signed. |
| unsigned IsSigned : 1; |
| |
| /// The storage size in bits which should be used when accessing this |
| /// bitfield. |
| unsigned StorageSize; |
| |
| /// The offset of the bitfield storage from the start of the struct. |
| CharUnits StorageOffset; |
| |
| CGBitFieldInfo() |
| : Offset(), Size(), IsSigned(), StorageSize(), StorageOffset() {} |
| |
| CGBitFieldInfo(unsigned Offset, unsigned Size, bool IsSigned, |
| unsigned StorageSize, CharUnits StorageOffset) |
| : Offset(Offset), Size(Size), IsSigned(IsSigned), |
| StorageSize(StorageSize), StorageOffset(StorageOffset) {} |
| |
| void print(raw_ostream &OS) const; |
| void dump() const; |
| |
| /// Given a bit-field decl, build an appropriate helper object for |
| /// accessing that field (which is expected to have the given offset and |
| /// size). |
| static CGBitFieldInfo MakeInfo(class CodeGenTypes &Types, |
| const FieldDecl *FD, |
| uint64_t Offset, uint64_t Size, |
| uint64_t StorageSize, |
| CharUnits StorageOffset); |
| }; |
| |
| /// CGRecordLayout - This class handles struct and union layout info while |
| /// lowering AST types to LLVM types. |
| /// |
| /// These layout objects are only created on demand as IR generation requires. |
| class CGRecordLayout { |
| friend class CodeGenTypes; |
| |
| CGRecordLayout(const CGRecordLayout &) = delete; |
| void operator=(const CGRecordLayout &) = delete; |
| |
| private: |
| /// The LLVM type corresponding to this record layout; used when |
| /// laying it out as a complete object. |
| llvm::StructType *CompleteObjectType; |
| |
| /// The LLVM type for the non-virtual part of this record layout; |
| /// used when laying it out as a base subobject. |
| llvm::StructType *BaseSubobjectType; |
| |
| /// Map from (non-bit-field) struct field to the corresponding llvm struct |
| /// type field no. This info is populated by record builder. |
| llvm::DenseMap<const FieldDecl *, unsigned> FieldInfo; |
| |
| /// Map from (bit-field) struct field to the corresponding llvm struct type |
| /// field no. This info is populated by record builder. |
| llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields; |
| |
| // FIXME: Maybe we could use a CXXBaseSpecifier as the key and use a single |
| // map for both virtual and non-virtual bases. |
| llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases; |
| |
| /// Map from virtual bases to their field index in the complete object. |
| llvm::DenseMap<const CXXRecordDecl *, unsigned> CompleteObjectVirtualBases; |
| |
| /// False if any direct or indirect subobject of this class, when |
| /// considered as a complete object, requires a non-zero bitpattern |
| /// when zero-initialized. |
| bool IsZeroInitializable : 1; |
| |
| /// False if any direct or indirect subobject of this class, when |
| /// considered as a base subobject, requires a non-zero bitpattern |
| /// when zero-initialized. |
| bool IsZeroInitializableAsBase : 1; |
| |
| public: |
| CGRecordLayout(llvm::StructType *CompleteObjectType, |
| llvm::StructType *BaseSubobjectType, |
| bool IsZeroInitializable, |
| bool IsZeroInitializableAsBase) |
| : CompleteObjectType(CompleteObjectType), |
| BaseSubobjectType(BaseSubobjectType), |
| IsZeroInitializable(IsZeroInitializable), |
| IsZeroInitializableAsBase(IsZeroInitializableAsBase) {} |
| |
| /// Return the "complete object" LLVM type associated with |
| /// this record. |
| llvm::StructType *getLLVMType() const { |
| return CompleteObjectType; |
| } |
| |
| /// Return the "base subobject" LLVM type associated with |
| /// this record. |
| llvm::StructType *getBaseSubobjectLLVMType() const { |
| return BaseSubobjectType; |
| } |
| |
| /// Check whether this struct can be C++ zero-initialized |
| /// with a zeroinitializer. |
| bool isZeroInitializable() const { |
| return IsZeroInitializable; |
| } |
| |
| /// Check whether this struct can be C++ zero-initialized |
| /// with a zeroinitializer when considered as a base subobject. |
| bool isZeroInitializableAsBase() const { |
| return IsZeroInitializableAsBase; |
| } |
| |
| /// Return llvm::StructType element number that corresponds to the |
| /// field FD. |
| unsigned getLLVMFieldNo(const FieldDecl *FD) const { |
| FD = FD->getCanonicalDecl(); |
| assert(FieldInfo.count(FD) && "Invalid field for record!"); |
| return FieldInfo.lookup(FD); |
| } |
| |
| unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const { |
| assert(NonVirtualBases.count(RD) && "Invalid non-virtual base!"); |
| return NonVirtualBases.lookup(RD); |
| } |
| |
| /// Return the LLVM field index corresponding to the given |
| /// virtual base. Only valid when operating on the complete object. |
| unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const { |
| assert(CompleteObjectVirtualBases.count(base) && "Invalid virtual base!"); |
| return CompleteObjectVirtualBases.lookup(base); |
| } |
| |
| /// Return the BitFieldInfo that corresponds to the field FD. |
| const CGBitFieldInfo &getBitFieldInfo(const FieldDecl *FD) const { |
| FD = FD->getCanonicalDecl(); |
| assert(FD->isBitField() && "Invalid call for non-bit-field decl!"); |
| llvm::DenseMap<const FieldDecl *, CGBitFieldInfo>::const_iterator |
| it = BitFields.find(FD); |
| assert(it != BitFields.end() && "Unable to find bitfield info"); |
| return it->second; |
| } |
| |
| void print(raw_ostream &OS) const; |
| void dump() const; |
| }; |
| |
| } // end namespace CodeGen |
| } // end namespace clang |
| |
| #endif |