TypeInfo records more information about align requirement

[stevewan]

Summary

Extend the information preserved in TypeInfo by replacing the AlignIsRequired bool flag with a three-valued enum, the enum also indicates where the alignment attribute come from, which could be helpful in determining whether the attribute should overrule.

[stevewan]

Oops missed one flag.

[stevewan]

Fix enum usage

[rjmccall]

Thanks. Generally looks good; feel free to commit after adding a RequiredByEnum case and making sure it compiles.

clang/lib/AST/ASTContext.cpp

2300

Oh, I guess "record" is imprecise here. We might as well add a RequiredByEnum case, then, just to be fully accurate; there's no real harm to it.

clang/lib/AST/RecordLayoutBuilder.cpp

1981–1982

Bug here.

[stevewan]

Add RequiredByEnum case

[rjmccall]

Thanks, LGTM

clang/include/clang/AST/ASTContext.h

 class Context;
 
 } // namespace interp
 
 namespace serialization {
 template <class> class AbstractTypeReader;
 } // namespace serialization
 
+enum class AlignRequirementKind {
+  /// The alignment was not explicit in code.
+  None,
+
+  /// The alignment comes from an alignment attribute on a typedef.
+  RequiredByTypedef,
+
+  /// The alignment comes from an alignment attribute on a record type.
+  RequiredByRecord,
+
+  /// The alignment comes from an alignment attribute on a enum type.
+  RequiredByEnum,
+};
+
 struct TypeInfo {
   uint64_t Width = 0;
   unsigned Align = 0;
-  bool AlignIsRequired : 1;
+  AlignRequirementKind AlignRequirement;
 
-  TypeInfo() : AlignIsRequired(false) {}
-  TypeInfo(uint64_t Width, unsigned Align, bool AlignIsRequired)
-      : Width(Width), Align(Align), AlignIsRequired(AlignIsRequired) {}
+  TypeInfo() : AlignRequirement(AlignRequirementKind::None) {}
+  TypeInfo(uint64_t Width, unsigned Align,
+           AlignRequirementKind AlignRequirement)
+      : Width(Width), Align(Align), AlignRequirement(AlignRequirement) {}
+  bool isAlignRequired() {
+    return AlignRequirement != AlignRequirementKind::None;
+  }
 };
 
 struct TypeInfoChars {
   CharUnits Width;
   CharUnits Align;
-  bool AlignIsRequired : 1;
+  AlignRequirementKind AlignRequirement;
 
-  TypeInfoChars() : AlignIsRequired(false) {}
-  TypeInfoChars(CharUnits Width, CharUnits Align, bool AlignIsRequired)
-      : Width(Width), Align(Align), AlignIsRequired(AlignIsRequired) {}
+  TypeInfoChars() : AlignRequirement(AlignRequirementKind::None) {}
+  TypeInfoChars(CharUnits Width, CharUnits Align,
+                AlignRequirementKind AlignRequirement)
+      : Width(Width), Align(Align), AlignRequirement(AlignRequirement) {}
+  bool isAlignRequired() {
+    return AlignRequirement != AlignRequirementKind::None;
+  }
 };
 
 /// Holds long-lived AST nodes (such as types and decls) that can be
 /// referred to throughout the semantic analysis of a file.
 class ASTContext : public RefCountedBase<ASTContext> {
   friend class NestedNameSpecifier;
 
   mutable SmallVector<Type *, 0> Types;

clang/lib/AST/ASTContext.cpp

assert((Size == 0 || static_cast<uint64_t>(EltInfo.Width.getQuantity()) <=
          "Overflow in array type char size evaluation");
   uint64_t Width = EltInfo.Width.getQuantity() * Size;
   unsigned Align = EltInfo.Align.getQuantity();
   if (!Context.getTargetInfo().getCXXABI().isMicrosoft() ||
       Context.getTargetInfo().getPointerWidth(0) == 64)
     Width = llvm::alignTo(Width, Align);
   return TypeInfoChars(CharUnits::fromQuantity(Width),
                        CharUnits::fromQuantity(Align),
-                       EltInfo.AlignIsRequired);
+                       EltInfo.AlignRequirement);
 }
 
 TypeInfoChars ASTContext::getTypeInfoInChars(const Type *T) const {
   if (const auto *CAT = dyn_cast<ConstantArrayType>(T))
     return getConstantArrayInfoInChars(*this, CAT);
   TypeInfo Info = getTypeInfo(T);
   return TypeInfoChars(toCharUnitsFromBits(Info.Width),
-                       toCharUnitsFromBits(Info.Align),
-                       Info.AlignIsRequired);
+                       toCharUnitsFromBits(Info.Align), Info.AlignRequirement);
 }
 
 TypeInfoChars ASTContext::getTypeInfoInChars(QualType T) const {
   return getTypeInfoInChars(T.getTypePtr());
 }
 
 bool ASTContext::isAlignmentRequired(const Type *T) const {
-  return getTypeInfo(T).AlignIsRequired;
+  return getTypeInfo(T).AlignRequirement != AlignRequirementKind::None;
 }
 
 bool ASTContext::isAlignmentRequired(QualType T) const {
   return isAlignmentRequired(T.getTypePtr());
 }
 
 unsigned ASTContext::getTypeAlignIfKnown(QualType T,
                                          bool NeedsPreferredAlignment) const {

 /// method does not work on incomplete types.
 ///
 /// FIXME: Pointers into different addr spaces could have different sizes and
 /// alignment requirements: getPointerInfo should take an AddrSpace, this
 /// should take a QualType, &c.
 TypeInfo ASTContext::getTypeInfoImpl(const Type *T) const {
   uint64_t Width = 0;
   unsigned Align = 8;
-  bool AlignIsRequired = false;
+  AlignRequirementKind AlignRequirement = AlignRequirementKind::None;
   unsigned AS = 0;
   switch (T->getTypeClass()) {
 #define TYPE(Class, Base)
 #define ABSTRACT_TYPE(Class, Base)
 #define NON_CANONICAL_TYPE(Class, Base)
 #define DEPENDENT_TYPE(Class, Base) case Type::Class:
 #define NON_CANONICAL_UNLESS_DEPENDENT_TYPE(Class, Base)                       \
   case Type::Class:                                                            \
case Type::ConstantArray: {
     if (const auto *CAT = dyn_cast<ConstantArrayType>(T))
       Size = CAT->getSize().getZExtValue();
 
     TypeInfo EltInfo = getTypeInfo(cast<ArrayType>(T)->getElementType());
     assert((Size == 0 || EltInfo.Width <= (uint64_t)(-1) / Size) &&
            "Overflow in array type bit size evaluation");
     Width = EltInfo.Width * Size;
     Align = EltInfo.Align;
-    AlignIsRequired = EltInfo.AlignIsRequired;
+    AlignRequirement = EltInfo.AlignRequirement;
     if (!getTargetInfo().getCXXABI().isMicrosoft() ||
         getTargetInfo().getPointerWidth(0) == 64)
       Width = llvm::alignTo(Width, Align);
     break;
   }
 
   case Type::ExtVector:
   case Type::Vector: {
case Type::Enum: {
     }
 
     if (const auto *ET = dyn_cast<EnumType>(TT)) {
       const EnumDecl *ED = ET->getDecl();
       TypeInfo Info =
           getTypeInfo(ED->getIntegerType()->getUnqualifiedDesugaredType());
       if (unsigned AttrAlign = ED->getMaxAlignment()) {
         Info.Align = AttrAlign;
-        Info.AlignIsRequired = true;
+        Info.AlignRequirement = AlignRequirementKind::RequiredByEnum;
       }
       return Info;
     }
 
     const auto *RT = cast<RecordType>(TT);
     const RecordDecl *RD = RT->getDecl();
     const ASTRecordLayout &Layout = getASTRecordLayout(RD);
     Width = toBits(Layout.getSize());
     Align = toBits(Layout.getAlignment());
-    AlignIsRequired = RD->hasAttr<AlignedAttr>();
+    AlignRequirement = RD->hasAttr<AlignedAttr>()
+                           ? AlignRequirementKind::RequiredByRecord
+                           : AlignRequirementKind::None;
     break;
   }
 
   case Type::SubstTemplateTypeParm:
     return getTypeInfo(cast<SubstTemplateTypeParmType>(T)->
                        getReplacementType().getTypePtr());
 
   case Type::Auto:
#include "clang/Basic/RISCVVTypes.def"
   case Type::Typedef: {
     const TypedefNameDecl *Typedef = cast<TypedefType>(T)->getDecl();
     TypeInfo Info = getTypeInfo(Typedef->getUnderlyingType().getTypePtr());
     // If the typedef has an aligned attribute on it, it overrides any computed
     // alignment we have.  This violates the GCC documentation (which says that
     // attribute(aligned) can only round up) but matches its implementation.
     if (unsigned AttrAlign = Typedef->getMaxAlignment()) {
       Align = AttrAlign;
-      AlignIsRequired = true;
+      AlignRequirement = AlignRequirementKind::RequiredByTypedef;
     } else {
       Align = Info.Align;
-      AlignIsRequired = Info.AlignIsRequired;
+      AlignRequirement = Info.AlignRequirement;
     }
     Width = Info.Width;
     break;
   }
 
   case Type::Elaborated:
     return getTypeInfo(cast<ElaboratedType>(T)->getNamedType().getTypePtr());
 
#include "clang/Basic/RISCVVTypes.def"
 
   case Type::Pipe:
     Width = Target->getPointerWidth(getTargetAddressSpace(LangAS::opencl_global));
     Align = Target->getPointerAlign(getTargetAddressSpace(LangAS::opencl_global));
     break;
   }
 
   assert(llvm::isPowerOf2_32(Align) && "Alignment must be power of 2");
-  return TypeInfo(Width, Align, AlignIsRequired);
+  return TypeInfo(Width, Align, AlignRequirement);
 }
 
 unsigned ASTContext::getTypeUnadjustedAlign(const Type *T) const {
   UnadjustedAlignMap::iterator I = MemoizedUnadjustedAlign.find(T);
   if (I != MemoizedUnadjustedAlign.end())
     return I->second;
 
   unsigned UnadjustedAlign;
unsigned ASTContext::getPreferredTypeAlign(const Type *T) const {
   if (!Target->allowsLargerPreferedTypeAlignment())
     return ABIAlign;
 
   if (const auto *RT = T->getAs<RecordType>()) {
     const RecordDecl *RD = RT->getDecl();
 
     // When used as part of a typedef, or together with a 'packed' attribute,
     // the 'aligned' attribute can be used to decrease alignment.
-    if ((TI.AlignIsRequired && T->getAs<TypedefType>() != nullptr) ||
+    if ((TI.isAlignRequired() && T->getAs<TypedefType>() != nullptr) ||
         RD->isInvalidDecl())
       return ABIAlign;
 
     unsigned PreferredAlign = static_cast<unsigned>(
         toBits(getASTRecordLayout(RD).PreferredAlignment));
     assert(PreferredAlign >= ABIAlign &&
            "PreferredAlign should be at least as large as ABIAlign.");
     return PreferredAlign;
   }
 
   // Double (and, for targets supporting AIX `power` alignment, long double) and
   // long long should be naturally aligned (despite requiring less alignment) if
   // possible.
   if (const auto *CT = T->getAs<ComplexType>())
     T = CT->getElementType().getTypePtr();
   if (const auto *ET = T->getAs<EnumType>())
     T = ET->getDecl()->getIntegerType().getTypePtr();
   if (T->isSpecificBuiltinType(BuiltinType::Double) ||
       T->isSpecificBuiltinType(BuiltinType::LongLong) ||
       T->isSpecificBuiltinType(BuiltinType::ULongLong) ||
       (T->isSpecificBuiltinType(BuiltinType::LongDouble) &&
        Target->defaultsToAIXPowerAlignment()))
     // Don't increase the alignment if an alignment attribute was specified on a
     // typedef declaration.
-    if (!TI.AlignIsRequired)
+    if (!TI.isAlignRequired())
       return std::max(ABIAlign, (unsigned)getTypeSize(T));
 
   return ABIAlign;
 }
 
 /// getTargetDefaultAlignForAttributeAligned - Return the default alignment
 /// for __attribute__((aligned)) on this target, to be used if no alignment
 /// value is specified.

clang/lib/AST/RecordLayoutBuilder.cpp

 }
 
 void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
   uint64_t FieldSize = D->getBitWidthValue(Context);
   TypeInfo FieldInfo = Context.getTypeInfo(D->getType());
   uint64_t StorageUnitSize = FieldInfo.Width;
   unsigned FieldAlign = FieldInfo.Align;
-  bool AlignIsRequired = FieldInfo.AlignIsRequired;
+  bool AlignIsRequired = FieldInfo.isAlignRequired();
 
   // UnfilledBitsInLastUnit is the difference between the end of the
   // last allocated bitfield (i.e. the first bit offset available for
   // bitfields) and the end of the current data size in bits (i.e. the
   // first bit offset available for non-bitfields).  The current data
   // size in bits is always a multiple of the char size; additionally,
   // for ms_struct records it's also a multiple of the
   // LastBitfieldStorageUnitSize (if set).
void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
 
   uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
   // Reset the unfilled bits.
   UnfilledBitsInLastUnit = 0;
   LastBitfieldStorageUnitSize = 0;
 
   bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
 
-  bool AlignIsRequired = false;
+  AlignRequirementKind AlignRequirement = AlignRequirementKind::None;
   CharUnits FieldSize;
   CharUnits FieldAlign;
   // The amount of this class's dsize occupied by the field.
   // This is equal to FieldSize unless we're permitted to pack
   // into the field's tail padding.
   CharUnits EffectiveFieldSize;
 
   auto setDeclInfo = [&](bool IsIncompleteArrayType) {
     auto TI = Context.getTypeInfoInChars(D->getType());
     FieldAlign = TI.Align;
     // Flexible array members don't have any size, but they have to be
     // aligned appropriately for their element type.
     EffectiveFieldSize = FieldSize =
         IsIncompleteArrayType ? CharUnits::Zero() : TI.Width;
-    AlignIsRequired = TI.AlignIsRequired;
+    AlignRequirement = TI.AlignRequirement;
   };
 
   if (D->getType()->isIncompleteArrayType()) {
     setDeclInfo(true /* IsIncompleteArrayType */);
   } else if (const ReferenceType *RT = D->getType()->getAs<ReferenceType>()) {
     unsigned AS = Context.getTargetAddressSpace(RT->getPointeeType());
     EffectiveFieldSize = FieldSize = Context.toCharUnitsFromBits(
         Context.getTargetInfo().getPointerWidth(AS));
void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
   // whose recursively "first" member or element is such a type). The alignment
   // associated with these types for subsequent members use an alignment value
   // where the floating-point data type is considered to have 4-byte alignment.
   //
   // For the purposes of the foregoing: vtable pointers, non-empty base classes,
   // and zero-width bit-fields count as prior members; members of empty class
   // types marked `no_unique_address` are not considered to be prior members.
   CharUnits PreferredAlign = FieldAlign;
-  if (DefaultsToAIXPowerAlignment && !AlignIsRequired &&
+  if (DefaultsToAIXPowerAlignment &&
+      AlignRequirement == AlignRequirementKind::None &&
       (FoundFirstNonOverlappingEmptyFieldForAIX || IsNaturalAlign)) {
     auto performBuiltinTypeAlignmentUpgrade = [&](const BuiltinType *BTy) {
       if (BTy->getKind() == BuiltinType::Double ||
           BTy->getKind() == BuiltinType::LongDouble) {
         assert(PreferredAlign == CharUnits::fromQuantity(4) &&
                "No need to upgrade the alignment value.");
         PreferredAlign = CharUnits::fromQuantity(8);
       }

clang/lib/CodeGen/CGDebugInfo.cpp

 #include "llvm/Support/MD5.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TimeProfiler.h"
 using namespace clang;
 using namespace clang::CodeGen;
 
 static uint32_t getTypeAlignIfRequired(const Type *Ty, const ASTContext &Ctx) {
   auto TI = Ctx.getTypeInfo(Ty);
-  return TI.AlignIsRequired ? TI.Align : 0;
+  return TI.isAlignRequired() ? TI.Align : 0;
 }
 
 static uint32_t getTypeAlignIfRequired(QualType Ty, const ASTContext &Ctx) {
   return getTypeAlignIfRequired(Ty.getTypePtr(), Ctx);
 }
 
 static uint32_t getDeclAlignIfRequired(const Decl *D, const ASTContext &Ctx) {
   return D->hasAttr<AlignedAttr>() ? D->getMaxAlignment() : 0;
for (const BlockLayoutChunk &Chunk : chunks) {
     }
 
     const VarDecl *variable = capture->getVariable();
     StringRef name = variable->getName();
 
     llvm::DIType *fieldType;
     if (capture->isByRef()) {
       TypeInfo PtrInfo = C.getTypeInfo(C.VoidPtrTy);
-      auto Align = PtrInfo.AlignIsRequired ? PtrInfo.Align : 0;
+      auto Align = PtrInfo.isAlignRequired() ? PtrInfo.Align : 0;
       // FIXME: This recomputes the layout of the BlockByRefWrapper.
       uint64_t xoffset;
       fieldType =
           EmitTypeForVarWithBlocksAttr(variable, &xoffset).BlockByRefWrapper;
       fieldType = DBuilder.createPointerType(fieldType, PtrInfo.Width);
       fieldType = DBuilder.createMemberType(tunit, name, tunit, line,
                                             PtrInfo.Width, Align, offsetInBits,
                                             llvm::DINode::FlagZero, fieldType);

clang/lib/CodeGen/MicrosoftCXXABI.cpp

case llvm::Triple::thumb:
     return RAA_Indirect;
 
   case llvm::Triple::x86: {
     // If the argument has *required* alignment greater than four bytes, pass
     // it indirectly. Prior to MSVC version 19.14, passing overaligned
     // arguments was not supported and resulted in a compiler error. In 19.14
     // and later versions, such arguments are now passed indirectly.
     TypeInfo Info = getContext().getTypeInfo(RD->getTypeForDecl());
-    if (Info.AlignIsRequired && Info.Align > 4)
+    if (Info.isAlignRequired() && Info.Align > 4)
       return RAA_Indirect;
 
     // If C++ prohibits us from making a copy, construct the arguments directly
     // into argument memory.
     return RAA_DirectInMemory;
   }
 
   case llvm::Triple::x86_64:

clang/lib/CodeGen/TargetInfo.cpp

if (shouldAggregateUseDirect(Ty, State, InReg, NeedsPadding)) {
         return ABIArgInfo::getDirectInReg(Result);
       else
         return ABIArgInfo::getDirect(Result);
     }
     llvm::IntegerType *PaddingType = NeedsPadding ? Int32 : nullptr;
 
     // Pass over-aligned aggregates on Windows indirectly. This behavior was
     // added in MSVC 2015.
-    if (IsWin32StructABI && TI.AlignIsRequired && TI.Align > 32)
+    if (IsWin32StructABI && TI.isAlignRequired() && TI.Align > 32)
       return getIndirectResult(Ty, /*ByVal=*/false, State);
 
     // Expand small (<= 128-bit) record types when we know that the stack layout
     // of those arguments will match the struct. This is important because the
     // LLVM backend isn't smart enough to remove byval, which inhibits many
     // optimizations.
     // Don't do this for the MCU if there are still free integer registers
     // (see X86_64 ABI for full explanation).
Address ARMABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
   } else if (getABIKind() == ARMABIInfo::AAPCS16_VFP) {
     // ARMv7k allows type alignment up to 16 bytes.
     TyAlignForABI = std::max(TyAlignForABI, CharUnits::fromQuantity(4));
     TyAlignForABI = std::min(TyAlignForABI, CharUnits::fromQuantity(16));
   } else {
     TyAlignForABI = CharUnits::fromQuantity(4);
   }
 
-  TypeInfoChars TyInfo(TySize, TyAlignForABI, false);
+  TypeInfoChars TyInfo(TySize, TyAlignForABI, AlignRequirementKind::None);
   return emitVoidPtrVAArg(CGF, VAListAddr, Ty, IsIndirect, TyInfo,
                           SlotSize, /*AllowHigherAlign*/ true);
 }
 
 //===----------------------------------------------------------------------===//
 // NVPTX ABI Implementation
 //===----------------------------------------------------------------------===//