[AIX] Port power alignment rules to clang

[Xiangling_L]

Summary

Address the following aspects of power alignment rules:

• Implemented double/long double alignment when not first struct member
• A double member in union is always treated as the first member, and should not use special alignment rule
• Fixed the alignment issue caused by virtual function
• Applied AIX Alignment rule when layout base class
• Fixed AIX layout for zero sized bitfield followed by double

[jasonliu]

clang/test/Layout/aix-double-struct-member.cpp

136

1. I think we also want to test empty base class with a derived class contains double as first. And also a non-empty base class with derived contains double as first to show that it has effect on basic inheritance as well.
2. We need one more test for seeing how pack align interact with AIX alignment.

[jasonliu]

clang/include/clang/AST/RecordLayout.h

177

Not sure if aixOffset is a thing? Might be better to just say "aix offset alignment"?

[jasonliu]

clang/include/clang/AST/RecordLayout.h

81

AIX Alignment -> AIX alignment

clang/lib/AST/RecordLayoutBuilder.cpp

1013

Consistent spelling as: AIX-abi?

1853

Consistent spelling as AIX-abi?

clang/test/Layout/aix-double-struct-member.cpp

136

We also want to test if MaxFieldAlignment could override the AIX alignment.

[Xiangling_L]

Adjust some comments style;
Add more testcases;

[Xiangling_L]

Current implementation conflicts with __AlignOf behavior as we discussed in [RFC] Adding AIX power alignment rule in clang front end (http://lists.llvm.org/pipermail/cfe-dev/2020-April/065324.html) . Drop this revision and a new implementation will be put on Phabricator when it's ready.

clang/include/clang/AST/RecordLayout.h

private:
   // UnadjustedAlignment - Maximum of the alignments of the record members in
   // characters.
   CharUnits UnadjustedAlignment;
 
   /// RequiredAlignment - The required alignment of the object.  In the MS-ABI
   /// the __declspec(align()) trumps #pramga pack and must always be obeyed.
   CharUnits RequiredAlignment;
 
+  /// AIXOffsetAlignment - The special AIX Alignment for the object that
+  /// contains floating-point member or sub-member. This is for AIX-abi only.
+  CharUnits AIXOffsetAlignment;
+
   /// FieldOffsets - Array of field offsets in bits.
   ASTVector<uint64_t> FieldOffsets;
 
   /// CXXRecordLayoutInfo - Contains C++ specific layout information.
   struct CXXRecordLayoutInfo {
     /// NonVirtualSize - The non-virtual size (in chars) of an object, which is
     /// the size of the object without virtual bases.
     CharUnits NonVirtualSize;
struct CXXRecordLayoutInfo {
     VBaseOffsetsMapTy VBaseOffsets;
   };
 
   /// CXXInfo - If the record layout is for a C++ record, this will have
   /// C++ specific information about the record.
   CXXRecordLayoutInfo *CXXInfo = nullptr;
 
   ASTRecordLayout(const ASTContext &Ctx, CharUnits size, CharUnits alignment,
-                  CharUnits unadjustedAlignment,
-                  CharUnits requiredAlignment, CharUnits datasize,
+                  CharUnits unadjustedAlignment, CharUnits requiredAlignment,
+                  CharUnits aixOffsetAlignment, CharUnits datasize,
                   ArrayRef<uint64_t> fieldoffsets);
 
   using BaseOffsetsMapTy = CXXRecordLayoutInfo::BaseOffsetsMapTy;
 
   // Constructor for C++ records.
-  ASTRecordLayout(const ASTContext &Ctx,
-                  CharUnits size, CharUnits alignment,
-                  CharUnits unadjustedAlignment,
-                  CharUnits requiredAlignment,
-                  bool hasOwnVFPtr, bool hasExtendableVFPtr,
-                  CharUnits vbptroffset,
-                  CharUnits datasize,
-                  ArrayRef<uint64_t> fieldoffsets,
+  ASTRecordLayout(const ASTContext &Ctx, CharUnits size, CharUnits alignment,
+                  CharUnits unadjustedAlignment, CharUnits requiredAlignment,
+                  CharUnits aixOffsetAlignment, bool hasOwnVFPtr,
+                  bool hasExtendableVFPtr, CharUnits vbptroffset,
+                  CharUnits datasize, ArrayRef<uint64_t> fieldoffsets,
                   CharUnits nonvirtualsize, CharUnits nonvirtualalignment,
                   CharUnits SizeOfLargestEmptySubobject,
-                  const CXXRecordDecl *PrimaryBase,
-                  bool IsPrimaryBaseVirtual,
+                  const CXXRecordDecl *PrimaryBase, bool IsPrimaryBaseVirtual,
                   const CXXRecordDecl *BaseSharingVBPtr,
-                  bool EndsWithZeroSizedObject,
-                  bool LeadsWithZeroSizedBase,
-                  const BaseOffsetsMapTy& BaseOffsets,
-                  const VBaseOffsetsMapTy& VBaseOffsets);
+                  bool EndsWithZeroSizedObject, bool LeadsWithZeroSizedBase,
+                  const BaseOffsetsMapTy &BaseOffsets,
+                  const VBaseOffsetsMapTy &VBaseOffsets);
 
   ~ASTRecordLayout() = default;
 
   void Destroy(ASTContext &Ctx);
 
 public:
   ASTRecordLayout(const ASTRecordLayout &) = delete;
   ASTRecordLayout &operator=(const ASTRecordLayout &) = delete;
 
   /// getAlignment - Get the record alignment in characters.
   CharUnits getAlignment() const { return Alignment; }
 
+  /// getAIXOffsetAlignment - Get the record of aixOffset alignment in
+  /// characters.
+  CharUnits getAIXOffsetAlignment() const { return AIXOffsetAlignment; }
+
   /// getUnadjustedAlignment - Get the record alignment in characters, before
   /// alignment adjustement.
   CharUnits getUnadjustedAlignment() const { return UnadjustedAlignment; }
 
   /// getSize - Get the record size in characters.
   CharUnits getSize() const { return Size; }
 
   /// getFieldCount - Get the number of fields in the layout.
   unsigned getFieldCount() const { return FieldOffsets.size(); }
 
   /// getFieldOffset - Get the offset of the given field index, in
   /// bits.
   uint64_t getFieldOffset(unsigned FieldNo) const {
     return FieldOffsets[FieldNo];
   }
 
   /// getDataSize() - Get the record data size, which is the record size
   /// without tail padding, in characters.
-  CharUnits getDataSize() const {
-    return DataSize;
-  }
+  CharUnits getDataSize() const { return DataSize; }
 
   /// getNonVirtualSize - Get the non-virtual size (in chars) of an object,
   /// which is the size of the object without virtual bases.
   CharUnits getNonVirtualSize() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
 
     return CXXInfo->NonVirtualSize;
   }
public:
   }
 
   /// hasVBPtr - Does this class have a virtual function table pointer.
   bool hasVBPtr() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
     return !CXXInfo->VBPtrOffset.isNegative();
   }
 
-  CharUnits getRequiredAlignment() const {
-    return RequiredAlignment;
-  }
+  CharUnits getRequiredAlignment() const { return RequiredAlignment; }
 
   bool endsWithZeroSizedObject() const {
     return CXXInfo && CXXInfo->EndsWithZeroSizedObject;
   }
 
   bool leadsWithZeroSizedBase() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
     return CXXInfo->LeadsWithZeroSizedBase;

clang/lib/AST/RecordLayout.cpp

void ASTRecordLayout::Destroy(ASTContext &Ctx) {
   this->~ASTRecordLayout();
   Ctx.Deallocate(this);
 }
 
 ASTRecordLayout::ASTRecordLayout(const ASTContext &Ctx, CharUnits size,
                                  CharUnits alignment,
                                  CharUnits unadjustedAlignment,
                                  CharUnits requiredAlignment,
+                                 CharUnits aixOffsetAlignment,
                                  CharUnits datasize,
                                  ArrayRef<uint64_t> fieldoffsets)
     : Size(size), DataSize(datasize), Alignment(alignment),
       UnadjustedAlignment(unadjustedAlignment),
-      RequiredAlignment(requiredAlignment) {
+      RequiredAlignment(requiredAlignment),
+      AIXOffsetAlignment(aixOffsetAlignment) {
   FieldOffsets.append(Ctx, fieldoffsets.begin(), fieldoffsets.end());
 }
 
 // Constructor for C++ records.
-ASTRecordLayout::ASTRecordLayout(const ASTContext &Ctx,
-                                 CharUnits size, CharUnits alignment,
-                                 CharUnits unadjustedAlignment,
-                                 CharUnits requiredAlignment,
-                                 bool hasOwnVFPtr, bool hasExtendableVFPtr,
-                                 CharUnits vbptroffset,
-                                 CharUnits datasize,
-                                 ArrayRef<uint64_t> fieldoffsets,
-                                 CharUnits nonvirtualsize,
-                                 CharUnits nonvirtualalignment,
-                                 CharUnits SizeOfLargestEmptySubobject,
-                                 const CXXRecordDecl *PrimaryBase,
-                                 bool IsPrimaryBaseVirtual,
-                                 const CXXRecordDecl *BaseSharingVBPtr,
-                                 bool EndsWithZeroSizedObject,
-                                 bool LeadsWithZeroSizedBase,
-                                 const BaseOffsetsMapTy& BaseOffsets,
-                                 const VBaseOffsetsMapTy& VBaseOffsets)
+ASTRecordLayout::ASTRecordLayout(
+    const ASTContext &Ctx, CharUnits size, CharUnits alignment,
+    CharUnits unadjustedAlignment, CharUnits requiredAlignment,
+    CharUnits aixOffsetAlignment, bool hasOwnVFPtr, bool hasExtendableVFPtr,
+    CharUnits vbptroffset, CharUnits datasize, ArrayRef<uint64_t> fieldoffsets,
+    CharUnits nonvirtualsize, CharUnits nonvirtualalignment,
+    CharUnits SizeOfLargestEmptySubobject, const CXXRecordDecl *PrimaryBase,
+    bool IsPrimaryBaseVirtual, const CXXRecordDecl *BaseSharingVBPtr,
+    bool EndsWithZeroSizedObject, bool LeadsWithZeroSizedBase,
+    const BaseOffsetsMapTy &BaseOffsets, const VBaseOffsetsMapTy &VBaseOffsets)
     : Size(size), DataSize(datasize), Alignment(alignment),
       UnadjustedAlignment(unadjustedAlignment),
-    RequiredAlignment(requiredAlignment), CXXInfo(new (Ctx) CXXRecordLayoutInfo)
-{
+      RequiredAlignment(requiredAlignment),
+      AIXOffsetAlignment(aixOffsetAlignment),
+      CXXInfo(new (Ctx) CXXRecordLayoutInfo) {
   FieldOffsets.append(Ctx, fieldoffsets.begin(), fieldoffsets.end());
 
   CXXInfo->PrimaryBase.setPointer(PrimaryBase);
   CXXInfo->PrimaryBase.setInt(IsPrimaryBaseVirtual);
   CXXInfo->NonVirtualSize = nonvirtualsize;
   CXXInfo->NonVirtualAlignment = nonvirtualalignment;
   CXXInfo->SizeOfLargestEmptySubobject = SizeOfLargestEmptySubobject;
   CXXInfo->BaseOffsets = BaseOffsets;

clang/lib/AST/RecordLayoutBuilder.cpp

 //=== RecordLayoutBuilder.cpp - Helper class for building record layouts ---==//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/AST/RecordLayout.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTDiagnostic.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/Expr.h"
+#include "clang/AST/RecordLayout.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/MathExtras.h"
 
 using namespace clang;
 
 namespace {
protected:
   CharUnits Alignment;
 
   /// The alignment if attribute packed is not used.
   CharUnits UnpackedAlignment;
 
   /// \brief The maximum of the alignments of top-level members.
   CharUnits UnadjustedAlignment;
 
+  /// \breif The AIX special alignment for object contains floating-point
+  /// member or sub-members
+  CharUnits AIXOffsetAlignment;
+
   SmallVector<uint64_t, 16> FieldOffsets;
 
   /// Whether the external AST source has provided a layout for this
   /// record.
   unsigned UseExternalLayout : 1;
 
   /// Whether we need to infer alignment, even when we have an
   /// externally-provided layout.
protected:
   /// Valid if UseExternalLayout is true.
   ExternalLayout External;
 
   ItaniumRecordLayoutBuilder(const ASTContext &Context,
                              EmptySubobjectMap *EmptySubobjects)
       : Context(Context), EmptySubobjects(EmptySubobjects), Size(0),
         Alignment(CharUnits::One()), UnpackedAlignment(CharUnits::One()),
         UnadjustedAlignment(CharUnits::One()),
-        UseExternalLayout(false), InferAlignment(false), Packed(false),
-        IsUnion(false), IsMac68kAlign(false), IsMsStruct(false),
-        UnfilledBitsInLastUnit(0), LastBitfieldTypeSize(0),
-        MaxFieldAlignment(CharUnits::Zero()), DataSize(0),
-        NonVirtualSize(CharUnits::Zero()),
+        AIXOffsetAlignment(CharUnits::One()), UseExternalLayout(false),
+        InferAlignment(false), Packed(false), IsUnion(false),
+        IsMac68kAlign(false), IsMsStruct(false), UnfilledBitsInLastUnit(0),
+        LastBitfieldTypeSize(0), MaxFieldAlignment(CharUnits::Zero()),
+        DataSize(0), NonVirtualSize(CharUnits::Zero()),
         NonVirtualAlignment(CharUnits::One()),
         PaddedFieldSize(CharUnits::Zero()), PrimaryBase(nullptr),
-        PrimaryBaseIsVirtual(false), HasOwnVFPtr(false),
-        HasPackedField(false), FirstNearlyEmptyVBase(nullptr) {}
+        PrimaryBaseIsVirtual(false), HasOwnVFPtr(false), HasPackedField(false),
+        FirstNearlyEmptyVBase(nullptr) {}
 
   void Layout(const RecordDecl *D);
   void Layout(const CXXRecordDecl *D);
   void Layout(const ObjCInterfaceDecl *D);
 
   void LayoutFields(const RecordDecl *D);
   void LayoutField(const FieldDecl *D, bool InsertExtraPadding);
   void LayoutWideBitField(uint64_t FieldSize, uint64_t TypeSize,
protected:
 
   /// InitializeLayout - Initialize record layout for the given record decl.
   void InitializeLayout(const Decl *D);
 
   /// FinishLayout - Finalize record layout. Adjust record size based on the
   /// alignment.
   void FinishLayout(const NamedDecl *D);
 
-  void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment);
+  void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment,
+                       CharUnits AIXOffsetNewAlignment);
+  void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment) {
+    UpdateAlignment(NewAlignment, UnpackedNewAlignment, UnpackedNewAlignment);
+  }
   void UpdateAlignment(CharUnits NewAlignment) {
-    UpdateAlignment(NewAlignment, NewAlignment);
+    UpdateAlignment(NewAlignment, NewAlignment, NewAlignment);
   }
 
   /// Retrieve the externally-supplied field offset for the given
   /// field.
   ///
   /// \param Field The field whose offset is being queried.
   /// \param ComputedOffset The offset that we've computed for this field.
   uint64_t updateExternalFieldOffset(const FieldDecl *Field,
protected:
   void setDataSize(CharUnits NewSize) { DataSize = Context.toBits(NewSize); }
   void setDataSize(uint64_t NewSize) { DataSize = NewSize; }
 
   ItaniumRecordLayoutBuilder(const ItaniumRecordLayoutBuilder &) = delete;
   void operator=(const ItaniumRecordLayoutBuilder &) = delete;
 };
 } // end anonymous namespace
 
+static bool isAIXLayout(const ASTContext &Context) {
+  return Context.getTargetInfo().getTriple().getOS() == llvm::Triple::AIX;
+}
+
 void ItaniumRecordLayoutBuilder::SelectPrimaryVBase(const CXXRecordDecl *RD) {
   for (const auto &I : RD->bases()) {
     assert(!I.getType()->isDependentType() &&
            "Cannot layout class with dependent bases.");
 
     const CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
 
     // Check if this is a nearly empty virtual base.
if (!MaxFieldAlignment.isZero()) {
     BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
     UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
   }
 
   // Round up the current record size to pointer alignment.
   setSize(getSize().alignTo(BaseAlign));
 
   // Update the alignment.
-  UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+  UpdateAlignment(BaseAlign, UnpackedBaseAlign,
+                  /*AIXOffsetAlignment : used by AIX-ABI*/
+                  BaseAlign);
 }
 
 void ItaniumRecordLayoutBuilder::LayoutNonVirtualBases(
     const CXXRecordDecl *RD) {
   // Then, determine the primary base class.
   DeterminePrimaryBase(RD);
 
   // Compute base subobject info.
if (Base->IsVirtual)
       HasExternalLayout = External.getExternalNVBaseOffset(Base->Class, Offset);
     else
       HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset);
   }
 
   // Clang <= 6 incorrectly applied the 'packed' attribute to base classes.
   // Per GCC's documentation, it only applies to non-static data members.
   CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
+  CharUnits AIXOffsetBaseAlign = Layout.getAIXOffsetAlignment();
   CharUnits BaseAlign =
       (Packed && ((Context.getLangOpts().getClangABICompat() <=
                    LangOptions::ClangABI::Ver6) ||
                   Context.getTargetInfo().getTriple().isPS4()))
           ? CharUnits::One()
           : UnpackedBaseAlign;
 
   // If we have an empty base class, try to place it at offset 0.
   if (Base->Class->isEmpty() &&
       (!HasExternalLayout || Offset == CharUnits::Zero()) &&
       EmptySubobjects->CanPlaceBaseAtOffset(Base, CharUnits::Zero())) {
     setSize(std::max(getSize(), Layout.getSize()));
-    UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+    UpdateAlignment(BaseAlign, UnpackedBaseAlign, AIXOffsetBaseAlign);
 
     return CharUnits::Zero();
   }
 
+  // Use AIX special alignment if current base is not the first member
+  // and the struct is not a union
+  if (isAIXLayout(Context) && !getDataSize().isZero() && !IsUnion) {
+    BaseAlign = AIXOffsetBaseAlign;
+  }
+
   // The maximum field alignment overrides base align.
   if (!MaxFieldAlignment.isZero()) {
     BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
     UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
   }
 
   if (!HasExternalLayout) {
     // Round up the current record size to the base's alignment boundary.
if (!Base->Class->isEmpty()) {
     // Update the data size.
     setDataSize(Offset + Layout.getNonVirtualSize());
 
     setSize(std::max(getSize(), getDataSize()));
   } else
     setSize(std::max(getSize(), Offset + Layout.getSize()));
 
   // Remember max struct/class alignment.
-  UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+  UpdateAlignment(BaseAlign, UnpackedBaseAlign, AIXOffsetBaseAlign);
 
   return Offset;
 }
 
 void ItaniumRecordLayoutBuilder::InitializeLayout(const Decl *D) {
   if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
     IsUnion = RD->isUnion();
     IsMsStruct = RD->isMsStruct(Context);
if (IsMsStruct) {
         }
         if (TypeSize > FieldAlign &&
             llvm::isPowerOf2_64(TypeSize.getQuantity()))
           FieldAlign = TypeSize;
       }
     }
   }
 
+  // AIX abi has this special rule that in aggregates, the first member of
+  // floating point data type(or aggregate type contains floating point data
+  // type) is aligned according to its natural alignment value, subsequent
+  // of such data type members of the aggregate are aligned on 4-byte
+  // boundaries.
+  CharUnits AIXOffsetFieldAlign = FieldAlign;
+  if (isAIXLayout(Context)) {
+    if (const BuiltinType *BTy =
+            Context.getBaseElementType(D->getType())->getAs<BuiltinType>()) {
+      if (BTy->isFloatingPoint()) {
+        AIXOffsetFieldAlign = CharUnits::fromQuantity(4);
+      }
+    } else if (const RecordType *RT = D->getType()
+                                          ->getBaseElementTypeUnsafe()
+                                          ->getAs<RecordType>()) {
+      if (const RecordDecl *RD = RT->getDecl()) {
+        const ASTRecordLayout &FieldRecord = Context.getASTRecordLayout(RD);
+        AIXOffsetFieldAlign = FieldRecord.getAIXOffsetAlignment();
+      }
+    }
+    // Field offset could still be 0 if we have 0 size bitfield as first member
+    // So if field index is not 0 and the struct is not a union, we should use
+    // AIX special alignment as well.
+    if (FieldOffset != CharUnits::Zero() ||
+        (D->getFieldIndex() != 0 && !IsUnion))
+      FieldAlign = AIXOffsetFieldAlign;
+  }
+
   // The align if the field is not packed. This is to check if the attribute
   // was unnecessary (-Wpacked).
   CharUnits UnpackedFieldAlign = FieldAlign;
   CharUnits UnpackedFieldOffset = FieldOffset;
 
-  if (FieldPacked)
+  if (FieldPacked) {
     FieldAlign = CharUnits::One();
+    AIXOffsetFieldAlign = CharUnits::One();
+  }
   CharUnits MaxAlignmentInChars =
     Context.toCharUnitsFromBits(D->getMaxAlignment());
   FieldAlign = std::max(FieldAlign, MaxAlignmentInChars);
   UnpackedFieldAlign = std::max(UnpackedFieldAlign, MaxAlignmentInChars);
+  AIXOffsetFieldAlign = std::max(AIXOffsetFieldAlign, MaxAlignmentInChars);
 
   // The maximum field alignment overrides the aligned attribute.
   if (!MaxFieldAlignment.isZero()) {
     FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
     UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignment);
+    AIXOffsetFieldAlign = std::min(AIXOffsetFieldAlign, MaxFieldAlignment);
   }
 
   // Round up the current record size to the field's alignment boundary.
   FieldOffset = FieldOffset.alignTo(FieldAlign);
   UnpackedFieldOffset = UnpackedFieldOffset.alignTo(UnpackedFieldAlign);
 
   if (UseExternalLayout) {
     FieldOffset = Context.toCharUnitsFromBits(
if (!IsOverlappingEmptyField) {
     setSize(std::max(getSizeInBits(), getDataSizeInBits()));
   } else {
     setSize(std::max(getSizeInBits(),
                      (uint64_t)Context.toBits(FieldOffset + FieldSize)));
   }
 
   // Remember max struct/class alignment.
   UnadjustedAlignment = std::max(UnadjustedAlignment, FieldAlign);
-  UpdateAlignment(FieldAlign, UnpackedFieldAlign);
+  UpdateAlignment(FieldAlign, UnpackedFieldAlign, AIXOffsetFieldAlign);
 }
 
 void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
   // In C++, records cannot be of size 0.
   if (Context.getLangOpts().CPlusPlus && getSizeInBits() == 0) {
     if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
       // Compatibility with gcc requires a class (pod or non-pod)
       // which is not empty but of size 0; such as having fields of
if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
     if (Packed && UnpackedAlignment <= Alignment &&
         UnpackedSizeInBits == getSizeInBits() && !HasPackedField)
       Diag(D->getLocation(), diag::warn_unnecessary_packed)
           << Context.getTypeDeclType(RD);
   }
 }
 
 void ItaniumRecordLayoutBuilder::UpdateAlignment(
-    CharUnits NewAlignment, CharUnits UnpackedNewAlignment) {
+    CharUnits NewAlignment, CharUnits UnpackedNewAlignment,
+    CharUnits AIXOffsetNewAlignment) {
   // The alignment is not modified when using 'mac68k' alignment or when
   // we have an externally-supplied layout that also provides overall alignment.
   if (IsMac68kAlign || (UseExternalLayout && !InferAlignment))
     return;
 
   if (NewAlignment > Alignment) {
     assert(llvm::isPowerOf2_64(NewAlignment.getQuantity()) &&
            "Alignment not a power of 2");
     Alignment = NewAlignment;
   }
 
   if (UnpackedNewAlignment > UnpackedAlignment) {
     assert(llvm::isPowerOf2_64(UnpackedNewAlignment.getQuantity()) &&
            "Alignment not a power of 2");
     UnpackedAlignment = UnpackedNewAlignment;
   }
+
+  if (AIXOffsetNewAlignment > AIXOffsetAlignment) {
+    assert(llvm::isPowerOf2_64(AIXOffsetNewAlignment.getQuantity()) &&
+           "Alignment not a power of 2");
+    AIXOffsetAlignment = AIXOffsetNewAlignment;
+  }
 }
 
 uint64_t
 ItaniumRecordLayoutBuilder::updateExternalFieldOffset(const FieldDecl *Field,
                                                       uint64_t ComputedOffset) {
   uint64_t ExternalFieldOffset = External.getExternalFieldOffset(Field);
 
   if (InferAlignment && ExternalFieldOffset < ComputedOffset) {
ASTContext::getASTRecordLayout(const RecordDecl *D) const {
 
   if (isMsLayout(*this)) {
     MicrosoftRecordLayoutBuilder Builder(*this);
     if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
       Builder.cxxLayout(RD);
       NewEntry = new (*this) ASTRecordLayout(
           *this, Builder.Size, Builder.Alignment, Builder.Alignment,
           Builder.RequiredAlignment,
+          /*AIXOffsetAlignment : used by AIX-ABI*/ Builder.Alignment,
           Builder.HasOwnVFPtr, Builder.HasOwnVFPtr || Builder.PrimaryBase,
           Builder.VBPtrOffset, Builder.DataSize, Builder.FieldOffsets,
           Builder.NonVirtualSize, Builder.Alignment, CharUnits::Zero(),
           Builder.PrimaryBase, false, Builder.SharedVBPtrBase,
           Builder.EndsWithZeroSizedObject, Builder.LeadsWithZeroSizedBase,
           Builder.Bases, Builder.VBases);
     } else {
       Builder.layout(D);
       NewEntry = new (*this) ASTRecordLayout(
           *this, Builder.Size, Builder.Alignment, Builder.Alignment,
           Builder.RequiredAlignment,
+          /*AIXOffsetAlignment : used by AIX-ABI*/ Builder.Alignment,
           Builder.Size, Builder.FieldOffsets);
     }
   } else {
     if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
       EmptySubobjectMap EmptySubobjects(*this, RD);
       ItaniumRecordLayoutBuilder Builder(*this, &EmptySubobjects);
       Builder.Layout(RD);
 
       // In certain situations, we are allowed to lay out objects in the
       // tail-padding of base classes.  This is ABI-dependent.
       // FIXME: this should be stored in the record layout.
       bool skipTailPadding =
           mustSkipTailPadding(getTargetInfo().getCXXABI(), RD);
 
       // FIXME: This should be done in FinalizeLayout.
       CharUnits DataSize =
           skipTailPadding ? Builder.getSize() : Builder.getDataSize();
       CharUnits NonVirtualSize =
           skipTailPadding ? DataSize : Builder.NonVirtualSize;
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
+          *this, Builder.getSize(), Builder.Alignment,
+          Builder.UnadjustedAlignment,
           /*RequiredAlignment : used by MS-ABI)*/
-          Builder.Alignment, Builder.HasOwnVFPtr, RD->isDynamicClass(),
+          Builder.Alignment,
+          /*AIXOffsetAlignment : used by AIX-ABI)*/
+          Builder.AIXOffsetAlignment, Builder.HasOwnVFPtr, RD->isDynamicClass(),
           CharUnits::fromQuantity(-1), DataSize, Builder.FieldOffsets,
           NonVirtualSize, Builder.NonVirtualAlignment,
           EmptySubobjects.SizeOfLargestEmptySubobject, Builder.PrimaryBase,
           Builder.PrimaryBaseIsVirtual, nullptr, false, false, Builder.Bases,
           Builder.VBases);
     } else {
       ItaniumRecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/nullptr);
       Builder.Layout(D);
 
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
+          *this, Builder.getSize(), Builder.Alignment,
+          Builder.UnadjustedAlignment,
           /*RequiredAlignment : used by MS-ABI)*/
-          Builder.Alignment, Builder.getSize(), Builder.FieldOffsets);
+          Builder.Alignment,
+          /*AIXOffsetAlignment : used by AIX-ABI)*/
+          Builder.AIXOffsetAlignment, Builder.getSize(), Builder.FieldOffsets);
     }
   }
 
   ASTRecordLayouts[D] = NewEntry;
 
   if (getLangOpts().DumpRecordLayouts) {
     llvm::outs() << "\n*** Dumping AST Record Layout\n";
     DumpRecordLayout(D, llvm::outs(), getLangOpts().DumpRecordLayoutsSimple);
if (Impl) {
     // frequently.
     if (SynthCount == 0)
       return getObjCLayout(D, nullptr);
   }
 
   ItaniumRecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/nullptr);
   Builder.Layout(D);
 
-  const ASTRecordLayout *NewEntry =
-    new (*this) ASTRecordLayout(*this, Builder.getSize(),
-                                Builder.Alignment,
-                                Builder.UnadjustedAlignment,
-                                /*RequiredAlignment : used by MS-ABI)*/
-                                Builder.Alignment,
-                                Builder.getDataSize(),
-                                Builder.FieldOffsets);
+  const ASTRecordLayout *NewEntry = new (*this) ASTRecordLayout(
+      *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
+      /*AIXOffsetAlignment : used by AIX-ABI)*/
+      Builder.Alignment, Builder.getDataSize(), Builder.FieldOffsets);
 
   ObjCLayouts[Key] = NewEntry;
 
   return *NewEntry;
 }
 
 static void PrintOffset(raw_ostream &OS,
                         CharUnits Offset, unsigned IndentLevel) {

clang/test/Layout/aix-double-struct-member.cpp

+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc-ibm-aix-xcoff \
+// RUN: -fdump-record-layouts -fsyntax-only %s 2>/dev/null | FileCheck %s
+
+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc64-ibm-aix-xcoff \
+// RUN: -fdump-record-layouts -fsyntax-only %s 2>/dev/null | FileCheck %s
+
+namespace test1 {
+// Test double alignment when it is/is not the first struct member.
+struct D {
+  double d1;
+  int i1;
+};
+
+struct DoubleFirst {
+  struct D d2;
+  int i2;
+};
+
+struct IntFirst {
+  int i3;
+  struct D d3;
+};
+
+int a = sizeof(DoubleFirst);
+int b = sizeof(IntFirst);
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test1::D
+// CHECK-NEXT:         0 |   double d1
+// CHECK-NEXT:         8 |   int i1
+// CHECK-NEXT:           | [sizeof=16, dsize=16, align=8,
+// CHECK-NEXT:           |  nvsize=16, nvalign=8]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test1::DoubleFirst
+// CHECK-NEXT:         0 |   struct test1::D d2
+// CHECK-NEXT:         0 |     double d1
+// CHECK-NEXT:         8 |     int i1
+// CHECK-NEXT:        16 |   int i2
+// CHECK-NEXT:           | [sizeof=24, dsize=24, align=8,
+// CHECK-NEXT:           |  nvsize=24, nvalign=8]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test1::IntFirst
+// CHECK-NEXT:         0 |   int i3
+// CHECK-NEXT:         4 |   struct test1::D d3
+// CHECK-NEXT:         4 |     double d1
+// CHECK-NEXT:        12 |     int i1
+// CHECK-NEXT:           | [sizeof=20, dsize=20, align=4,
+// CHECK-NEXT:           |  nvsize=20, nvalign=4]
+}; // namespace test1
+
+namespace test2 {
+// Test AIX layout for zero sized bitfield followed by double.
+struct Double {
+  int : 0;
+  double d;
+};
+
+int a = sizeof(Double);
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test2::Double
+// CHECK-NEXT:       0:- |   int
+// CHECK-NEXT:         0 |   double d
+// CHECK-NEXT:           | [sizeof=8, dsize=8, align=4,
+// CHECK-NEXT:           |  nvsize=8, nvalign=4]
+}; // namespace test2
+
+namespace test3 {
+// Test the alignment of a double member in union.
+union A {
+  int *b;
+  double d;
+};
+
+struct UnionStruct {
+  union A a;
+  int i;
+};
+
+int a = sizeof(UnionStruct);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | union test3::A
+// CHECK-NEXT:          0 |   int * b
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test3::UnionStruct
+// CHECK-NEXT:          0 |   union test3::A a
+// CHECK-NEXT:          0 |     int * b
+// CHECK-NEXT:          0 |     double d
+// CHECK-NEXT:          8 |   int i
+// CHECK-NEXT:            | [sizeof=16, dsize=16, align=8,
+// CHECK-NEXT:            |  nvsize=16, nvalign=8]
+}; // namespace test3
+
+namespace test4 {
+// Test the AIX Alignment rule when layout base class.
+struct A {
+  int a;
+};
+
+struct B {
+  double d;
+};
+
+class S : A, B {
+};
+
+int a = sizeof(S);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test4::A
+// CHECK-NEXT:          0 |   int a
+// CHECK-NEXT:            | [sizeof=4, dsize=4, align=4,
+// CHECK-NEXT:            |  nvsize=4, nvalign=4]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test4::B
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | class test4::S
+// CHECK-NEXT:          0 |   struct test4::A (base)
+// CHECK-NEXT:          0 |     int a
+// CHECK-NEXT:          4 |   struct test4::B (base)
+// CHECK-NEXT:          4 |     double d
+// CHECK-NEXT:            | [sizeof=12, dsize=12, align=4,
+// CHECK-NEXT:            |  nvsize=12, nvalign=4]
+}; // namespace test4

clang/test/Layout/aix-virtual-function-alignment.cpp

+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc-ibm-aix-xcoff \
+// RUN: -fdump-record-layouts -fsyntax-only %s 2>/dev/null | FileCheck \
+// RUN: --check-prefix=CHECK32 %s
+
+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc64-ibm-aix-xcoff \
+// RUN: -fdump-record-layouts -fsyntax-only %s 2>/dev/null | FileCheck \
+// RUN: --check-prefix=CHECK64 %s
+
+struct A {
+  virtual void boo() {}
+};
+
+struct B {
+  bool b;
+  A a;
+};
+
+int i = sizeof(B);
+
+// CHECK32:      *** Dumping AST Record Layout
+// CHECK32-NEXT:          0 | struct A
+// CHECK32-NEXT:          0 |   (A vtable pointer)
+// CHECK32-NEXT:            | [sizeof=4, dsize=4, align=4,
+// CHECK32-NEXT:            |  nvsize=4, nvalign=4]
+
+// CHECK32:      *** Dumping AST Record Layout
+// CHECK32-NEXT:          0 | struct B
+// CHECK32-NEXT:          0 |   _Bool b
+// CHECK32-NEXT:          4 |   struct A a
+// CHECK32-NEXT:          4 |     (A vtable pointer)
+// CHECK32-NEXT:            | [sizeof=8, dsize=8, align=4,
+// CHECK32-NEXT:            |  nvsize=8, nvalign=4]
+
+// CHECK64:      *** Dumping AST Record Layout
+// CHECK64-NEXT:          0 | struct A
+// CHECK64-NEXT:          0 |   (A vtable pointer)
+// CHECK64-NEXT:            | [sizeof=8, dsize=8, align=8,
+// CHECK64-NEXT:            |  nvsize=8, nvalign=8]
+
+// CHECK64:      *** Dumping AST Record Layout
+// CHECK64-NEXT:          0 | struct B
+// CHECK64-NEXT:          0 |   _Bool b
+// CHECK64-NEXT:          8 |   struct A a
+// CHECK64-NEXT:          8 |     (A vtable pointer)
+// CHECK64-NEXT:            | [sizeof=16, dsize=16, align=8,
+// CHECK64-NEXT:            |  nvsize=16, nvalign=8]