[AIX] Implement AIX special alignment rule about double/long double

Implement AIX default `power` alignment rule by adding `PreferredAlignment` and
`PreferredNVAlignment` in ASTRecordLayout class.

The patchh aims at returning correct value for `__alignof(x)` and `alignof(x)`
under `power` alignment rules.

Differential Revision: https://reviews.llvm.org/D79719

clang/include/clang/AST/RecordLayout.h

@@ -70,6 +70,11 @@ class ASTRecordLayout {
   // Alignment - Alignment of record in characters.
   CharUnits Alignment;
 
+  // PreferredAlignment - Preferred alignment of record in characters. This
+  // can be different than Alignment in cases where it is beneficial for
+  // performance or backwards compatibility preserving (e.g. AIX-ABI).
+  CharUnits PreferredAlignment;
+
   // UnadjustedAlignment - Maximum of the alignments of the record members in
   // characters.
   CharUnits UnadjustedAlignment;
@@ -91,6 +96,11 @@ class ASTRecordLayout {
     /// which is the alignment of the object without virtual bases.
     CharUnits NonVirtualAlignment;
 
+    /// PreferredNVAlignment - The preferred non-virtual alignment (in chars) of
+    /// an object, which is the preferred alignment of the object without
+    /// virtual bases.
+    CharUnits PreferredNVAlignment;
+
     /// SizeOfLargestEmptySubobject - The size of the largest empty subobject
     /// (either a base or a member). Will be zero if the class doesn't contain
     /// any empty subobjects.
@@ -139,30 +149,26 @@ class ASTRecordLayout {
   CXXRecordLayoutInfo *CXXInfo = nullptr;
 
   ASTRecordLayout(const ASTContext &Ctx, CharUnits size, CharUnits alignment,
-                  CharUnits unadjustedAlignment,
+                  CharUnits preferredAlignment, CharUnits unadjustedAlignment,
                   CharUnits requiredAlignment, 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 preferredAlignment, CharUnits unadjustedAlignment,
+                  CharUnits requiredAlignment, bool hasOwnVFPtr,
+                  bool hasExtendableVFPtr, CharUnits vbptroffset,
+                  CharUnits datasize, ArrayRef<uint64_t> fieldoffsets,
                   CharUnits nonvirtualsize, CharUnits nonvirtualalignment,
+                  CharUnits preferrednvalignment,
                   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;
 
@@ -175,6 +181,10 @@ class ASTRecordLayout {
   /// getAlignment - Get the record alignment in characters.
   CharUnits getAlignment() const { return Alignment; }
 
+  /// getPreferredFieldAlignment - Get the record preferred alignment in
+  /// characters.
+  CharUnits getPreferredAlignment() const { return PreferredAlignment; }
+
   /// getUnadjustedAlignment - Get the record alignment in characters, before
   /// alignment adjustement.
   CharUnits getUnadjustedAlignment() const { return UnadjustedAlignment; }
@@ -193,9 +203,7 @@ class ASTRecordLayout {
 
   /// 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.
@@ -205,14 +213,23 @@ class ASTRecordLayout {
     return CXXInfo->NonVirtualSize;
   }
 
-  /// getNonVirtualSize - Get the non-virtual alignment (in chars) of an object,
-  /// which is the alignment of the object without virtual bases.
+  /// getNonVirtualAlignment - Get the non-virtual alignment (in chars) of an
+  /// object, which is the alignment of the object without virtual bases.
   CharUnits getNonVirtualAlignment() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
 
     return CXXInfo->NonVirtualAlignment;
   }
 
+  /// getPreferredNVAlignment - Get the preferred non-virtual alignment (in
+  /// chars) of an object, which is the preferred alignment of the object
+  /// without virtual bases.
+  CharUnits getPreferredNVAlignment() const {
+    assert(CXXInfo && "Record layout does not have C++ specific info!");
+
+    return CXXInfo->PreferredNVAlignment;
+  }
+
   /// getPrimaryBase - Get the primary base for this record.
   const CXXRecordDecl *getPrimaryBase() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
@@ -287,9 +304,7 @@ class ASTRecordLayout {
     return !CXXInfo->VBPtrOffset.isNegative();
   }
 
-  CharUnits getRequiredAlignment() const {
-    return RequiredAlignment;
-  }
+  CharUnits getRequiredAlignment() const { return RequiredAlignment; }
 
   bool endsWithZeroSizedObject() const {
     return CXXInfo && CXXInfo->EndsWithZeroSizedObject;

clang/include/clang/Basic/TargetInfo.h

@@ -1401,6 +1401,9 @@ class TargetInfo : public virtual TransferrableTargetInfo,
   /// Whether target allows to overalign ABI-specified preferred alignment
   virtual bool allowsLargerPreferedTypeAlignment() const { return true; }
 
+  /// Whether target defaults to the `power` alignment rules of AIX.
+  virtual bool defaultsToAIXPowerAlignment() const { return false; }
+
   /// Set supported OpenCL extensions and optional core features.
   virtual void setSupportedOpenCLOpts() {}
 

clang/lib/AST/ASTContext.cpp

@@ -2439,8 +2439,8 @@ CharUnits ASTContext::getTypeUnadjustedAlignInChars(const Type *T) const {
 
 /// getPreferredTypeAlign - Return the "preferred" alignment of the specified
 /// type for the current target in bits.  This can be different than the ABI
-/// alignment in cases where it is beneficial for performance to overalign
-/// a data type.
+/// alignment in cases where it is beneficial for performance or backwards
+/// compatibility preserving to overalign a data type.
 unsigned ASTContext::getPreferredTypeAlign(const Type *T) const {
   TypeInfo TI = getTypeInfo(T);
   unsigned ABIAlign = TI.Align;
@@ -2450,18 +2450,33 @@ unsigned ASTContext::getPreferredTypeAlign(const Type *T) const {
   // The preferred alignment of member pointers is that of a pointer.
   if (T->isMemberPointerType())
     return getPreferredTypeAlign(getPointerDiffType().getTypePtr());
-
+ 
   if (!Target->allowsLargerPreferedTypeAlignment())
     return ABIAlign;
 
-  // Double and long long should be naturally aligned if possible.
+  if (const auto *RT = T->getAs<RecordType>()) {
+    if (TI.AlignIsRequired)
+      return ABIAlign;
+
+    unsigned PreferredAlign = static_cast<unsigned>(
+        toBits(getASTRecordLayout(RT->getDecl()).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::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)

clang/lib/AST/RecordLayout.cpp

@@ -29,45 +29,42 @@ void ASTRecordLayout::Destroy(ASTContext &Ctx) {
 
 ASTRecordLayout::ASTRecordLayout(const ASTContext &Ctx, CharUnits size,
                                  CharUnits alignment,
+                                 CharUnits preferredAlignment,
                                  CharUnits unadjustedAlignment,
                                  CharUnits requiredAlignment,
                                  CharUnits datasize,
                                  ArrayRef<uint64_t> fieldoffsets)
     : Size(size), DataSize(datasize), Alignment(alignment),
+      PreferredAlignment(preferredAlignment),
       UnadjustedAlignment(unadjustedAlignment),
       RequiredAlignment(requiredAlignment) {
   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)
-  : Size(size), DataSize(datasize), Alignment(alignment),
-    UnadjustedAlignment(unadjustedAlignment),
-    RequiredAlignment(requiredAlignment), CXXInfo(new (Ctx) CXXRecordLayoutInfo)
-{
+ASTRecordLayout::ASTRecordLayout(
+    const ASTContext &Ctx, CharUnits size, CharUnits alignment,
+    CharUnits preferredAlignment, CharUnits unadjustedAlignment,
+    CharUnits requiredAlignment, bool hasOwnVFPtr, bool hasExtendableVFPtr,
+    CharUnits vbptroffset, CharUnits datasize, ArrayRef<uint64_t> fieldoffsets,
+    CharUnits nonvirtualsize, CharUnits nonvirtualalignment,
+    CharUnits preferrednvalignment, 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),
+      PreferredAlignment(preferredAlignment),
+      UnadjustedAlignment(unadjustedAlignment),
+      RequiredAlignment(requiredAlignment),
+      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->PreferredNVAlignment = preferrednvalignment;
   CXXInfo->SizeOfLargestEmptySubobject = SizeOfLargestEmptySubobject;
   CXXInfo->BaseOffsets = BaseOffsets;
   CXXInfo->VBaseOffsets = VBaseOffsets;