[ARM,AArch64] Fix ABI bugs with over-sized bitfields (#126774)

This fixes two bugs in the ABI for over-sized bitfields for ARM and
AArch64:

The container type picked for an over-sized bitfield already contributes
to the alignment of the structure, but it should also contribute to the
"unadjusted alignment" which is used by the ARM and AArch64 PCS.

AAPCS64 defines the bitfield layout algorithm for over-sized bitfields
as picking a container which is the fundamental integer data type with
the largest size less than or equal to the bit-field width. Since
AAPCS64 has a 128-bit integer fundamental data type, we need to consider
Int128 as a container type for AArch64.

Author: ostannard

clang/include/clang/Basic/TargetInfo.h

@@ -199,6 +199,10 @@ struct TransferrableTargetInfo {
   /// zero length bitfield, regardless of the zero length bitfield type.
   unsigned ZeroLengthBitfieldBoundary;
 
+  /// The largest container size which should be used for an over-sized
+  /// bitfield, in bits.
+  unsigned LargestOverSizedBitfieldContainer;
+
   /// If non-zero, specifies a maximum alignment to truncate alignment
   /// specified in the aligned attribute of a static variable to this value.
   unsigned MaxAlignedAttribute;
@@ -954,6 +958,10 @@ class TargetInfo : public TransferrableTargetInfo,
     return ZeroLengthBitfieldBoundary;
   }
 
+  unsigned getLargestOverSizedBitfieldContainer() const {
+    return LargestOverSizedBitfieldContainer;
+  }
+
   /// Get the maximum alignment in bits for a static variable with
   /// aligned attribute.
   unsigned getMaxAlignedAttribute() const { return MaxAlignedAttribute; }

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -1469,15 +1469,18 @@ void ItaniumRecordLayoutBuilder::LayoutWideBitField(uint64_t FieldSize,
   //   sizeof(T')*8 <= n.
 
   QualType IntegralPODTypes[] = {
-    Context.UnsignedCharTy, Context.UnsignedShortTy, Context.UnsignedIntTy,
-    Context.UnsignedLongTy, Context.UnsignedLongLongTy
+      Context.UnsignedCharTy,     Context.UnsignedShortTy,
+      Context.UnsignedIntTy,      Context.UnsignedLongTy,
+      Context.UnsignedLongLongTy, Context.UnsignedInt128Ty,
   };
 
   QualType Type;
+  uint64_t MaxSize =
+      Context.getTargetInfo().getLargestOverSizedBitfieldContainer();
   for (const QualType &QT : IntegralPODTypes) {
     uint64_t Size = Context.getTypeSize(QT);
 
-    if (Size > FieldSize)
+    if (Size > FieldSize || Size > MaxSize)
       break;
 
     Type = QT;
@@ -1520,6 +1523,7 @@ void ItaniumRecordLayoutBuilder::LayoutWideBitField(uint64_t FieldSize,
   setSize(std::max(getSizeInBits(), getDataSizeInBits()));
 
   // Remember max struct/class alignment.
+  UnadjustedAlignment = std::max(UnadjustedAlignment, TypeAlign);
   UpdateAlignment(TypeAlign);
 }
 

clang/lib/Basic/TargetInfo.cpp

@@ -141,6 +141,7 @@ TargetInfo::TargetInfo(const llvm::Triple &T) : Triple(T) {
   UseLeadingZeroLengthBitfield = true;
   UseExplicitBitFieldAlignment = true;
   ZeroLengthBitfieldBoundary = 0;
+  LargestOverSizedBitfieldContainer = 64;
   MaxAlignedAttribute = 0;
   HalfFormat = &llvm::APFloat::IEEEhalf();
   FloatFormat = &llvm::APFloat::IEEEsingle();

clang/lib/Basic/Targets/AArch64.cpp

@@ -261,6 +261,10 @@ AArch64TargetInfo::AArch64TargetInfo(const llvm::Triple &Triple,
   assert(UseBitFieldTypeAlignment && "bitfields affect type alignment");
   UseZeroLengthBitfieldAlignment = true;
 
+  // AAPCS64 allows any "fundamental integer data type" to be used for
+  // over-sized bitfields, which includes 128-bit integers.
+  LargestOverSizedBitfieldContainer = 128;
+
   HasUnalignedAccess = true;
 
   // AArch64 targets default to using the ARM C++ ABI.

clang/test/CodeGen/aapcs-align.cpp

@@ -6,6 +6,11 @@
 
 extern "C" {
 
+// CHECK: @sizeof_OverSizedBitfield ={{.*}} global i32 8
+// CHECK: @alignof_OverSizedBitfield ={{.*}} global i32 8
+// CHECK: @sizeof_VeryOverSizedBitfield ={{.*}} global i32 16
+// CHECK: @alignof_VeryOverSizedBitfield ={{.*}} global i32 8
+
 // Base case, nothing interesting.
 struct S {
   int x, y;
@@ -138,4 +143,42 @@ void g6() {
 // CHECK: call void @f6m(i32 noundef 1, i32 noundef 2, i32 noundef 3, i32 noundef 4, i32 noundef 5, [4 x i32] [i32 6, i32 7, i32 0, i32 undef])
 // CHECK: declare void @f6(i32 noundef, [4 x i32])
 // CHECK: declare void @f6m(i32 noundef, i32 noundef, i32 noundef, i32 noundef, i32 noundef, [4 x i32])
+
+// Over-sized bitfield, which results in a 64-bit container type, so 64-bit
+// alignment.
+struct OverSizedBitfield {
+  int x : 64;
+};
+
+unsigned sizeof_OverSizedBitfield = sizeof(OverSizedBitfield);
+unsigned alignof_OverSizedBitfield = alignof(OverSizedBitfield);
+
+// CHECK: define{{.*}} void @g7
+// CHECK: call void @f7(i32 noundef 1, [1 x i64] [i64 42])
+// CHECK: declare void @f7(i32 noundef, [1 x i64])
+void f7(int a, OverSizedBitfield b);
+void g7() {
+  OverSizedBitfield s = {42};
+  f7(1, s);
+}
+
+// There are no 128-bit fundamental data types defined by AAPCS32, so this gets
+// a 64-bit container plus 64 bits of padding, giving it a size of 16 bytes and
+// alignment of 8 bytes.
+struct VeryOverSizedBitfield {
+  int x : 128;
+};
+
+unsigned sizeof_VeryOverSizedBitfield = sizeof(VeryOverSizedBitfield);
+unsigned alignof_VeryOverSizedBitfield = alignof(VeryOverSizedBitfield);
+
+// CHECK: define{{.*}} void @g8
+// CHECK: call void @f8(i32 noundef 1, [2 x i64] [i64 42, i64 0])
+// CHECK: declare void @f8(i32 noundef, [2 x i64])
+void f8(int a, VeryOverSizedBitfield b);
+void g8() {
+  VeryOverSizedBitfield s = {42};
+  f8(1, s);
+}
+
 }

clang/test/CodeGen/aapcs64-align.cpp

@@ -5,6 +5,13 @@
 
 extern "C" {
 
+// CHECK: @sizeof_OverSizedBitfield ={{.*}} global i32 8
+// CHECK: @alignof_OverSizedBitfield ={{.*}} global i32 8
+// CHECK: @sizeof_VeryOverSizedBitfield ={{.*}} global i32 16
+// CHECK: @alignof_VeryOverSizedBitfield ={{.*}} global i32 16
+// CHECK: @sizeof_RidiculouslyOverSizedBitfield ={{.*}} global i32 32
+// CHECK: @alignof_RidiculouslyOverSizedBitfield ={{.*}} global i32 16
+
 // Base case, nothing interesting.
 struct S {
   long x, y;
@@ -161,5 +168,62 @@ int test_bitint8(){
 }
 // CHECK:  ret i32 1
 
+// Over-sized bitfield, which results in a 64-bit container type, so 64-bit
+// alignment.
+struct OverSizedBitfield {
+  int x : 64;
+};
+
+unsigned sizeof_OverSizedBitfield = sizeof(OverSizedBitfield);
+unsigned alignof_OverSizedBitfield = alignof(OverSizedBitfield);
+
+// CHECK: define{{.*}} void @g7
+// CHECK: call void @f7(i32 noundef 1, i64 42)
+// CHECK: declare void @f7(i32 noundef, i64)
+void f7(int a, OverSizedBitfield b);
+void g7() {
+  OverSizedBitfield s = {42};
+  f7(1, s);
+}
+
+// AAPCS64 does have a 128-bit integer fundamental data type, so this gets a
+// 128-bit container with 128-bit alignment. This is just within the limit of
+// what can be passed directly.
+struct VeryOverSizedBitfield {
+  int x : 128;
+};
+
+unsigned sizeof_VeryOverSizedBitfield = sizeof(VeryOverSizedBitfield);
+unsigned alignof_VeryOverSizedBitfield = alignof(VeryOverSizedBitfield);
+
+// CHECK: define{{.*}} void @g8
+// CHECK: call void @f8(i32 noundef 1, i128 42)
+// CHECK: declare void @f8(i32 noundef, i128)
+void f8(int a, VeryOverSizedBitfield b);
+void g8() {
+  VeryOverSizedBitfield s = {42};
+  f8(1, s);
+}
+
+// There are no bigger fundamental data types, so this gets a 128-bit container
+// and 128 bits of padding, giving the struct a size of 32 bytes, and an
+// alignment of 16 bytes. This is over the PCS size limit of 16 bytes, so it
+// will be passed indirectly.
+struct RidiculouslyOverSizedBitfield {
+  int x : 256;
+};
+
+unsigned sizeof_RidiculouslyOverSizedBitfield = sizeof(RidiculouslyOverSizedBitfield);
+unsigned alignof_RidiculouslyOverSizedBitfield = alignof(RidiculouslyOverSizedBitfield);
+
+// CHECK: define{{.*}} void @g9
+// CHECK: call void @f9(i32 noundef 1, ptr noundef nonnull %agg.tmp)
+// CHECK: declare void @f9(i32 noundef, ptr noundef)
+void f9(int a, RidiculouslyOverSizedBitfield b);
+void g9() {
+  RidiculouslyOverSizedBitfield s = {42};
+  f9(1, s);
+}
+
 }
 

clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp

@@ -248,8 +248,8 @@ struct S15 {
 };
 
 // CHECK-LABEL: define dso_local void @_Z4fS15v
-// CHECK:                        alloca %struct.S15, align 8
-// CHECK-NEXT:    [[TMP0:%.*]] = alloca %struct.S15, align 8
+// CHECK:                        alloca %struct.S15, align 16
+// CHECK-NEXT:    [[TMP0:%.*]] = alloca %struct.S15, align 16
 // CHECK:         #dbg_declare(ptr [[TMP0]], [[S15_A:![0-9]+]], !DIExpression(DW_OP_LLVM_extract_bits_sext, 0, 32),
 // CHECK-NEXT:    #dbg_declare(ptr [[TMP0]], [[S15_B:![0-9]+]], !DIExpression(DW_OP_plus_uconst, 16, DW_OP_LLVM_extract_bits_zext, 0, 32),
 //