diff --git a/clang/include/clang/Basic/TargetInfo.h b/clang/include/clang/Basic/TargetInfo.h
index 070cc792ca7db..db23afa6d6f0b 100644
--- a/clang/include/clang/Basic/TargetInfo.h
+++ b/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; }
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index ae6d299024c6d..d9380c4b6ae96 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/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);
 }
 
diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index c0bf4e686cf03..0699ec686e4e6 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/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();
diff --git a/clang/lib/Basic/Targets/AArch64.cpp b/clang/lib/Basic/Targets/AArch64.cpp
index fad8d773bfc52..3633bab6e0df9 100644
--- a/clang/lib/Basic/Targets/AArch64.cpp
+++ b/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.
diff --git a/clang/test/CodeGen/aapcs-align.cpp b/clang/test/CodeGen/aapcs-align.cpp
index 4f393d9e6b7f3..c7bc5ba0bbfef 100644
--- a/clang/test/CodeGen/aapcs-align.cpp
+++ b/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);
+}
+
 }
diff --git a/clang/test/CodeGen/aapcs64-align.cpp b/clang/test/CodeGen/aapcs64-align.cpp
index 7a8151022852e..e69faf231936c 100644
--- a/clang/test/CodeGen/aapcs64-align.cpp
+++ b/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);
+}
+
 }
 
diff --git a/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp b/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp
index e475f032f5ce3..b7aad6a5bcd21 100644
--- a/clang/test/CodeGenCXX/debug-info-structured-binding-bitfield.cpp
+++ b/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),
 //