Revert "ADT: Migrate users of AlignedCharArrayUnion to std::aligned_union_t, NFC"

We determined that the MSVC implementation of std::aligned* isn't suited to our needs. It doesn't support 16 byte alignment or higher, and it doesn't really guarantee 8 byte alignment. See https://github.com/microsoft/STL/issues/1533 Also reverts "ADT: Change AlignedCharArrayUnion to an alias of std::aligned_union_t, NFC" Also reverts "ADT: Remove AlignedCharArrayUnion, NFC" to bring back AlignedCharArrayUnion. This reverts commit 4d8bf870a82765eb0d4fe53c82f796b957c05954. This reverts commit d10f9863a5ac1cb681af07719650c44b48f289ce. This reverts commit 4b5dc150b9862271720b3d56a3e723a55dd81838.
2024-11-25 04:02:41 +01:00 · 2020-12-14 16:56:04 -08:00 · 2020-12-14 16:56:04 -08:00 · b945e1014a
commit b945e1014a
parent 23ab920e40
13 changed files with 299 additions and 19 deletions
--- a/include/llvm/ADT/DenseMap.h
+++ b/include/llvm/ADT/DenseMap.h
@ -15,6 +15,7 @@

 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/EpochTracker.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemAlloc.h"
@ -900,7 +901,7 @@ class SmallDenseMap

  /// A "union" of an inline bucket array and the struct representing
  /// a large bucket. This union will be discriminated by the 'Small' bit.
-  std::aligned_union_t<1, BucketT[InlineBuckets], LargeRep> storage;
+  AlignedCharArrayUnion<BucketT[InlineBuckets], LargeRep> storage;

 public:
  explicit SmallDenseMap(unsigned NumInitBuckets = 0) {
@ -1040,7 +1041,7 @@ public:

    if (Small) {
      // First move the inline buckets into a temporary storage.
-      std::aligned_union_t<1, BucketT[InlineBuckets]> TmpStorage;
+      AlignedCharArrayUnion<BucketT[InlineBuckets]> TmpStorage;
      BucketT *TmpBegin = reinterpret_cast<BucketT *>(&TmpStorage);
      BucketT *TmpEnd = TmpBegin;

--- a/include/llvm/ADT/IntervalMap.h
+++ b/include/llvm/ADT/IntervalMap.h
@ -101,6 +101,7 @@
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/bit.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/RecyclingAllocator.h"
 #include <algorithm>
@ -108,7 +109,6 @@
 #include <cstdint>
 #include <iterator>
 #include <new>
-#include <type_traits>
 #include <utility>

 namespace llvm {
@ -963,7 +963,7 @@ public:

 private:
  // The root data is either a RootLeaf or a RootBranchData instance.
-  std::aligned_union_t<1, RootLeaf, RootBranchData> data;
+  AlignedCharArrayUnion<RootLeaf, RootBranchData> data;

  // Tree height.
  // 0: Leaves in root.
--- a/include/llvm/CodeGen/DIE.h
+++ b/include/llvm/CodeGen/DIE.h
@ -22,6 +22,7 @@
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/CodeGen/DwarfStringPoolEntry.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Allocator.h"
 #include <cassert>
 #include <cstddef>
@ -367,9 +368,9 @@ private:
  ///
  /// All values that aren't standard layout (or are larger than 8 bytes)
  /// should be stored by reference instead of by value.
-  using ValTy = std::aligned_union_t<1, DIEInteger, DIEString, DIEExpr,
-                                     DIELabel, DIEDelta *, DIEEntry, DIEBlock *,
-                                     DIELoc *, DIELocList, DIEBaseTypeRef *>;
+  using ValTy = AlignedCharArrayUnion<DIEInteger, DIEString, DIEExpr, DIELabel,
+                                      DIEDelta *, DIEEntry, DIEBlock *,
+                                      DIELoc *, DIELocList, DIEBaseTypeRef *>;

  static_assert(sizeof(ValTy) <= sizeof(uint64_t) ||
                    sizeof(ValTy) <= sizeof(void *),
--- a/include/llvm/CodeGen/SelectionDAGNodes.h
+++ b/include/llvm/CodeGen/SelectionDAGNodes.h
@ -38,6 +38,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Operator.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/AtomicOrdering.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
@ -2634,9 +2635,10 @@ template <> struct GraphTraits<SDNode*> {
 ///
 /// This needs to be a union because the largest node differs on 32 bit systems
 /// with 4 and 8 byte pointer alignment, respectively.
-using LargestSDNode =
-    std::aligned_union_t<1, AtomicSDNode, TargetIndexSDNode, BlockAddressSDNode,
-                         GlobalAddressSDNode, PseudoProbeSDNode>;
+using LargestSDNode = AlignedCharArrayUnion<AtomicSDNode, TargetIndexSDNode,
+                                            BlockAddressSDNode,
+                                            GlobalAddressSDNode,
+                                            PseudoProbeSDNode>;

 /// The SDNode class with the greatest alignment requirement.
 using MostAlignedSDNode = GlobalAddressSDNode;
--- a/include/llvm/Support/AlignOf.h
+++ b/include/llvm/Support/AlignOf.h
@ -0,0 +1,33 @@
+//===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the AlignedCharArrayUnion class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_ALIGNOF_H
+#define LLVM_SUPPORT_ALIGNOF_H
+
+#include <type_traits>
+
+namespace llvm {
+
+/// A suitably aligned and sized character array member which can hold elements
+/// of any type.
+///
+/// These types may be arrays, structs, or any other types. This exposes a
+/// `buffer` member which can be used as suitable storage for a placement new of
+/// any of these types.
+template <typename T, typename... Ts> struct AlignedCharArrayUnion {
+  using AlignedUnion = std::aligned_union_t<1, T, Ts...>;
+  alignas(alignof(AlignedUnion)) char buffer[sizeof(AlignedUnion)];
+};
+
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_ALIGNOF_H
--- a/include/llvm/Support/Error.h
+++ b/include/llvm/Support/Error.h
@ -19,6 +19,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Config/abi-breaking.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@ -677,8 +678,8 @@ private:
  }

  union {
-    std::aligned_union_t<1, storage_type> TStorage;
-    std::aligned_union_t<1, error_type> ErrorStorage;
+    AlignedCharArrayUnion<storage_type> TStorage;
+    AlignedCharArrayUnion<error_type> ErrorStorage;
  };
  bool HasError : 1;
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
--- a/include/llvm/Support/ErrorOr.h
+++ b/include/llvm/Support/ErrorOr.h
@ -15,6 +15,7 @@
 #ifndef LLVM_SUPPORT_ERROROR_H
 #define LLVM_SUPPORT_ERROROR_H

+#include "llvm/Support/AlignOf.h"
 #include <cassert>
 #include <system_error>
 #include <type_traits>
@ -252,8 +253,8 @@ private:
  }

  union {
-    std::aligned_union_t<1, storage_type> TStorage;
-    std::aligned_union_t<1, std::error_code> ErrorStorage;
+    AlignedCharArrayUnion<storage_type> TStorage;
+    AlignedCharArrayUnion<std::error_code> ErrorStorage;
  };
  bool HasError : 1;
 };
--- a/include/llvm/Support/JSON.h
+++ b/include/llvm/Support/JSON.h
@ -479,8 +479,8 @@ private:
  };
  // All members mutable, see moveFrom().
  mutable ValueType Type;
-  mutable std::aligned_union_t<1, bool, double, int64_t, llvm::StringRef,
-                               std::string, json::Array, json::Object>
+  mutable llvm::AlignedCharArrayUnion<bool, double, int64_t, llvm::StringRef,
+                                      std::string, json::Array, json::Object>
      Union;
  friend bool operator==(const Value &, const Value &);
 };
--- a/include/llvm/Support/TrailingObjects.h
+++ b/include/llvm/Support/TrailingObjects.h
@ -46,6 +46,7 @@
 #ifndef LLVM_SUPPORT_TRAILINGOBJECTS_H
 #define LLVM_SUPPORT_TRAILINGOBJECTS_H

+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
--- a/include/llvm/Support/YAMLTraits.h
+++ b/include/llvm/Support/YAMLTraits.h
@ -15,6 +15,7 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Regex.h"
@ -1312,7 +1313,7 @@ struct MappingNormalization {
  TNorm* operator->() { return BufPtr; }

 private:
-  using Storage = std::aligned_union_t<1, TNorm>;
+  using Storage = AlignedCharArrayUnion<TNorm>;

  Storage       Buffer;
  IO           &io;
@ -1349,7 +1350,7 @@ struct MappingNormalizationHeap {
  TNorm* operator->() { return BufPtr; }

 private:
-  using Storage = std::aligned_union_t<1, TNorm>;
+  using Storage = AlignedCharArrayUnion<TNorm>;

  Storage       Buffer;
  IO           &io;
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@ -26,6 +26,7 @@
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Value.h"
+#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/InstCombine/InstCombiner.h"
@ -119,7 +120,7 @@ namespace {
    // is overkill of this end.
    short IntVal = 0;

-    std::aligned_union_t<1, APFloat> FpValBuf;
+    AlignedCharArrayUnion<APFloat> FpValBuf;
  };

  /// FAddend is used to represent floating-point addend. An addend is
--- a/unittests/Support/AlignOfTest.cpp
+++ b/unittests/Support/AlignOfTest.cpp
@ -0,0 +1,237 @@
+//=== - llvm/unittest/Support/AlignOfTest.cpp - Alignment utility tests ---===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef _MSC_VER
+// Disable warnings about alignment-based structure padding.
+// This must be above the includes to suppress warnings in included templates.
+#pragma warning(disable:4324)
+#endif
+
+#include "llvm/Support/AlignOf.h"
+#include "llvm/Support/Compiler.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+// Disable warnings about questionable type definitions.
+// We're testing that even questionable types work with the alignment utilities.
+#ifdef _MSC_VER
+#pragma warning(disable:4584)
+#endif
+
+// Suppress direct base '{anonymous}::S1' inaccessible in '{anonymous}::D9'
+// due to ambiguity warning.
+#ifdef __clang__
+#pragma clang diagnostic ignored "-Wunknown-pragmas"
+#pragma clang diagnostic ignored "-Winaccessible-base"
+#elif ((__GNUC__ * 100) + __GNUC_MINOR__) >= 402
+// Pragma based warning suppression was introduced in GGC 4.2.  Additionally
+// this warning is "enabled by default".  The warning still appears if -Wall is
+// suppressed.  Apparently GCC suppresses it when -w is specifed, which is odd.
+#pragma GCC diagnostic warning "-w"
+#endif
+
+// Define some fixed alignment types to use in these tests.
+struct alignas(1) A1 {};
+struct alignas(2) A2 {};
+struct alignas(4) A4 {};
+struct alignas(8) A8 {};
+
+struct S1 {};
+struct S2 { char a; };
+struct S3 { int x; };
+struct S4 { double y; };
+struct S5 { A1 a1; A2 a2; A4 a4; A8 a8; };
+struct S6 { double f(); };
+struct D1 : S1 {};
+struct D2 : S6 { float g(); };
+struct D3 : S2 {};
+struct D4 : S2 { int x; };
+struct D5 : S3 { char c; };
+struct D6 : S2, S3 {};
+struct D7 : S1, S3 {};
+struct D8 : S1, D4, D5 { double x[2]; };
+struct D9 : S1, D1 { S1 s1; };
+struct V1 { virtual ~V1(); };
+struct V2 { int x; virtual ~V2(); };
+struct V3 : V1 {
+  ~V3() override;
+};
+struct V4 : virtual V2 { int y;
+  ~V4() override;
+};
+struct V5 : V4, V3 { double z;
+  ~V5() override;
+};
+struct V6 : S1 { virtual ~V6(); };
+struct V7 : virtual V2, virtual V6 {
+  ~V7() override;
+};
+struct V8 : V5, virtual V6, V7 { double zz;
+  ~V8() override;
+};
+
+double S6::f() { return 0.0; }
+float D2::g() { return 0.0f; }
+V1::~V1() {}
+V2::~V2() {}
+V3::~V3() {}
+V4::~V4() {}
+V5::~V5() {}
+V6::~V6() {}
+V7::~V7() {}
+V8::~V8() {}
+
+template <typename M> struct T { M m; };
+
+TEST(AlignOfTest, BasicAlignedArray) {
+  EXPECT_LE(1u, alignof(AlignedCharArrayUnion<A1>));
+  EXPECT_LE(2u, alignof(AlignedCharArrayUnion<A2>));
+  EXPECT_LE(4u, alignof(AlignedCharArrayUnion<A4>));
+  EXPECT_LE(8u, alignof(AlignedCharArrayUnion<A8>));
+
+  EXPECT_LE(1u, sizeof(AlignedCharArrayUnion<A1>));
+  EXPECT_LE(2u, sizeof(AlignedCharArrayUnion<A2>));
+  EXPECT_LE(4u, sizeof(AlignedCharArrayUnion<A4>));
+  EXPECT_LE(8u, sizeof(AlignedCharArrayUnion<A8>));
+
+  EXPECT_EQ(1u, (alignof(AlignedCharArrayUnion<A1>)));
+  EXPECT_EQ(2u, (alignof(AlignedCharArrayUnion<A1, A2>)));
+  EXPECT_EQ(4u, (alignof(AlignedCharArrayUnion<A1, A2, A4>)));
+  EXPECT_EQ(8u, (alignof(AlignedCharArrayUnion<A1, A2, A4, A8>)));
+
+  EXPECT_EQ(1u, sizeof(AlignedCharArrayUnion<A1>));
+  EXPECT_EQ(2u, sizeof(AlignedCharArrayUnion<A1, A2>));
+  EXPECT_EQ(4u, sizeof(AlignedCharArrayUnion<A1, A2, A4>));
+  EXPECT_EQ(8u, sizeof(AlignedCharArrayUnion<A1, A2, A4, A8>));
+
+  EXPECT_EQ(1u, (alignof(AlignedCharArrayUnion<A1[1]>)));
+  EXPECT_EQ(2u, (alignof(AlignedCharArrayUnion<A1[2], A2[1]>)));
+  EXPECT_EQ(4u, (alignof(AlignedCharArrayUnion<A1[42], A2[55], A4[13]>)));
+  EXPECT_EQ(8u, (alignof(AlignedCharArrayUnion<A1[2], A2[1], A4, A8>)));
+
+  EXPECT_EQ(1u,  sizeof(AlignedCharArrayUnion<A1[1]>));
+  EXPECT_EQ(2u,  sizeof(AlignedCharArrayUnion<A1[2], A2[1]>));
+  EXPECT_EQ(4u,  sizeof(AlignedCharArrayUnion<A1[3], A2[2], A4>));
+  EXPECT_EQ(16u, sizeof(AlignedCharArrayUnion<A1, A2[3],
+                                              A4[3], A8>));
+
+  // For other tests we simply assert that the alignment of the union mathes
+  // that of the fundamental type and hope that we have any weird type
+  // productions that would trigger bugs.
+  EXPECT_EQ(alignof(T<char>), alignof(AlignedCharArrayUnion<char>));
+  EXPECT_EQ(alignof(T<short>), alignof(AlignedCharArrayUnion<short>));
+  EXPECT_EQ(alignof(T<int>), alignof(AlignedCharArrayUnion<int>));
+  EXPECT_EQ(alignof(T<long>), alignof(AlignedCharArrayUnion<long>));
+  EXPECT_EQ(alignof(T<long long>), alignof(AlignedCharArrayUnion<long long>));
+  EXPECT_EQ(alignof(T<float>), alignof(AlignedCharArrayUnion<float>));
+  EXPECT_EQ(alignof(T<double>), alignof(AlignedCharArrayUnion<double>));
+  EXPECT_EQ(alignof(T<long double>),
+            alignof(AlignedCharArrayUnion<long double>));
+  EXPECT_EQ(alignof(T<void *>), alignof(AlignedCharArrayUnion<void *>));
+  EXPECT_EQ(alignof(T<int *>), alignof(AlignedCharArrayUnion<int *>));
+  EXPECT_EQ(alignof(T<double (*)(double)>),
+            alignof(AlignedCharArrayUnion<double (*)(double)>));
+  EXPECT_EQ(alignof(T<double (S6::*)()>),
+            alignof(AlignedCharArrayUnion<double (S6::*)()>));
+  EXPECT_EQ(alignof(S1), alignof(AlignedCharArrayUnion<S1>));
+  EXPECT_EQ(alignof(S2), alignof(AlignedCharArrayUnion<S2>));
+  EXPECT_EQ(alignof(S3), alignof(AlignedCharArrayUnion<S3>));
+  EXPECT_EQ(alignof(S4), alignof(AlignedCharArrayUnion<S4>));
+  EXPECT_EQ(alignof(S5), alignof(AlignedCharArrayUnion<S5>));
+  EXPECT_EQ(alignof(S6), alignof(AlignedCharArrayUnion<S6>));
+  EXPECT_EQ(alignof(D1), alignof(AlignedCharArrayUnion<D1>));
+  EXPECT_EQ(alignof(D2), alignof(AlignedCharArrayUnion<D2>));
+  EXPECT_EQ(alignof(D3), alignof(AlignedCharArrayUnion<D3>));
+  EXPECT_EQ(alignof(D4), alignof(AlignedCharArrayUnion<D4>));
+  EXPECT_EQ(alignof(D5), alignof(AlignedCharArrayUnion<D5>));
+  EXPECT_EQ(alignof(D6), alignof(AlignedCharArrayUnion<D6>));
+  EXPECT_EQ(alignof(D7), alignof(AlignedCharArrayUnion<D7>));
+  EXPECT_EQ(alignof(D8), alignof(AlignedCharArrayUnion<D8>));
+  EXPECT_EQ(alignof(D9), alignof(AlignedCharArrayUnion<D9>));
+  EXPECT_EQ(alignof(V1), alignof(AlignedCharArrayUnion<V1>));
+  EXPECT_EQ(alignof(V2), alignof(AlignedCharArrayUnion<V2>));
+  EXPECT_EQ(alignof(V3), alignof(AlignedCharArrayUnion<V3>));
+  EXPECT_EQ(alignof(V4), alignof(AlignedCharArrayUnion<V4>));
+  EXPECT_EQ(alignof(V5), alignof(AlignedCharArrayUnion<V5>));
+  EXPECT_EQ(alignof(V6), alignof(AlignedCharArrayUnion<V6>));
+  EXPECT_EQ(alignof(V7), alignof(AlignedCharArrayUnion<V7>));
+
+  // Some versions of MSVC get this wrong somewhat disturbingly. The failure
+  // appears to be benign: alignof(V8) produces a preposterous value: 12
+#ifndef _MSC_VER
+  EXPECT_EQ(alignof(V8), alignof(AlignedCharArrayUnion<V8>));
+#endif
+
+  EXPECT_EQ(sizeof(char), sizeof(AlignedCharArrayUnion<char>));
+  EXPECT_EQ(sizeof(char[1]), sizeof(AlignedCharArrayUnion<char[1]>));
+  EXPECT_EQ(sizeof(char[2]), sizeof(AlignedCharArrayUnion<char[2]>));
+  EXPECT_EQ(sizeof(char[3]), sizeof(AlignedCharArrayUnion<char[3]>));
+  EXPECT_EQ(sizeof(char[4]), sizeof(AlignedCharArrayUnion<char[4]>));
+  EXPECT_EQ(sizeof(char[5]), sizeof(AlignedCharArrayUnion<char[5]>));
+  EXPECT_EQ(sizeof(char[8]), sizeof(AlignedCharArrayUnion<char[8]>));
+  EXPECT_EQ(sizeof(char[13]), sizeof(AlignedCharArrayUnion<char[13]>));
+  EXPECT_EQ(sizeof(char[16]), sizeof(AlignedCharArrayUnion<char[16]>));
+  EXPECT_EQ(sizeof(char[21]), sizeof(AlignedCharArrayUnion<char[21]>));
+  EXPECT_EQ(sizeof(char[32]), sizeof(AlignedCharArrayUnion<char[32]>));
+  EXPECT_EQ(sizeof(short), sizeof(AlignedCharArrayUnion<short>));
+  EXPECT_EQ(sizeof(int), sizeof(AlignedCharArrayUnion<int>));
+  EXPECT_EQ(sizeof(long), sizeof(AlignedCharArrayUnion<long>));
+  EXPECT_EQ(sizeof(long long),
+            sizeof(AlignedCharArrayUnion<long long>));
+  EXPECT_EQ(sizeof(float), sizeof(AlignedCharArrayUnion<float>));
+  EXPECT_EQ(sizeof(double), sizeof(AlignedCharArrayUnion<double>));
+  EXPECT_EQ(sizeof(long double),
+            sizeof(AlignedCharArrayUnion<long double>));
+  EXPECT_EQ(sizeof(void *), sizeof(AlignedCharArrayUnion<void *>));
+  EXPECT_EQ(sizeof(int *), sizeof(AlignedCharArrayUnion<int *>));
+  EXPECT_EQ(sizeof(double (*)(double)),
+            sizeof(AlignedCharArrayUnion<double (*)(double)>));
+  EXPECT_EQ(sizeof(double (S6::*)()),
+            sizeof(AlignedCharArrayUnion<double (S6::*)()>));
+  EXPECT_EQ(sizeof(S1), sizeof(AlignedCharArrayUnion<S1>));
+  EXPECT_EQ(sizeof(S2), sizeof(AlignedCharArrayUnion<S2>));
+  EXPECT_EQ(sizeof(S3), sizeof(AlignedCharArrayUnion<S3>));
+  EXPECT_EQ(sizeof(S4), sizeof(AlignedCharArrayUnion<S4>));
+  EXPECT_EQ(sizeof(S5), sizeof(AlignedCharArrayUnion<S5>));
+  EXPECT_EQ(sizeof(S6), sizeof(AlignedCharArrayUnion<S6>));
+  EXPECT_EQ(sizeof(D1), sizeof(AlignedCharArrayUnion<D1>));
+  EXPECT_EQ(sizeof(D2), sizeof(AlignedCharArrayUnion<D2>));
+  EXPECT_EQ(sizeof(D3), sizeof(AlignedCharArrayUnion<D3>));
+  EXPECT_EQ(sizeof(D4), sizeof(AlignedCharArrayUnion<D4>));
+  EXPECT_EQ(sizeof(D5), sizeof(AlignedCharArrayUnion<D5>));
+  EXPECT_EQ(sizeof(D6), sizeof(AlignedCharArrayUnion<D6>));
+  EXPECT_EQ(sizeof(D7), sizeof(AlignedCharArrayUnion<D7>));
+  EXPECT_EQ(sizeof(D8), sizeof(AlignedCharArrayUnion<D8>));
+  EXPECT_EQ(sizeof(D9), sizeof(AlignedCharArrayUnion<D9>));
+  EXPECT_EQ(sizeof(D9[1]), sizeof(AlignedCharArrayUnion<D9[1]>));
+  EXPECT_EQ(sizeof(D9[2]), sizeof(AlignedCharArrayUnion<D9[2]>));
+  EXPECT_EQ(sizeof(D9[3]), sizeof(AlignedCharArrayUnion<D9[3]>));
+  EXPECT_EQ(sizeof(D9[4]), sizeof(AlignedCharArrayUnion<D9[4]>));
+  EXPECT_EQ(sizeof(D9[5]), sizeof(AlignedCharArrayUnion<D9[5]>));
+  EXPECT_EQ(sizeof(D9[8]), sizeof(AlignedCharArrayUnion<D9[8]>));
+  EXPECT_EQ(sizeof(D9[13]), sizeof(AlignedCharArrayUnion<D9[13]>));
+  EXPECT_EQ(sizeof(D9[16]), sizeof(AlignedCharArrayUnion<D9[16]>));
+  EXPECT_EQ(sizeof(D9[21]), sizeof(AlignedCharArrayUnion<D9[21]>));
+  EXPECT_EQ(sizeof(D9[32]), sizeof(AlignedCharArrayUnion<D9[32]>));
+  EXPECT_EQ(sizeof(V1), sizeof(AlignedCharArrayUnion<V1>));
+  EXPECT_EQ(sizeof(V2), sizeof(AlignedCharArrayUnion<V2>));
+  EXPECT_EQ(sizeof(V3), sizeof(AlignedCharArrayUnion<V3>));
+  EXPECT_EQ(sizeof(V4), sizeof(AlignedCharArrayUnion<V4>));
+  EXPECT_EQ(sizeof(V5), sizeof(AlignedCharArrayUnion<V5>));
+  EXPECT_EQ(sizeof(V6), sizeof(AlignedCharArrayUnion<V6>));
+  EXPECT_EQ(sizeof(V7), sizeof(AlignedCharArrayUnion<V7>));
+
+  // Some versions of MSVC also get this wrong. The failure again appears to be
+  // benign: sizeof(V8) is only 52 bytes, but our array reserves 56.
+#ifndef _MSC_VER
+  EXPECT_EQ(sizeof(V8), sizeof(AlignedCharArrayUnion<V8>));
+#endif
+}
+} // end anonymous namespace
--- a/unittests/Support/CMakeLists.txt
+++ b/unittests/Support/CMakeLists.txt
@ -4,6 +4,7 @@ set(LLVM_LINK_COMPONENTS

 add_llvm_unittest(SupportTests
  AlignmentTest.cpp
+  AlignOfTest.cpp
  AllocatorTest.cpp
  AnnotationsTest.cpp
  ARMAttributeParser.cpp