diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -20,7 +20,7 @@
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/PointerUnion.h"
-#include "llvm/Support/AlignOf.h"
+#include <type_traits>
 
 namespace clang {
   class AddrLabelExpr;
@@ -286,9 +286,10 @@
   struct MemberPointerData;
 
   // We ensure elsewhere that Data is big enough for LV and MemberPointerData.
-  typedef llvm::AlignedCharArrayUnion<void *, APSInt, APFloat, ComplexAPSInt,
-                                      ComplexAPFloat, Vec, Arr, StructData,
-                                      UnionData, AddrLabelDiffData> DataType;
+  typedef std::aligned_union_t<1, void *, APSInt, APFloat, ComplexAPSInt,
+                               ComplexAPFloat, Vec, Arr, StructData, UnionData,
+                               AddrLabelDiffData>
+      DataType;
   static const size_t DataSize = sizeof(DataType);
 
   DataType Data;
diff --git a/clang/include/clang/AST/ASTContext.h b/clang/include/clang/AST/ASTContext.h
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -57,7 +57,6 @@
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/iterator_range.h"
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
diff --git a/clang/include/clang/AST/ASTTypeTraits.h b/clang/include/clang/AST/ASTTypeTraits.h
--- a/clang/include/clang/AST/ASTTypeTraits.h
+++ b/clang/include/clang/AST/ASTTypeTraits.h
@@ -22,7 +22,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/LLVM.h"
 #include "llvm/ADT/DenseMapInfo.h"
-#include "llvm/Support/AlignOf.h"
+#include <type_traits>
 
 namespace llvm {
 
@@ -456,9 +456,8 @@
   /// \c QualTypes, \c NestedNameSpecifierLocs, \c TypeLocs,
   /// \c TemplateArguments and \c TemplateArgumentLocs on the other hand do not
   /// have storage or unique pointers and thus need to be stored by value.
-  llvm::AlignedCharArrayUnion<const void *, TemplateArgument,
-                              TemplateArgumentLoc, NestedNameSpecifierLoc,
-                              QualType, TypeLoc>
+  std::aligned_union_t<1, const void *, TemplateArgument, TemplateArgumentLoc,
+                       NestedNameSpecifierLoc, QualType, TypeLoc>
       Storage;
 };
 
diff --git a/clang/include/clang/AST/ParentMapContext.h b/clang/include/clang/AST/ParentMapContext.h
--- a/clang/include/clang/AST/ParentMapContext.h
+++ b/clang/include/clang/AST/ParentMapContext.h
@@ -89,7 +89,7 @@
 /// Container for either a single DynTypedNode or for an ArrayRef to
 /// DynTypedNode. For use with ParentMap.
 class DynTypedNodeList {
-  llvm::AlignedCharArrayUnion<DynTypedNode, ArrayRef<DynTypedNode>> Storage;
+  std::aligned_union_t<1, DynTypedNode, ArrayRef<DynTypedNode>> Storage;
   bool IsSingleNode;
 
 public:
diff --git a/clang/include/clang/Frontend/PrecompiledPreamble.h b/clang/include/clang/Frontend/PrecompiledPreamble.h
--- a/clang/include/clang/Frontend/PrecompiledPreamble.h
+++ b/clang/include/clang/Frontend/PrecompiledPreamble.h
@@ -17,7 +17,6 @@
 #include "clang/Lex/Preprocessor.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/MD5.h"
 #include <cstddef>
 #include <memory>
@@ -198,7 +197,7 @@
 
   private:
     Kind StorageKind = Kind::Empty;
-    llvm::AlignedCharArrayUnion<TempPCHFile, InMemoryPreamble> Storage = {};
+    std::aligned_union_t<1, TempPCHFile, InMemoryPreamble> Storage = {};
   };
 
   /// Data used to determine if a file used in the preamble has been changed.
diff --git a/clang/include/clang/Sema/Overload.h b/clang/include/clang/Sema/Overload.h
--- a/clang/include/clang/Sema/Overload.h
+++ b/clang/include/clang/Sema/Overload.h
@@ -31,7 +31,6 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
diff --git a/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp b/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
--- a/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
+++ b/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
@@ -11,7 +11,6 @@
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Errno.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/Path.h"
diff --git a/clang/lib/DirectoryWatcher/windows/DirectoryWatcher-windows.cpp b/clang/lib/DirectoryWatcher/windows/DirectoryWatcher-windows.cpp
--- a/clang/lib/DirectoryWatcher/windows/DirectoryWatcher-windows.cpp
+++ b/clang/lib/DirectoryWatcher/windows/DirectoryWatcher-windows.cpp
@@ -14,7 +14,6 @@
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Errno.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/Path.h"
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -39,7 +39,6 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Path.h"
 #include <algorithm>
diff --git a/llvm/include/llvm/ADT/DenseMap.h b/llvm/include/llvm/ADT/DenseMap.h
--- a/llvm/include/llvm/ADT/DenseMap.h
+++ b/llvm/include/llvm/ADT/DenseMap.h
@@ -15,7 +15,6 @@
 
 #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"
@@ -901,7 +900,7 @@
 
   /// A "union" of an inline bucket array and the struct representing
   /// a large bucket. This union will be discriminated by the 'Small' bit.
-  AlignedCharArrayUnion<BucketT[InlineBuckets], LargeRep> storage;
+  std::aligned_union_t<1, BucketT[InlineBuckets], LargeRep> storage;
 
 public:
   explicit SmallDenseMap(unsigned NumInitBuckets = 0) {
@@ -1041,7 +1040,7 @@
 
     if (Small) {
       // First move the inline buckets into a temporary storage.
-      AlignedCharArrayUnion<BucketT[InlineBuckets]> TmpStorage;
+      std::aligned_union_t<1, BucketT[InlineBuckets]> TmpStorage;
       BucketT *TmpBegin = reinterpret_cast<BucketT *>(&TmpStorage);
       BucketT *TmpEnd = TmpBegin;
 
diff --git a/llvm/include/llvm/ADT/IntervalMap.h b/llvm/include/llvm/ADT/IntervalMap.h
--- a/llvm/include/llvm/ADT/IntervalMap.h
+++ b/llvm/include/llvm/ADT/IntervalMap.h
@@ -101,7 +101,6 @@
 #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>
@@ -109,6 +108,7 @@
 #include <cstdint>
 #include <iterator>
 #include <new>
+#include <type_traits>
 #include <utility>
 
 namespace llvm {
@@ -963,7 +963,7 @@
 
 private:
   // The root data is either a RootLeaf or a RootBranchData instance.
-  AlignedCharArrayUnion<RootLeaf, RootBranchData> data;
+  std::aligned_union_t<1, RootLeaf, RootBranchData> data;
 
   // Tree height.
   // 0: Leaves in root.
diff --git a/llvm/include/llvm/CodeGen/DIE.h b/llvm/include/llvm/CodeGen/DIE.h
--- a/llvm/include/llvm/CodeGen/DIE.h
+++ b/llvm/include/llvm/CodeGen/DIE.h
@@ -22,7 +22,6 @@
 #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>
@@ -368,9 +367,9 @@
   ///
   /// All values that aren't standard layout (or are larger than 8 bytes)
   /// should be stored by reference instead of by value.
-  using ValTy = AlignedCharArrayUnion<DIEInteger, DIEString, DIEExpr, DIELabel,
-                                      DIEDelta *, DIEEntry, DIEBlock *,
-                                      DIELoc *, DIELocList, DIEBaseTypeRef *>;
+  using ValTy = std::aligned_union_t<1, DIEInteger, DIEString, DIEExpr,
+                                     DIELabel, DIEDelta *, DIEEntry, DIEBlock *,
+                                     DIELoc *, DIELocList, DIEBaseTypeRef *>;
 
   static_assert(sizeof(ValTy) <= sizeof(uint64_t) ||
                     sizeof(ValTy) <= sizeof(void *),
diff --git a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
--- a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
+++ b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
@@ -38,7 +38,6 @@
 #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"
@@ -2628,10 +2627,9 @@
 ///
 /// 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 = AlignedCharArrayUnion<AtomicSDNode, TargetIndexSDNode,
-                                            BlockAddressSDNode,
-                                            GlobalAddressSDNode,
-                                            PseudoProbeSDNode>;
+using LargestSDNode =
+    std::aligned_union_t<1, AtomicSDNode, TargetIndexSDNode, BlockAddressSDNode,
+                         GlobalAddressSDNode, PseudoProbeSDNode>;
 
 /// The SDNode class with the greatest alignment requirement.
 using MostAlignedSDNode = GlobalAddressSDNode;
diff --git a/llvm/include/llvm/Support/Error.h b/llvm/include/llvm/Support/Error.h
--- a/llvm/include/llvm/Support/Error.h
+++ b/llvm/include/llvm/Support/Error.h
@@ -19,7 +19,6 @@
 #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"
@@ -678,8 +677,8 @@
   }
 
   union {
-    AlignedCharArrayUnion<storage_type> TStorage;
-    AlignedCharArrayUnion<error_type> ErrorStorage;
+    std::aligned_union_t<1, storage_type> TStorage;
+    std::aligned_union_t<1, error_type> ErrorStorage;
   };
   bool HasError : 1;
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
diff --git a/llvm/include/llvm/Support/ErrorOr.h b/llvm/include/llvm/Support/ErrorOr.h
--- a/llvm/include/llvm/Support/ErrorOr.h
+++ b/llvm/include/llvm/Support/ErrorOr.h
@@ -15,7 +15,6 @@
 #ifndef LLVM_SUPPORT_ERROROR_H
 #define LLVM_SUPPORT_ERROROR_H
 
-#include "llvm/Support/AlignOf.h"
 #include <cassert>
 #include <system_error>
 #include <type_traits>
@@ -253,8 +252,8 @@
   }
 
   union {
-    AlignedCharArrayUnion<storage_type> TStorage;
-    AlignedCharArrayUnion<std::error_code> ErrorStorage;
+    std::aligned_union_t<1, storage_type> TStorage;
+    std::aligned_union_t<1, std::error_code> ErrorStorage;
   };
   bool HasError : 1;
 };
diff --git a/llvm/include/llvm/Support/JSON.h b/llvm/include/llvm/Support/JSON.h
--- a/llvm/include/llvm/Support/JSON.h
+++ b/llvm/include/llvm/Support/JSON.h
@@ -479,8 +479,8 @@
   };
   // All members mutable, see moveFrom().
   mutable ValueType Type;
-  mutable llvm::AlignedCharArrayUnion<bool, double, int64_t, llvm::StringRef,
-                                      std::string, json::Array, json::Object>
+  mutable std::aligned_union_t<1, bool, double, int64_t, llvm::StringRef,
+                               std::string, json::Array, json::Object>
       Union;
   friend bool operator==(const Value &, const Value &);
 };
diff --git a/llvm/include/llvm/Support/TrailingObjects.h b/llvm/include/llvm/Support/TrailingObjects.h
--- a/llvm/include/llvm/Support/TrailingObjects.h
+++ b/llvm/include/llvm/Support/TrailingObjects.h
@@ -46,7 +46,6 @@
 #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"
diff --git a/llvm/include/llvm/Support/YAMLTraits.h b/llvm/include/llvm/Support/YAMLTraits.h
--- a/llvm/include/llvm/Support/YAMLTraits.h
+++ b/llvm/include/llvm/Support/YAMLTraits.h
@@ -15,7 +15,6 @@
 #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"
@@ -1311,7 +1310,7 @@
   TNorm* operator->() { return BufPtr; }
 
 private:
-  using Storage = AlignedCharArrayUnion<TNorm>;
+  using Storage = std::aligned_union_t<1, TNorm>;
 
   Storage       Buffer;
   IO           &io;
@@ -1348,7 +1347,7 @@
   TNorm* operator->() { return BufPtr; }
 
 private:
-  using Storage = AlignedCharArrayUnion<TNorm>;
+  using Storage = std::aligned_union_t<1, TNorm>;
 
   Storage       Buffer;
   IO           &io;
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -26,7 +26,6 @@
 #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"
@@ -120,7 +119,7 @@
     // is overkill of this end.
     short IntVal = 0;
 
-    AlignedCharArrayUnion<APFloat> FpValBuf;
+    std::aligned_union_t<1, APFloat> FpValBuf;
   };
 
   /// FAddend is used to represent floating-point addend. An addend is