Replace AlignedCharArrayUnion maxed arity with a variadic template

[mehdi_amini]

Summary

This is NFC but for lifting the limitation to 10 types.

[zturner]

llvm/include/llvm/Support/AlignOf.h

38–40

How about

constexpr size_t lhs = max_alignof<T0>();
constexpr size_t rhs = max_alignof<T1, Ts...>();
return std::max(lhs, rhs);

[mehdi_amini]

llvm/include/llvm/Support/AlignOf.h

38–40

I tried this first but got a warning because this isn't c++11 (only c++14)

[zturner]

llvm/include/llvm/Support/AlignOf.h

38–40

Ahh I wasn't sure if that was still C++11.

llvm/include/llvm/Support/AlignOf.h

 /// This template is used to explicitly build up a collection of aligned
 /// character array types.
 template<std::size_t Alignment, std::size_t Size>
 struct AlignedCharArray {
   LLVM_ALIGNAS(Alignment) char buffer[Size];
 };
 
 namespace detail {
-template <typename T1,
-          typename T2 = char, typename T3 = char, typename T4 = char,
-          typename T5 = char, typename T6 = char, typename T7 = char,
-          typename T8 = char, typename T9 = char, typename T10 = char>
-class AlignerImpl {
-  T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
 
-  AlignerImpl() = delete;
-};
+/// Compute the maximum alignment over the types in the variadic pack.
+template <typename T0> constexpr size_t max_alignof() { return alignof(T0); }
+template <typename T0, typename T1, typename... Ts>
+constexpr size_t max_alignof() {
+  return (max_alignof<T0>() > max_alignof<T1, Ts...>())
+             ? max_alignof<T0>()
+             : max_alignof<T1, Ts...>();
+}
+
+/// Compute the maximum size over the types in the variadic pack.
+template <typename T0> constexpr size_t max_sizeof() { return sizeof(T0); }
+template <typename T0, typename T1, typename... Ts>
+constexpr size_t max_sizeof() {
+  return (max_sizeof<T0>() > max_sizeof<T1, Ts...>()) ? max_sizeof<T0>()
+                                                      : max_sizeof<T1, Ts...>();
+}
 
-template <typename T1,
-          typename T2 = char, typename T3 = char, typename T4 = char,
-          typename T5 = char, typename T6 = char, typename T7 = char,
-          typename T8 = char, typename T9 = char, typename T10 = char>
-union SizerImpl {
-  char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
-       arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
-       arr9[sizeof(T9)], arr10[sizeof(T10)];
-};
 } // end namespace detail
 
 /// \brief This union template exposes a suitably aligned and sized character
-/// array member which can hold elements of any of up to ten types.
+/// array member which can hold any of the requested types.
 ///
 /// These types may be arrays, structs, or any other types. The goal is to
 /// expose a char array buffer member which can be used as suitable storage for
-/// a placement new of any of these types. Support for more than ten types can
-/// be added at the cost of more boilerplate.
-template <typename T1,
-          typename T2 = char, typename T3 = char, typename T4 = char,
-          typename T5 = char, typename T6 = char, typename T7 = char,
-          typename T8 = char, typename T9 = char, typename T10 = char>
-struct AlignedCharArrayUnion : llvm::AlignedCharArray<
-    alignof(llvm::detail::AlignerImpl<T1, T2, T3, T4, T5,
-                                      T6, T7, T8, T9, T10>),
-    sizeof(::llvm::detail::SizerImpl<T1, T2, T3, T4, T5,
-                                     T6, T7, T8, T9, T10>)> {
-};
+/// a placement new of any of these types.
+template <typename... Ts>
+struct AlignedCharArrayUnion
+    : llvm::AlignedCharArray<detail::max_alignof<Ts...>(),
+                             detail::max_sizeof<Ts...>()> {};
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_ALIGNOF_H