[PATCH] D27314: Replace AlignedCharArrayUnion maxed arity with a variadic template

[Mehdi Amini via llvm-commits]

MSVC seems OK, however it seems that GCC added it in 5.1 according to the release notes.

> On Dec 1, 2016, at 12:55 PM, Mehdi Amini via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Do we have MSVC support?
>> On Dec 1, 2016, at 12:52 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>> 
>> Any chance we can just replace this all with http://en.cppreference.com/w/cpp/types/aligned_union <http://en.cppreference.com/w/cpp/types/aligned_union> ?
>> 
>> On Thu, Dec 1, 2016 at 11:56 AM Mehdi AMINI via Phabricator <reviews at reviews.llvm.org <mailto:reviews at reviews.llvm.org>> wrote:
>> mehdi_amini created this revision.
>> mehdi_amini added reviewers: zturner, dblaikie.
>> mehdi_amini added a subscriber: llvm-commits.
>> 
>> This is NFC but for lifting the limitation to 10 types.
>> 
>> 
>> https://reviews.llvm.org/D27314 <https://reviews.llvm.org/D27314>
>> 
>> Files:
>>   llvm/include/llvm/Support/AlignOf.h
>> 
>> 
>> Index: llvm/include/llvm/Support/AlignOf.h
>> ===================================================================
>> --- llvm/include/llvm/Support/AlignOf.h
>> +++ llvm/include/llvm/Support/AlignOf.h
>> @@ -30,44 +30,36 @@
>>  };
>> 
>>  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
>> 
>> 
> 
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