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Document that AlignedCharArrayUnion exists to work around an MSVC bug

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Differential Revision: https://reviews.llvm.org/D93355
This commit is contained in:
Reid Kleckner 2020-12-15 15:59:21 -08:00
parent e77001771a
commit 45f3869c8b
1 changed files with 4 additions and 3 deletions
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7
include/llvm/Support/AlignOf.h
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@ -20,9 +20,10 @@ 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.
/// This template is equivalent to std::aligned_union_t<1, ...>, but we cannot
/// use it due to a bug in the MSVC x86 compiler:
/// https://github.com/microsoft/STL/issues/1533
/// Using `alignas` here works around the bug.
template <typename T, typename... Ts> struct AlignedCharArrayUnion {
using AlignedUnion = std::aligned_union_t<1, T, Ts...>;
alignas(alignof(AlignedUnion)) char buffer[sizeof(AlignedUnion)];