maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

ADT: Rely on std::aligned_union_t for math in AlignedCharArrayUnion, NFC 

Instead of computing the alignment and size of the `char` buffer in
`AlignedCharArrayUnion`, rely on the math in `std::aligned_union_t`.
Because some users of this rely on the `buffer` field existing with a
type convertible to `char *`, we can't change the field type, but we can
still avoid duplicating the logic.

A potential follow up would be to delete `AlignedCharArrayUnion` after
updating its users to use `std::aligned_union_t` directly; or if we like
our template parameters better, could update users to stop peeking
inside and then replace the definition with:
```
template <class T, class... Ts>
using AlignedCharArrayUnion = std::aligned_union_t<1, T, Ts...>;
```

Differential Revision: https://reviews.llvm.org/D92500
This commit is contained in:
Duncan P. N. Exon Smith 2020-12-02 11:43:15 -08:00
parent bab72dd5d5
commit 65c5c9f92e
1 changed files with 3 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
llvm/include/llvm/Support/AlignOf.h
View File

@ -13,32 +13,10 @@
#ifndef LLVM_SUPPORT_ALIGNOF_H
#define LLVM_SUPPORT_ALIGNOF_H
#include "llvm/Support/Compiler.h"
#include <cstddef>
#include <type_traits>
namespace llvm {
namespace detail {
template <typename T, typename... Ts> class AlignerImpl {
T t;
AlignerImpl<Ts...> rest;
AlignerImpl() = delete;
};
template <typename T> class AlignerImpl<T> {
T t;
AlignerImpl() = delete;
};
template <typename T, typename... Ts> union SizerImpl {
char arr[sizeof(T)];
SizerImpl<Ts...> rest;
};
template <typename T> union SizerImpl<T> { char arr[sizeof(T)]; };
} // end namespace detail
/// A suitably aligned and sized character array member which can hold elements
/// of any type.
///
@ -46,8 +24,8 @@ template <typename T> union SizerImpl<T> { char arr[sizeof(T)]; };
/// `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 {
alignas(::llvm::detail::AlignerImpl<T, Ts...>) char buffer[sizeof(
llvm::detail::SizerImpl<T, Ts...>)];
using AlignedUnion = std::aligned_union_t<1, T, Ts...>;
alignas(alignof(AlignedUnion)) char buffer[sizeof(AlignedUnion)];
};
} // end namespace llvm