[llvm] 8b6d1c0 - [ADT] Use alignas + sizeof for inline storage, NFC

[David Blaikie via llvm-commits]

FWIW, I think there's some value in using a utility here - saves writing
the same type T twice, possibly having them get out of sync, Bit more
readable by using a named construct for what's being done, etc.

On Wed, Oct 14, 2020 at 4:16 PM Reid Kleckner via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
> Author: Reid Kleckner
> Date: 2020-10-14T16:16:02-07:00
> New Revision: 8b6d1c0467b2dfa14cb2d2dec7637bf95c78364b
>
> URL:
> https://github.com/llvm/llvm-project/commit/8b6d1c0467b2dfa14cb2d2dec7637bf95c78364b
> DIFF:
> https://github.com/llvm/llvm-project/commit/8b6d1c0467b2dfa14cb2d2dec7637bf95c78364b.diff
>
> LOG: [ADT] Use alignas + sizeof for inline storage, NFC
>
> AlignedCharArrayUnion is really only needed to handle the "union" case
> when we need memory of suitable size and alignment for multiple types.
> SmallVector only needs storage for one type, so use that directly.
>
> Added:
>
>
> Modified:
>     clang/include/clang/AST/APValue.h
>     llvm/include/llvm/ADT/SmallVector.h
>     llvm/include/llvm/ADT/iterator_range.h
>
> Removed:
>
>
>
>
> ################################################################################
> diff  --git a/clang/include/clang/AST/APValue.h
> b/clang/include/clang/AST/APValue.h
> index ac8ed0818af0..5eb1f68f7690 100644
> --- a/clang/include/clang/AST/APValue.h
> +++ b/clang/include/clang/AST/APValue.h
> @@ -17,9 +17,10 @@
>  #include "llvm/ADT/APFixedPoint.h"
>  #include "llvm/ADT/APFloat.h"
>  #include "llvm/ADT/APSInt.h"
> +#include "llvm/ADT/FoldingSet.h"
>  #include "llvm/ADT/PointerIntPair.h"
>  #include "llvm/ADT/PointerUnion.h"
> -#include "llvm/ADT/FoldingSet.h"
> +#include "llvm/Support/AlignOf.h"
>
>  namespace clang {
>    class AddrLabelExpr;
>
> diff  --git a/llvm/include/llvm/ADT/SmallVector.h
> b/llvm/include/llvm/ADT/SmallVector.h
> index c3c6a366dab2..dd5cd9531ded 100644
> --- a/llvm/include/llvm/ADT/SmallVector.h
> +++ b/llvm/include/llvm/ADT/SmallVector.h
> @@ -14,7 +14,6 @@
>  #define LLVM_ADT_SMALLVECTOR_H
>
>  #include "llvm/ADT/iterator_range.h"
> -#include "llvm/Support/AlignOf.h"
>  #include "llvm/Support/Compiler.h"
>  #include "llvm/Support/ErrorHandling.h"
>  #include "llvm/Support/MathExtras.h"
> @@ -97,8 +96,9 @@ using SmallVectorSizeType =
>
>  /// Figure out the offset of the first element.
>  template <class T, typename = void> struct SmallVectorAlignmentAndSize {
> -  AlignedCharArrayUnion<SmallVectorBase<SmallVectorSizeType<T>>> Base;
> -  AlignedCharArrayUnion<T> FirstEl;
> +  alignas(SmallVectorBase<SmallVectorSizeType<T>>) char Base[sizeof(
> +      SmallVectorBase<SmallVectorSizeType<T>>)];
> +  alignas(T) char FirstEl[sizeof(T)];
>  };
>
>  /// This is the part of SmallVectorTemplateBase which does not depend on
> whether
> @@ -870,13 +870,13 @@ SmallVectorImpl<T>
> &SmallVectorImpl<T>::operator=(SmallVectorImpl<T> &&RHS) {
>  /// to avoid allocating unnecessary storage.
>  template <typename T, unsigned N>
>  struct SmallVectorStorage {
> -  AlignedCharArrayUnion<T> InlineElts[N];
> +  alignas(T) char InlineElts[N * sizeof(T)];
>  };
>
>  /// We need the storage to be properly aligned even for small-size of 0
> so that
>  /// the pointer math in \a SmallVectorTemplateCommon::getFirstEl() is
>  /// well-defined.
> -template <typename T> struct alignas(alignof(T)) SmallVectorStorage<T, 0>
> {};
> +template <typename T> struct alignas(T) SmallVectorStorage<T, 0> {};
>
>  /// This is a 'vector' (really, a variable-sized array), optimized
>  /// for the case when the array is small.  It contains some number of
> elements
>
> diff  --git a/llvm/include/llvm/ADT/iterator_range.h
> b/llvm/include/llvm/ADT/iterator_range.h
> index f038f6bf2128..a9b46a3aa45b 100644
> --- a/llvm/include/llvm/ADT/iterator_range.h
> +++ b/llvm/include/llvm/ADT/iterator_range.h
> @@ -18,7 +18,6 @@
>  #ifndef LLVM_ADT_ITERATOR_RANGE_H
>  #define LLVM_ADT_ITERATOR_RANGE_H
>
> -#include <iterator>
>  #include <utility>
>
>  namespace llvm {
>
>
>
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