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[ADT] Use a constexpr function in SmallVector (NFC) #149455

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[ADT] Use a constexpr function in SmallVector (NFC) #149455

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21 changes: 9 additions & 12 deletions llvm/include/llvm/ADT/SmallVector.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1122,20 +1122,18 @@ template <typename T> struct alignas(T) SmallVectorStorage<T, 0> {};
/// `sizeof(SmallVector<T, 0>)`.
template <typename T, unsigned N> class LLVM_GSL_OWNER SmallVector;

/// Helper class for calculating the default number of inline elements for
/// Helper function for calculating the default number of inline elements for
/// `SmallVector<T>`.
///
/// This should be migrated to a constexpr function when our minimum
/// compiler support is enough for multi-statement constexpr functions.
template <typename T> struct CalculateSmallVectorDefaultInlinedElements {
template <typename T>
constexpr size_t calculateSmallVectorDefaultInlinedElements() {
// Parameter controlling the default number of inlined elements
// for `SmallVector<T>`.
//
// The default number of inlined elements ensures that
// 1. There is at least one inlined element.
// 2. `sizeof(SmallVector<T>) <= kPreferredSmallVectorSizeof` unless
// it contradicts 1.
static constexpr size_t kPreferredSmallVectorSizeof = 64;
constexpr size_t kPreferredSmallVectorSizeof = 64;

// static_assert that sizeof(T) is not "too big".
//
Expand Down Expand Up @@ -1168,12 +1166,11 @@ template <typename T> struct CalculateSmallVectorDefaultInlinedElements {

// Discount the size of the header itself when calculating the maximum inline
// bytes.
static constexpr size_t PreferredInlineBytes =
constexpr size_t PreferredInlineBytes =
kPreferredSmallVectorSizeof - sizeof(SmallVector<T, 0>);
static constexpr size_t NumElementsThatFit = PreferredInlineBytes / sizeof(T);
static constexpr size_t value =
NumElementsThatFit == 0 ? 1 : NumElementsThatFit;
};
constexpr size_t NumElementsThatFit = PreferredInlineBytes / sizeof(T);
return NumElementsThatFit == 0 ? 1 : NumElementsThatFit;
}

/// This is a 'vector' (really, a variable-sized array), optimized
/// for the case when the array is small. It contains some number of elements
Expand All @@ -1192,7 +1189,7 @@ template <typename T> struct CalculateSmallVectorDefaultInlinedElements {
///
/// \see https://llvm.org/docs/ProgrammersManual.html#llvm-adt-smallvector-h
template <typename T,
unsigned N = CalculateSmallVectorDefaultInlinedElements<T>::value>
unsigned N = calculateSmallVectorDefaultInlinedElements<T>()>
class LLVM_GSL_OWNER SmallVector : public SmallVectorImpl<T>,
SmallVectorStorage<T, N> {
public:
Expand Down
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