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QArrayData: add allocate1 and allocate2 for 1- and 2-byte types

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This makes the two most-often used QTypedArrayData::allocate() -- the
ones for char (for QByteArray) and char16_t (for QString) -- go to
specialized versions, which have much simpler code. After all,
multiplications by 1 are quite trivial.

I didn't check whether an LTO compiler was const-propagating the sizes
in inlined calls from qstring.cpp and qbytearray.cpp. But not everyone
uses LTO, so this benefits everyone, in a very hot path, for minimal
cost.

Change-Id: Ifa1111900d6945ea8e05fffd177dd1ce659b3fd5
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit 4d7864f0517679ebe70a2a96afdae5dc4f5a2d62)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Thiago Macieira 2023-08-22 14:28:39 -07:00 committed by Qt Cherry-pick Bot
parent 377066e407
commit 5d534ee9a9
2 changed files with 73 additions and 23 deletions
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64
src/corelib/tools/qarraydata.cpp
View File

@ -151,21 +151,19 @@ namespace {
struct alignas(std::max_align_t) AlignedQArrayData : QArrayData
{
};
struct AllocationResult {
void *data;
QArrayData *header;
};
}
void *QArrayData::allocate(QArrayData **dptr, qsizetype objectSize, qsizetype alignment,
qsizetype capacity, QArrayData::AllocationOption option) noexcept
static inline AllocationResult
allocateHelper(qsizetype objectSize, qsizetype alignment, qsizetype capacity,
QArrayData::AllocationOption option) noexcept
{
Q_ASSERT(dptr);
// Alignment is a power of two
Q_ASSERT(alignment >= qsizetype(alignof(QArrayData))
&& !(alignment & (alignment - 1)));
if (capacity == 0) {
*dptr = nullptr;
return nullptr;
}
if (capacity == 0)
return {};
qsizetype headerSize = sizeof(AlignedQArrayData);
const qsizetype headerAlignment = alignof(AlignedQArrayData);
@ -181,10 +179,8 @@ void *QArrayData::allocate(QArrayData **dptr, qsizetype objectSize, qsizetype al
auto blockSize = calculateBlockSize(capacity, objectSize, headerSize, option);
capacity = blockSize.elementCount;
qsizetype allocSize = blockSize.size;
if (Q_UNLIKELY(allocSize < 0)) { // handle overflow. cannot allocate reliably
*dptr = nullptr;
return nullptr;
}
if (Q_UNLIKELY(allocSize < 0)) // handle overflow. cannot allocate reliably
return {};
QArrayData *header = allocateData(allocSize);
void *data = nullptr;
@ -194,8 +190,40 @@ void *QArrayData::allocate(QArrayData **dptr, qsizetype objectSize, qsizetype al
header->alloc = qsizetype(capacity);
}
*dptr = header;
return data;
return { data, header };
}
// Generic size and alignment allocation function
void *QArrayData::allocate(QArrayData **dptr, qsizetype objectSize, qsizetype alignment,
qsizetype capacity, AllocationOption option) noexcept
{
Q_ASSERT(dptr);
// Alignment is a power of two
Q_ASSERT(alignment >= qsizetype(alignof(QArrayData))
&& !(alignment & (alignment - 1)));
auto r = allocateHelper(objectSize, alignment, capacity, option);
*dptr = r.header;
return r.data;
}
// Fixed size and alignment allocation functions
void *QArrayData::allocate1(QArrayData **dptr, qsizetype capacity, AllocationOption option) noexcept
{
Q_ASSERT(dptr);
auto r = allocateHelper(1, alignof(AlignedQArrayData), capacity, option);
*dptr = r.header;
return r.data;
}
void *QArrayData::allocate2(QArrayData **dptr, qsizetype capacity, AllocationOption option) noexcept
{
Q_ASSERT(dptr);
auto r = allocateHelper(2, alignof(AlignedQArrayData), capacity, option);
*dptr = r.header;
return r.data;
}
QPair<QArrayData *, void *>

32
src/corelib/tools/qarraydata.h
View File

@ -11,6 +11,12 @@
QT_BEGIN_NAMESPACE
#if __has_cpp_attribute(gnu::malloc)
# define Q_DECL_MALLOCLIKE [[nodiscard, gnu::malloc]]
#else
# define Q_DECL_MALLOCLIKE [[nodiscard]]
#endif
template <class T> struct QTypedArrayData;
struct QArrayData
@ -78,12 +84,16 @@ struct QArrayData
return newSize;
}
[[nodiscard]]
#if defined(Q_CC_GNU)
__attribute__((__malloc__))
#endif
Q_DECL_MALLOCLIKE
static Q_CORE_EXPORT void *allocate(QArrayData **pdata, qsizetype objectSize, qsizetype alignment,
qsizetype capacity, AllocationOption option = QArrayData::KeepSize) noexcept;
Q_DECL_MALLOCLIKE
static Q_CORE_EXPORT void *allocate1(QArrayData **pdata, qsizetype capacity,
AllocationOption option = QArrayData::KeepSize) noexcept;
Q_DECL_MALLOCLIKE
static Q_CORE_EXPORT void *allocate2(QArrayData **pdata, qsizetype capacity,
AllocationOption option = QArrayData::KeepSize) noexcept;
[[nodiscard]] static Q_CORE_EXPORT QPair<QArrayData *, void *> reallocateUnaligned(QArrayData *data, void *dataPointer,
qsizetype objectSize, qsizetype newCapacity, AllocationOption option) noexcept;
static Q_CORE_EXPORT void deallocate(QArrayData *data, qsizetype objectSize,
@ -102,8 +112,18 @@ struct QTypedArrayData
{
static_assert(sizeof(QTypedArrayData) == sizeof(QArrayData));
QArrayData *d;
void *result = QArrayData::allocate(&d, sizeof(T), alignof(AlignmentDummy), capacity, option);
void *result;
if constexpr (sizeof(T) == 1) {
// necessarily, alignof(T) == 1
result = allocate1(&d, capacity, option);
} else if constexpr (sizeof(T) == 2) {
// alignof(T) may be 1, but that makes no difference
result = allocate2(&d, capacity, option);
} else {
result = QArrayData::allocate(&d, sizeof(T), alignof(AlignmentDummy), capacity, option);
}
#if __has_builtin(__builtin_assume_aligned)
// and yet we do offer results that have stricter alignment
result = __builtin_assume_aligned(result, Q_ALIGNOF(AlignmentDummy));
#endif
return qMakePair(static_cast<QTypedArrayData *>(d), static_cast<T *>(result));
@ -172,6 +192,8 @@ struct Q_CORE_EXPORT QContainerImplHelper
};
}
#undef Q_DECL_MALLOCLIKE
QT_END_NAMESPACE
#endif // include guard