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Utils: Improve memory layout code

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Actually, the layout is the same, but we move the control block. To prevent
padding of the short string, we use pragma pack(1). To align the pointer
again, we add some dummy data with the size of a pointer minus a control
block because alignas is not working like expected on GCC.

Change-Id: Ide86ace243dab5f487da63492ebac018da45098a
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
This commit is contained in:
Marco Bubke
2022-08-07 03:35:53 +02:00
parent 735346adb5
commit cf064500aa
3 changed files with 85 additions and 116 deletions
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74
src/libs/utils/smallstring.h
View File

@@ -63,7 +63,7 @@
namespace Utils {
template<uint Size>
class BasicSmallString
class alignas(16) BasicSmallString
{
public:
using const_iterator = Internal::SmallStringIterator<std::random_access_iterator_tag, const char>;
@@ -97,14 +97,14 @@ public:
BasicSmallString(const char *string, size_type size, size_type capacity)
{
if (Q_LIKELY(capacity <= shortStringCapacity())) {
std::char_traits<char>::copy(m_data.shortString.string, string, size);
m_data.shortString.string[size] = 0;
m_data.shortString.control.setShortStringSize(size);
m_data.shortString.control.setIsShortString(true);
m_data.shortString.control.setIsReadOnlyReference(false);
std::char_traits<char>::copy(m_data.shortString, string, size);
m_data.shortString[size] = 0;
m_data.control.setShortStringSize(size);
m_data.control.setIsShortString(true);
m_data.control.setIsReadOnlyReference(false);
} else {
m_data.allocated.data.pointer = Memory::allocate(capacity + 1);
std::char_traits<char>::copy(m_data.allocated.data.pointer, string, size);
m_data.reference.pointer = Memory::allocate(capacity + 1);
std::char_traits<char>::copy(m_data.reference.pointer, string, size);
initializeLongString(size, capacity);
}
}
@@ -167,7 +167,7 @@ public:
~BasicSmallString() noexcept
{
if (Q_UNLIKELY(hasAllocatedMemory()))
Memory::deallocate(m_data.allocated.data.pointer);
Memory::deallocate(m_data.reference.pointer);
}
BasicSmallString(const BasicSmallString &other)
@@ -182,7 +182,7 @@ public:
{
if (Q_LIKELY(this != &other)) {
if (Q_UNLIKELY(hasAllocatedMemory()))
Memory::deallocate(m_data.allocated.data.pointer);
Memory::deallocate(m_data.reference.pointer);
if (Q_LIKELY(other.isShortString() || other.isReadOnlyReference()))
m_data = other.m_data;
@@ -203,7 +203,7 @@ public:
{
if (Q_LIKELY(this != &other)) {
if (Q_UNLIKELY(hasAllocatedMemory()))
Memory::deallocate(m_data.allocated.data.pointer);
Memory::deallocate(m_data.reference.pointer);
m_data = std::move(other.m_data);
other.m_data.reset();
@@ -218,9 +218,9 @@ public:
BasicSmallString clonedString(m_data);
if (Q_UNLIKELY(hasAllocatedMemory()))
new (&clonedString) BasicSmallString{m_data.allocated.data.pointer,
m_data.allocated.data.size,
m_data.allocated.data.capacity};
new (&clonedString) BasicSmallString{m_data.reference.pointer,
m_data.reference.size,
m_data.reference.capacity};
return clonedString;
}
@@ -274,11 +274,11 @@ public:
{
if (fitsNotInCapacity(newCapacity)) {
if (Q_UNLIKELY(hasAllocatedMemory())) {
m_data.allocated.data.pointer = Memory::reallocate(m_data.allocated.data.pointer,
m_data.reference.pointer = Memory::reallocate(m_data.reference.pointer,
newCapacity + 1);
m_data.allocated.data.capacity = newCapacity;
m_data.reference.capacity = newCapacity;
} else if (newCapacity <= shortStringCapacity()) {
new (this) BasicSmallString{m_data.allocated.data.pointer, m_data.allocated.data.size};
new (this) BasicSmallString{m_data.reference.pointer, m_data.reference.size};
} else {
const size_type oldSize = size();
newCapacity = std::max(newCapacity, oldSize);
@@ -286,7 +286,7 @@ public:
char *newData = Memory::allocate(newCapacity + 1);
std::char_traits<char>::copy(newData, oldData, oldSize);
m_data.allocated.data.pointer = newData;
m_data.reference.pointer = newData;
initializeLongString(oldSize, newCapacity);
}
}
@@ -307,12 +307,12 @@ public:
char *data() noexcept
{
return Q_LIKELY(isShortString()) ? m_data.shortString.string : m_data.allocated.data.pointer;
return Q_LIKELY(isShortString()) ? m_data.shortString : m_data.reference.pointer;
}
const char *data() const noexcept
{
return Q_LIKELY(isShortString()) ? m_data.shortString.string : m_data.allocated.data.pointer;
return Q_LIKELY(isShortString()) ? m_data.shortString : m_data.reference.pointer;
}
const char *constData() const noexcept
@@ -442,15 +442,15 @@ public:
size_type size() const noexcept
{
if (!isShortString())
return m_data.allocated.data.size;
return m_data.reference.size;
return m_data.shortString.control.shortStringSize();
return m_data.control.shortStringSize();
}
size_type capacity() const noexcept
{
if (!isShortString())
return m_data.allocated.data.capacity;
return m_data.reference.capacity;
return shortStringCapacity();
}
@@ -603,11 +603,7 @@ public:
return size;
}
constexpr
size_type shortStringSize() const
{
return m_data.shortString.control.shortStringSize();
}
constexpr size_type shortStringSize() const { return m_data.control.shortStringSize(); }
static
BasicSmallString join(std::initializer_list<SmallStringView> list)
@@ -721,13 +717,13 @@ unittest_public:
constexpr
bool isShortString() const noexcept
{
return m_data.shortString.control.isShortString();
return m_data.control.isShortString();
}
constexpr
bool isReadOnlyReference() const noexcept
{
return m_data.shortString.control.isReadOnlyReference();
return m_data.control.isReadOnlyReference();
}
constexpr
@@ -739,7 +735,7 @@ unittest_public:
bool fitsNotInCapacity(size_type capacity) const noexcept
{
return (isShortString() && capacity > shortStringCapacity())
|| (!isShortString() && capacity > m_data.allocated.data.capacity);
|| (!isShortString() && capacity > m_data.reference.capacity);
}
static
@@ -802,12 +798,12 @@ private:
constexpr void initializeLongString(size_type size, size_type capacity)
{
m_data.allocated.data.pointer[size] = 0;
m_data.allocated.data.size = size;
m_data.allocated.data.capacity = capacity;
m_data.shortString.control.setShortStringSize(0);
m_data.shortString.control.setIsReference(true);
m_data.shortString.control.setIsReadOnlyReference(false);
m_data.reference.pointer[size] = 0;
m_data.reference.size = size;
m_data.reference.capacity = capacity;
m_data.control.setShortStringSize(0);
m_data.control.setIsReference(true);
m_data.control.setIsReadOnlyReference(false);
}
char &at(size_type index)
@@ -945,9 +941,9 @@ private:
void setSize(size_type size)
{
if (isShortString())
m_data.shortString.control.setShortStringSize(size);
m_data.control.setShortStringSize(size);
else
m_data.allocated.data.size = size;
m_data.reference.size = size;
}
private:

109
src/libs/utils/smallstringlayout.h
View File

@@ -96,56 +96,17 @@ private:
ControlType m_isReference : 1;
};
template<uint MaximumShortStringDataAreaSize>
struct alignas(16) AllocatedLayout
{
struct Data
{
struct ReferenceLayout
{ union {
const char *constPointer;
char *pointer;
};
size_type size;
size_type capacity;
};
ControlBlock<MaximumShortStringDataAreaSize> control;
Data data;
};
template<uint MaximumShortStringDataAreaSize>
struct alignas(16) ReferenceLayout
{
constexpr ReferenceLayout() noexcept = default;
constexpr ReferenceLayout(const char *stringPointer,
size_type size,
size_type capacity) noexcept
: control(0, true, true),
data{stringPointer, size, capacity}
{}
struct Data
{
const char *pointer;
size_type size;
size_type capacity;
};
ControlBlock<MaximumShortStringDataAreaSize> control;
Data data;
};
template<uint MaximumShortStringDataAreaSize>
struct alignas(16) ShortStringLayout
{
constexpr ShortStringLayout(
typename ControlBlock<MaximumShortStringDataAreaSize>::SizeType shortStringSize) noexcept
: control(shortStringSize, false, false)
{}
ControlBlock<MaximumShortStringDataAreaSize> control;
char string[MaximumShortStringDataAreaSize];
};
template<uint MaximumShortStringDataAreaSize, typename = void>
struct StringDataLayout
struct alignas(16) StringDataLayout
{
static_assert(MaximumShortStringDataAreaSize >= 15, "Size must be greater equal than 15 bytes!");
static_assert(MaximumShortStringDataAreaSize < 32, "Size must be less than 32 bytes!");
@@ -156,17 +117,19 @@ struct StringDataLayout
StringDataLayout() noexcept { reset(); }
constexpr StringDataLayout(const char *string, size_type size) noexcept
: reference(string, size, 0)
: control{0, true, true}
, reference{{string}, size, 0}
{}
template<size_type Size>
constexpr StringDataLayout(const char (&string)[Size]) noexcept
{
if constexpr (Size <= MaximumShortStringDataAreaSize) {
shortString = {Size - 1};
control = {Size - 1, false, false};
for (size_type i = 0; i < Size; ++i)
shortString.string[i] = string[i];
shortString[i] = string[i];
} else {
control = {0, true, true};
reference = {string, Size - 1, 0};
}
}
@@ -178,19 +141,26 @@ struct StringDataLayout
constexpr void reset()
{
shortString.control = ControlBlock<MaximumShortStringDataAreaSize>();
shortString.string[0] = '\0';
control = ControlBlock<MaximumShortStringDataAreaSize>();
shortString[0] = '\0';
}
#pragma pack(push)
#pragma pack(1)
ControlBlock<MaximumShortStringDataAreaSize> control;
union {
AllocatedLayout<MaximumShortStringDataAreaSize> allocated;
ReferenceLayout<MaximumShortStringDataAreaSize> reference;
ShortStringLayout<MaximumShortStringDataAreaSize> shortString;
char shortString[MaximumShortStringDataAreaSize];
struct
{
char dummy[sizeof(void *) - sizeof(ControlBlock<MaximumShortStringDataAreaSize>)];
ReferenceLayout reference;
};
};
#pragma pack(pop)
};
template<uint MaximumShortStringDataAreaSize>
struct StringDataLayout<MaximumShortStringDataAreaSize,
struct alignas(16) StringDataLayout<MaximumShortStringDataAreaSize,
std::enable_if_t<MaximumShortStringDataAreaSize >= 32>>
{
static_assert(MaximumShortStringDataAreaSize > 31, "Size must be greater than 31 bytes!");
@@ -203,17 +173,19 @@ struct StringDataLayout<MaximumShortStringDataAreaSize,
StringDataLayout() noexcept { reset(); }
constexpr StringDataLayout(const char *string, size_type size) noexcept
: reference(string, size, 0)
: control{0, true, true}
, reference{string, size, 0}
{}
template<size_type Size>
constexpr StringDataLayout(const char (&string)[Size]) noexcept
{
if constexpr (Size <= MaximumShortStringDataAreaSize) {
shortString = {Size - 1};
control = {Size - 1, false, false};
for (size_type i = 0; i < Size; ++i)
shortString.string[i] = string[i];
shortString[i] = string[i];
} else {
control = {0, true, true};
reference = {string, Size - 1, 0};
}
}
@@ -223,11 +195,9 @@ struct StringDataLayout<MaximumShortStringDataAreaSize,
StringDataLayout &operator=(const StringDataLayout &other) noexcept
{
constexpr auto controlBlockSize = sizeof(ControlBlock<MaximumShortStringDataAreaSize>);
auto shortStringLayoutSize = other.shortString.control.stringSize() + controlBlockSize;
constexpr auto referenceLayoutSize = sizeof(ReferenceLayout<MaximumShortStringDataAreaSize>);
std::memcpy(&shortString,
&other.shortString,
std::max(shortStringLayoutSize, referenceLayoutSize));
auto shortStringLayoutSize = other.control.stringSize() + controlBlockSize;
constexpr auto referenceLayoutSize = sizeof(ReferenceLayout);
std::memcpy(this, &other, std::max(shortStringLayoutSize, referenceLayoutSize));
return *this;
}
@@ -239,16 +209,23 @@ struct StringDataLayout<MaximumShortStringDataAreaSize,
constexpr void reset()
{
shortString.control = ControlBlock<MaximumShortStringDataAreaSize>();
shortString.string[0] = '\0';
control = ControlBlock<MaximumShortStringDataAreaSize>();
shortString[0] = '\0';
}
#pragma pack(push)
#pragma pack(1)
ControlBlock<MaximumShortStringDataAreaSize> control;
union {
AllocatedLayout<MaximumShortStringDataAreaSize> allocated;
ReferenceLayout<MaximumShortStringDataAreaSize> reference;
ShortStringLayout<MaximumShortStringDataAreaSize> shortString;
char shortString[MaximumShortStringDataAreaSize];
struct
{
char dummy[sizeof(void *) - sizeof(ControlBlock<MaximumShortStringDataAreaSize>)];
ReferenceLayout reference;
};
};
#pragma pack(pop)
};
} // namespace Internal
} // namespace Utils

12
src/libs/utils/smallstringliteral.h
View File

@@ -58,12 +58,12 @@ public:
const char *data() const noexcept
{
return Q_LIKELY(isShortString()) ? m_data.shortString.string : m_data.allocated.data.pointer;
return Q_LIKELY(isShortString()) ? m_data.shortString : m_data.reference.constPointer;
}
size_type size() const noexcept
{
return Q_LIKELY(isShortString()) ? m_data.shortString.control.shortStringSize() : m_data.allocated.data.size;
return Q_LIKELY(isShortString()) ? m_data.control.shortStringSize() : m_data.reference.size;
}
constexpr
@@ -94,16 +94,12 @@ public:
return Internal::StringDataLayout<Size>::shortStringCapacity();
}
constexpr
bool isShortString() const noexcept
{
return m_data.shortString.control.isShortString();
}
constexpr bool isShortString() const noexcept { return m_data.control.isShortString(); }
constexpr
bool isReadOnlyReference() const noexcept
{
return m_data.shortString.control.isReadOnlyReference();
return m_data.control.isReadOnlyReference();
}
constexpr