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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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76
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,
newCapacity + 1);
m_data.allocated.data.capacity = newCapacity;
m_data.reference.pointer = Memory::reallocate(m_data.reference.pointer,
newCapacity + 1);
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: