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Utils: Optimze SmallString copies for larger sizes

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So far the whole class was always copied. For a large SmallString
classes this were often many zeros if it was empty. Now only the non
zero area is copied in that case.

Change-Id: Ic0ea2d6f763513858a993bba3e829c9fc947e1a6
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
This commit is contained in:
Marco Bubke
2022-07-30 19:08:41 +02:00
parent 8a0f7db8eb
commit fa32b652c8
2 changed files with 162 additions and 23 deletions
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103
src/libs/utils/smallstringlayout.h
View File

@@ -28,6 +28,7 @@
#include <QtGlobal>
#include <cstdint>
#include <cstring>
#include <memory>
#include <type_traits>
@@ -95,8 +96,8 @@ private:
ControlType m_isReference : 1;
};
template <uint MaximumShortStringDataAreaSize>
struct AllocatedLayout
template<uint MaximumShortStringDataAreaSize>
struct alignas(16) AllocatedLayout
{
struct Data
{
@@ -109,8 +110,8 @@ struct AllocatedLayout
Data data;
};
template <uint MaximumShortStringDataAreaSize>
struct ReferenceLayout
template<uint MaximumShortStringDataAreaSize>
struct alignas(16) ReferenceLayout
{
constexpr ReferenceLayout() noexcept = default;
constexpr ReferenceLayout(const char *stringPointer,
@@ -131,10 +132,9 @@ struct ReferenceLayout
Data data;
};
template <uint MaximumShortStringDataAreaSize>
struct ShortStringLayout
template<uint MaximumShortStringDataAreaSize>
struct alignas(16) ShortStringLayout
{
constexpr ShortStringLayout() noexcept = default;
constexpr ShortStringLayout(
typename ControlBlock<MaximumShortStringDataAreaSize>::SizeType shortStringSize) noexcept
: control(shortStringSize, false, false)
@@ -144,22 +144,19 @@ struct ShortStringLayout
char string[MaximumShortStringDataAreaSize];
};
template <uint MaximumShortStringDataAreaSize>
struct StringDataLayout {
template<uint MaximumShortStringDataAreaSize, typename = void>
struct StringDataLayout
{
static_assert(MaximumShortStringDataAreaSize >= 15, "Size must be greater equal than 15 bytes!");
static_assert(MaximumShortStringDataAreaSize < 64
? ((MaximumShortStringDataAreaSize + 1) % 16) == 0
: ((MaximumShortStringDataAreaSize + 2) % 16) == 0,
"Size + 1 must be dividable by 16 if under 64 and Size + 2 must be dividable by 16 if over 64!");
static_assert(MaximumShortStringDataAreaSize < 32, "Size must be less than 32 bytes!");
static_assert(((MaximumShortStringDataAreaSize + 1) % 16) == 0,
"Size + 1 must be dividable by 16 if under 64 and Size + 2 must be dividable by "
"16 if over 64!");
StringDataLayout() noexcept
{
reset();
}
StringDataLayout() noexcept { reset(); }
constexpr StringDataLayout(const char *string,
size_type size) noexcept
: reference(string, size, 0)
constexpr StringDataLayout(const char *string, size_type size) noexcept
: reference(string, size, 0)
{}
template<size_type Size>
@@ -174,13 +171,73 @@ struct StringDataLayout {
}
}
constexpr static
size_type shortStringCapacity() noexcept
constexpr static size_type shortStringCapacity() noexcept
{
return MaximumShortStringDataAreaSize - 1;
}
void reset()
constexpr void reset()
{
shortString.control = ControlBlock<MaximumShortStringDataAreaSize>();
shortString.string[0] = '\0';
}
union {
AllocatedLayout<MaximumShortStringDataAreaSize> allocated;
ReferenceLayout<MaximumShortStringDataAreaSize> reference;
ShortStringLayout<MaximumShortStringDataAreaSize> shortString;
};
};
template<uint MaximumShortStringDataAreaSize>
struct StringDataLayout<MaximumShortStringDataAreaSize,
std::enable_if_t<MaximumShortStringDataAreaSize >= 32>>
{
static_assert(MaximumShortStringDataAreaSize > 31, "Size must be greater than 31 bytes!");
static_assert(MaximumShortStringDataAreaSize < 64
? ((MaximumShortStringDataAreaSize + 1) % 16) == 0
: ((MaximumShortStringDataAreaSize + 2) % 16) == 0,
"Size + 1 must be dividable by 16 if under 64 and Size + 2 must be dividable by "
"16 if over 64!");
StringDataLayout() noexcept { reset(); }
constexpr StringDataLayout(const char *string, size_type size) noexcept
: reference(string, size, 0)
{}
template<size_type Size>
constexpr StringDataLayout(const char (&string)[Size]) noexcept
{
if constexpr (Size <= MaximumShortStringDataAreaSize) {
shortString = {Size - 1};
for (size_type i = 0; i < Size; ++i)
shortString.string[i] = string[i];
} else {
reference = {string, Size - 1, 0};
}
}
StringDataLayout(const StringDataLayout &other) noexcept { *this = other; }
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));
return *this;
}
constexpr static size_type shortStringCapacity() noexcept
{
return MaximumShortStringDataAreaSize - 1;
}
constexpr void reset()
{
shortString.control = ControlBlock<MaximumShortStringDataAreaSize>();
shortString.string[0] = '\0';

82
tests/unit/unittest/smallstring-test.cpp
View File

@@ -38,6 +38,14 @@ using Utils::SmallString;
using Utils::SmallStringLiteral;
using Utils::SmallStringView;
static_assert(32 == sizeof(Utils::BasicSmallString<31>));
static_assert(64 == sizeof(Utils::BasicSmallString<63>));
static_assert(192 == sizeof(Utils::BasicSmallString<190>));
static_assert(16 == alignof(Utils::BasicSmallString<31>));
static_assert(16 == alignof(Utils::BasicSmallString<63>));
static_assert(16 == alignof(Utils::BasicSmallString<190>));
TEST(SmallString, BasicStringEqual)
{
ASSERT_THAT(SmallString("text"), Eq(SmallString("text")));
@@ -1524,6 +1532,80 @@ TEST(SmallString, LongSmallStringMoveConstuctor)
ASSERT_THAT(copy, SmallString("this is a very very very very long text"));
}
TEST(SmallString, ShortPathStringMoveConstuctor)
{
PathString text("text");
auto copy = std::move(text);
ASSERT_TRUE(text.isEmpty());
ASSERT_THAT(copy, SmallString("text"));
}
TEST(SmallString, LongPathStringMoveConstuctor)
{
PathString text(
"this is a very very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very long text");
auto copy = std::move(text);
ASSERT_TRUE(text.isEmpty());
ASSERT_THAT(
copy,
PathString(
"this is a very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very very very long "
"text"));
}
TEST(SmallString, ShortSmallStringMoveConstuctorToSelf)
{
SmallString text("text");
text = std::move(text);
ASSERT_THAT(text, SmallString("text"));
}
TEST(SmallString, LongSmallStringMoveConstuctorToSelf)
{
SmallString text("this is a very very very very long text");
text = std::move(text);
ASSERT_THAT(text, SmallString("this is a very very very very long text"));
}
TEST(SmallString, ShortPathStringMoveConstuctorToSelf)
{
PathString text("text");
text = std::move(text);
ASSERT_THAT(text, SmallString("text"));
}
TEST(SmallString, LongPathStringMoveConstuctorToSelf)
{
PathString text(
"this is a very very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very long text");
text = std::move(text);
ASSERT_THAT(
text,
PathString(
"this is a very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very very very very "
"very very very very very very very very very very very very very very very very long "
"text"));
}
TEST(SmallString, ShortSmallStringCopyAssignment)
{
SmallString text("text");