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AK: Remove String-from-StringView optimization

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We had an unusual optimization in AK::StringView where constructing
a StringView from a String would cause it to remember the internal
StringImpl pointer of the String.

This was used to make constructing a String from a StringView fast
and copy-free.

I tried removing this optimization and indeed we started seeing a
ton of allocation traffic. However, all of it was due to a silly
pattern where functions would take a StringView and then go on
to create a String from it.

I've gone through most of the code and updated those functions to
simply take a String directly instead, which now makes this
optimization unnecessary, and indeed a source of bloat instead.

So, let's get rid of it and make StringView a little smaller. :^)
This commit is contained in:
Andreas Kling 2021-04-17 01:18:39 +02:00
parent 94b247c5a9
commit 873da38d0e
4 changed files with 5 additions and 17 deletions
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5
AK/String.cpp
View file

@ -38,10 +38,7 @@ namespace AK {
String::String(const StringView& view)
{
if (view.m_impl)
m_impl = *view.m_impl;
else
m_impl = StringImpl::create(view.characters_without_null_termination(), view.length());
m_impl = StringImpl::create(view.characters_without_null_termination(), view.length());
}
bool String::operator==(const FlyString& fly_string) const

2
AK/StringUtils.cpp
View file

@ -219,8 +219,6 @@ static inline char to_lowercase(char c)
bool equals_ignoring_case(const StringView& a, const StringView& b)
{
if (a.impl() && a.impl() == b.impl())
return true;
if (a.length() != b.length())
return false;
for (size_t i = 0; i < a.length(); ++i) {

10
AK/StringView.cpp
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@ -35,15 +35,13 @@
namespace AK {
StringView::StringView(const String& string)
: m_impl(string.impl())
, m_characters(string.characters())
: m_characters(string.characters())
, m_length(string.length())
{
}
StringView::StringView(const FlyString& string)
: m_impl(string.impl())
, m_characters(string.characters())
: m_characters(string.characters())
, m_length(string.length())
{
}
@ -251,8 +249,6 @@ unsigned StringView::hash() const
{
if (is_empty())
return 0;
if (m_impl)
return m_impl->hash();
return string_hash(characters_without_null_termination(), length());
}

5
AK/StringView.h
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@ -209,8 +209,6 @@ public:
return m_length < other.m_length;
}
const StringImpl* impl() const { return m_impl; }
[[nodiscard]] String to_string() const;
[[nodiscard]] bool is_whitespace() const { return StringUtils::is_whitespace(*this); }
@ -227,7 +225,6 @@ private:
[[nodiscard]] bool is_one_of() const { return false; }
friend class String;
const StringImpl* m_impl { nullptr };
const char* m_characters { nullptr };
size_t m_length { 0 };
};