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LibJS: Put vector of regs+consts+locals+args in tail of ExecutionContext

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By doing that we avoid doing separate allocation for each such vector,
which was really expensive on js heavy websites. For example this change
helps to get EC allocation down from ~17% to ~2% on Google Maps. This
comes at cost of adding extra complexity to custom execution context
allocator, because EC no longer has fixed size and we need to maintain
a list of buckets.
This commit is contained in:
Aliaksandr Kalenik 2025-04-23 19:44:54 +02:00 • committed by Andreas Kling
commit 5a92929282
Notes: github-actions[bot] 2025-04-24 08:32:21 +00:00
3 changed files with 110 additions and 34 deletions
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38
Libraries/LibJS/Runtime/ExecutionContext.h
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@ -2,6 +2,7 @@
* Copyright (c) 2020-2024, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
* Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
* Copyright (c) 2024-2025, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -42,7 +43,7 @@ struct ExecutionContext {
private:
friend class ExecutionContextAllocator;
ExecutionContext();
ExecutionContext(u32 registers_and_constants_and_locals_count, u32 arguments_count);
public:
void operator delete(void* ptr);
@ -70,17 +71,27 @@ public:
// FIXME: Move this out of LibJS (e.g. by using the CustomData concept), as it's used exclusively by LibWeb.
size_t skip_when_determining_incumbent_counter { 0 };
Span<Value> registers_and_constants_and_locals_and_arguments_span()
{
return { registers_and_constants_and_locals_and_arguments(), registers_and_constants_and_locals_and_arguments_count };
}
Value const* registers_and_constants_and_locals_and_arguments() const
{
return reinterpret_cast<Value*>(reinterpret_cast<uintptr_t>(this) + sizeof(ExecutionContext));
}
Value argument(size_t index) const
{
auto arguments_size = registers_and_constants_and_locals_and_arguments.size() - arguments_offset;
auto arguments_size = registers_and_constants_and_locals_and_arguments_count - arguments_offset;
if (index >= arguments_size) [[unlikely]]
return js_undefined();
return registers_and_constants_and_locals_and_arguments[arguments_offset + index];
return registers_and_constants_and_locals_and_arguments()[arguments_offset + index];
}
Value& local(size_t index)
{
return registers_and_constants_and_locals_and_arguments[index];
return registers_and_constants_and_locals_and_arguments()[index];
}
u32 arguments_offset { 0 };
@ -89,22 +100,27 @@ public:
Span<Value> arguments()
{
return registers_and_constants_and_locals_and_arguments.span().slice(arguments_offset);
return { registers_and_constants_and_locals_and_arguments() + arguments_offset, registers_and_constants_and_locals_and_arguments_count - arguments_offset };
}
ReadonlySpan<Value> arguments() const
{
return registers_and_constants_and_locals_and_arguments.span().slice(arguments_offset);
return { registers_and_constants_and_locals_and_arguments() + arguments_offset, registers_and_constants_and_locals_and_arguments_count - arguments_offset };
}
private:
friend class Bytecode::Interpreter;
Vector<Value> registers_and_constants_and_locals_and_arguments;
public:
Vector<Bytecode::UnwindInfo> unwind_contexts;
Vector<Optional<size_t>> previously_scheduled_jumps;
Vector<GC::Ptr<Environment>> saved_lexical_environments;
private:
friend class Bytecode::Interpreter;
Value* registers_and_constants_and_locals_and_arguments()
{
return reinterpret_cast<Value*>(reinterpret_cast<uintptr_t>(this) + sizeof(ExecutionContext));
}
u32 registers_and_constants_and_locals_and_arguments_count { 0 };
};
struct StackTraceElement {