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LibJS: Generate bytecode in basic blocks instead of one big block

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This limits the size of each block (currently set to 1K), and gets us
closer to a canonical, more easily analysable bytecode format.
As a result of this, "Labels" are now simply entries to basic blocks.
Since there is no more 'conditional' jump (as all jumps are always
taken), JumpIf{True,False} are unified to JumpConditional, and
JumpIfNullish is renamed to JumpNullish.
Also fixes #7914 as a result of reimplementing the loop logic.
This commit is contained in:
Ali Mohammad Pur 2021-06-09 06:49:58 +04:30 • committed by Andreas Kling
commit 01e8f0889a
Notes: sideshowbarker 2024-07-18 12:35:35 +09:00
16 changed files with 392 additions and 174 deletions
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69
Userland/Libraries/LibJS/Bytecode/Block.cpp
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@ -1,69 +0,0 @@
/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/String.h>
#include <LibJS/Bytecode/Block.h>
#include <LibJS/Bytecode/Op.h>
#include <sys/mman.h>
namespace JS::Bytecode {
NonnullOwnPtr<Block> Block::create()
{
return adopt_own(*new Block);
}
Block::Block()
{
// FIXME: This is not the smartest solution ever. Find something cleverer!
// The main issue we're working around here is that we don't want pointers into the bytecode stream to become invalidated
// during code generation due to dynamic buffer resizing. Otherwise we could just use a Vector.
m_buffer_capacity = 64 * KiB;
m_buffer = (u8*)mmap(nullptr, m_buffer_capacity, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
VERIFY(m_buffer != MAP_FAILED);
}
Block::~Block()
{
Bytecode::InstructionStreamIterator it(instruction_stream());
while (!it.at_end()) {
auto& to_destroy = (*it);
++it;
Instruction::destroy(const_cast<Instruction&>(to_destroy));
}
munmap(m_buffer, m_buffer_capacity);
}
void Block::seal()
{
// FIXME: mprotect the instruction stream as PROT_READ
// This is currently not possible because instructions can have destructors (that clean up strings)
// Instructions should instead be destructor-less and refer to strings in a string table on the Bytecode::Block.
// It also doesn't work because instructions that have String members use RefPtr internally which must be in writable memory.
}
void Block::dump() const
{
Bytecode::InstructionStreamIterator it(instruction_stream());
while (!it.at_end()) {
warnln("[{:4x}] {}", it.offset(), (*it).to_string());
++it;
}
}
void Block::grow(size_t additional_size)
{
m_buffer_size += additional_size;
VERIFY(m_buffer_size <= m_buffer_capacity);
}
void InstructionStreamIterator::operator++()
{
m_offset += dereference().length();
}
}