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LibJS/Bytecode: Rewrite Jump-to-Return-or-End as just Return or End

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Instead of wasting time jumping to a shared Return or End instruction,
we can also emit a Return or End directly in many cases.
This commit is contained in:
Andreas Kling 2024-06-01 10:20:12 +02:00
parent 7971cfdd89
commit 044539c60b
Notes: sideshowbarker 2024-07-17 04:34:25 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/044539c60b
Pull-request: https://github.com/SerenityOS/serenity/pull/24524
1 changed files with 25 additions and 1 deletions
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26
Userland/Libraries/LibJS/Bytecode/Generator.cpp
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@ -340,9 +340,10 @@ CodeGenerationErrorOr<NonnullGCPtr<Executable>> Generator::compile(VM& vm, ASTNo
while (!it.at_end()) {
auto& instruction = const_cast<Instruction&>(*it);
// OPTIMIZATION: Don't emit jumps that just jump to the next block.
if (instruction.type() == Instruction::Type::Jump) {
auto& jump = static_cast<Bytecode::Op::Jump&>(instruction);
// OPTIMIZATION: Don't emit jumps that just jump to the next block.
if (jump.target().basic_block_index() == block->index() + 1) {
if (basic_block_start_offsets.last() == bytecode.size()) {
// This block is empty, just skip it.
@ -351,6 +352,29 @@ CodeGenerationErrorOr<NonnullGCPtr<Executable>> Generator::compile(VM& vm, ASTNo
++it;
continue;
}
// OPTIMIZATION: For jumps to a return-or-end-only block, we can emit a `Return` or `End` directly instead.
auto& target_block = *generator.m_root_basic_blocks[jump.target().basic_block_index()];
if (target_block.is_terminated()) {
auto target_instruction_iterator = InstructionStreamIterator { target_block.instruction_stream() };
auto& target_instruction = *target_instruction_iterator;
if (target_instruction.type() == Instruction::Type::Return) {
auto& return_instruction = static_cast<Bytecode::Op::Return const&>(target_instruction);
Op::Return return_op(return_instruction.value());
bytecode.append(reinterpret_cast<u8 const*>(&return_op), return_op.length());
++it;
continue;
}
if (target_instruction.type() == Instruction::Type::End) {
auto& return_instruction = static_cast<Bytecode::Op::End const&>(target_instruction);
Op::End end_op(return_instruction.value());
bytecode.append(reinterpret_cast<u8 const*>(&end_op), end_op.length());
++it;
continue;
}
}
}
// OPTIMIZATION: For `JumpIf` where one of the targets is the very next block,