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LibJS/Bytecode: Do basic compare-and-jump peephole optimization

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We now fuse sequences like [LessThan, JumpIf] to JumpLessThan.
This is only allowed for temporaries (i.e VM registers) with no other
references to them.
This commit is contained in:
Andreas Kling 2024-05-09 15:13:31 +02:00 • committed by Alexander Kalenik
commit 7654da3851
Notes: sideshowbarker 2024-07-18 00:41:35 +09:00
8 changed files with 166 additions and 28 deletions
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34
Userland/Libraries/LibJS/Bytecode/Generator.cpp
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@ -833,4 +833,38 @@ ScopedOperand Generator::accumulator()
return m_accumulator;
}
bool Generator::fuse_compare_and_jump(ScopedOperand const& condition, Label true_target, Label false_target)
{
auto& last_instruction = *reinterpret_cast<Instruction const*>(m_current_basic_block->data() + m_current_basic_block->last_instruction_start_offset());
#define HANDLE_COMPARISON_OP(op_TitleCase, op_snake_case) \
if (last_instruction.type() == Instruction::Type::op_TitleCase) { \
auto& comparison = static_cast<Op::op_TitleCase const&>(last_instruction); \
VERIFY(comparison.dst() == condition); \
auto lhs = comparison.lhs(); \
auto rhs = comparison.rhs(); \
m_current_basic_block->rewind(); \
emit<Op::Jump##op_TitleCase>(lhs, rhs, true_target, false_target); \
return true; \
}
JS_ENUMERATE_COMPARISON_OPS(HANDLE_COMPARISON_OP);
#undef HANDLE_COMPARISON_OP
return false;
}
void Generator::emit_jump_if(ScopedOperand const& condition, Label true_target, Label false_target)
{
// NOTE: It's only safe to fuse compare-and-jump if the condition is a temporary with no other dependents.
if (condition.operand().is_register()
&& condition.ref_count() == 1
&& m_current_basic_block->size() > 0) {
if (fuse_compare_and_jump(condition, true_target, false_target))
return;
}
emit<Op::JumpIf>(condition, true_target, false_target);
}
}