79 lines
2.6 KiB
Rust
79 lines
2.6 KiB
Rust
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//! Tools used by the compiler to optimize a chunk's bytecode.
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use crate::{instruction::SetLocal, Chunk, Operation};
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/// Optimizes a short control flow pattern.
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///
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/// Comparison and test instructions (which are always followed by a JUMP) can be optimized when
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/// the next instructions are two constant or boolean loaders. The first loader is set to skip
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/// an instruction if it is run while the second loader is modified to use the first's register.
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/// This makes the following two code snippets compile to the same bytecode:
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///
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/// ```dust
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/// 4 == 4
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/// ```
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///
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/// ```dust
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/// if 4 == 4 { true } else { false }
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/// ```
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///
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/// The instructions must be in the following order:
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/// - `Operation::Equal` | `Operation::Less` | `Operation::LessEqual` | `Operation::Test`
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/// - `Operation::Jump`
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/// - `Operation::LoadBoolean` | `Operation::LoadConstant`
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/// - `Operation::LoadBoolean` | `Operation::LoadConstant`
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pub fn optimize_control_flow(chunk: &mut Chunk) {
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if !matches!(
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chunk.get_last_operations(),
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Some([
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Operation::Equal | Operation::Less | Operation::LessEqual | Operation::Test,
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Operation::Jump,
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Operation::LoadBoolean | Operation::LoadConstant,
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Operation::LoadBoolean | Operation::LoadConstant,
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])
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) {
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return;
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}
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log::debug!("Consolidating registers for control flow optimization");
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let instructions = chunk.instructions_mut();
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let first_loader = &mut instructions.iter_mut().nth_back(1).unwrap().0;
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first_loader.set_c_to_boolean(true);
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let first_loader_register = first_loader.a();
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let second_loader = &mut instructions.last_mut().unwrap().0;
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let second_loader_new = *second_loader.clone().set_a(first_loader_register);
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*second_loader = second_loader_new;
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}
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pub fn optimize_set_local(chunk: &mut Chunk) {
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if !matches!(
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chunk.get_last_operations(),
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Some([
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Operation::Add
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| Operation::Subtract
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| Operation::Multiply
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| Operation::Divide
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| Operation::Modulo,
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Operation::SetLocal,
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])
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) {
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return;
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}
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log::debug!("Condensing math and SetLocal to math instruction");
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let instructions = chunk.instructions_mut();
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let set_local = SetLocal::from(&instructions.pop().unwrap().0);
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let math_instruction = instructions.last_mut().unwrap().0;
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let math_instruction_new = *math_instruction
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.clone()
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.set_a(set_local.local_index)
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.set_a_is_local(true);
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instructions.last_mut().unwrap().0 = math_instruction_new;
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}
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