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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,151 @@ | ||
| use crate::Pass; | ||
| use common::cfg::{self, Cfg, Dominators}; | ||
| use dataflow_analysis::{run_analysis, DataflowAnalyses, ReachingDefinitions}; | ||
| use std::collections::HashSet; | ||
|
|
||
| pub struct LoopInvariantCodeMotionPass {} | ||
|
|
||
| impl Pass for LoopInvariantCodeMotionPass { | ||
| fn apply(&mut self, mut program: bril_rs::Program) -> bril_rs::Program { | ||
| let mut output_program = cfg::convert_to_ssa(program); | ||
| for function in output_program.functions.iter_mut() { | ||
| function.instrs = common::cfg::convert_cfg_to_instruction_stream( | ||
| self.process_cfg(Cfg::new(function)), | ||
| ); | ||
| } | ||
| output_program | ||
| } | ||
| } | ||
|
|
||
| fn find_back_edges( | ||
| cfg: &Cfg, | ||
| dominators: &Dominators, | ||
| ) -> HashSet<(usize /*Start index*/, usize /*End index*/)> { | ||
| if cfg.dag.number_of_nodes() == 0 { | ||
| return HashSet::new(); | ||
| } | ||
| let mut back_edges = HashSet::new(); | ||
| let mut visited = vec![false; cfg.dag.number_of_nodes()]; | ||
| let mut nodes_to_visit = vec![0]; | ||
| while !nodes_to_visit.is_empty() { | ||
| let node = nodes_to_visit.pop().unwrap(); | ||
| visited[node] = true; | ||
| for &successor in cfg.dag.get_successor_indices(node) { | ||
| // If the successor is visited and is a dominator of the current node, then it is a back edge. | ||
| if visited[successor] && dominators.set_per_node[node].contains(&successor) { | ||
| back_edges.insert((node, successor)); | ||
| } else { | ||
| nodes_to_visit.push(successor); | ||
| } | ||
| } | ||
| } | ||
| back_edges | ||
| } | ||
|
|
||
| fn find_loop_nodes( | ||
| cfg: &Cfg, | ||
| dominators: &Dominators, | ||
| loop_header: usize, | ||
| seed: usize, | ||
| ) -> Vec<usize> { | ||
| let mut loop_nodes = vec![loop_header]; | ||
| let mut visited = vec![false; cfg.dag.number_of_nodes()]; | ||
| visited[loop_header] = true; | ||
| let mut nodes_to_visit = vec![seed]; | ||
| while !nodes_to_visit.is_empty() { | ||
| let node = nodes_to_visit.pop().unwrap(); | ||
| visited[node] = true; | ||
| loop_nodes.push(node); | ||
| for &predecessor in cfg.dag.get_predecessor_indices(node) { | ||
| // If the predecessor is not visited and if the loop header dominates the predecessor, then add it to the list of nodes to visit. | ||
| // All nodes in the loop should have the loop header as a dominator. | ||
| if !visited[predecessor] && dominators.set_per_node[predecessor].contains(&loop_header) | ||
| { | ||
| nodes_to_visit.push(predecessor); | ||
| } | ||
| } | ||
| } | ||
| loop_nodes | ||
| } | ||
|
|
||
| impl LoopInvariantCodeMotionPass { | ||
| pub fn new() -> Self { | ||
| LoopInvariantCodeMotionPass {} | ||
| } | ||
| fn process_cfg(&mut self, cfg: Cfg) -> Cfg { | ||
| // Precondition: We make the assumption that the CFG is reducible. | ||
| let dominators = cfg::Dominators::new(&cfg); | ||
| let (reaching_definitions_in, reaching_definitions_out) = | ||
| ReachingDefinitions {}.run_analysis(&cfg, Some(false)); | ||
| find_back_edges(&cfg, &dominators) | ||
| .iter() | ||
| .map(|(src, loop_header)| { | ||
| // For each back edge, find the loop nodes. | ||
| assert!( | ||
| dominators.set_per_node[*src].contains(&loop_header), | ||
| "{src}->{loop_header}| dominators of {} are: {:#?}", | ||
| loop_header, | ||
| dominators.set_per_node[*loop_header] | ||
| ); | ||
| ( | ||
| *loop_header, | ||
| find_loop_nodes(&cfg, &dominators, *loop_header, *src), | ||
| ) | ||
| }) | ||
| .for_each( | ||
| |(loop_header, loop_nodes)| // For each loop, find the loop invariant instructions. | ||
| { | ||
| // todo!("Find loop invariant instructions for loop: {:#?}", loop_nodes); | ||
| }, | ||
| ); | ||
|
|
||
| cfg | ||
| } | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use crate::Pass; | ||
| use bril_rs::Program; | ||
|
|
||
| fn parse_program(text: &str) -> Program { | ||
| let program = common::parse_bril_text(text); | ||
| assert!(program.is_ok(), "{}", program.err().unwrap()); | ||
| program.unwrap() | ||
| } | ||
|
|
||
| #[test] | ||
| fn test_loop_invariant_code_motion() { | ||
| let program = parse_program(indoc::indoc! {r#" | ||
| @main { | ||
| n: int = const 10; | ||
| inc: int = const 5; | ||
| one: int = const 1; | ||
| invariant: int = const 100; | ||
| i: int = const 0; | ||
| sum: int = const 0; | ||
| .loop: | ||
| cond: bool = lt i n; | ||
| br cond .body .done; | ||
| .body: | ||
| temp: int = add invariant inc; | ||
| sum: int = add sum temp; | ||
| i: int = add i one; | ||
| body_cond: bool = lt temp sum; | ||
| br body_cond .body_left .body_right; | ||
| .body_left: | ||
| jmp .body_join; | ||
| .body_right: | ||
| dead_store: int = const 0; | ||
| jmp .body_join; | ||
| .body_join: | ||
| jmp .loop; | ||
| .done: | ||
| print sum; | ||
| ret; | ||
| } | ||
| "#}); | ||
| let optimized_program = super::LoopInvariantCodeMotionPass::new().apply(program); | ||
| println!("{}", optimized_program); | ||
| } | ||
| } |