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use std::{
collections::{HashMap, HashSet},
hash::{DefaultHasher, Hash, Hasher},
};
use itertools::Itertools;
use crate::ir::{memory::Memory, Guard, IfStmt, LivetimeEquivalences, Stmt, StreamReference};
use super::{ChangeSet, RewriteError, RewriteRule};
#[derive(Debug, Clone, Copy)]
/// Tries to find guard conditions that are used in multiple conditionals in sequences/parallel and moves them outside
pub struct MoveCommonGuardsOutside;
impl RewriteRule for MoveCommonGuardsOutside {
fn rewrite_stmt(
&self,
stmt: Stmt,
_memory: &HashMap<StreamReference, Memory>,
_liveness_equivalences: &LivetimeEquivalences,
) -> Result<(Stmt, ChangeSet), RewriteError> {
match stmt {
Stmt::Seq(inner) => {
let inner_len = inner.len();
let new_inner = inner
.into_iter()
.coalesce(|lhs, rhs| match (lhs, rhs) {
(
Stmt::If(IfStmt {
guard: g1,
cons: c1,
alt: a1,
}),
Stmt::If(IfStmt {
guard: g2,
cons: c2,
alt: a2,
}),
) if matches!(*a1, Stmt::Skip) && matches!(*a2, Stmt::Skip) => {
let lhs_conjuncts = g1.implied_subguards().collect::<HashSet<_>>();
let rhs_conjuncts = g2.implied_subguards().collect::<HashSet<_>>();
let common = lhs_conjuncts
.intersection(&rhs_conjuncts)
.collect::<Vec<_>>();
if common.is_empty() {
Err((
Stmt::If(IfStmt {
guard: g1,
cons: c1,
alt: a1,
}),
Stmt::If(IfStmt {
guard: g2,
cons: c2,
alt: a2,
}),
))
} else {
// we keep the inner guards and rely on the `ImpliedGuards` rewriting rule to remove those
let common_guard = common
.into_iter()
.cloned()
.reduce(|a, b| Guard::And {
lhs: Box::new(a),
rhs: Box::new(b),
})
.unwrap();
Ok(Stmt::If(IfStmt {
guard: common_guard,
cons: Box::new(Stmt::Seq(vec![
Stmt::If(IfStmt {
guard: g1,
cons: c1,
alt: Box::new(Stmt::Skip),
}),
Stmt::If(IfStmt {
guard: g2,
cons: c2,
alt: Box::new(Stmt::Skip),
}),
])),
alt: Box::new(Stmt::Skip),
}))
}
}
(lhs, rhs) => Err((lhs, rhs)),
})
.collect::<Vec<_>>();
if inner_len == new_inner.len() {
Ok((Stmt::Seq(new_inner), ChangeSet::default()))
} else {
Ok((Stmt::Seq(new_inner), ChangeSet::local_change()))
}
}
Stmt::Parallel(inner) => {
let subguard_map = inner
.iter()
.enumerate()
.flat_map(|(i, stmt)| match stmt {
Stmt::If(IfStmt {
guard,
cons: _,
alt,
}) if matches!(**alt, Stmt::Skip) => {
guard.implied_subguards().map(|g| (i, g)).collect()
}
_ => vec![],
})
.fold(HashMap::<_, HashSet<_>>::new(), |mut hm, (i, g)| {
hm.entry(g).or_default().insert(i);
hm
});
let Some((guard, stmts)) = subguard_map
.iter()
.sorted_by_key(|(g, _)| {
// for the tests we want some deterministic order
// (disregard hash collisions for now)
let mut hasher = DefaultHasher::new();
g.hash(&mut hasher);
hasher.finish()
})
.max_by_key(|(_, stmts)| stmts.len())
.filter(|(_, stmts)| stmts.len() > 1)
else {
// there are no common if condition in the parallel statement
return Ok((Stmt::Parallel(inner), ChangeSet::default()));
};
let mut inner = inner;
let combination = stmts
.iter()
.sorted()
.rev()
.map(|stmt_idx| inner.remove(*stmt_idx))
.collect::<Vec<_>>();
inner.push(Stmt::If(IfStmt {
guard: guard.clone(),
cons: Box::new(Stmt::Parallel(combination)),
alt: Box::new(Stmt::Skip),
}));
Ok((Stmt::Parallel(inner), ChangeSet::local_change()))
}
other => Ok((other, ChangeSet::default())),
}
}
}
#[cfg(test)]
mod tests {
use crate::{
ir::parse::parse_ir,
rewrite_rules::{
CombineSeq, ImpliedGuards, MoveCommonGuardsOutside, RemoveIfs, Rewriter, SimplifyGuard,
},
};
#[test]
fn test() {
let ir = parse_ir(
"
seq {
input 0 ;
if @0 && Expr(s0) && @2 then
input 1
fi ;
if Expr(s0) && (@3 || @4) then
input 2
fi ;
if Expr(s0) && (@3 || @4) then
input 3
fi ;
input 4
}",
);
let reference = parse_ir(
"
seq {
input 0;
if Expr(s0) then
seq {
if @0 && @2 then
input 1
fi ;
if @3 || @4 then
input 2
fi ;
if @3 || @4 then
input 3
fi
}
fi ;
input 4
}",
);
let rewriter = Rewriter::new(vec![
Box::new(MoveCommonGuardsOutside),
Box::new(ImpliedGuards),
Box::new(SimplifyGuard),
Box::new(RemoveIfs),
Box::new(CombineSeq),
]);
let (res, changed) = rewriter.apply(ir).unwrap();
assert!(changed);
assert!(res.stmt.eq(&reference.stmt));
let reference2 = parse_ir(
"
seq {
input 0;
if Expr(s0) then
seq {
if @0 && @2 then
input 1
fi ;
if @3 || @4 then
seq {
input 2;
input 3
}
fi
}
fi ;
input 4
}",
);
let (res2, changed) = rewriter.apply(res).unwrap();
assert!(changed);
assert!(res2.stmt.eq(&reference2.stmt));
}
#[test]
fn test2() {
let ir = parse_ir(
"par {
if @0 && @1 then
input 0
fi ;
if @1 && @2 then
input 1
fi ;
if @0 && @1 && @2 then
input 2
fi ;
if @2 && @3 && @4 then
input 3
fi
}",
);
let rewriter = Rewriter::new(vec![
Box::new(MoveCommonGuardsOutside),
Box::new(ImpliedGuards),
Box::new(SimplifyGuard),
Box::new(RemoveIfs),
Box::new(CombineSeq),
]);
let res = rewriter.run(ir).unwrap();
let reference = parse_ir(
"par {
if @2 && @3 && @4 then
input 3
fi ;
if @1 then
par {
if @2 then
input 1
fi ;
if @0 then
par {
input 0 ;
if @2 then
input 2
fi
}
fi
}
fi
}",
);
assert!(res.stmt.eq(&reference.stmt));
}
#[test]
fn test3() {
let ir = parse_ir(
"par {
if @0 && Expr(s0) then
input 0
fi ;
if @1 && (@0 && @2) then
input 0
fi ;
}",
);
let rewriter = Rewriter::new(vec![
Box::new(MoveCommonGuardsOutside),
Box::new(ImpliedGuards),
Box::new(SimplifyGuard),
Box::new(RemoveIfs),
Box::new(CombineSeq),
]);
let res = rewriter.run(ir).unwrap();
println!("{}", res.display());
}
}