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use crate::{analysis::PredecessorTable, ir::prelude::*, opt::prelude::*};
use std::collections::{HashMap, HashSet};
pub struct VarToPhiPromotion;
impl Pass for VarToPhiPromotion {
fn run_on_cfg(_ctx: &PassContext, unit: &mut UnitBuilder) -> bool {
info!("VTPP [{}]", unit.name());
let mut modified = false;
let pt = unit.predtbl();
let dfg = &unit;
let mut block_outs = HashMap::new();
let mut value_table = HashMap::new();
let mut vars = HashMap::new();
for block in unit.blocks() {
let mut store_table = HashMap::new();
for inst in unit.insts(block) {
let data = &dfg[inst];
match data.opcode() {
Opcode::Var => {
store_table.insert(unit.inst_result(inst), data.args()[0]);
vars.entry(inst).or_insert_with(Vec::new);
}
Opcode::St => {
let var = data.args()[0];
let val = data.args()[1];
store_table.insert(var, val);
vars.entry(unit.value_inst(var))
.or_insert_with(Vec::new)
.push(inst);
}
Opcode::Ld => {
let v = match store_table.get(&data.args()[0]) {
Some(&v) => Var::Value(v),
None => Var::Incoming(data.args()[0], block),
};
value_table.insert(unit.inst_result(inst), v);
}
_ => continue,
}
}
block_outs.insert(block, store_table);
}
trace!("Value table:");
for (&ld, &v) in &value_table {
let v = match v {
Var::Incoming(var, bb) => format!("{} into {}", var.dump(&unit), bb.dump(&unit)),
Var::Value(v) => format!("{}", v.dump(&unit)),
};
trace!(" ld {} = {}", ld.dump(&unit), v);
}
trace!("Variables leaving blocks:");
for (&block, vars) in &block_outs {
trace!(" Block {}:", block.dump(&unit));
for (&var, &value) in vars {
trace!(" st {} = {}", var.dump(&unit), value.dump(&unit));
}
}
for (ld, slot) in value_table {
trace!("Replacing {} with {:?}", ld.dump(&unit), slot);
let inst = unit.value_inst(ld);
let value = match slot {
Var::Incoming(var, bb) => {
materialize_value(unit, &pt, var, bb, &block_outs, &mut HashSet::new())
.expect("cannot materialize var value")
}
Var::Value(v) => v,
};
debug!("Replacing {} with {}", inst.dump(&unit), value.dump(&unit));
unit.replace_use(ld, value);
unit.prune_if_unused(inst);
modified |= true;
}
for (var_inst, store_insts) in vars {
for store_inst in store_insts {
debug!("Removing {}", store_inst.dump(&unit));
unit.delete_inst(store_inst);
}
debug!("Removing {}", var_inst.dump(&unit));
unit.delete_inst(var_inst);
modified |= true;
}
modified
}
}
#[derive(Debug, Clone, Copy)]
enum Var {
Incoming(Value, Block),
Value(Value),
}
fn materialize_value(
unit: &mut UnitBuilder,
pt: &PredecessorTable,
var: Value,
block: Block,
block_outs: &HashMap<Block, HashMap<Value, Value>>,
stack: &mut HashSet<Block>,
) -> Option<Value> {
if stack.contains(&block) {
trace!(" Breaking recursion at {}", block.dump(&unit));
return None;
}
trace!(" Materialize {} in {}", var.dump(&unit), block.dump(&unit));
stack.insert(block);
let incoming_values: Vec<_> = pt
.pred(block)
.flat_map(|bb| {
block_outs
.get(&bb)
.and_then(|vars| vars.get(&var).cloned())
.or_else(|| materialize_value(unit, pt, var, bb, block_outs, stack))
.map(|v| (bb, v))
})
.collect();
let distinct_values: HashSet<Value> = incoming_values.iter().map(|&(_, v)| v).collect();
let value = if distinct_values.is_empty() {
None
} else if distinct_values.len() == 1 {
distinct_values.into_iter().next()
} else {
trace!(" Insert phi node in {}", block.dump(&unit));
for &(from, value) in &incoming_values {
trace!(
" Incoming {} from {}",
value.dump(&unit),
from.dump(&unit)
);
}
unit.prepend_to(block);
let phi = unit.ins().phi(
incoming_values.iter().map(|&(_, v)| v).collect(),
incoming_values.iter().map(|&(bb, _)| bb).collect(),
);
debug!(
"Insert {} in {}",
unit.value_inst(phi).dump(&unit),
block.dump(&unit)
);
Some(phi)
};
stack.remove(&block);
value
}