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use anyhow::Result;
use std::collections::HashMap;
use crate::config::{Config, SLICE_CAP, SPILL_AREA};
use crate::mir::{Instruction, Mir};
use crate::symbol::Loc;
#[derive(Clone, Debug)]
pub struct Compactor {
config: Config,
code: Vec<Instruction>, // the revised mir
live: HashMap<Loc, usize>, // the map of live Stack slots and their last used position
stack: HashMap<Loc, Loc>, // the map of old Stack slots to new Stack slots
pool: Vec<Loc>, // the pool of Stack slots available to reuse
count_stack: u32, // next stack id to use if the pool is empty
depth: isize, // loop depth
fixed: u32,
}
impl Compactor {
pub fn new(config: Config) -> Compactor {
let fixed = if config.is_complex() {
(2 * SLICE_CAP + SPILL_AREA) as u32
} else {
(SLICE_CAP + SPILL_AREA) as u32
};
Compactor {
config,
code: Vec::new(),
live: HashMap::new(),
stack: HashMap::new(),
pool: Vec::new(),
count_stack: fixed,
depth: 0,
fixed,
}
}
pub fn compact(&mut self, mir: &mut Mir) -> Result<usize> {
self.collect_last(mir); // first pass, collect live info
self.compact_stack(mir); // second pass, rename stack slots
mir.code = std::mem::take(&mut self.code);
Ok((self.fixed + self.count_stack) as usize)
}
fn push(&mut self, ins: Instruction) {
self.code.push(ins);
}
fn collect_last(&mut self, mir: &Mir) {
for (ip, ins) in mir.code.iter().enumerate() {
match *ins {
Instruction::Load { loc, .. }
| Instruction::IfElse { cond: loc, .. }
| Instruction::LoadMath { loc, .. }
| Instruction::LoadComplex { loc, .. } => {
if let Loc::Stack(idx) = loc {
if idx >= self.fixed {
if let Some(x) = self.live.get_mut(&loc) {
*x = ip;
}
}
}
}
Instruction::Save { loc, .. } | Instruction::SaveComplex { loc, .. } => {
if let Loc::Stack(idx) = loc {
if idx >= self.fixed {
self.live.insert(loc, ip);
}
}
}
_ => {}
}
}
}
fn save(&mut self, loc: Loc) -> Loc {
if let Loc::Stack(idx) = loc {
if idx < self.fixed {
loc
} else if let Some(Loc::Stack(s)) = self.stack.get(&loc) {
// A stack slot can be assigned more than once in loops (ϕ-constructs)
Loc::Stack(*s)
} else {
let l = match self.pool.pop() {
Some(l) => l, // pool is not empty
None => {
let l = Loc::Stack(self.count_stack);
self.count_stack += if self.config.is_complex() { 2 } else { 1 };
l
}
};
self.stack.insert(loc, l);
l
}
} else {
loc
}
}
fn load(&mut self, loc: Loc, ip: usize) -> Loc {
if let Loc::Stack(idx) = loc {
if idx < self.fixed {
loc
} else {
let l = self
.stack
.get(&loc)
.expect(&format!("cannot find {:?}", loc));
let last = self.live.get(&loc).unwrap();
// stack slots are not returned to the pool inside loops.
// We can do better by delaying return to the branch at
// the end of the loop, but this would add complexity.
if *last == ip && self.depth == 0 {
self.pool.push(*l);
}
*l
}
} else {
loc
}
}
fn compact_stack(&mut self, mir: &Mir) {
for (ip, ins) in mir.code.iter().enumerate() {
match ins {
Instruction::Load { dst, loc } => {
let l = self.load(*loc, ip);
self.push(Instruction::Load { dst: *dst, loc: l });
}
Instruction::LoadComplex { xd, yd, loc } => {
let l = self.load(*loc, ip);
self.push(Instruction::LoadComplex {
xd: *xd,
yd: *yd,
loc: l,
});
}
Instruction::LoadMath { op, dst, s1, loc } => {
let l = self.load(*loc, ip);
self.push(Instruction::LoadMath {
op: *op,
dst: *dst,
s1: *s1,
loc: l,
})
}
Instruction::IfElse {
dst,
true_val,
false_val,
cond,
} => {
let l = self.load(*cond, ip);
self.push(Instruction::IfElse {
dst: *dst,
true_val: *true_val,
false_val: *false_val,
cond: l,
});
}
Instruction::Save { src, loc } => {
let l = self.save(*loc);
self.push(Instruction::Save { src: *src, loc: l });
}
Instruction::SaveComplex { xs, ys, loc } => {
let l = self.save(*loc);
self.push(Instruction::SaveComplex {
xs: *xs,
ys: *ys,
loc: l,
});
}
Instruction::Label { label } => {
self.depth += 1;
self.push(Instruction::Label {
label: label.clone(),
});
}
Instruction::Branch { label } => {
self.depth -= 1;
self.push(Instruction::Branch {
label: label.clone(),
});
}
Instruction::BranchIf {
cond,
label,
is_else,
} => {
self.depth -= 1;
self.push(Instruction::BranchIf {
cond: *cond,
label: label.clone(),
is_else: *is_else,
});
}
_ => {
self.push(ins.clone());
}
}
}
}
}