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use std::{collections::hash_map::Entry, hash::Hash, hash::Hasher, iter};
use crate::MirPass;
use rustc_data_structures::fx::FxHashMap;
use rustc_middle::mir::visit::MutVisitor;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use super::simplify::simplify_cfg;
pub struct DeduplicateBlocks;
impl<'tcx> MirPass<'tcx> for DeduplicateBlocks {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.mir_opt_level() >= 4
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!("Running DeduplicateBlocks on `{:?}`", body.source);
let duplicates = find_duplicates(body);
let has_opts_to_apply = !duplicates.is_empty();
if has_opts_to_apply {
let mut opt_applier = OptApplier { tcx, duplicates };
opt_applier.visit_body(body);
simplify_cfg(tcx, body);
}
}
}
struct OptApplier<'tcx> {
tcx: TyCtxt<'tcx>,
duplicates: FxHashMap<BasicBlock, BasicBlock>,
}
impl<'tcx> MutVisitor<'tcx> for OptApplier<'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) {
for target in terminator.successors_mut() {
if let Some(replacement) = self.duplicates.get(target) {
debug!("SUCCESS: Replacing: `{:?}` with `{:?}`", target, replacement);
*target = *replacement;
}
}
self.super_terminator(terminator, location);
}
}
fn find_duplicates(body: &Body<'_>) -> FxHashMap<BasicBlock, BasicBlock> {
let mut duplicates = FxHashMap::default();
let bbs_to_go_through =
body.basic_blocks.iter_enumerated().filter(|(_, bbd)| !bbd.is_cleanup).count();
let mut same_hashes =
FxHashMap::with_capacity_and_hasher(bbs_to_go_through, Default::default());
for (bb, bbd) in body.basic_blocks.iter_enumerated().rev().filter(|(_, bbd)| !bbd.is_cleanup) {
if bbd.statements.len() > 10 {
continue;
}
let to_hash = BasicBlockHashable { basic_block_data: bbd };
let entry = same_hashes.entry(to_hash);
match entry {
Entry::Occupied(occupied) => {
let value = *occupied.get();
debug!("Inserting {:?} -> {:?}", bb, value);
duplicates.try_insert(bb, value).expect("key was already inserted");
}
Entry::Vacant(vacant) => {
vacant.insert(bb);
}
}
}
duplicates
}
struct BasicBlockHashable<'tcx, 'a> {
basic_block_data: &'a BasicBlockData<'tcx>,
}
impl Hash for BasicBlockHashable<'_, '_> {
fn hash<H: Hasher>(&self, state: &mut H) {
hash_statements(state, self.basic_block_data.statements.iter());
self.basic_block_data.terminator().kind.hash(state);
}
}
impl Eq for BasicBlockHashable<'_, '_> {}
impl PartialEq for BasicBlockHashable<'_, '_> {
fn eq(&self, other: &Self) -> bool {
self.basic_block_data.statements.len() == other.basic_block_data.statements.len()
&& &self.basic_block_data.terminator().kind == &other.basic_block_data.terminator().kind
&& iter::zip(&self.basic_block_data.statements, &other.basic_block_data.statements)
.all(|(x, y)| statement_eq(&x.kind, &y.kind))
}
}
fn hash_statements<'a, 'tcx, H: Hasher>(
hasher: &mut H,
iter: impl Iterator<Item = &'a Statement<'tcx>>,
) where
'tcx: 'a,
{
for stmt in iter {
statement_hash(hasher, &stmt.kind);
}
}
fn statement_hash<H: Hasher>(hasher: &mut H, stmt: &StatementKind<'_>) {
match stmt {
StatementKind::Assign(box (place, rvalue)) => {
place.hash(hasher);
rvalue_hash(hasher, rvalue)
}
x => x.hash(hasher),
};
}
fn rvalue_hash<H: Hasher>(hasher: &mut H, rvalue: &Rvalue<'_>) {
match rvalue {
Rvalue::Use(op) => operand_hash(hasher, op),
x => x.hash(hasher),
};
}
fn operand_hash<H: Hasher>(hasher: &mut H, operand: &Operand<'_>) {
match operand {
Operand::Constant(box Constant { user_ty: _, literal, span: _ }) => literal.hash(hasher),
x => x.hash(hasher),
};
}
fn statement_eq<'tcx>(lhs: &StatementKind<'tcx>, rhs: &StatementKind<'tcx>) -> bool {
let res = match (lhs, rhs) {
(
StatementKind::Assign(box (place, rvalue)),
StatementKind::Assign(box (place2, rvalue2)),
) => place == place2 && rvalue_eq(rvalue, rvalue2),
(x, y) => x == y,
};
debug!("statement_eq lhs: `{:?}` rhs: `{:?}` result: {:?}", lhs, rhs, res);
res
}
fn rvalue_eq<'tcx>(lhs: &Rvalue<'tcx>, rhs: &Rvalue<'tcx>) -> bool {
let res = match (lhs, rhs) {
(Rvalue::Use(op1), Rvalue::Use(op2)) => operand_eq(op1, op2),
(x, y) => x == y,
};
debug!("rvalue_eq lhs: `{:?}` rhs: `{:?}` result: {:?}", lhs, rhs, res);
res
}
fn operand_eq<'tcx>(lhs: &Operand<'tcx>, rhs: &Operand<'tcx>) -> bool {
let res = match (lhs, rhs) {
(
Operand::Constant(box Constant { user_ty: _, literal, span: _ }),
Operand::Constant(box Constant { user_ty: _, literal: literal2, span: _ }),
) => literal == literal2,
(x, y) => x == y,
};
debug!("operand_eq lhs: `{:?}` rhs: `{:?}` result: {:?}", lhs, rhs, res);
res
}