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use crate::{simplify, MirPass};
use itertools::Itertools as _;
use rustc_index::{bit_set::BitSet, vec::IndexVec};
use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::{self, List, Ty, TyCtxt};
use rustc_target::abi::VariantIdx;
use std::iter::{once, Enumerate, Peekable};
use std::slice::Iter;
pub struct SimplifyArmIdentity;
#[derive(Debug)]
struct ArmIdentityInfo<'tcx> {
local_temp_0: Local,
local_1: Local,
vf_s0: VarField<'tcx>,
get_variant_field_stmt: usize,
field_tmp_assignments: Vec<(Local, Local)>,
local_tmp_s1: Local,
local_0: Local,
vf_s1: VarField<'tcx>,
set_discr_local: Local,
set_discr_var_idx: VariantIdx,
stmt_to_overwrite: usize,
source_info: SourceInfo,
storage_stmts: Vec<(usize, usize, Local)>,
stmts_to_remove: Vec<usize>,
dbg_info_to_adjust: Vec<usize>,
dbg_projection: &'tcx List<PlaceElem<'tcx>>,
}
fn get_arm_identity_info<'a, 'tcx>(
stmts: &'a [Statement<'tcx>],
locals_count: usize,
debug_info: &'a [VarDebugInfo<'tcx>],
) -> Option<ArmIdentityInfo<'tcx>> {
if stmts.len() < 3 {
return None;
}
let mut tmp_assigns = Vec::new();
let mut nop_stmts = Vec::new();
let mut storage_stmts = Vec::new();
let mut storage_live_stmts = Vec::new();
let mut storage_dead_stmts = Vec::new();
type StmtIter<'a, 'tcx> = Peekable<Enumerate<Iter<'a, Statement<'tcx>>>>;
fn is_storage_stmt(stmt: &Statement<'_>) -> bool {
matches!(stmt.kind, StatementKind::StorageLive(_) | StatementKind::StorageDead(_))
}
fn try_eat<'a, 'tcx>(
stmt_iter: &mut StmtIter<'a, 'tcx>,
test: impl Fn(&'a Statement<'tcx>) -> bool,
mut action: impl FnMut(usize, &'a Statement<'tcx>),
) {
while stmt_iter.peek().map_or(false, |(_, stmt)| test(stmt)) {
let (idx, stmt) = stmt_iter.next().unwrap();
action(idx, stmt);
}
}
fn try_eat_storage_stmts(
stmt_iter: &mut StmtIter<'_, '_>,
storage_live_stmts: &mut Vec<(usize, Local)>,
storage_dead_stmts: &mut Vec<(usize, Local)>,
) {
try_eat(stmt_iter, is_storage_stmt, |idx, stmt| {
if let StatementKind::StorageLive(l) = stmt.kind {
storage_live_stmts.push((idx, l));
} else if let StatementKind::StorageDead(l) = stmt.kind {
storage_dead_stmts.push((idx, l));
}
})
}
fn is_tmp_storage_stmt(stmt: &Statement<'_>) -> bool {
use rustc_middle::mir::StatementKind::Assign;
if let Assign(box (place, Rvalue::Use(Operand::Copy(p) | Operand::Move(p)))) = &stmt.kind {
place.as_local().is_some() && p.as_local().is_some()
} else {
false
}
}
fn try_eat_assign_tmp_stmts(
stmt_iter: &mut StmtIter<'_, '_>,
tmp_assigns: &mut Vec<(Local, Local)>,
nop_stmts: &mut Vec<usize>,
) {
try_eat(stmt_iter, is_tmp_storage_stmt, |idx, stmt| {
use rustc_middle::mir::StatementKind::Assign;
if let Assign(box (place, Rvalue::Use(Operand::Copy(p) | Operand::Move(p)))) =
&stmt.kind
{
tmp_assigns.push((place.as_local().unwrap(), p.as_local().unwrap()));
nop_stmts.push(idx);
}
})
}
fn find_storage_live_dead_stmts_for_local(
local: Local,
stmts: &[Statement<'_>],
) -> Option<(usize, usize)> {
trace!("looking for {:?}", local);
let mut storage_live_stmt = None;
let mut storage_dead_stmt = None;
for (idx, stmt) in stmts.iter().enumerate() {
if stmt.kind == StatementKind::StorageLive(local) {
storage_live_stmt = Some(idx);
} else if stmt.kind == StatementKind::StorageDead(local) {
storage_dead_stmt = Some(idx);
}
}
Some((storage_live_stmt?, storage_dead_stmt.unwrap_or(usize::MAX)))
}
let mut stmt_iter = stmts.iter().enumerate().peekable();
try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
let (get_variant_field_stmt, stmt) = stmt_iter.next()?;
let (local_tmp_s0, local_1, vf_s0, dbg_projection) = match_get_variant_field(stmt)?;
try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
try_eat_assign_tmp_stmts(&mut stmt_iter, &mut tmp_assigns, &mut nop_stmts);
try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
try_eat_assign_tmp_stmts(&mut stmt_iter, &mut tmp_assigns, &mut nop_stmts);
let (idx, stmt) = stmt_iter.next()?;
let (local_tmp_s1, local_0, vf_s1) = match_set_variant_field(stmt)?;
nop_stmts.push(idx);
let (idx, stmt) = stmt_iter.next()?;
let (set_discr_local, set_discr_var_idx) = match_set_discr(stmt)?;
let discr_stmt_source_info = stmt.source_info;
nop_stmts.push(idx);
try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts);
for (live_idx, live_local) in storage_live_stmts {
if let Some(i) = storage_dead_stmts.iter().rposition(|(_, l)| *l == live_local) {
let (dead_idx, _) = storage_dead_stmts.swap_remove(i);
storage_stmts.push((live_idx, dead_idx, live_local));
if live_local == local_tmp_s0 {
nop_stmts.push(get_variant_field_stmt);
}
}
}
nop_stmts.sort_unstable();
let (live_idx, dead_idx) = find_storage_live_dead_stmts_for_local(local_tmp_s0, stmts)?;
let stmt_to_overwrite =
nop_stmts.iter().find(|stmt_idx| live_idx < **stmt_idx && **stmt_idx < dead_idx);
let mut tmp_assigned_vars = BitSet::new_empty(locals_count);
for (l, r) in &tmp_assigns {
tmp_assigned_vars.insert(*l);
tmp_assigned_vars.insert(*r);
}
let dbg_info_to_adjust: Vec<_> = debug_info
.iter()
.enumerate()
.filter_map(|(i, var_info)| {
if let VarDebugInfoContents::Place(p) = var_info.value {
if tmp_assigned_vars.contains(p.local) {
return Some(i);
}
}
None
})
.collect();
Some(ArmIdentityInfo {
local_temp_0: local_tmp_s0,
local_1,
vf_s0,
get_variant_field_stmt,
field_tmp_assignments: tmp_assigns,
local_tmp_s1,
local_0,
vf_s1,
set_discr_local,
set_discr_var_idx,
stmt_to_overwrite: *stmt_to_overwrite?,
source_info: discr_stmt_source_info,
storage_stmts,
stmts_to_remove: nop_stmts,
dbg_info_to_adjust,
dbg_projection,
})
}
fn optimization_applies<'tcx>(
opt_info: &ArmIdentityInfo<'tcx>,
local_decls: &IndexVec<Local, LocalDecl<'tcx>>,
local_uses: &IndexVec<Local, usize>,
var_debug_info: &[VarDebugInfo<'tcx>],
) -> bool {
trace!("testing if optimization applies...");
if opt_info.local_0 == opt_info.local_1 {
trace!("NO: moving into ourselves");
return false;
} else if opt_info.vf_s0 != opt_info.vf_s1 {
trace!("NO: the field-and-variant information do not match");
return false;
} else if local_decls[opt_info.local_0].ty != local_decls[opt_info.local_1].ty {
trace!("NO: source and target locals have different types");
return false;
} else if (opt_info.local_0, opt_info.vf_s0.var_idx)
!= (opt_info.set_discr_local, opt_info.set_discr_var_idx)
{
trace!("NO: the discriminants do not match");
return false;
}
if opt_info.field_tmp_assignments.is_empty() {
trace!("NO: no assignments found");
return false;
}
let mut last_assigned_to = opt_info.field_tmp_assignments[0].1;
let source_local = last_assigned_to;
for (l, r) in &opt_info.field_tmp_assignments {
if *r != last_assigned_to {
trace!("NO: found unexpected assignment {:?} = {:?}", l, r);
return false;
}
last_assigned_to = *l;
}
for (l, r) in &opt_info.field_tmp_assignments {
if local_uses[*l] != 2 {
warn!("NO: FAILED assignment chain local {:?} was used more than twice", l);
return false;
} else if local_uses[*r] != 2 {
warn!("NO: FAILED assignment chain local {:?} was used more than twice", r);
return false;
}
}
for dbg_idx in &opt_info.dbg_info_to_adjust {
let dbg_info = &var_debug_info[*dbg_idx];
if let VarDebugInfoContents::Place(p) = dbg_info.value {
if !p.projection.is_empty() {
trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, p);
return false;
}
}
}
if source_local != opt_info.local_temp_0 {
trace!(
"NO: start of assignment chain does not match enum variant temp: {:?} != {:?}",
source_local,
opt_info.local_temp_0
);
return false;
} else if last_assigned_to != opt_info.local_tmp_s1 {
trace!(
"NO: end of assignment chain does not match written enum temp: {:?} != {:?}",
last_assigned_to,
opt_info.local_tmp_s1
);
return false;
}
trace!("SUCCESS: optimization applies!");
true
}
impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
if !tcx.sess.opts.unstable_opts.unsound_mir_opts {
return;
}
let source = body.source;
trace!("running SimplifyArmIdentity on {:?}", source);
let local_uses = LocalUseCounter::get_local_uses(body);
for bb in body.basic_blocks.as_mut() {
if let Some(opt_info) =
get_arm_identity_info(&bb.statements, body.local_decls.len(), &body.var_debug_info)
{
trace!("got opt_info = {:#?}", opt_info);
if !optimization_applies(
&opt_info,
&body.local_decls,
&local_uses,
&body.var_debug_info,
) {
debug!("optimization skipped for {:?}", source);
continue;
}
for (live_idx, dead_idx, local) in &opt_info.storage_stmts {
if *local == opt_info.local_temp_0 {
bb.statements[opt_info.get_variant_field_stmt].make_nop();
}
for (left, right) in &opt_info.field_tmp_assignments {
if local == left || local == right {
bb.statements[*live_idx].make_nop();
bb.statements[*dead_idx].make_nop();
}
}
}
for stmt_idx in opt_info.stmts_to_remove {
bb.statements[stmt_idx].make_nop();
}
let stmt = &mut bb.statements[opt_info.stmt_to_overwrite];
stmt.source_info = opt_info.source_info;
stmt.kind = StatementKind::Assign(Box::new((
opt_info.local_0.into(),
Rvalue::Use(Operand::Move(opt_info.local_1.into())),
)));
bb.statements.retain(|stmt| stmt.kind != StatementKind::Nop);
for dbg_index in opt_info.dbg_info_to_adjust {
let dbg_info = &mut body.var_debug_info[dbg_index];
assert!(
matches!(dbg_info.value, VarDebugInfoContents::Place(_)),
"value was not a Place"
);
if let VarDebugInfoContents::Place(p) = &mut dbg_info.value {
assert!(p.projection.is_empty());
p.local = opt_info.local_0;
p.projection = opt_info.dbg_projection;
}
}
trace!("block is now {:?}", bb.statements);
}
}
}
}
struct LocalUseCounter {
local_uses: IndexVec<Local, usize>,
}
impl LocalUseCounter {
fn get_local_uses(body: &Body<'_>) -> IndexVec<Local, usize> {
let mut counter = LocalUseCounter { local_uses: IndexVec::from_elem(0, &body.local_decls) };
counter.visit_body(body);
counter.local_uses
}
}
impl Visitor<'_> for LocalUseCounter {
fn visit_local(&mut self, local: Local, context: PlaceContext, _location: Location) {
if context.is_storage_marker()
|| context == PlaceContext::NonUse(NonUseContext::VarDebugInfo)
{
return;
}
self.local_uses[local] += 1;
}
}
fn match_get_variant_field<'tcx>(
stmt: &Statement<'tcx>,
) -> Option<(Local, Local, VarField<'tcx>, &'tcx List<PlaceElem<'tcx>>)> {
match &stmt.kind {
StatementKind::Assign(box (
place_into,
Rvalue::Use(Operand::Copy(pf) | Operand::Move(pf)),
)) => {
let local_into = place_into.as_local()?;
let (local_from, vf) = match_variant_field_place(*pf)?;
Some((local_into, local_from, vf, pf.projection))
}
_ => None,
}
}
fn match_set_variant_field<'tcx>(stmt: &Statement<'tcx>) -> Option<(Local, Local, VarField<'tcx>)> {
match &stmt.kind {
StatementKind::Assign(box (place_from, Rvalue::Use(Operand::Move(place_into)))) => {
let local_into = place_into.as_local()?;
let (local_from, vf) = match_variant_field_place(*place_from)?;
Some((local_into, local_from, vf))
}
_ => None,
}
}
fn match_set_discr(stmt: &Statement<'_>) -> Option<(Local, VariantIdx)> {
match &stmt.kind {
StatementKind::SetDiscriminant { place, variant_index } => {
Some((place.as_local()?, *variant_index))
}
_ => None,
}
}
#[derive(PartialEq, Debug)]
struct VarField<'tcx> {
field: Field,
field_ty: Ty<'tcx>,
var_idx: VariantIdx,
}
fn match_variant_field_place<'tcx>(place: Place<'tcx>) -> Option<(Local, VarField<'tcx>)> {
match place.as_ref() {
PlaceRef {
local,
projection: &[ProjectionElem::Downcast(_, var_idx), ProjectionElem::Field(field, ty)],
} => Some((local, VarField { field, field_ty: ty, var_idx })),
_ => None,
}
}
pub struct SimplifyBranchSame;
impl<'tcx> MirPass<'tcx> for SimplifyBranchSame {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
if !tcx.sess.opts.unstable_opts.unsound_mir_opts {
return;
}
trace!("Running SimplifyBranchSame on {:?}", body.source);
let finder = SimplifyBranchSameOptimizationFinder { body, tcx };
let opts = finder.find();
let did_remove_blocks = opts.len() > 0;
for opt in opts.iter() {
trace!("SUCCESS: Applying optimization {:?}", opt);
body.basic_blocks_mut()[opt.bb_to_opt_terminator].terminator_mut().kind =
TerminatorKind::Goto { target: opt.bb_to_goto };
}
if did_remove_blocks {
simplify::remove_dead_blocks(tcx, body);
}
}
}
#[derive(Debug)]
struct SimplifyBranchSameOptimization {
bb_to_goto: BasicBlock,
bb_to_opt_terminator: BasicBlock,
}
struct SwitchTargetAndValue {
target: BasicBlock,
value: Option<u128>,
}
struct SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
body: &'a Body<'tcx>,
tcx: TyCtxt<'tcx>,
}
impl<'tcx> SimplifyBranchSameOptimizationFinder<'_, 'tcx> {
fn find(&self) -> Vec<SimplifyBranchSameOptimization> {
self.body
.basic_blocks
.iter_enumerated()
.filter_map(|(bb_idx, bb)| {
let (discr_switched_on, targets_and_values) = match &bb.terminator().kind {
TerminatorKind::SwitchInt { targets, discr, .. } => {
let targets_and_values: Vec<_> = targets.iter()
.map(|(val, target)| SwitchTargetAndValue { target, value: Some(val) })
.chain(once(SwitchTargetAndValue { target: targets.otherwise(), value: None }))
.collect();
(discr, targets_and_values)
},
_ => return None,
};
let adt_matched_on = match &bb.statements.last()?.kind {
StatementKind::Assign(box (place, rhs))
if Some(*place) == discr_switched_on.place() =>
{
match rhs {
Rvalue::Discriminant(adt_place) if adt_place.ty(self.body, self.tcx).ty.is_enum() => adt_place,
_ => {
trace!("NO: expected a discriminant read of an enum instead of: {:?}", rhs);
return None;
}
}
}
other => {
trace!("NO: expected an assignment of a discriminant read to a place. Found: {:?}", other);
return None
},
};
let mut iter_bbs_reachable = targets_and_values
.iter()
.map(|target_and_value| (target_and_value, &self.body.basic_blocks[target_and_value.target]))
.filter(|(_, bb)| {
bb.terminator().kind != TerminatorKind::Unreachable
})
.peekable();
let bb_first = iter_bbs_reachable.peek().map_or(&targets_and_values[0], |(idx, _)| *idx);
let mut all_successors_equivalent = StatementEquality::TrivialEqual;
for ((target_and_value_l,bb_l), (target_and_value_r,bb_r)) in iter_bbs_reachable.tuple_windows() {
let trivial_checks = bb_l.is_cleanup == bb_r.is_cleanup
&& bb_l.terminator().kind == bb_r.terminator().kind
&& bb_l.statements.len() == bb_r.statements.len();
let statement_check = || {
bb_l.statements.iter().zip(&bb_r.statements).try_fold(StatementEquality::TrivialEqual, |acc,(l,r)| {
let stmt_equality = self.statement_equality(*adt_matched_on, &l, target_and_value_l, &r, target_and_value_r);
if matches!(stmt_equality, StatementEquality::NotEqual) {
None
} else {
Some(acc.combine(&stmt_equality))
}
})
.unwrap_or(StatementEquality::NotEqual)
};
if !trivial_checks {
all_successors_equivalent = StatementEquality::NotEqual;
break;
}
all_successors_equivalent = all_successors_equivalent.combine(&statement_check());
};
match all_successors_equivalent{
StatementEquality::TrivialEqual => {
trace!("Statements are trivially equal");
Some(SimplifyBranchSameOptimization {
bb_to_goto: bb_first.target,
bb_to_opt_terminator: bb_idx,
})
}
StatementEquality::ConsideredEqual(bb_to_choose) => {
trace!("Statements are considered equal");
Some(SimplifyBranchSameOptimization {
bb_to_goto: bb_to_choose,
bb_to_opt_terminator: bb_idx,
})
}
StatementEquality::NotEqual => {
trace!("NO: not all successors of basic block {:?} were equivalent", bb_idx);
None
}
}
})
.collect()
}
fn statement_equality(
&self,
adt_matched_on: Place<'tcx>,
x: &Statement<'tcx>,
x_target_and_value: &SwitchTargetAndValue,
y: &Statement<'tcx>,
y_target_and_value: &SwitchTargetAndValue,
) -> StatementEquality {
let helper = |rhs: &Rvalue<'tcx>,
place: &Place<'tcx>,
variant_index: VariantIdx,
switch_value: u128,
side_to_choose| {
let place_type = place.ty(self.body, self.tcx).ty;
let adt = match *place_type.kind() {
ty::Adt(adt, _) if adt.is_enum() => adt,
_ => return StatementEquality::NotEqual,
};
let variant_discr = adt.discriminant_for_variant(self.tcx, variant_index).val;
if variant_discr != switch_value {
trace!(
"NO: variant discriminant {} does not equal switch value {}",
variant_discr,
switch_value
);
return StatementEquality::NotEqual;
}
let variant_is_fieldless = adt.variant(variant_index).fields.is_empty();
if !variant_is_fieldless {
trace!("NO: variant {:?} was not fieldless", variant_index);
return StatementEquality::NotEqual;
}
match rhs {
Rvalue::Use(operand) if operand.place() == Some(adt_matched_on) => {
StatementEquality::ConsideredEqual(side_to_choose)
}
_ => {
trace!(
"NO: RHS of assignment was {:?}, but expected it to match the adt being matched on in the switch, which is {:?}",
rhs,
adt_matched_on
);
StatementEquality::NotEqual
}
}
};
match (&x.kind, &y.kind) {
(x, y) if x == y => StatementEquality::TrivialEqual,
(
StatementKind::Assign(box (_, rhs)),
&StatementKind::SetDiscriminant { ref place, variant_index },
) if y_target_and_value.value.is_some() => {
helper(
rhs,
place,
variant_index,
y_target_and_value.value.unwrap(),
x_target_and_value.target,
)
}
(
&StatementKind::SetDiscriminant { ref place, variant_index },
&StatementKind::Assign(box (_, ref rhs)),
) if x_target_and_value.value.is_some() => {
helper(
rhs,
place,
variant_index,
x_target_and_value.value.unwrap(),
y_target_and_value.target,
)
}
_ => {
trace!("NO: statements `{:?}` and `{:?}` not considered equal", x, y);
StatementEquality::NotEqual
}
}
}
}
#[derive(Copy, Clone, Eq, PartialEq)]
enum StatementEquality {
TrivialEqual,
ConsideredEqual(BasicBlock),
NotEqual,
}
impl StatementEquality {
fn combine(&self, other: &StatementEquality) -> StatementEquality {
use StatementEquality::*;
match (self, other) {
(TrivialEqual, TrivialEqual) => TrivialEqual,
(TrivialEqual, ConsideredEqual(b)) | (ConsideredEqual(b), TrivialEqual) => {
ConsideredEqual(*b)
}
(ConsideredEqual(b1), ConsideredEqual(b2)) => {
if b1 == b2 {
ConsideredEqual(*b1)
} else {
NotEqual
}
}
(_, NotEqual) | (NotEqual, _) => NotEqual,
}
}
}