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Redundant move eliminator.

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This commit is contained in:
Chris Fallin
2021-06-08 00:08:28 -07:00
parent c6bcd3c941
commit 940bc40fae
1 changed files with 177 additions and 120 deletions
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297
src/ion/mod.rs
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@@ -809,6 +809,135 @@ impl<'a> std::iter::Iterator for RegTraversalIter<'a> {
}
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum RedundantMoveState {
Copy(Allocation, Option<VReg>),
Orig(VReg),
None,
}
#[derive(Clone, Debug, Default)]
struct RedundantMoveEliminator {
allocs: HashMap<Allocation, RedundantMoveState>,
reverse_allocs: HashMap<Allocation, SmallVec<[Allocation; 4]>>,
}
#[derive(Copy, Clone, Debug)]
struct RedundantMoveAction {
elide: bool,
def_alloc: Option<(Allocation, VReg)>,
}
impl RedundantMoveEliminator {
fn process_move(
&mut self,
from: Allocation,
to: Allocation,
to_vreg: Option<VReg>,
) -> RedundantMoveAction {
// Look up the src and dest.
let from_state = self
.allocs
.get(&from)
.map(|&p| p)
.unwrap_or(RedundantMoveState::None);
let to_state = self
.allocs
.get(&to)
.map(|&p| p)
.unwrap_or(RedundantMoveState::None);
log::debug!(
" -> redundant move tracker: from {} to {} to_vreg {:?}",
from,
to,
to_vreg
);
log::debug!(
" -> from_state {:?} to_state {:?}",
from_state,
to_state
);
if from == to && to_vreg.is_some() {
self.clear_alloc(to);
self.allocs
.insert(to, RedundantMoveState::Orig(to_vreg.unwrap()));
return RedundantMoveAction {
elide: true,
def_alloc: Some((to, to_vreg.unwrap())),
};
}
let src_vreg = match from_state {
RedundantMoveState::Copy(_, opt_r) => opt_r,
RedundantMoveState::Orig(r) => Some(r),
_ => None,
};
log::debug!(" -> src_vreg {:?}", src_vreg);
let dst_vreg = to_vreg.or(src_vreg);
log::debug!(" -> dst_vreg {:?}", dst_vreg);
let existing_dst_vreg = match to_state {
RedundantMoveState::Copy(_, opt_r) => opt_r,
RedundantMoveState::Orig(r) => Some(r),
_ => None,
};
log::debug!(" -> existing_dst_vreg {:?}", existing_dst_vreg);
let elide = match (from_state, to_state) {
(_, RedundantMoveState::Copy(orig_alloc, _)) if orig_alloc == from => true,
(RedundantMoveState::Copy(new_alloc, _), _) if new_alloc == to => true,
_ => false,
};
log::debug!(" -> elide {}", elide);
let def_alloc = if dst_vreg != existing_dst_vreg && dst_vreg.is_some() && elide {
Some((to, dst_vreg.unwrap()))
} else {
None
};
log::debug!(" -> def_alloc {:?}", def_alloc);
// Invalidate all existing copies of `to` if `to` actually changed value.
if !elide {
self.clear_alloc(to);
}
// Set up forward and reverse mapping. Don't track stack-to-stack copies.
if from.is_reg() || to.is_reg() {
self.allocs
.insert(to, RedundantMoveState::Copy(from, dst_vreg));
log::debug!(
" -> create mapping {} -> {:?}",
to,
RedundantMoveState::Copy(from, dst_vreg)
);
self.reverse_allocs
.entry(from)
.or_insert_with(|| smallvec![])
.push(to);
}
RedundantMoveAction { elide, def_alloc }
}
fn clear(&mut self) {
log::debug!(" redundant move eliminator cleared");
self.allocs.clear();
self.reverse_allocs.clear();
}
fn clear_alloc(&mut self, alloc: Allocation) {
log::debug!(" redundant move eliminator: clear {:?}", alloc);
if let Some(ref mut existing_copies) = self.reverse_allocs.get_mut(&alloc) {
for to_inval in existing_copies.iter() {
log::debug!(" -> clear existing copy: {:?}", to_inval);
self.allocs.remove(to_inval);
}
existing_copies.clear();
}
self.allocs.remove(&alloc);
}
}
impl<'a, F: Function> Env<'a, F> {
pub(crate) fn new(
func: &'a F,
@@ -4502,85 +4631,30 @@ impl<'a, F: Function> Env<'a, F> {
self.inserted_moves
.sort_unstable_by_key(|m| (m.pos.to_index(), m.prio));
// Simple redundant-spill/reload removal: track which
// stackslot each preg is a clean copy of, if any, and remove
// spills and reloads that are unnecessary.
let mut preg_state: [(Block, SpillSlot); PReg::MAX_INDEX] =
[(Block::new(0), SpillSlot::invalid()); PReg::MAX_INDEX];
// Redundant-move elimination state tracker.
let mut redundant_moves = RedundantMoveEliminator::default();
fn process_move_maybe_elide(
preg_state: &mut [(Block, SpillSlot); PReg::MAX_INDEX],
block: Block,
from: Allocation,
to: Allocation,
) -> bool {
if from.is_reg() && to.is_reg() {
let from = from.as_reg().unwrap().hw_enc();
let to = to.as_reg().unwrap().hw_enc();
if preg_state[to] == preg_state[from]
&& preg_state[from].1.is_valid()
&& preg_state[from].0 == block
{
true
} else {
preg_state[to] = preg_state[from];
false
}
} else if from.is_stack() && to.is_stack() {
let from = from.as_stack().unwrap();
let to = to.as_stack().unwrap();
update_copies_of_slot(preg_state, to, from);
false
} else if from.is_reg() && to.is_stack() {
// Reg-to-stack spill: determine if value in slot is
// still up-to-date, and skip the store if so.
let from = from.as_reg().unwrap().hw_enc();
let to = to.as_stack().unwrap();
if preg_state[from] == (block, to) {
// Redundant spill: elide.
true
} else {
// Don't elide; but this register now has a clean
// copy of the slot (because its value is now
// being written to the slot). However, no other
// register that previously had a clean copy of
// this slot does anymore.
update_copies_of_slot(preg_state, to, SpillSlot::invalid());
preg_state[from] = (block, to);
false
}
} else {
// Stack-to-reg reload: determine if reg is already an
// up-to-date copy of value in slot, and skip reload
// if so. Otherwise, don't skip reload, and update
// metadata to indicate reg is now up-to-date.
let from = from.as_stack().unwrap();
let to = to.as_reg().unwrap().hw_enc();
if preg_state[to] == (block, from) {
true
} else {
preg_state[to] = (block, from);
false
}
}
}
fn update_copies_of_slot(
preg_state: &mut [(Block, SpillSlot); PReg::MAX_INDEX],
slot: SpillSlot,
updated: SpillSlot,
) {
for entry in preg_state.iter_mut() {
if entry.1 == slot {
entry.1 = updated;
}
}
}
fn clear_preg_state<'a, F: Function>(
fn redundant_move_process_side_effects<'a, F: Function>(
this: &Env<'a, F>,
preg_state: &mut [(Block, SpillSlot); PReg::MAX_INDEX],
redundant_moves: &mut RedundantMoveEliminator,
from: ProgPoint,
to: ProgPoint,
) {
// If any safepoints in range, clear and return.
// Also, if we cross a block boundary, clear and return.
if this.cfginfo.insn_block[from.inst().index()]
!= this.cfginfo.insn_block[to.inst().index()]
{
redundant_moves.clear();
return;
}
for inst in from.inst().index()..=to.inst().index() {
if this.func.is_safepoint(Inst::new(inst)) {
redundant_moves.clear();
return;
}
}
let start_inst = if from.pos() == InstPosition::Before {
from.inst()
} else {
@@ -4593,34 +4667,17 @@ impl<'a, F: Function> Env<'a, F> {
};
for inst in start_inst.index()..end_inst.index() {
let inst = Inst::new(inst);
if this.func.is_safepoint(inst) {
for entry in preg_state.iter_mut() {
entry.1 = SpillSlot::invalid();
}
continue;
}
for (i, op) in this.func.inst_operands(inst).iter().enumerate() {
match op.kind() {
OperandKind::Def | OperandKind::Use => {
let alloc = this.get_alloc(inst, i);
if let Some(preg) = alloc.as_reg() {
preg_state[preg.hw_enc()].1 = SpillSlot::invalid();
} else if let Some(stack) = alloc.as_stack() {
update_copies_of_slot(preg_state, stack, SpillSlot::invalid());
}
redundant_moves.clear_alloc(alloc);
}
_ => {}
}
}
for reg in this.func.inst_clobbers(inst) {
preg_state[reg.hw_enc()].1 = SpillSlot::invalid();
}
}
if to.pos() == InstPosition::Before && this.func.is_safepoint(to.inst()) {
for entry in preg_state.iter_mut() {
entry.1 = SpillSlot::invalid();
redundant_moves.clear_alloc(Allocation::reg(*reg));
}
}
}
@@ -4639,9 +4696,7 @@ impl<'a, F: Function> Env<'a, F> {
}
let moves = &self.inserted_moves[start..i];
let block = self.cfginfo.insn_block[pos.inst().index()];
clear_preg_state(self, &mut preg_state, last_pos, pos);
redundant_move_process_side_effects(self, &mut redundant_moves, last_pos, pos);
last_pos = pos;
// Gather all the moves with Int class and Float class
@@ -4676,15 +4731,11 @@ impl<'a, F: Function> Env<'a, F> {
}
for m in &self_moves {
self.add_edit(
pos,
prio,
Edit::Move {
from: m.from_alloc,
to: m.to_alloc,
to_vreg: m.to_vreg,
},
);
let action = redundant_moves.process_move(m.from_alloc, m.to_alloc, m.to_vreg);
assert!(action.elide);
if let Some((alloc, vreg)) = action.def_alloc {
self.add_edit(pos, prio, Edit::DefAlloc { alloc, vreg });
}
}
for &(regclass, moves) in
@@ -4708,22 +4759,28 @@ impl<'a, F: Function> Env<'a, F> {
for (src, dst, to_vreg) in resolved {
log::debug!(" resolved: {} -> {} ({:?})", src, dst, to_vreg);
if process_move_maybe_elide(&mut preg_state, block, src, dst) {
log::debug!(" -> eliding (redundant)!");
if let Some(vreg) = to_vreg {
self.add_edit(pos, prio, Edit::DefAlloc { alloc: dst, vreg });
}
continue;
let action = redundant_moves.process_move(src, dst, to_vreg);
if !action.elide {
self.add_edit(
pos,
prio,
Edit::Move {
from: src,
to: dst,
to_vreg,
},
);
} else {
log::debug!(" -> redundant move elided");
}
if let Some((alloc, vreg)) = action.def_alloc {
log::debug!(
" -> converted to DefAlloc: alloc {} vreg {}",
alloc,
vreg
);
self.add_edit(pos, prio, Edit::DefAlloc { alloc, vreg });
}
self.add_edit(
pos,
prio,
Edit::Move {
from: src,
to: dst,
to_vreg,
},
);
}
}
}