bjoernager/rust
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Remove small dominators optimization from SsaLocals

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The optimization is now part of the general implementation.
This commit is contained in:
Tomasz Miąsko 2023-10-05 00:00:00 +00:00
parent 0528d378b6
commit 6c348b77fe
1 changed files with 23 additions and 41 deletions
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64
compiler/rustc_mir_transform/src/ssa.rs
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@ -27,49 +27,12 @@ pub struct SsaLocals {
direct_uses: IndexVec<Local, u32>,
}
/// We often encounter MIR bodies with 1 or 2 basic blocks. In those cases, it's unnecessary to
/// actually compute dominators, we can just compare block indices because bb0 is always the first
/// block, and in any body all other blocks are always dominated by bb0.
struct SmallDominators<'a> {
inner: Option<&'a Dominators<BasicBlock>>,
}
impl SmallDominators<'_> {
fn dominates(&self, first: Location, second: Location) -> bool {
if first.block == second.block {
first.statement_index <= second.statement_index
} else if let Some(inner) = &self.inner {
inner.dominates(first.block, second.block)
} else {
first.block < second.block
}
}
fn check_dominates(&mut self, set: &mut Set1<LocationExtended>, loc: Location) {
let assign_dominates = match *set {
Set1::Empty | Set1::Many => false,
Set1::One(LocationExtended::Arg) => true,
Set1::One(LocationExtended::Plain(assign)) => {
self.dominates(assign.successor_within_block(), loc)
}
};
// We are visiting a use that is not dominated by an assignment.
// Either there is a cycle involved, or we are reading for uninitialized local.
// Bail out.
if !assign_dominates {
*set = Set1::Many;
}
}
}
impl SsaLocals {
pub fn new<'tcx>(body: &Body<'tcx>) -> SsaLocals {
let assignment_order = Vec::with_capacity(body.local_decls.len());
let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls);
let dominators =
if body.basic_blocks.len() > 2 { Some(body.basic_blocks.dominators()) } else { None };
let dominators = SmallDominators { inner: dominators };
let dominators = body.basic_blocks.dominators();
let direct_uses = IndexVec::from_elem(0, &body.local_decls);
let mut visitor = SsaVisitor { assignments, assignment_order, dominators, direct_uses };
@ -231,12 +194,31 @@ enum LocationExtended {
}
struct SsaVisitor<'a> {
dominators: SmallDominators<'a>,
dominators: &'a Dominators<BasicBlock>,
assignments: IndexVec<Local, Set1<LocationExtended>>,
assignment_order: Vec<Local>,
direct_uses: IndexVec<Local, u32>,
}
impl SsaVisitor<'_> {
fn check_dominates(&mut self, local: Local, loc: Location) {
let set = &mut self.assignments[local];
let assign_dominates = match *set {
Set1::Empty | Set1::Many => false,
Set1::One(LocationExtended::Arg) => true,
Set1::One(LocationExtended::Plain(assign)) => {
assign.successor_within_block().dominates(loc, self.dominators)
}
};
// We are visiting a use that is not dominated by an assignment.
// Either there is a cycle involved, or we are reading for uninitialized local.
// Bail out.
if !assign_dominates {
*set = Set1::Many;
}
}
}
impl<'tcx> Visitor<'tcx> for SsaVisitor<'_> {
fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) {
match ctxt {
@ -254,7 +236,7 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor<'_> {
self.assignments[local] = Set1::Many;
}
PlaceContext::NonMutatingUse(_) => {
self.dominators.check_dominates(&mut self.assignments[local], loc);
self.check_dominates(local, loc);
self.direct_uses[local] += 1;
}
PlaceContext::NonUse(_) => {}
@ -269,7 +251,7 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor<'_> {
let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy);
self.visit_projection(place.as_ref(), new_ctxt, loc);
self.dominators.check_dominates(&mut self.assignments[place.local], loc);
self.check_dominates(place.local, loc);
}
return;
} else {