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Merged
bors merged 2 commits into from
May 17, 2023
Merged

Merge return place with other locals in CopyProp. #111556

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f40f235
Merge return place with other locals in CopyProp.
cjgillot May 14, 2023
adfffc7
Simplify implementation.
cjgillot May 14, 2023
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Simplify implementation.
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@cjgillot
cjgillot committed May 14, 2023
commit adfffc7e123a0cca1fefdfc48a7c7860a428c7f4
38 changes: 16 additions & 22 deletions compiler/rustc_mir_transform/src/ssa.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -101,14 +101,15 @@ impl SsaLocals {
.retain(|&local| matches!(visitor.assignments[local], Set1::One(_)));
debug!(?visitor.assignment_order);

let copy_classes = compute_copy_classes(&mut visitor, body);

SsaLocals {
let mut ssa = SsaLocals {
assignments: visitor.assignments,
assignment_order: visitor.assignment_order,
direct_uses: visitor.direct_uses,
copy_classes,
}
// This is filled by `compute_copy_classes`.
copy_classes: IndexVec::default(),
};
compute_copy_classes(&mut ssa, body);
ssa
}

pub fn num_locals(&self) -> usize {
Expand Down Expand Up @@ -261,27 +262,19 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
}

#[instrument(level = "trace", skip(ssa, body))]
fn compute_copy_classes(ssa: &mut SsaVisitor, body: &Body<'_>) -> IndexVec<Local, Local> {
fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
let mut direct_uses = std::mem::take(&mut ssa.direct_uses);
let mut copies = IndexVec::from_fn_n(|l| l, body.local_decls.len());

for &local in &ssa.assignment_order {
debug!(?local);

// This is not SSA: mark that we don't know the value.
debug!(assignments = ?ssa.assignments[local]);
let Set1::One(LocationExtended::Plain(loc)) = ssa.assignments[local] else { continue };

// `loc` must point to a direct assignment to `local`.
let Either::Left(stmt) = body.stmt_at(loc) else { bug!() };
let Some((_target, rvalue)) = stmt.kind.as_assign() else { bug!() };
assert_eq!(_target.as_local(), Some(local));

for (local, rvalue, _) in ssa.assignments(body) {
let (Rvalue::Use(Operand::Copy(place) | Operand::Move(place)) | Rvalue::CopyForDeref(place))
= rvalue
else { continue };

let Some(rhs) = place.as_local() else { continue };
let Set1::One(_) = ssa.assignments[rhs] else { continue };
if !ssa.is_ssa(rhs) {
continue;
}

// We visit in `assignment_order`, ie. reverse post-order, so `rhs` has been
// visited before `local`, and we just have to copy the representing local.
Expand All @@ -302,11 +295,11 @@ fn compute_copy_classes(ssa: &mut SsaVisitor, body: &Body<'_>) -> IndexVec<Local
} else {
copies[local] = head;
}
ssa.direct_uses[rhs] -= 1;
direct_uses[rhs] -= 1;
}

debug!(?copies);
debug!(?ssa.direct_uses);
debug!(?direct_uses);

// Invariant: `copies` must point to the head of an equivalence class.
#[cfg(debug_assertions)]
Expand All @@ -315,7 +308,8 @@ fn compute_copy_classes(ssa: &mut SsaVisitor, body: &Body<'_>) -> IndexVec<Local
}
debug_assert_eq!(copies[RETURN_PLACE], RETURN_PLACE);

copies
ssa.direct_uses = direct_uses;
ssa.copy_classes = copies;
}

#[derive(Debug)]
Expand Down