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Simplify implementation.

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This commit is contained in:
Camille GILLOT 2023-05-14 12:10:24 +00:00
parent f40f235879
commit adfffc7e12
1 changed files with 16 additions and 22 deletions
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38
compiler/rustc_mir_transform/src/ssa.rs
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@ -101,14 +101,15 @@ impl SsaLocals {
.retain(|&local| matches!(visitor.assignments[local], Set1::One(_))); .retain(|&local| matches!(visitor.assignments[local], Set1::One(_)));
debug!(?visitor.assignment_order); debug!(?visitor.assignment_order);
let copy_classes = compute_copy_classes(&mut visitor, body); let mut ssa = SsaLocals {
SsaLocals {
assignments: visitor.assignments, assignments: visitor.assignments,
assignment_order: visitor.assignment_order, assignment_order: visitor.assignment_order,
direct_uses: visitor.direct_uses, 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 { pub fn num_locals(&self) -> usize {
@ -261,27 +262,19 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
} }
#[instrument(level = "trace", skip(ssa, body))] #[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()); let mut copies = IndexVec::from_fn_n(|l| l, body.local_decls.len());
for &local in &ssa.assignment_order { for (local, rvalue, _) in ssa.assignments(body) {
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));
let (Rvalue::Use(Operand::Copy(place) | Operand::Move(place)) | Rvalue::CopyForDeref(place)) let (Rvalue::Use(Operand::Copy(place) | Operand::Move(place)) | Rvalue::CopyForDeref(place))
= rvalue = rvalue
else { continue }; else { continue };
let Some(rhs) = place.as_local() 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 // 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. // visited before `local`, and we just have to copy the representing local.
@ -302,11 +295,11 @@ fn compute_copy_classes(ssa: &mut SsaVisitor, body: &Body<'_>) -> IndexVec<Local
} else { } else {
copies[local] = head; copies[local] = head;
} }
ssa.direct_uses[rhs] -= 1; direct_uses[rhs] -= 1;
} }
debug!(?copies); debug!(?copies);
debug!(?ssa.direct_uses); debug!(?direct_uses);
// Invariant: `copies` must point to the head of an equivalence class. // Invariant: `copies` must point to the head of an equivalence class.
#[cfg(debug_assertions)] #[cfg(debug_assertions)]
@ -315,7 +308,8 @@ fn compute_copy_classes(ssa: &mut SsaVisitor, body: &Body<'_>) -> IndexVec<Local
} }
debug_assert_eq!(copies[RETURN_PLACE], RETURN_PLACE); debug_assert_eq!(copies[RETURN_PLACE], RETURN_PLACE);
copies ssa.direct_uses = direct_uses;
ssa.copy_classes = copies;
} }
#[derive(Debug)] #[derive(Debug)]