diff options
Diffstat (limited to 'compiler/rustc_mir_transform')
-rw-r--r-- | compiler/rustc_mir_transform/src/copy_prop.rs | 30 | ||||
-rw-r--r-- | compiler/rustc_mir_transform/src/ssa.rs | 62 |
2 files changed, 50 insertions, 42 deletions
diff --git a/compiler/rustc_mir_transform/src/copy_prop.rs b/compiler/rustc_mir_transform/src/copy_prop.rs index c565d6f13b1..319f3a79705 100644 --- a/compiler/rustc_mir_transform/src/copy_prop.rs +++ b/compiler/rustc_mir_transform/src/copy_prop.rs @@ -162,20 +162,22 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> { } fn visit_statement(&mut self, stmt: &mut Statement<'tcx>, loc: Location) { - match stmt.kind { - // When removing storage statements, we need to remove both (#107511). - StatementKind::StorageLive(l) | StatementKind::StorageDead(l) - if self.storage_to_remove.contains(l) => - { - stmt.make_nop() - } - StatementKind::Assign(box (ref place, ref mut rvalue)) - if place.as_local().is_some() => - { - // Do not replace assignments. - self.visit_rvalue(rvalue, loc) - } - _ => self.super_statement(stmt, loc), + // When removing storage statements, we need to remove both (#107511). + if let StatementKind::StorageLive(l) | StatementKind::StorageDead(l) = stmt.kind + && self.storage_to_remove.contains(l) + { + stmt.make_nop(); + return + } + + self.super_statement(stmt, loc); + + // Do not leave tautological assignments around. + if let StatementKind::Assign(box (lhs, ref rhs)) = stmt.kind + && let Rvalue::Use(Operand::Copy(rhs) | Operand::Move(rhs)) | Rvalue::CopyForDeref(rhs) = *rhs + && lhs == rhs + { + stmt.make_nop(); } } } diff --git a/compiler/rustc_mir_transform/src/ssa.rs b/compiler/rustc_mir_transform/src/ssa.rs index a7b45366662..2b404efccc7 100644 --- a/compiler/rustc_mir_transform/src/ssa.rs +++ b/compiler/rustc_mir_transform/src/ssa.rs @@ -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 { @@ -261,49 +262,54 @@ 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); - - if local == RETURN_PLACE { - // `_0` is special, we cannot rename it. - continue; - } - - // 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. - copies[local] = copies[rhs]; - ssa.direct_uses[rhs] -= 1; + let head = copies[rhs]; + + if local == RETURN_PLACE { + // `_0` is special, we cannot rename it. Instead, rename the class of `rhs` to + // `RETURN_PLACE`. This is only possible if the class head is a temporary, not an + // argument. + if body.local_kind(head) != LocalKind::Temp { + continue; + } + for h in copies.iter_mut() { + if *h == head { + *h = RETURN_PLACE; + } + } + } else { + copies[local] = head; + } + 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)] for &head in copies.iter() { assert_eq!(copies[head], head); } + debug_assert_eq!(copies[RETURN_PLACE], RETURN_PLACE); - copies + ssa.direct_uses = direct_uses; + ssa.copy_classes = copies; } #[derive(Debug)] |