| //! These two passes provide no value to the compiler, so are off at every level. |
| //! |
| //! However, they can be enabled on the command line |
| //! (`-Zmir-enable-passes=+ReorderBasicBlocks,+ReorderLocals`) |
| //! to make the MIR easier to read for humans. |
| |
| use rustc_index::{bit_set::BitSet, IndexSlice, IndexVec}; |
| use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor}; |
| use rustc_middle::mir::*; |
| use rustc_middle::ty::TyCtxt; |
| use rustc_session::Session; |
| |
| /// Rearranges the basic blocks into a *reverse post-order*. |
| /// |
| /// Thus after this pass, all the successors of a block are later than it in the |
| /// `IndexVec`, unless that successor is a back-edge (such as from a loop). |
| pub struct ReorderBasicBlocks; |
| |
| impl<'tcx> MirPass<'tcx> for ReorderBasicBlocks { |
| fn is_enabled(&self, _session: &Session) -> bool { |
| false |
| } |
| |
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { |
| let rpo: IndexVec<BasicBlock, BasicBlock> = |
| body.basic_blocks.reverse_postorder().iter().copied().collect(); |
| if rpo.iter().is_sorted() { |
| return; |
| } |
| |
| let mut updater = BasicBlockUpdater { map: rpo.invert_bijective_mapping(), tcx }; |
| debug_assert_eq!(updater.map[START_BLOCK], START_BLOCK); |
| updater.visit_body(body); |
| |
| permute(body.basic_blocks.as_mut(), &updater.map); |
| } |
| } |
| |
| /// Rearranges the locals into *use* order. |
| /// |
| /// Thus after this pass, a local with a smaller [`Location`] where it was first |
| /// assigned or referenced will have a smaller number. |
| /// |
| /// (Does not reorder arguments nor the [`RETURN_PLACE`].) |
| pub struct ReorderLocals; |
| |
| impl<'tcx> MirPass<'tcx> for ReorderLocals { |
| fn is_enabled(&self, _session: &Session) -> bool { |
| false |
| } |
| |
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { |
| let mut finder = |
| LocalFinder { map: IndexVec::new(), seen: BitSet::new_empty(body.local_decls.len()) }; |
| |
| // We can't reorder the return place or the arguments |
| for local in (0..=body.arg_count).map(Local::from_usize) { |
| finder.track(local); |
| } |
| |
| for (bb, bbd) in body.basic_blocks.iter_enumerated() { |
| finder.visit_basic_block_data(bb, bbd); |
| } |
| |
| // track everything in case there are some locals that we never saw, |
| // such as in non-block things like debug info or in non-uses. |
| for local in body.local_decls.indices() { |
| finder.track(local); |
| } |
| |
| if finder.map.iter().is_sorted() { |
| return; |
| } |
| |
| let mut updater = LocalUpdater { map: finder.map.invert_bijective_mapping(), tcx }; |
| |
| for local in (0..=body.arg_count).map(Local::from_usize) { |
| debug_assert_eq!(updater.map[local], local); |
| } |
| |
| updater.visit_body_preserves_cfg(body); |
| |
| permute(&mut body.local_decls, &updater.map); |
| } |
| } |
| |
| fn permute<I: rustc_index::Idx + Ord, T>(data: &mut IndexVec<I, T>, map: &IndexSlice<I, I>) { |
| // FIXME: It would be nice to have a less-awkward way to apply permutations, |
| // but I don't know one that exists. `sort_by_cached_key` has logic for it |
| // internally, but not in a way that we're allowed to use here. |
| let mut enumerated: Vec<_> = std::mem::take(data).into_iter_enumerated().collect(); |
| enumerated.sort_by_key(|p| map[p.0]); |
| *data = enumerated.into_iter().map(|p| p.1).collect(); |
| } |
| |
| struct BasicBlockUpdater<'tcx> { |
| map: IndexVec<BasicBlock, BasicBlock>, |
| tcx: TyCtxt<'tcx>, |
| } |
| |
| impl<'tcx> MutVisitor<'tcx> for BasicBlockUpdater<'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| |
| fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, _location: Location) { |
| for succ in terminator.successors_mut() { |
| *succ = self.map[*succ]; |
| } |
| } |
| } |
| |
| struct LocalFinder { |
| map: IndexVec<Local, Local>, |
| seen: BitSet<Local>, |
| } |
| |
| impl LocalFinder { |
| fn track(&mut self, l: Local) { |
| if self.seen.insert(l) { |
| self.map.push(l); |
| } |
| } |
| } |
| |
| impl<'tcx> Visitor<'tcx> for LocalFinder { |
| fn visit_local(&mut self, l: Local, context: PlaceContext, _location: Location) { |
| // Exclude non-uses to keep `StorageLive` from controlling where we put |
| // a `Local`, since it might not actually be assigned until much later. |
| if context.is_use() { |
| self.track(l); |
| } |
| } |
| } |
| |
| struct LocalUpdater<'tcx> { |
| pub map: IndexVec<Local, Local>, |
| pub tcx: TyCtxt<'tcx>, |
| } |
| |
| impl<'tcx> MutVisitor<'tcx> for LocalUpdater<'tcx> { |
| fn tcx(&self) -> TyCtxt<'tcx> { |
| self.tcx |
| } |
| |
| fn visit_local(&mut self, l: &mut Local, _: PlaceContext, _: Location) { |
| *l = self.map[*l]; |
| } |
| } |