MIR: opt-in normalization of BasicBlock and Local numbering
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,150 @@ | ||
| //! 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. | ||
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| use crate::MirPass; | ||
| 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; | ||
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| /// 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; | ||
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| impl<'tcx> MirPass<'tcx> for ReorderBasicBlocks { | ||
| fn is_enabled(&self, _session: &Session) -> bool { | ||
| false | ||
| } | ||
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| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| let rpo: IndexVec<BasicBlock, BasicBlock> = | ||
| body.basic_blocks.postorder().iter().copied().rev().collect(); | ||
| if rpo.iter().is_sorted() { | ||
| return; | ||
| } | ||
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| let mut updater = BasicBlockUpdater { map: rpo.invert_bijective_mapping(), tcx }; | ||
| debug_assert_eq!(updater.map[START_BLOCK], START_BLOCK); | ||
| updater.visit_body(body); | ||
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| permute(body.basic_blocks.as_mut(), &updater.map); | ||
| } | ||
| } | ||
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| /// 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; | ||
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| impl<'tcx> MirPass<'tcx> for ReorderLocals { | ||
| fn is_enabled(&self, _session: &Session) -> bool { | ||
| false | ||
| } | ||
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| 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()) }; | ||
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| // We can't reorder the return place or the arguments | ||
| for local in (0..=body.arg_count).map(Local::from_usize) { | ||
| finder.track(local); | ||
| } | ||
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| for (bb, bbd) in body.basic_blocks.iter_enumerated() { | ||
| finder.visit_basic_block_data(bb, bbd); | ||
| } | ||
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| // 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); | ||
| } | ||
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| if finder.map.iter().is_sorted() { | ||
| return; | ||
| } | ||
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| let mut updater = LocalUpdater { map: finder.map.invert_bijective_mapping(), tcx }; | ||
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| for local in (0..=body.arg_count).map(Local::from_usize) { | ||
| debug_assert_eq!(updater.map[local], local); | ||
| } | ||
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| updater.visit_body_preserves_cfg(body); | ||
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| permute(&mut body.local_decls, &updater.map); | ||
| } | ||
| } | ||
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| 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(); | ||
| } | ||
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| struct BasicBlockUpdater<'tcx> { | ||
| map: IndexVec<BasicBlock, BasicBlock>, | ||
| tcx: TyCtxt<'tcx>, | ||
| } | ||
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| impl<'tcx> MutVisitor<'tcx> for BasicBlockUpdater<'tcx> { | ||
| fn tcx(&self) -> TyCtxt<'tcx> { | ||
| self.tcx | ||
| } | ||
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| fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, _location: Location) { | ||
| for succ in terminator.successors_mut() { | ||
| *succ = self.map[*succ]; | ||
| } | ||
| } | ||
| } | ||
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| struct LocalFinder { | ||
| map: IndexVec<Local, Local>, | ||
| seen: BitSet<Local>, | ||
| } | ||
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| impl LocalFinder { | ||
| fn track(&mut self, l: Local) { | ||
| if self.seen.insert(l) { | ||
| self.map.push(l); | ||
| } | ||
| } | ||
| } | ||
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| 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() { | ||
|
There was a problem hiding this comment. Because otherwise @rustbot author |
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| self.track(l); | ||
| } | ||
| } | ||
| } | ||
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| struct LocalUpdater<'tcx> { | ||
| pub map: IndexVec<Local, Local>, | ||
| pub tcx: TyCtxt<'tcx>, | ||
| } | ||
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| impl<'tcx> MutVisitor<'tcx> for LocalUpdater<'tcx> { | ||
| fn tcx(&self) -> TyCtxt<'tcx> { | ||
| self.tcx | ||
| } | ||
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| fn visit_local(&mut self, l: &mut Local, _: PlaceContext, _: Location) { | ||
| *l = self.map[*l]; | ||
| } | ||
| } | ||
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Could you doc-comment in which order the blocks are ordered?