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Scalar replacement of enums #88628
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Scalar replacement of enums #88628
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,307 @@ | ||
| use crate::transform::MirPass; | ||
| use rustc_data_structures::fx::{FxHashMap, FxHashSet}; | ||
| use rustc_index::vec::{Idx, IndexVec}; | ||
| use rustc_middle::mir::interpret::Scalar; | ||
| use rustc_middle::mir::visit::*; | ||
| use rustc_middle::mir::*; | ||
| use rustc_middle::ty::{ParamEnv, Ty, TyCtxt}; | ||
| use std::collections::hash_map::Entry; | ||
|
|
||
| pub struct FlattenLocals; | ||
|
|
||
| impl<'tcx> MirPass<'tcx> for FlattenLocals { | ||
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| if tcx.sess.mir_opt_level() < 4 { | ||
| return; | ||
| } | ||
|
|
||
| let replacements = compute_flattening(tcx, body); | ||
| let mut all_dead_locals = FxHashSet::default(); | ||
| all_dead_locals.extend(replacements.discr.keys().copied()); | ||
| all_dead_locals.extend(replacements.fields.keys().map(|p| p.local)); | ||
| if all_dead_locals.is_empty() { | ||
| return; | ||
| } | ||
|
|
||
| ReplacementVisitor { tcx, map: &replacements, all_dead_locals }.visit_body(body); | ||
|
|
||
| let mut replaced_locals: IndexVec<_, _> = IndexVec::new(); | ||
| for (k, v) in replacements.fields { | ||
| replaced_locals.ensure_contains_elem(k.local, || Vec::new()); | ||
| replaced_locals[k.local].push(v) | ||
| } | ||
| // Sort locals to avoid depending on FxHashMap order. | ||
| for v in replaced_locals.iter_mut() { | ||
| v.sort_unstable() | ||
| } | ||
| for bbdata in body.basic_blocks_mut().iter_mut() { | ||
| bbdata.expand_statements(|stmt| { | ||
| let source_info = stmt.source_info; | ||
| let (live, origin_local) = match &stmt.kind { | ||
| StatementKind::StorageLive(l) => (true, *l), | ||
| StatementKind::StorageDead(l) => (false, *l), | ||
| _ => return None, | ||
| }; | ||
| replaced_locals.get(origin_local).map(move |final_locals| { | ||
| final_locals.iter().map(move |&l| { | ||
| let kind = if live { | ||
| StatementKind::StorageLive(l) | ||
| } else { | ||
| StatementKind::StorageDead(l) | ||
| }; | ||
| Statement { source_info, kind } | ||
| }) | ||
| }) | ||
| }); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn escaping_locals(body: &Body<'_>) -> FxHashSet<Local> { | ||
| let mut set: FxHashSet<_> = (0..body.arg_count + 1).map(Local::new).collect(); | ||
| for (local, decl) in body.local_decls().iter_enumerated() { | ||
| if decl.ty.is_union() { | ||
| set.insert(local); | ||
| } | ||
| } | ||
| let mut visitor = EscapeVisitor { set }; | ||
| visitor.visit_body(body); | ||
| return visitor.set; | ||
|
|
||
| struct EscapeVisitor { | ||
| set: FxHashSet<Local>, | ||
| } | ||
|
|
||
| impl Visitor<'_> for EscapeVisitor { | ||
| fn visit_local(&mut self, local: &Local, _: PlaceContext, _: Location) { | ||
| self.set.insert(*local); | ||
| } | ||
|
|
||
| fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) { | ||
| // Mirror the implementation in PreFlattenVisitor. | ||
| match &place.projection[..] { | ||
| &[PlaceElem::Field(..), ..] | ||
| | &[PlaceElem::Downcast(..), PlaceElem::Field(..), ..] => {} | ||
| _ => self.super_place(place, context, location), | ||
| } | ||
| } | ||
|
|
||
| fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { | ||
| match rvalue { | ||
| // Getting discriminant on an enum is ok. | ||
| Rvalue::Discriminant(place) if place.projection.is_empty() => {} | ||
|
|
||
| // Raw pointers may be used to access anything inside the enclosing place. | ||
| Rvalue::AddressOf(.., place) | Rvalue::Ref(.., place) if !place.is_indirect() => { | ||
| self.set.insert(place.local); | ||
| } | ||
|
|
||
| _ => self.super_rvalue(rvalue, location), | ||
| } | ||
| } | ||
|
|
||
| fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { | ||
| match &statement.kind { | ||
| // Setting discriminant on an enum is ok. | ||
| StatementKind::SetDiscriminant { place, .. } if place.projection.is_empty() => {} | ||
|
|
||
| // Storage statements are expanded in run_pass. | ||
| StatementKind::StorageLive(..) | StatementKind::StorageDead(..) => {} | ||
|
|
||
| _ => self.super_statement(statement, location), | ||
| } | ||
| } | ||
|
|
||
| fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) { | ||
| if let TerminatorKind::Drop { place, .. } | ||
| | TerminatorKind::DropAndReplace { place, .. } = terminator.kind | ||
| { | ||
| if !place.is_indirect() { | ||
| // Raw pointers may be used to access anything inside the enclosing place. | ||
| self.set.insert(place.local); | ||
| return; | ||
| } | ||
| } | ||
| self.super_terminator(terminator, location); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| #[derive(Default, Debug)] | ||
| struct ReplacementMap<'tcx> { | ||
| discr: FxHashMap<Local, (Local, Ty<'tcx>)>, | ||
| fields: FxHashMap<PlaceRef<'tcx>, Local>, | ||
| } | ||
|
|
||
| fn compute_flattening<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> ReplacementMap<'tcx> { | ||
| let escaping = escaping_locals(&*body); | ||
| let (basic_blocks, local_decls, var_debug_info) = | ||
| body.basic_blocks_local_decls_mut_and_var_debug_info(); | ||
| let mut visitor = | ||
| PreFlattenVisitor { tcx, escaping, local_decls: local_decls, map: Default::default() }; | ||
| for (block, bbdata) in basic_blocks.iter_enumerated() { | ||
| visitor.visit_basic_block_data(block, bbdata); | ||
| } | ||
| for var_debug_info in &*var_debug_info { | ||
| visitor.visit_var_debug_info(var_debug_info); | ||
| } | ||
| return visitor.map; | ||
|
|
||
| struct PreFlattenVisitor<'tcx, 'll> { | ||
| tcx: TyCtxt<'tcx>, | ||
| local_decls: &'ll mut LocalDecls<'tcx>, | ||
| escaping: FxHashSet<Local>, | ||
| map: ReplacementMap<'tcx>, | ||
| } | ||
|
|
||
| impl<'tcx, 'll> PreFlattenVisitor<'tcx, 'll> { | ||
| fn create_discriminant(&mut self, local: Local) -> bool { | ||
| if self.escaping.contains(&local) { | ||
| return false; | ||
| } | ||
|
|
||
| if let Entry::Vacant(v) = self.map.discr.entry(local) { | ||
| let ty = self.local_decls[local].ty.discriminant_ty(self.tcx); | ||
| let local = self.local_decls.push(LocalDecl { | ||
| ty, | ||
| user_ty: None, | ||
| ..self.local_decls[local].clone() | ||
| }); | ||
| v.insert((local, ty)); | ||
| } | ||
|
|
||
| true | ||
| } | ||
|
|
||
| fn create_place(&mut self, place: PlaceRef<'tcx>) { | ||
| if self.escaping.contains(&place.local) { | ||
| return; | ||
| } | ||
|
|
||
| if let Entry::Vacant(v) = self.map.fields.entry(place) { | ||
| let ty = place.ty(&*self.local_decls, self.tcx).ty; | ||
| let local = self.local_decls.push(LocalDecl { | ||
| ty, | ||
| user_ty: None, | ||
| ..self.local_decls[place.local].clone() | ||
| }); | ||
| v.insert(local); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<'tcx, 'll> Visitor<'tcx> for PreFlattenVisitor<'tcx, 'll> { | ||
| fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { | ||
| if let StatementKind::SetDiscriminant { place, .. } = &statement.kind { | ||
| if place.projection.is_empty() { | ||
| if self.create_discriminant(place.local) { | ||
| return; | ||
| } | ||
| } | ||
| } | ||
| self.super_statement(statement, location) | ||
| } | ||
|
|
||
| fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { | ||
| if let Rvalue::Discriminant(place) = rvalue { | ||
| if let Some(local) = place.as_local() { | ||
| if self.create_discriminant(local) { | ||
| return; | ||
| } | ||
| } | ||
| } | ||
| self.super_rvalue(rvalue, location) | ||
| } | ||
|
|
||
| fn visit_place(&mut self, place: &Place<'tcx>, _: PlaceContext, _: Location) { | ||
| let nproj = match &place.projection[..] { | ||
| &[PlaceElem::Field(..), ..] => 1, | ||
| &[PlaceElem::Downcast(..), PlaceElem::Field(..), ..] => 2, | ||
| _ => return, | ||
| }; | ||
| let pr = PlaceRef { local: place.local, projection: &place.projection[..nproj] }; | ||
| self.create_place(pr) | ||
| } | ||
| } | ||
| } | ||
|
|
||
| struct ReplacementVisitor<'tcx, 'll> { | ||
| tcx: TyCtxt<'tcx>, | ||
| map: &'ll ReplacementMap<'tcx>, | ||
| all_dead_locals: FxHashSet<Local>, | ||
| } | ||
|
|
||
| impl<'tcx, 'll> MutVisitor<'tcx> for ReplacementVisitor<'tcx, 'll> { | ||
| fn tcx(&self) -> TyCtxt<'tcx> { | ||
| self.tcx | ||
| } | ||
|
|
||
| fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) { | ||
| match &statement.kind { | ||
| // Storage statements are expanded in run_pass. | ||
| StatementKind::StorageLive(..) | StatementKind::StorageDead(..) => return, | ||
|
|
||
| StatementKind::SetDiscriminant { place, variant_index } | ||
| if place.projection.is_empty() => | ||
| { | ||
| if let Some((local, discr_ty)) = self.map.discr.get(&place.local) { | ||
| let param_env_and_ty = ParamEnv::empty().and(*discr_ty); | ||
| let type_size = self.tcx.layout_of(param_env_and_ty).unwrap().size; | ||
| let scalar = Scalar::try_from_uint(variant_index.as_u32(), type_size).unwrap(); | ||
| statement.kind = StatementKind::Assign(Box::new(( | ||
| Place::from(*local), | ||
| Rvalue::Use(Operand::const_from_scalar( | ||
| self.tcx, | ||
| discr_ty, | ||
| scalar, | ||
| statement.source_info.span, | ||
| )), | ||
| ))); | ||
|
|
||
| return; | ||
| } | ||
| } | ||
|
|
||
| _ => {} | ||
| }; | ||
| self.super_statement(statement, location) | ||
| } | ||
|
|
||
| fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) { | ||
| if let Rvalue::Discriminant(place) = rvalue { | ||
| if let Some(local) = place.as_local() { | ||
| if let Some((local, _)) = self.map.discr.get(&local) { | ||
| *rvalue = Rvalue::Use(Operand::Copy(Place::from(*local))); | ||
| } | ||
| } | ||
| } | ||
| self.super_rvalue(rvalue, location) | ||
| } | ||
|
|
||
| fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) { | ||
| match &place.projection[..] { | ||
| &[PlaceElem::Field(..), ref rest @ ..] => { | ||
| let pr = PlaceRef { local: place.local, projection: &place.projection[..1] }; | ||
| if let Some(local) = self.map.fields.get(&pr) { | ||
| *place = | ||
| Place { local: *local, projection: self.tcx.intern_place_elems(&rest) }; | ||
| return; | ||
| } | ||
| } | ||
| &[PlaceElem::Downcast(..), PlaceElem::Field(..), ref rest @ ..] => { | ||
| let pr = PlaceRef { local: place.local, projection: &place.projection[..2] }; | ||
| if let Some(local) = self.map.fields.get(&pr) { | ||
| *place = | ||
| Place { local: *local, projection: self.tcx.intern_place_elems(&rest) }; | ||
| return; | ||
| } | ||
| } | ||
| _ => {} | ||
| }; | ||
| self.super_place(place, context, location) | ||
| } | ||
|
|
||
| fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) { | ||
| assert!(!self.all_dead_locals.contains(local)); | ||
| } | ||
| } | ||
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Discriminant value used by specific variant can be arbitrary:
discriminant_for_variant.