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compute union-find of locals flowing into the output of statics
Co-authored-by: lqd <remy.rakic+github@gmail.com> Co-authored-by: nikomatsakis <niko@alum.mit.edu>
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| // Copyright 2016 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
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| //! A MIR walk gathering a union-crfind of assigned locals, for the purpose of locating the ones | ||
| //! escaping into the output. | ||
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| use rustc::mir::visit::Visitor; | ||
| use rustc::mir::*; | ||
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| use rustc_data_structures::indexed_vec::Idx; | ||
| use rustc_data_structures::unify as ut; | ||
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| crate struct EscapingLocals { | ||
| unification_table: ut::UnificationTable<ut::InPlace<AssignedLocal>>, | ||
| } | ||
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| impl EscapingLocals { | ||
| crate fn compute(mir: &Mir<'_>) -> Self { | ||
| let mut visitor = GatherAssignedLocalsVisitor::new(); | ||
| visitor.visit_mir(mir); | ||
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| EscapingLocals { unification_table: visitor.unification_table } | ||
| } | ||
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| /// True if `local` is known to escape into static | ||
| /// memory. | ||
| crate fn escapes_into_return(&mut self, local: Local) -> bool { | ||
| let return_place = AssignedLocal::from(RETURN_PLACE); | ||
| let other_place = AssignedLocal::from(local); | ||
| self.unification_table.unioned(return_place, other_place) | ||
| } | ||
| } | ||
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| /// The MIR visitor gathering the union-find of the locals used in | ||
| /// assignments. | ||
| struct GatherAssignedLocalsVisitor { | ||
| unification_table: ut::UnificationTable<ut::InPlace<AssignedLocal>>, | ||
| } | ||
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| #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)] | ||
| struct AssignedLocal(u32); | ||
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| impl ut::UnifyKey for AssignedLocal { | ||
| type Value = (); | ||
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| fn index(&self) -> u32 { | ||
| self.0 | ||
| } | ||
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| fn from_index(i: u32) -> AssignedLocal { | ||
| AssignedLocal(i) | ||
| } | ||
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| fn tag() -> &'static str { | ||
| "AssignedLocal" | ||
| } | ||
| } | ||
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| impl From<Local> for AssignedLocal { | ||
| fn from(item: Local) -> Self { | ||
| // newtype_indexes use usize but are u32s. | ||
| assert!(item.index() < ::std::u32::MAX as usize); | ||
| AssignedLocal(item.index() as u32) | ||
| } | ||
| } | ||
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| impl GatherAssignedLocalsVisitor { | ||
| fn new() -> Self { | ||
| Self { | ||
| unification_table: ut::UnificationTable::new(), | ||
| } | ||
| } | ||
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| fn union_locals_if_needed(&mut self, lvalue: Option<Local>, rvalue: Option<Local>) { | ||
| if let Some(lvalue) = lvalue { | ||
| if let Some(rvalue) = rvalue { | ||
| if lvalue != rvalue { | ||
| self.unification_table | ||
| .union(AssignedLocal::from(lvalue), AssignedLocal::from(rvalue)); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| // Returns the potential `Local` associated to this `Place` or `PlaceProjection` | ||
| fn find_local_in_place(place: &Place) -> Option<Local> { | ||
| match place { | ||
| Place::Local(local) => Some(*local), | ||
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| // If you do e.g. `x = a.f` then only *part* of the type of | ||
| // `a` escapes into `x` (the part contained in `f`); if `a`'s | ||
| // type has regions that don't appear in `f`, those might not | ||
| // escape. | ||
| Place::Projection(..) => None, | ||
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| Place::Static { .. } | Place::Promoted { .. } => None, | ||
| } | ||
| } | ||
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| // Returns the potential `Local` in this `Operand`. | ||
| fn find_local_in_operand(op: &Operand) -> Option<Local> { | ||
| // Conservatively check a subset of `Operand`s we know our | ||
| // benchmarks track, for example `html5ever`. | ||
| match op { | ||
| Operand::Copy(place) | Operand::Move(place) => find_local_in_place(place), | ||
| Operand::Constant(_) => None, | ||
| } | ||
| } | ||
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| impl<'tcx> Visitor<'tcx> for GatherAssignedLocalsVisitor { | ||
| fn visit_mir(&mut self, mir: &Mir<'tcx>) { | ||
| // We need as many union-find keys as there are locals | ||
| for _ in 0..mir.local_decls.len() { | ||
| self.unification_table.new_key(()); | ||
| } | ||
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| self.super_mir(mir); | ||
| } | ||
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| fn visit_assign( | ||
| &mut self, | ||
| block: BasicBlock, | ||
| place: &Place<'tcx>, | ||
| rvalue: &Rvalue<'tcx>, | ||
| location: Location, | ||
| ) { | ||
| let local = find_local_in_place(place); | ||
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| // Conservatively check a subset of `Rvalue`s we know our | ||
| // benchmarks track, for example `html5ever`. | ||
| match rvalue { | ||
| Rvalue::Use(op) => self.union_locals_if_needed(local, find_local_in_operand(op)), | ||
| Rvalue::Ref(_, _, place) => { | ||
| self.union_locals_if_needed(local, find_local_in_place(place)) | ||
| } | ||
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| Rvalue::Cast(kind, op, _) => match kind { | ||
| CastKind::Unsize => self.union_locals_if_needed(local, find_local_in_operand(op)), | ||
| _ => (), | ||
| }, | ||
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| Rvalue::Aggregate(_, ops) => { | ||
| for rvalue in ops.iter().map(find_local_in_operand) { | ||
| self.union_locals_if_needed(local, rvalue); | ||
| } | ||
| } | ||
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| _ => (), | ||
| }; | ||
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| self.super_assign(block, place, rvalue, location); | ||
| } | ||
| } |
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