bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Only consider a local to be SSA if assignment dominates all uses.

Browse source
This commit is contained in:
Camille GILLOT 2023-01-15 20:16:28 +00:00
parent 38b55dc684
commit d45815eb4a
3 changed files with 76 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

23
compiler/rustc_mir_transform/src/copy_prop.rs
View file

@ -1,4 +1,5 @@
use either::Either;
use rustc_data_structures::graph::dominators::Dominators;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;
use rustc_middle::middle::resolve_lifetime::Set1;
@ -65,6 +66,7 @@ enum LocationExtended {
#[derive(Debug)]
struct SsaLocals {
dominators: Dominators<BasicBlock>,
/// Assignments to each local. This defines whether the local is SSA.
assignments: IndexVec<Local, Set1<LocationExtended>>,
/// We visit the body in reverse postorder, to ensure each local is assigned before it is used.
@ -78,7 +80,8 @@ impl SsaLocals {
let assignment_order = Vec::new();
let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls);
let mut this = SsaLocals { assignments, assignment_order };
let dominators = body.basic_blocks.dominators();
let mut this = SsaLocals { assignments, assignment_order, dominators };
let borrowed = borrowed_locals(body);
for (local, decl) in body.local_decls.iter_enumerated() {
@ -117,7 +120,23 @@ impl<'tcx> Visitor<'tcx> for SsaLocals {
PlaceContext::MutatingUse(_) => self.assignments[local] = Set1::Many,
// Immutable borrows and AddressOf are taken into account in `SsaLocals::new` by
// removing non-freeze locals.
PlaceContext::NonMutatingUse(_) | PlaceContext::NonUse(_) => {}
PlaceContext::NonMutatingUse(_) => {
let set = &mut self.assignments[local];
let assign_dominates = match *set {
Set1::Empty | Set1::Many => false,
Set1::One(LocationExtended::Arg) => true,
Set1::One(LocationExtended::Plain(assign)) => {
assign.dominates(loc, &self.dominators)
}
};
// We are visiting a use that is not dominated by an assignment.
// Either there is a cycle involved, or we are reading for uninitialized local.
// Bail out.
if !assign_dominates {
*set = Set1::Many;
}
}
PlaceContext::NonUse(_) => {}
}
}
}