rustc_mir_transform/
erase_deref_temps.rs

1//! This pass converts all `DerefTemp` locals into normal temporaries
2//! and turns their `CopyForDeref` rvalues into normal copies.
3
4use rustc_middle::mir::visit::MutVisitor;
5use rustc_middle::mir::*;
6use rustc_middle::ty::TyCtxt;
7
8struct EraseDerefTempsVisitor<'tcx> {
9    tcx: TyCtxt<'tcx>,
10}
11
12impl<'tcx> MutVisitor<'tcx> for EraseDerefTempsVisitor<'tcx> {
13    fn tcx(&self) -> TyCtxt<'tcx> {
14        self.tcx
15    }
16
17    fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, _: Location) {
18        if let &mut Rvalue::CopyForDeref(place) = rvalue {
19            // We do *NOT* want a retag here! This assignment might copy a mutable reference we
20            // can't actually copy, we just need it temporarily to create another pointer.
21            *rvalue = Rvalue::Use(Operand::Copy(place), WithRetag::No)
22        }
23    }
24
25    fn visit_local_decl(&mut self, _: Local, local_decl: &mut LocalDecl<'tcx>) {
26        if local_decl.is_deref_temp() {
27            let info = local_decl.local_info.as_mut().unwrap_crate_local();
28            **info = LocalInfo::Boring;
29        }
30    }
31}
32
33pub(super) struct EraseDerefTemps;
34
35impl<'tcx> crate::MirPass<'tcx> for EraseDerefTemps {
36    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
37        EraseDerefTempsVisitor { tcx }.visit_body_preserves_cfg(body);
38    }
39
40    fn is_required(&self) -> bool {
41        true
42    }
43}
rustc_mir_transform/erase_deref_temps.rs

rustc_mir_transform/
erase_deref_temps.rs
