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//! This module provides a pass that removes parts of MIR that are no longer relevant after
//! analysis phase and borrowck. In particular, it removes false edges, user type annotations and
//! replaces following statements with [`Nop`]s:
//!
//! - [`AscribeUserType`]
//! - [`FakeRead`]
//! - [`Assign`] statements with a [`Fake`] borrow
//! - [`Coverage`] statements of kind [`BlockMarker`] or [`SpanMarker`]
//!
//! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
//! [`Assign`]: rustc_middle::mir::StatementKind::Assign
//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
//! [`Nop`]: rustc_middle::mir::StatementKind::Nop
//! [`Fake`]: rustc_middle::mir::BorrowKind::Fake
//! [`Coverage`]: rustc_middle::mir::StatementKind::Coverage
//! [`BlockMarker`]: rustc_middle::mir::coverage::CoverageKind::BlockMarker
//! [`SpanMarker`]: rustc_middle::mir::coverage::CoverageKind::SpanMarker
use rustc_middle::mir::coverage::CoverageKind;
use rustc_middle::mir::{Body, BorrowKind, CastKind, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::TyCtxt;
use crate::MirPass;
pub struct CleanupPostBorrowck;
impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
for basic_block in body.basic_blocks.as_mut() {
for statement in basic_block.statements.iter_mut() {
match statement.kind {
StatementKind::AscribeUserType(..)
| StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Fake(_), _)))
| StatementKind::Coverage(
// These kinds of coverage statements are markers inserted during
// MIR building, and are not needed after InstrumentCoverage.
CoverageKind::BlockMarker { .. } | CoverageKind::SpanMarker { .. },
)
| StatementKind::FakeRead(..) => statement.make_nop(),
StatementKind::Assign(box (
_,
Rvalue::Cast(
ref mut cast_kind @ CastKind::PointerCoercion(
PointerCoercion::ArrayToPointer
| PointerCoercion::MutToConstPointer,
),
..,
),
)) => {
// BorrowCk needed to track whether these cases were coercions or casts,
// to know whether to check lifetimes in their pointees,
// but from now on that distinction doesn't matter,
// so just make them ordinary pointer casts instead.
*cast_kind = CastKind::PtrToPtr;
}
_ => (),
}
}
let terminator = basic_block.terminator_mut();
match terminator.kind {
TerminatorKind::FalseEdge { real_target, .. }
| TerminatorKind::FalseUnwind { real_target, .. } => {
terminator.kind = TerminatorKind::Goto { target: real_target };
}
_ => {}
}
}
body.user_type_annotations.raw.clear();
for decl in &mut body.local_decls {
decl.user_ty = None;
}
}
}