compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs

   1 //! This module provides a pass that removes parts of MIR that are no longer relevant after
   2 //! analysis phase and borrowck. In particular, it removes false edges, user type annotations and
   3 //! replaces following statements with [`Nop`]s:
   4 //!
   5 //!   - [`AscribeUserType`]
   6 //!   - [`FakeRead`]
   7 //!   - [`Assign`] statements with a [`Shallow`] borrow
   8 //!
   9 //! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
  10 //! [`Assign`]: rustc_middle::mir::StatementKind::Assign
  11 //! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
  12 //! [`Nop`]: rustc_middle::mir::StatementKind::Nop
  13 //! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
  14
  15 use crate::MirPass;
  16 use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind, TerminatorKind};
  17 use rustc_middle::ty::TyCtxt;
  18
  19 pub struct CleanupPostBorrowck;
  20
  21 impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
  22     fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  23         for basic_block in body.basic_blocks.as_mut() {
  24             for statement in basic_block.statements.iter_mut() {
  25                 match statement.kind {
  26                     StatementKind::AscribeUserType(..)
  27                     | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Shallow, _)))
  28                     | StatementKind::FakeRead(..) => statement.make_nop(),
  29                     _ => (),
  30                 }
  31             }
  32             let terminator = basic_block.terminator_mut();
  33             match terminator.kind {
  34                 TerminatorKind::FalseEdge { real_target, .. }
  35                 | TerminatorKind::FalseUnwind { real_target, .. } => {
  36                     terminator.kind = TerminatorKind::Goto { target: real_target };
  37                 }
  38                 _ => {}
  39             }
  40         }
  41
  42         body.user_type_annotations.raw.clear();
  43
  44         for decl in &mut body.local_decls {
  45             decl.user_ty = None;
  46         }
  47     }
  48 }