1 files changed, 59 insertions, 0 deletions
diff --git a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
new file mode 100644
index 000000000..611d29a4e
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
@@ -0,0 +1,59 @@
+//! This module provides a pass to replacing the following statements with
+//! [`Nop`]s
+//!
+//!   - [`AscribeUserType`]
+//!   - [`FakeRead`]
+//!   - [`Assign`] statements with a [`Shallow`] borrow
+//!
+//! The `CleanFakeReadsAndBorrows` "pass" is actually implemented as two
+//! traversals (aka visits) of the input MIR. The first traversal,
+//! `DeleteAndRecordFakeReads`, deletes the fake reads and finds the
+//! temporaries read by [`ForMatchGuard`] reads, and `DeleteFakeBorrows`
+//! deletes the initialization of those temporaries.
+//!
+//! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
+//! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
+//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
+//! [`Assign`]: rustc_middle::mir::StatementKind::Assign
+//! [`ForMatchGuard`]: rustc_middle::mir::FakeReadCause::ForMatchGuard
+//! [`Nop`]: rustc_middle::mir::StatementKind::Nop
+
+use crate::MirPass;
+use rustc_middle::mir::visit::MutVisitor;
+use rustc_middle::mir::{Body, BorrowKind, Location, Rvalue};
+use rustc_middle::mir::{Statement, StatementKind};
+use rustc_middle::ty::TyCtxt;
+
+pub struct CleanupNonCodegenStatements;
+
+pub struct DeleteNonCodegenStatements<'tcx> {
+    tcx: TyCtxt<'tcx>,
+}
+
+impl<'tcx> MirPass<'tcx> for CleanupNonCodegenStatements {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        let mut delete = DeleteNonCodegenStatements { tcx };
+        delete.visit_body(body);
+        body.user_type_annotations.raw.clear();
+
+        for decl in &mut body.local_decls {
+            decl.user_ty = None;
+        }
+    }
+}
+
+impl<'tcx> MutVisitor<'tcx> for DeleteNonCodegenStatements<'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
+        match statement.kind {
+            StatementKind::AscribeUserType(..)
+            | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Shallow, _)))
+            | StatementKind::FakeRead(..) => statement.make_nop(),
+            _ => (),
+        }
+        self.super_statement(statement, location);
+    }
+}