New mir-opt deref_separator

compiler/rustc_mir_transform/src/deref_separator.rs

@@ -0,0 +1,63 @@
+use crate::MirPass;
+use rustc_middle::mir::patch::MirPatch;
+use rustc_middle::mir::*;
+use rustc_middle::ty::TyCtxt;
+pub struct Derefer;
+
+pub fn deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    let mut patch = MirPatch::new(body);
+    let (basic_blocks, local_decl) = body.basic_blocks_and_local_decls_mut();
+    for (block, data) in basic_blocks.iter_enumerated_mut() {
+        for (i, stmt) in data.statements.iter_mut().enumerate() {
+            match stmt.kind {
+                StatementKind::Assign(box (og_place, Rvalue::Ref(region, borrow_knd, place))) => {
+                    if borrow_knd == (BorrowKind::Mut { allow_two_phase_borrow: false }) {
+                        for (idx, (p_ref, p_elem)) in place.iter_projections().enumerate() {
+                            if p_elem == ProjectionElem::Deref {
+                                // The type that we are derefing
+                                let ty = p_ref.ty(local_decl, tcx).ty;
+                                let temp = patch.new_temp(ty, stmt.source_info.span);
+
+                                // Because we are assigning this right before original statement
+                                // we are using index i of statement
+                                let loc = Location { block: block, statement_index: i };
+                                patch.add_statement(loc, StatementKind::StorageLive(temp));
+
+                                // We are adding current p_ref's projections to our
+                                // temp value
+                                let deref_place =
+                                    Place::from(p_ref.local).project_deeper(p_ref.projection, tcx);
+                                patch.add_assign(
+                                    loc,
+                                    Place::from(temp),
+                                    Rvalue::Use(Operand::Move(deref_place)),
+                                );
+
+                                // We are creating a place by using our temp value's location
+                                // and copying derefed values we need to it
+                                let temp_place =
+                                    Place::from(temp).project_deeper(&place.projection[idx..], tcx);
+                                patch.add_assign(
+                                    loc,
+                                    og_place,
+                                    Rvalue::Ref(region, borrow_knd, temp_place),
+                                );
+                                // We have to delete the original statement since we just
+                                // replaced it
+                                stmt.make_nop();
+                            }
+                        }
+                    }
+                }
+                _ => (),
+            }
+        }
+    }
+    patch.apply(body);
+}
+
+impl<'tcx> MirPass<'tcx> for Derefer {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        deref_finder(tcx, body);
+    }
+}