support multiple derefs

3 files changed, 135 insertions, 13 deletions

diff --git a/compiler/rustc_mir_transform/src/deref_separator.rs b/compiler/rustc_mir_transform/src/deref_separator.rs
index 79aac163550..d8660d4f2fd 100644
--- a/compiler/rustc_mir_transform/src/deref_separator.rs
+++ b/compiler/rustc_mir_transform/src/deref_separator.rs
@@ -11,6 +11,8 @@ pub fn deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         for (i, stmt) in data.statements.iter_mut().enumerate() {
             match stmt.kind {
                 StatementKind::Assign(box (og_place, Rvalue::Ref(region, borrow_knd, place))) => {
+                    let mut place_local = place.local;
+                    let mut last_len = 0;
                     for (idx, (p_ref, p_elem)) in place.iter_projections().enumerate() {
                         if p_elem == ProjectionElem::Deref && !p_ref.projection.is_empty() {
                             // The type that we are derefing.
@@ -23,14 +25,30 @@ pub fn deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
                             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)),
-                            );
+                            // temp value, excluding projections we already covered.
+                            if idx == 1 {
+                                let deref_place = Place::from(place_local)
+                                    .project_deeper(&p_ref.projection[last_len..], tcx);
+                                patch.add_assign(
+                                    loc,
+                                    Place::from(temp),
+                                    Rvalue::Use(Operand::Move(deref_place)),
+                                );
+
+                                place_local = temp;
+                                last_len = p_ref.projection.len();
+                            } else {
+                                let deref_place = Place::from(place_local)
+                                    .project_deeper(&p_ref.projection[last_len..], tcx);
+                                patch.add_assign(
+                                    loc,
+                                    Place::from(temp),
+                                    Rvalue::Use(Operand::Move(deref_place)),
+                                );
+
+                                place_local = temp;
+                                last_len = p_ref.projection.len();
+                            }
 
                             // We are creating a place by using our temp value's location
                             // and copying derefed values which we need to create new statement.
@@ -50,11 +68,6 @@ pub fn deref_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
                             // Since our job with the temp is done it should be gone
                             let loc = Location { block: block, statement_index: i + 1 };
                             patch.add_statement(loc, StatementKind::StorageDead(temp));
-
-                            // As all projections are off the base projection, if there are
-                            // multiple derefs in the middle of projection, it might cause
-                            // unsoundness, to not let that happen we break the loop.
-                            break;
                         }
                     }
                 }
diff --git a/src/test/mir-opt/derefer_test_multiple.main.Derefer.diff b/src/test/mir-opt/derefer_test_multiple.main.Derefer.diff
new file mode 100644
index 00000000000..d465724326e
--- /dev/null
+++ b/src/test/mir-opt/derefer_test_multiple.main.Derefer.diff
@@ -0,0 +1,100 @@
+- // MIR for `main` before Derefer
++ // MIR for `main` after Derefer
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/derefer_test_multiple.rs:2:12: 2:12
+      let mut _1: (i32, i32);              // in scope 0 at $DIR/derefer_test_multiple.rs:3:9: 3:14
+      let mut _3: &mut (i32, i32);         // in scope 0 at $DIR/derefer_test_multiple.rs:4:22: 4:28
+      let mut _5: &mut (i32, &mut (i32, i32)); // in scope 0 at $DIR/derefer_test_multiple.rs:5:22: 5:28
+      let mut _7: &mut (i32, &mut (i32, &mut (i32, i32))); // in scope 0 at $DIR/derefer_test_multiple.rs:6:22: 6:28
++     let mut _10: &mut (i32, &mut (i32, &mut (i32, i32))); // in scope 0 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++     let mut _11: &mut (i32, &mut (i32, i32)); // in scope 0 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++     let mut _12: &mut (i32, i32);        // in scope 0 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++     let mut _13: &mut (i32, &mut (i32, &mut (i32, i32))); // in scope 0 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++     let mut _14: &mut (i32, &mut (i32, i32)); // in scope 0 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++     let mut _15: &mut (i32, i32);        // in scope 0 at $DIR/derefer_test_multiple.rs:8:13: 8:30
+      scope 1 {
+          debug a => _1;                   // in scope 1 at $DIR/derefer_test_multiple.rs:3:9: 3:14
+          let mut _2: (i32, &mut (i32, i32)); // in scope 1 at $DIR/derefer_test_multiple.rs:4:9: 4:14
+          scope 2 {
+              debug b => _2;               // in scope 2 at $DIR/derefer_test_multiple.rs:4:9: 4:14
+              let mut _4: (i32, &mut (i32, &mut (i32, i32))); // in scope 2 at $DIR/derefer_test_multiple.rs:5:9: 5:14
+              scope 3 {
+                  debug c => _4;           // in scope 3 at $DIR/derefer_test_multiple.rs:5:9: 5:14
+                  let mut _6: (i32, &mut (i32, &mut (i32, &mut (i32, i32)))); // in scope 3 at $DIR/derefer_test_multiple.rs:6:9: 6:14
+                  scope 4 {
+                      debug d => _6;       // in scope 4 at $DIR/derefer_test_multiple.rs:6:9: 6:14
+                      let _8: &mut i32;    // in scope 4 at $DIR/derefer_test_multiple.rs:7:9: 7:10
+                      scope 5 {
+                          debug x => _8;   // in scope 5 at $DIR/derefer_test_multiple.rs:7:9: 7:10
+                          let _9: &mut i32; // in scope 5 at $DIR/derefer_test_multiple.rs:8:9: 8:10
+                          scope 6 {
+                              debug y => _9; // in scope 6 at $DIR/derefer_test_multiple.rs:8:9: 8:10
+                          }
+                      }
+                  }
+              }
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/derefer_test_multiple.rs:3:9: 3:14
+          (_1.0: i32) = const 42_i32;      // scope 0 at $DIR/derefer_test_multiple.rs:3:17: 3:25
+          (_1.1: i32) = const 43_i32;      // scope 0 at $DIR/derefer_test_multiple.rs:3:17: 3:25
+          StorageLive(_2);                 // scope 1 at $DIR/derefer_test_multiple.rs:4:9: 4:14
+          StorageLive(_3);                 // scope 1 at $DIR/derefer_test_multiple.rs:4:22: 4:28
+          _3 = &mut _1;                    // scope 1 at $DIR/derefer_test_multiple.rs:4:22: 4:28
+          (_2.0: i32) = const 99_i32;      // scope 1 at $DIR/derefer_test_multiple.rs:4:17: 4:29
+          (_2.1: &mut (i32, i32)) = move _3; // scope 1 at $DIR/derefer_test_multiple.rs:4:17: 4:29
+          StorageDead(_3);                 // scope 1 at $DIR/derefer_test_multiple.rs:4:28: 4:29
+          StorageLive(_4);                 // scope 2 at $DIR/derefer_test_multiple.rs:5:9: 5:14
+          StorageLive(_5);                 // scope 2 at $DIR/derefer_test_multiple.rs:5:22: 5:28
+          _5 = &mut _2;                    // scope 2 at $DIR/derefer_test_multiple.rs:5:22: 5:28
+          (_4.0: i32) = const 11_i32;      // scope 2 at $DIR/derefer_test_multiple.rs:5:17: 5:29
+          (_4.1: &mut (i32, &mut (i32, i32))) = move _5; // scope 2 at $DIR/derefer_test_multiple.rs:5:17: 5:29
+          StorageDead(_5);                 // scope 2 at $DIR/derefer_test_multiple.rs:5:28: 5:29
+          StorageLive(_6);                 // scope 3 at $DIR/derefer_test_multiple.rs:6:9: 6:14
+          StorageLive(_7);                 // scope 3 at $DIR/derefer_test_multiple.rs:6:22: 6:28
+          _7 = &mut _4;                    // scope 3 at $DIR/derefer_test_multiple.rs:6:22: 6:28
+          (_6.0: i32) = const 13_i32;      // scope 3 at $DIR/derefer_test_multiple.rs:6:17: 6:29
+          (_6.1: &mut (i32, &mut (i32, &mut (i32, i32)))) = move _7; // scope 3 at $DIR/derefer_test_multiple.rs:6:17: 6:29
+          StorageDead(_7);                 // scope 3 at $DIR/derefer_test_multiple.rs:6:28: 6:29
+          StorageLive(_8);                 // scope 4 at $DIR/derefer_test_multiple.rs:7:9: 7:10
+-         _8 = &mut ((*((*((*(_6.1: &mut (i32, &mut (i32, &mut (i32, i32))))).1: &mut (i32, &mut (i32, i32)))).1: &mut (i32, i32))).1: i32); // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         StorageLive(_10);                // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         _10 = move (_6.1: &mut (i32, &mut (i32, &mut (i32, i32)))); // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         StorageLive(_11);                // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         _11 = move ((*_10).1: &mut (i32, &mut (i32, i32))); // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         StorageLive(_12);                // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         _12 = move ((*_11).1: &mut (i32, i32)); // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         _8 = &mut ((*_12).1: i32);       // scope 4 at $DIR/derefer_test_multiple.rs:7:13: 7:30
++         StorageDead(_10);                // scope 5 at $DIR/derefer_test_multiple.rs:8:9: 8:10
++         StorageDead(_11);                // scope 5 at $DIR/derefer_test_multiple.rs:8:9: 8:10
++         StorageDead(_12);                // scope 5 at $DIR/derefer_test_multiple.rs:8:9: 8:10
+          StorageLive(_9);                 // scope 5 at $DIR/derefer_test_multiple.rs:8:9: 8:10
+-         _9 = &mut ((*((*((*(_6.1: &mut (i32, &mut (i32, &mut (i32, i32))))).1: &mut (i32, &mut (i32, i32)))).1: &mut (i32, i32))).1: i32); // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         StorageLive(_13);                // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         _13 = move (_6.1: &mut (i32, &mut (i32, &mut (i32, i32)))); // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         StorageLive(_14);                // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         _14 = move ((*_13).1: &mut (i32, &mut (i32, i32))); // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         StorageLive(_15);                // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         _15 = move ((*_14).1: &mut (i32, i32)); // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         _9 = &mut ((*_15).1: i32);       // scope 5 at $DIR/derefer_test_multiple.rs:8:13: 8:30
++         StorageDead(_13);                // scope 0 at $DIR/derefer_test_multiple.rs:2:12: 9:2
++         StorageDead(_14);                // scope 0 at $DIR/derefer_test_multiple.rs:2:12: 9:2
++         StorageDead(_15);                // scope 0 at $DIR/derefer_test_multiple.rs:2:12: 9:2
+          _0 = const ();                   // scope 0 at $DIR/derefer_test_multiple.rs:2:12: 9:2
+          StorageDead(_9);                 // scope 5 at $DIR/derefer_test_multiple.rs:9:1: 9:2
+          StorageDead(_8);                 // scope 4 at $DIR/derefer_test_multiple.rs:9:1: 9:2
+          StorageDead(_6);                 // scope 3 at $DIR/derefer_test_multiple.rs:9:1: 9:2
+          StorageDead(_4);                 // scope 2 at $DIR/derefer_test_multiple.rs:9:1: 9:2
+          StorageDead(_2);                 // scope 1 at $DIR/derefer_test_multiple.rs:9:1: 9:2
+          StorageDead(_1);                 // scope 0 at $DIR/derefer_test_multiple.rs:9:1: 9:2
+          return;                          // scope 0 at $DIR/derefer_test_multiple.rs:9:2: 9:2
++     }
++ 
++     bb1 (cleanup): {
++         resume;                          // scope 0 at $DIR/derefer_test_multiple.rs:2:1: 9:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/derefer_test_multiple.rs b/src/test/mir-opt/derefer_test_multiple.rs
new file mode 100644
index 00000000000..a27363447fe
--- /dev/null
+++ b/src/test/mir-opt/derefer_test_multiple.rs
@@ -0,0 +1,9 @@
+// EMIT_MIR derefer_test_multiple.main.Derefer.diff
+fn main () {
+    let mut a = (42, 43);
+    let mut b = (99, &mut a);
+    let mut c = (11, &mut b);
+    let mut d = (13, &mut c);
+    let x = &mut (*d.1).1.1.1;
+    let y = &mut (*d.1).1.1.1;
+}