Do not see through copies of mutable pointers.

Author: cjgillot

compiler/rustc_mir_transform/src/ref_prop.rs

@@ -208,13 +208,14 @@ fn compute_replacement<'tcx>(
             // have been visited before.
             Rvalue::Use(Operand::Copy(place) | Operand::Move(place))
             | Rvalue::CopyForDeref(place) => {
-                if let Some(rhs) = place.as_local() {
+                if let Some(rhs) = place.as_local() && ssa.is_ssa(rhs) {
                     let target = targets[rhs];
-                    if matches!(target, Value::Pointer(..)) {
+                    // Only see through immutable reference and pointers, as we do not know yet if
+                    // mutable references are fully replaced.
+                    if !needs_unique && matches!(target, Value::Pointer(..)) {
                         targets[local] = target;
-                    } else if ssa.is_ssa(rhs) {
-                        let refmut = body.local_decls[rhs].ty.is_mutable_ptr();
-                        targets[local] = Value::Pointer(tcx.mk_place_deref(rhs.into()), refmut);
+                    } else {
+                        targets[local] = Value::Pointer(tcx.mk_place_deref(rhs.into()), needs_unique);
                     }
                 }
             }

tests/mir-opt/reference_prop.mut_raw_then_mut_shr.ReferencePropagation.diff

@@ -37,14 +37,14 @@
 -         StorageLive(_2);                 // scope 1 at $DIR/reference_prop.rs:+2:9: +2:13
           _2 = &mut _1;                    // scope 1 at $DIR/reference_prop.rs:+2:16: +2:22
           StorageLive(_3);                 // scope 2 at $DIR/reference_prop.rs:+3:9: +3:13
-          StorageLive(_4);                 // scope 2 at $DIR/reference_prop.rs:+3:16: +3:36
+-         StorageLive(_4);                 // scope 2 at $DIR/reference_prop.rs:+3:16: +3:36
 -         StorageLive(_5);                 // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26
 -         _5 = &mut (*_2);                 // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26
 -         _4 = &raw mut (*_5);             // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26
 +         _4 = &raw mut _1;                // scope 2 at $DIR/reference_prop.rs:+3:16: +3:26
           _3 = _4;                         // scope 2 at $DIR/reference_prop.rs:+3:16: +3:36
 -         StorageDead(_5);                 // scope 2 at $DIR/reference_prop.rs:+3:36: +3:37
-          StorageDead(_4);                 // scope 2 at $DIR/reference_prop.rs:+3:36: +3:37
+-         StorageDead(_4);                 // scope 2 at $DIR/reference_prop.rs:+3:36: +3:37
           StorageLive(_6);                 // scope 3 at $DIR/reference_prop.rs:+4:9: +4:13
 -         _6 = &(*_2);                     // scope 3 at $DIR/reference_prop.rs:+4:16: +4:22
 +         _6 = &_1;                        // scope 3 at $DIR/reference_prop.rs:+4:16: +4:22

tests/mir-opt/reference_prop.unique_with_copies.ReferencePropagation.diff

@@ -28,12 +28,11 @@
           StorageLive(_1);                 // scope 0 at $DIR/reference_prop.rs:+1:9: +1:10
           StorageLive(_2);                 // scope 0 at $DIR/reference_prop.rs:+2:13: +2:18
           _2 = const 0_i32;                // scope 0 at $DIR/reference_prop.rs:+2:21: +2:22
-          StorageLive(_3);                 // scope 2 at $DIR/reference_prop.rs:+3:13: +3:14
+-         StorageLive(_3);                 // scope 2 at $DIR/reference_prop.rs:+3:13: +3:14
           _3 = &raw mut _2;                // scope 2 at $DIR/reference_prop.rs:+3:17: +3:27
           StorageLive(_4);                 // scope 3 at $DIR/reference_prop.rs:+5:9: +5:30
           StorageLive(_5);                 // scope 4 at $DIR/reference_prop.rs:+5:25: +5:27
--         _5 = (*_3);                      // scope 4 at $DIR/reference_prop.rs:+5:25: +5:27
-+         _5 = _2;                         // scope 4 at $DIR/reference_prop.rs:+5:25: +5:27
+          _5 = (*_3);                      // scope 4 at $DIR/reference_prop.rs:+5:25: +5:27
           _4 = opaque::<i32>(move _5) -> bb1; // scope 4 at $DIR/reference_prop.rs:+5:18: +5:28
                                            // mir::Constant
                                            // + span: $DIR/reference_prop.rs:452:18: 452:24
@@ -44,11 +43,12 @@
           StorageDead(_5);                 // scope 4 at $DIR/reference_prop.rs:+5:27: +5:28
           StorageDead(_4);                 // scope 3 at $DIR/reference_prop.rs:+5:30: +5:31
           _1 = _3;                         // scope 3 at $DIR/reference_prop.rs:+6:9: +6:10
-          StorageDead(_3);                 // scope 2 at $DIR/reference_prop.rs:+7:5: +7:6
+-         StorageDead(_3);                 // scope 2 at $DIR/reference_prop.rs:+7:5: +7:6
           StorageDead(_2);                 // scope 0 at $DIR/reference_prop.rs:+7:5: +7:6
           StorageLive(_6);                 // scope 1 at $DIR/reference_prop.rs:+9:5: +9:26
           StorageLive(_7);                 // scope 5 at $DIR/reference_prop.rs:+9:21: +9:23
-          _7 = (*_1);                      // scope 5 at $DIR/reference_prop.rs:+9:21: +9:23
+-         _7 = (*_1);                      // scope 5 at $DIR/reference_prop.rs:+9:21: +9:23
++         _7 = (*_3);                      // scope 5 at $DIR/reference_prop.rs:+9:21: +9:23
           _6 = opaque::<i32>(move _7) -> bb2; // scope 5 at $DIR/reference_prop.rs:+9:14: +9:24
                                            // mir::Constant
                                            // + span: $DIR/reference_prop.rs:456:14: 456:20