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Rollup merge of rust-lang#95857 - ouz-a:mir-opt, r=oli-obk
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Allow multiple derefs to be splitted in deref_separator

Previously in rust-lang#95649 only a single deref within projection was supported and multiple derefs caused a bunch of issues, this PR fixes those issues.

`@oli-obk` helped a ton again ❤️
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@Dylan-DPC
Dylan-DPC authored Apr 9, 2022
2 parents 8a37db8 + 80afd9d commit 6fab211
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Showing 3 changed files with 117 additions and 8 deletions.
16 changes: 8 additions & 8 deletions compiler/rustc_mir_transform/src/deref_separator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand All @@ -23,15 +25,18 @@ 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);
// temp value, excluding projections we already covered.
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.
let temp_place =
Expand All @@ -50,11 +55,6 @@ 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;
}
}
}
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100 changes: 100 additions & 0 deletions src/test/mir-opt/derefer_test_multiple.main.Derefer.diff
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Original file line number Diff line number Diff line change
@@ -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
}
}

9 changes: 9 additions & 0 deletions src/test/mir-opt/derefer_test_multiple.rs
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Original file line number Diff line number Diff line change
@@ -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;
}

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