mirror of https://github.com/rust-lang/rust.git
Auto merge of #108178 - cjgillot:ssa-deref, r=oli-obk
Do not consider `&mut *x` as mutating `x` in `CopyProp` This PR removes an unfortunate overly cautious case from the current implementation. Found by https://github.com/rust-lang/rust/pull/105274 cc `@saethlin`
This commit is contained in:
bors
commit
66a2d62210
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@ -53,7 +53,7 @@ impl SsaLocals {
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body: &Body<'tcx>,
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borrowed_locals: &BitSet<Local>,
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) -> SsaLocals {
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let assignment_order = Vec::new();
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let assignment_order = Vec::with_capacity(body.local_decls.len());
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let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls);
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let dominators =
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@ -179,12 +179,34 @@ struct SsaVisitor {
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assignment_order: Vec<Local>,
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}
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impl SsaVisitor {
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fn check_assignment_dominates(&mut self, local: Local, loc: Location) {
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let set = &mut self.assignments[local];
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let assign_dominates = match *set {
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Set1::Empty | Set1::Many => false,
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Set1::One(LocationExtended::Arg) => true,
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Set1::One(LocationExtended::Plain(assign)) => {
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assign.successor_within_block().dominates(loc, &self.dominators)
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}
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};
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// We are visiting a use that is not dominated by an assignment.
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// Either there is a cycle involved, or we are reading for uninitialized local.
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// Bail out.
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if !assign_dominates {
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*set = Set1::Many;
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}
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}
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}
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impl<'tcx> Visitor<'tcx> for SsaVisitor {
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fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) {
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match ctxt {
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PlaceContext::MutatingUse(MutatingUseContext::Store) => {
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self.assignments[local].insert(LocationExtended::Plain(loc));
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self.assignment_order.push(local);
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if let Set1::One(_) = self.assignments[local] {
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// Only record if SSA-like, to avoid growing the vector needlessly.
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self.assignment_order.push(local);
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}
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}
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// Anything can happen with raw pointers, so remove them.
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PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
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@ -192,24 +214,26 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
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// Immutable borrows are taken into account in `SsaLocals::new` by
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// removing non-freeze locals.
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PlaceContext::NonMutatingUse(_) => {
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let set = &mut self.assignments[local];
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let assign_dominates = match *set {
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Set1::Empty | Set1::Many => false,
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Set1::One(LocationExtended::Arg) => true,
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Set1::One(LocationExtended::Plain(assign)) => {
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assign.successor_within_block().dominates(loc, &self.dominators)
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}
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};
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// We are visiting a use that is not dominated by an assignment.
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// Either there is a cycle involved, or we are reading for uninitialized local.
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// Bail out.
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if !assign_dominates {
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*set = Set1::Many;
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}
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self.check_assignment_dominates(local, loc);
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}
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PlaceContext::NonUse(_) => {}
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}
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}
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fn visit_place(&mut self, place: &Place<'tcx>, ctxt: PlaceContext, loc: Location) {
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if place.projection.first() == Some(&PlaceElem::Deref) {
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// Do not do anything for storage statements and debuginfo.
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if ctxt.is_use() {
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// A use through a `deref` only reads from the local, and cannot write to it.
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let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection);
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self.visit_projection(place.as_ref(), new_ctxt, loc);
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self.check_assignment_dominates(place.local, loc);
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}
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return;
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}
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self.super_place(place, ctxt, loc);
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}
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}
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#[instrument(level = "trace", skip(ssa, body))]
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@ -0,0 +1,56 @@
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- // MIR for `demiraw` before CopyProp
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+ // MIR for `demiraw` after CopyProp
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fn demiraw(_1: u8) -> () {
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debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:12: +0:17
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let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:23: +0:23
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let _2: *mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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let mut _4: &mut u8; // in scope 0 at $DIR/reborrow.rs:+2:22: +2:29
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let _6: (); // in scope 0 at $DIR/reborrow.rs:+4:5: +4:14
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let mut _7: *mut u8; // in scope 0 at $DIR/reborrow.rs:+4:12: +4:13
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scope 1 {
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debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
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let _3: &mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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scope 2 {
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debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
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let _5: *mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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scope 4 {
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- debug c => _5; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
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+ debug c => _2; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
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}
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}
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scope 3 {
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}
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}
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bb0: {
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- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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_2 = &raw mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:23
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StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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StorageLive(_4); // scope 1 at $DIR/reborrow.rs:+2:22: +2:29
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_4 = &mut (*_2); // scope 3 at $DIR/reborrow.rs:+2:22: +2:29
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_3 = &mut (*_4); // scope 1 at $DIR/reborrow.rs:+2:22: +2:29
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StorageDead(_4); // scope 1 at $DIR/reborrow.rs:+2:31: +2:32
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- StorageLive(_5); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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- _5 = _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
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StorageLive(_6); // scope 4 at $DIR/reborrow.rs:+4:5: +4:14
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- StorageLive(_7); // scope 4 at $DIR/reborrow.rs:+4:12: +4:13
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- _7 = _5; // scope 4 at $DIR/reborrow.rs:+4:12: +4:13
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- _6 = opaque::<*mut u8>(move _7) -> bb1; // scope 4 at $DIR/reborrow.rs:+4:5: +4:14
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+ _6 = opaque::<*mut u8>(_2) -> bb1; // scope 4 at $DIR/reborrow.rs:+4:5: +4:14
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// mir::Constant
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// + span: $DIR/reborrow.rs:38:5: 38:11
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// + literal: Const { ty: fn(*mut u8) {opaque::<*mut u8>}, val: Value(<ZST>) }
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}
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bb1: {
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- StorageDead(_7); // scope 4 at $DIR/reborrow.rs:+4:13: +4:14
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StorageDead(_6); // scope 4 at $DIR/reborrow.rs:+4:14: +4:15
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_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:23: +5:2
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- StorageDead(_5); // scope 2 at $DIR/reborrow.rs:+5:1: +5:2
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StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+5:1: +5:2
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- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+5:1: +5:2
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return; // scope 0 at $DIR/reborrow.rs:+5:2: +5:2
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}
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}
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@ -0,0 +1,52 @@
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- // MIR for `miraw` before CopyProp
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+ // MIR for `miraw` after CopyProp
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fn miraw(_1: u8) -> () {
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debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:10: +0:15
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let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:21: +0:21
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let _2: *mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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let _5: (); // in scope 0 at $DIR/reborrow.rs:+4:5: +4:14
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let mut _6: *mut u8; // in scope 0 at $DIR/reborrow.rs:+4:12: +4:13
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scope 1 {
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debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
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let _3: *mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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scope 2 {
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debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
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let _4: *mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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scope 4 {
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- debug c => _4; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
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+ debug c => _2; // in scope 4 at $DIR/reborrow.rs:+3:9: +3:10
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}
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}
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scope 3 {
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}
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}
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bb0: {
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- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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_2 = &raw mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:23
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StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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_3 = &raw mut (*_2); // scope 3 at $DIR/reborrow.rs:+2:22: +2:33
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- StorageLive(_4); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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- _4 = _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
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StorageLive(_5); // scope 4 at $DIR/reborrow.rs:+4:5: +4:14
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- StorageLive(_6); // scope 4 at $DIR/reborrow.rs:+4:12: +4:13
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- _6 = _4; // scope 4 at $DIR/reborrow.rs:+4:12: +4:13
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- _5 = opaque::<*mut u8>(move _6) -> bb1; // scope 4 at $DIR/reborrow.rs:+4:5: +4:14
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+ _5 = opaque::<*mut u8>(_2) -> bb1; // scope 4 at $DIR/reborrow.rs:+4:5: +4:14
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// mir::Constant
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// + span: $DIR/reborrow.rs:30:5: 30:11
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// + literal: Const { ty: fn(*mut u8) {opaque::<*mut u8>}, val: Value(<ZST>) }
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}
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bb1: {
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- StorageDead(_6); // scope 4 at $DIR/reborrow.rs:+4:13: +4:14
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StorageDead(_5); // scope 4 at $DIR/reborrow.rs:+4:14: +4:15
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_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:21: +5:2
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- StorageDead(_4); // scope 2 at $DIR/reborrow.rs:+5:1: +5:2
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StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+5:1: +5:2
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- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+5:1: +5:2
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return; // scope 0 at $DIR/reborrow.rs:+5:2: +5:2
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}
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}
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@ -0,0 +1,50 @@
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- // MIR for `remut` before CopyProp
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+ // MIR for `remut` after CopyProp
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fn remut(_1: u8) -> () {
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debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:10: +0:15
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let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:21: +0:21
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let _2: &mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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let _5: (); // in scope 0 at $DIR/reborrow.rs:+4:5: +4:14
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let mut _6: &mut u8; // in scope 0 at $DIR/reborrow.rs:+4:12: +4:13
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scope 1 {
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debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
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let _3: &mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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scope 2 {
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debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
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let _4: &mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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scope 3 {
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- debug c => _4; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
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+ debug c => _2; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
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}
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}
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}
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bb0: {
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- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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_2 = &mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:19
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StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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_3 = &mut (*_2); // scope 1 at $DIR/reborrow.rs:+2:13: +2:20
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- StorageLive(_4); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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- _4 = move _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
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StorageLive(_5); // scope 3 at $DIR/reborrow.rs:+4:5: +4:14
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- StorageLive(_6); // scope 3 at $DIR/reborrow.rs:+4:12: +4:13
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- _6 = move _4; // scope 3 at $DIR/reborrow.rs:+4:12: +4:13
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- _5 = opaque::<&mut u8>(move _6) -> bb1; // scope 3 at $DIR/reborrow.rs:+4:5: +4:14
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+ _5 = opaque::<&mut u8>(move _2) -> bb1; // scope 3 at $DIR/reborrow.rs:+4:5: +4:14
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// mir::Constant
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// + span: $DIR/reborrow.rs:14:5: 14:11
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// + literal: Const { ty: fn(&mut u8) {opaque::<&mut u8>}, val: Value(<ZST>) }
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}
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bb1: {
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- StorageDead(_6); // scope 3 at $DIR/reborrow.rs:+4:13: +4:14
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StorageDead(_5); // scope 3 at $DIR/reborrow.rs:+4:14: +4:15
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_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:21: +5:2
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- StorageDead(_4); // scope 2 at $DIR/reborrow.rs:+5:1: +5:2
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StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+5:1: +5:2
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- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+5:1: +5:2
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return; // scope 0 at $DIR/reborrow.rs:+5:2: +5:2
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}
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}
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@ -0,0 +1,50 @@
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- // MIR for `reraw` before CopyProp
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+ // MIR for `reraw` after CopyProp
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fn reraw(_1: u8) -> () {
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debug x => _1; // in scope 0 at $DIR/reborrow.rs:+0:10: +0:15
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let mut _0: (); // return place in scope 0 at $DIR/reborrow.rs:+0:21: +0:21
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let _2: &mut u8; // in scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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let _5: (); // in scope 0 at $DIR/reborrow.rs:+4:5: +4:14
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let mut _6: &mut u8; // in scope 0 at $DIR/reborrow.rs:+4:12: +4:13
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scope 1 {
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debug a => _2; // in scope 1 at $DIR/reborrow.rs:+1:9: +1:10
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let _3: *mut u8; // in scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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scope 2 {
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debug b => _3; // in scope 2 at $DIR/reborrow.rs:+2:9: +2:10
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let _4: &mut u8; // in scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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scope 3 {
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- debug c => _4; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
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+ debug c => _2; // in scope 3 at $DIR/reborrow.rs:+3:9: +3:10
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}
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}
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}
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bb0: {
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- StorageLive(_2); // scope 0 at $DIR/reborrow.rs:+1:9: +1:10
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_2 = &mut _1; // scope 0 at $DIR/reborrow.rs:+1:13: +1:19
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StorageLive(_3); // scope 1 at $DIR/reborrow.rs:+2:9: +2:10
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_3 = &raw mut (*_2); // scope 1 at $DIR/reborrow.rs:+2:13: +2:24
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- StorageLive(_4); // scope 2 at $DIR/reborrow.rs:+3:9: +3:10
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- _4 = move _2; // scope 2 at $DIR/reborrow.rs:+3:13: +3:14
|
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StorageLive(_5); // scope 3 at $DIR/reborrow.rs:+4:5: +4:14
|
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- StorageLive(_6); // scope 3 at $DIR/reborrow.rs:+4:12: +4:13
|
||||
- _6 = move _4; // scope 3 at $DIR/reborrow.rs:+4:12: +4:13
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- _5 = opaque::<&mut u8>(move _6) -> bb1; // scope 3 at $DIR/reborrow.rs:+4:5: +4:14
|
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+ _5 = opaque::<&mut u8>(move _2) -> bb1; // scope 3 at $DIR/reborrow.rs:+4:5: +4:14
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// mir::Constant
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// + span: $DIR/reborrow.rs:22:5: 22:11
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// + literal: Const { ty: fn(&mut u8) {opaque::<&mut u8>}, val: Value(<ZST>) }
|
||||
}
|
||||
|
||||
bb1: {
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||||
- StorageDead(_6); // scope 3 at $DIR/reborrow.rs:+4:13: +4:14
|
||||
StorageDead(_5); // scope 3 at $DIR/reborrow.rs:+4:14: +4:15
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||||
_0 = const (); // scope 0 at $DIR/reborrow.rs:+0:21: +5:2
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||||
- StorageDead(_4); // scope 2 at $DIR/reborrow.rs:+5:1: +5:2
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StorageDead(_3); // scope 1 at $DIR/reborrow.rs:+5:1: +5:2
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- StorageDead(_2); // scope 0 at $DIR/reborrow.rs:+5:1: +5:2
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return; // scope 0 at $DIR/reborrow.rs:+5:2: +5:2
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||||
}
|
||||
}
|
||||
|
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|
|
@ -0,0 +1,46 @@
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// Check that CopyProp considers reborrows as not mutating the pointer.
|
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// unit-test: CopyProp
|
||||
|
||||
#![feature(raw_ref_op)]
|
||||
|
||||
#[inline(never)]
|
||||
fn opaque(_: impl Sized) {}
|
||||
|
||||
// EMIT_MIR reborrow.remut.CopyProp.diff
|
||||
fn remut(mut x: u8) {
|
||||
let a = &mut x;
|
||||
let b = &mut *a; //< this cannot mutate a.
|
||||
let c = a; //< so `c` and `a` can be merged.
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opaque(c);
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||||
}
|
||||
|
||||
// EMIT_MIR reborrow.reraw.CopyProp.diff
|
||||
fn reraw(mut x: u8) {
|
||||
let a = &mut x;
|
||||
let b = &raw mut *a; //< this cannot mutate a.
|
||||
let c = a; //< so `c` and `a` can be merged.
|
||||
opaque(c);
|
||||
}
|
||||
|
||||
// EMIT_MIR reborrow.miraw.CopyProp.diff
|
||||
fn miraw(mut x: u8) {
|
||||
let a = &raw mut x;
|
||||
let b = unsafe { &raw mut *a }; //< this cannot mutate a.
|
||||
let c = a; //< so `c` and `a` can be merged.
|
||||
opaque(c);
|
||||
}
|
||||
|
||||
// EMIT_MIR reborrow.demiraw.CopyProp.diff
|
||||
fn demiraw(mut x: u8) {
|
||||
let a = &raw mut x;
|
||||
let b = unsafe { &mut *a }; //< this cannot mutate a.
|
||||
let c = a; //< so `c` and `a` can be merged.
|
||||
opaque(c);
|
||||
}
|
||||
|
||||
fn main() {
|
||||
remut(0);
|
||||
reraw(0);
|
||||
miraw(0);
|
||||
demiraw(0);
|
||||
}
|
||||
Loading…
Reference in New Issue