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Rollup merge of #110954 - cjgillot:const-prop-ref, r=wesleywiser
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Reject borrows of projections in ConstProp.

Fixes #110947
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JohnTitor authored May 5, 2023
2 parents d98e174 + 1ffe905 commit 18d4e22
Showing 5 changed files with 80 additions and 9 deletions.
20 changes: 15 additions & 5 deletions compiler/rustc_mir_transform/src/const_prop.rs
Original file line number Diff line number Diff line change
@@ -714,13 +714,22 @@ impl CanConstProp {
}
}

impl Visitor<'_> for CanConstProp {
impl<'tcx> Visitor<'tcx> for CanConstProp {
fn visit_place(&mut self, place: &Place<'tcx>, mut context: PlaceContext, loc: Location) {
use rustc_middle::mir::visit::PlaceContext::*;

// Dereferencing just read the addess of `place.local`.
if place.projection.first() == Some(&PlaceElem::Deref) {
context = NonMutatingUse(NonMutatingUseContext::Copy);
}

self.visit_local(place.local, context, loc);
self.visit_projection(place.as_ref(), context, loc);
}

fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
use rustc_middle::mir::visit::PlaceContext::*;
match context {
// Projections are fine, because `&mut foo.x` will be caught by
// `MutatingUseContext::Borrow` elsewhere.
MutatingUse(MutatingUseContext::Projection)
// These are just stores, where the storing is not propagatable, but there may be later
// mutations of the same local via `Store`
| MutatingUse(MutatingUseContext::Call)
@@ -751,7 +760,6 @@ impl Visitor<'_> for CanConstProp {
NonMutatingUse(NonMutatingUseContext::Copy)
| NonMutatingUse(NonMutatingUseContext::Move)
| NonMutatingUse(NonMutatingUseContext::Inspect)
| NonMutatingUse(NonMutatingUseContext::Projection)
| NonMutatingUse(NonMutatingUseContext::PlaceMention)
| NonUse(_) => {}

@@ -771,6 +779,8 @@ impl Visitor<'_> for CanConstProp {
trace!("local {:?} can't be propagated because it's used: {:?}", local, context);
self.can_const_prop[local] = ConstPropMode::NoPropagation;
}
MutatingUse(MutatingUseContext::Projection)
| NonMutatingUse(NonMutatingUseContext::Projection) => bug!("visit_place should not pass {context:?} for {local:?}"),
}
}
}
46 changes: 46 additions & 0 deletions tests/mir-opt/const_prop/address_of_pair.fn0.ConstProp.diff
Original file line number Diff line number Diff line change
@@ -0,0 +1,46 @@
- // MIR for `fn0` before ConstProp
+ // MIR for `fn0` after ConstProp

fn fn0() -> bool {
let mut _0: bool; // return place in scope 0 at $DIR/address_of_pair.rs:+0:17: +0:21
let mut _1: !; // in scope 0 at $DIR/address_of_pair.rs:+0:22: +9:2
let mut _2: (i32, bool); // in scope 0 at $DIR/address_of_pair.rs:+1:9: +1:17
let _4: (); // in scope 0 at $DIR/address_of_pair.rs:+4:5: +6:6
let mut _6: bool; // in scope 0 at $DIR/address_of_pair.rs:+7:16: +7:22
scope 1 {
debug pair => _2; // in scope 1 at $DIR/address_of_pair.rs:+1:9: +1:17
let _3: *mut bool; // in scope 1 at $DIR/address_of_pair.rs:+2:9: +2:12
scope 2 {
debug ptr => _3; // in scope 2 at $DIR/address_of_pair.rs:+2:9: +2:12
let _5: bool; // in scope 2 at $DIR/address_of_pair.rs:+7:9: +7:12
scope 3 {
}
scope 4 {
debug ret => _5; // in scope 4 at $DIR/address_of_pair.rs:+7:9: +7:12
}
}
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/address_of_pair.rs:+1:9: +1:17
_2 = (const 1_i32, const false); // scope 0 at $DIR/address_of_pair.rs:+1:20: +1:30
StorageLive(_3); // scope 1 at $DIR/address_of_pair.rs:+2:9: +2:12
_3 = &raw mut (_2.1: bool); // scope 1 at $SRC_DIR/core/src/ptr/mod.rs:LL:COL
_2 = (const 1_i32, const false); // scope 2 at $DIR/address_of_pair.rs:+3:5: +3:22
StorageLive(_4); // scope 2 at $DIR/address_of_pair.rs:+4:5: +6:6
(*_3) = const true; // scope 3 at $DIR/address_of_pair.rs:+5:9: +5:20
_4 = const (); // scope 3 at $DIR/address_of_pair.rs:+4:5: +6:6
StorageDead(_4); // scope 2 at $DIR/address_of_pair.rs:+6:5: +6:6
StorageLive(_5); // scope 2 at $DIR/address_of_pair.rs:+7:9: +7:12
StorageLive(_6); // scope 2 at $DIR/address_of_pair.rs:+7:16: +7:22
_6 = (_2.1: bool); // scope 2 at $DIR/address_of_pair.rs:+7:16: +7:22
_5 = Not(move _6); // scope 2 at $DIR/address_of_pair.rs:+7:15: +7:22
StorageDead(_6); // scope 2 at $DIR/address_of_pair.rs:+7:21: +7:22
_0 = _5; // scope 4 at $DIR/address_of_pair.rs:+8:12: +8:15
StorageDead(_5); // scope 2 at $DIR/address_of_pair.rs:+9:1: +9:2
StorageDead(_3); // scope 1 at $DIR/address_of_pair.rs:+9:1: +9:2
StorageDead(_2); // scope 0 at $DIR/address_of_pair.rs:+9:1: +9:2
return; // scope 0 at $DIR/address_of_pair.rs:+9:2: +9:2
}
}

17 changes: 17 additions & 0 deletions tests/mir-opt/const_prop/address_of_pair.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
// unit-test: ConstProp

// EMIT_MIR address_of_pair.fn0.ConstProp.diff
pub fn fn0() -> bool {
let mut pair = (1, false);
let ptr = core::ptr::addr_of_mut!(pair.1);
pair = (1, false);
unsafe {
*ptr = true;
}
let ret = !pair.1;
return ret;
}

pub fn main() {
println!("{}", fn0());
}
3 changes: 1 addition & 2 deletions tests/mir-opt/const_prop_miscompile.bar.ConstProp.diff
Original file line number Diff line number Diff line change
@@ -19,8 +19,7 @@

bb0: {
StorageLive(_1); // scope 0 at $DIR/const_prop_miscompile.rs:+1:9: +1:14
- _1 = (const 1_i32,); // scope 0 at $DIR/const_prop_miscompile.rs:+1:17: +1:21
+ _1 = const (1_i32,); // scope 0 at $DIR/const_prop_miscompile.rs:+1:17: +1:21
_1 = (const 1_i32,); // scope 0 at $DIR/const_prop_miscompile.rs:+1:17: +1:21
StorageLive(_2); // scope 1 at $DIR/const_prop_miscompile.rs:+2:5: +4:6
StorageLive(_3); // scope 2 at $DIR/const_prop_miscompile.rs:+3:10: +3:22
_3 = &raw mut (_1.0: i32); // scope 2 at $DIR/const_prop_miscompile.rs:+3:10: +3:22
3 changes: 1 addition & 2 deletions tests/mir-opt/const_prop_miscompile.foo.ConstProp.diff
Original file line number Diff line number Diff line change
@@ -16,8 +16,7 @@

bb0: {
StorageLive(_1); // scope 0 at $DIR/const_prop_miscompile.rs:+1:9: +1:14
- _1 = (const 1_i32,); // scope 0 at $DIR/const_prop_miscompile.rs:+1:17: +1:21
+ _1 = const (1_i32,); // scope 0 at $DIR/const_prop_miscompile.rs:+1:17: +1:21
_1 = (const 1_i32,); // scope 0 at $DIR/const_prop_miscompile.rs:+1:17: +1:21
StorageLive(_2); // scope 1 at $DIR/const_prop_miscompile.rs:+2:6: +2:14
_2 = &mut (_1.0: i32); // scope 1 at $DIR/const_prop_miscompile.rs:+2:6: +2:14
(*_2) = const 5_i32; // scope 1 at $DIR/const_prop_miscompile.rs:+2:5: +2:18

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