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Rollup merge of #97597 - tmiasko:simplify-locals-side-effects, r=RalfJung,JakobDegen
Preserve unused pointer to address casts Fixes #97421. cc `@RalfJung`
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commit
d380b457d8
@ -2605,9 +2605,34 @@ pub enum Rvalue<'tcx> {
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static_assert_size!(Rvalue<'_>, 40);
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impl<'tcx> Rvalue<'tcx> {
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/// Returns true if rvalue can be safely removed when the result is unused.
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#[inline]
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pub fn is_pointer_int_cast(&self) -> bool {
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matches!(self, Rvalue::Cast(CastKind::PointerExposeAddress, _, _))
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pub fn is_safe_to_remove(&self) -> bool {
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match self {
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// Pointer to int casts may be side-effects due to exposing the provenance.
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// While the model is undecided, we should be conservative. See
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// <https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html>
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Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => false,
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Rvalue::Use(_)
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| Rvalue::Repeat(_, _)
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| Rvalue::Ref(_, _, _)
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| Rvalue::ThreadLocalRef(_)
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| Rvalue::AddressOf(_, _)
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| Rvalue::Len(_)
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| Rvalue::Cast(
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CastKind::Misc | CastKind::Pointer(_) | CastKind::PointerFromExposedAddress,
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_,
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_,
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)
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| Rvalue::BinaryOp(_, _)
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| Rvalue::CheckedBinaryOp(_, _)
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| Rvalue::NullaryOp(_, _)
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| Rvalue::UnaryOp(_, _)
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| Rvalue::Discriminant(_)
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| Rvalue::Aggregate(_, _)
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| Rvalue::ShallowInitBox(_, _) => true,
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}
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}
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}
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@ -244,13 +244,10 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeTransitiveLiveLocals<'a> {
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// Compute the place that we are storing to, if any
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let destination = match &statement.kind {
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StatementKind::Assign(assign) => {
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if assign.1.is_pointer_int_cast() {
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// Pointer to int casts may be side-effects due to exposing the provenance.
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// While the model is undecided, we should be conservative. See
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// <https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html>
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None
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} else {
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if assign.1.is_safe_to_remove() {
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Some(assign.0)
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} else {
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None
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}
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}
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StatementKind::SetDiscriminant { place, .. } | StatementKind::Deinit(place) => {
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@ -34,7 +34,7 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, borrowed: &BitS
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for (statement_index, statement) in bb_data.statements.iter().enumerate().rev() {
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let loc = Location { block: bb, statement_index };
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if let StatementKind::Assign(assign) = &statement.kind {
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if assign.1.is_pointer_int_cast() {
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if !assign.1.is_safe_to_remove() {
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continue;
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}
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}
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@ -494,8 +494,12 @@ impl<'tcx> Visitor<'tcx> for UsedLocals {
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StatementKind::StorageLive(_local) | StatementKind::StorageDead(_local) => {}
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StatementKind::Assign(box (ref place, ref rvalue)) => {
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self.visit_lhs(place, location);
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self.visit_rvalue(rvalue, location);
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if rvalue.is_safe_to_remove() {
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self.visit_lhs(place, location);
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self.visit_rvalue(rvalue, location);
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} else {
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self.super_statement(statement, location);
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}
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}
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StatementKind::SetDiscriminant { ref place, variant_index: _ }
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@ -62,6 +62,12 @@ fn t4() -> u32 {
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unsafe { X + 1 }
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}
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// EMIT_MIR simplify_locals.expose_addr.SimplifyLocals.diff
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fn expose_addr(p: *const usize) {
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// Used pointer to address cast. Has a side effect of exposing the provenance.
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p as usize;
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}
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fn main() {
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c();
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d1();
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@ -71,4 +77,5 @@ fn main() {
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t2();
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t3();
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t4();
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expose_addr(&0);
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}
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@ -0,0 +1,21 @@
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- // MIR for `expose_addr` before SimplifyLocals
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+ // MIR for `expose_addr` after SimplifyLocals
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fn expose_addr(_1: *const usize) -> () {
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debug p => _1; // in scope 0 at $DIR/simplify-locals.rs:66:16: 66:17
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let mut _0: (); // return place in scope 0 at $DIR/simplify-locals.rs:66:33: 66:33
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let _2: usize; // in scope 0 at $DIR/simplify-locals.rs:68:5: 68:15
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let mut _3: *const usize; // in scope 0 at $DIR/simplify-locals.rs:68:5: 68:6
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bb0: {
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StorageLive(_2); // scope 0 at $DIR/simplify-locals.rs:68:5: 68:15
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StorageLive(_3); // scope 0 at $DIR/simplify-locals.rs:68:5: 68:6
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_3 = _1; // scope 0 at $DIR/simplify-locals.rs:68:5: 68:6
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_2 = move _3 as usize (PointerExposeAddress); // scope 0 at $DIR/simplify-locals.rs:68:5: 68:15
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StorageDead(_3); // scope 0 at $DIR/simplify-locals.rs:68:14: 68:15
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StorageDead(_2); // scope 0 at $DIR/simplify-locals.rs:68:15: 68:16
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_0 = const (); // scope 0 at $DIR/simplify-locals.rs:66:33: 69:2
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return; // scope 0 at $DIR/simplify-locals.rs:69:2: 69:2
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}
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}
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