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Auto merge of #111517 - lukas-code:addr-of-mutate, r=tmiasko

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allow mutating function args through `&raw const`

Fixes https://github.com/rust-lang/rust/issues/111502 by "turning off the sketchy optimization while we figure out if this is ok", like `@JakobDegen` said.

The first commit in this PR removes some suspicious looking logic from the same method, but should have no functional changes, since it doesn't modify the `context` outside of the method. Best reviewed commit by commit.

r? opsem
This commit is contained in:
bors 2023-05-14 10:45:39 +00:00
commit 3603a84a3d
2 changed files with 51 additions and 17 deletions
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34
compiler/rustc_mir_transform/src/deduce_param_attrs.rs
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@ -8,7 +8,7 @@
use rustc_hir::def_id::LocalDefId;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::{Body, Local, Location, Operand, Terminator, TerminatorKind, RETURN_PLACE};
use rustc_middle::mir::{Body, Location, Operand, Place, Terminator, TerminatorKind, RETURN_PLACE};
use rustc_middle::ty::{self, DeducedParamAttrs, Ty, TyCtxt};
use rustc_session::config::OptLevel;
@ -29,31 +29,31 @@ impl DeduceReadOnly {
}
impl<'tcx> Visitor<'tcx> for DeduceReadOnly {
fn visit_local(&mut self, local: Local, mut context: PlaceContext, _: Location) {
fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
// We're only interested in arguments.
if local == RETURN_PLACE || local.index() > self.mutable_args.domain_size() {
if place.local == RETURN_PLACE || place.local.index() > self.mutable_args.domain_size() {
return;
}
// Replace place contexts that are moves with copies. This is safe in all cases except
// function argument position, which we already handled in `visit_terminator()` by using the
// ArgumentChecker. See the comment in that method for more details.
//
// In the future, we might want to move this out into a separate pass, but for now let's
// just do it on the fly because that's faster.
if matches!(context, PlaceContext::NonMutatingUse(NonMutatingUseContext::Move)) {
context = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy);
}
match context {
PlaceContext::MutatingUse(..)
| PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) => {
let mark_as_mutable = match context {
PlaceContext::MutatingUse(..) => {
// This is a mutation, so mark it as such.
self.mutable_args.insert(local.index() - 1);
true
}
PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf) => {
// Whether mutating though a `&raw const` is allowed is still undecided, so we
// disable any sketchy `readonly` optimizations for now.
// But we only need to do this if the pointer would point into the argument.
!place.is_indirect()
}
PlaceContext::NonMutatingUse(..) | PlaceContext::NonUse(..) => {
// Not mutating, so it's fine.
false
}
};
if mark_as_mutable {
self.mutable_args.insert(place.local.index() - 1);
}
}