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consider assignments of union field of ManuallyDrop type safe #78068

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Merged
merged 7 commits into from
Dec 15, 2020
Merged

consider assignments of union field of ManuallyDrop type safe #78068

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3ac1df8
consider assignments of union field of ManuallyDrop type safe
RalfJung Oct 18, 2020
64856e2
adjust union access unsafety check logic to take into account Deref a…
RalfJung Oct 24, 2020
63bdb3a
improve formatting
RalfJung Oct 26, 2020
af309cc
needs -> might need
RalfJung Oct 28, 2020
df1c55a
add function to iterate through all sub-places, and add PlaceRef::ty
RalfJung Nov 20, 2020
571da2c
refactor unsafety checking of places
RalfJung Nov 21, 2020
0bb82c4
expand iter_projections comment
RalfJung Nov 28, 2020
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9 changes: 9 additions & 0 deletions compiler/rustc_middle/src/mir/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1741,6 +1741,15 @@ impl<'tcx> Place<'tcx> {
pub fn as_ref(&self) -> PlaceRef<'tcx> {
PlaceRef { local: self.local, projection: &self.projection }
}

/// Iterate over the projections in evaluation order, i.e., the first element is the base with
/// its projection and then subsequently more projections are added.
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I think it would be useful to give an example based on Rust code. For example:

Given the place a.b.c, this would yield:

  • (a, b)
  • (a.b, c)

I am a bit surprised by this structure -- I guess I expected it to return a, a.b, and a.b.c, rather than a tuple, and to have people match on the "tail" projection (if any). But I guess this is ok too.

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I expanded the comment.

I expected it to return a, a.b, and a.b.c, rather than a tuple, and to have people match on the "tail" projection (if any). But I guess this is ok too.

I first thought of something like this, but it doesn't really match what clients need, at least what this particular client needs. The point is to check the projections, so the iterator really should yield as often as there are projections. And given that it also seemed odd to not make the projection itself directly available.

In a follow-up PR I hope to port more clients to this API, I guess then we will see how generally useful it is.

pub fn iter_projections(self) -> impl Iterator<Item=(PlaceRef<'tcx>, PlaceElem<'tcx>)> + DoubleEndedIterator {
self.projection.iter().enumerate().map(move |(i, proj)| {
let base = PlaceRef { local: self.local, projection: &self.projection[..i] };
(base, proj)
})
}
}

impl From<Local> for Place<'_> {
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9 changes: 9 additions & 0 deletions compiler/rustc_middle/src/mir/tcx.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,15 @@ impl<'tcx> Place<'tcx> {
}
}

impl<'tcx> PlaceRef<'tcx> {
pub fn ty<D>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> PlaceTy<'tcx>
where
D: HasLocalDecls<'tcx>,
{
Place::ty_from(self.local, &self.projection, local_decls, tcx)
}
}

pub enum RvalueInitializationState {
Shallow,
Deep,
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