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use rustc_middle::mir::visit::{
MutatingUseContext, NonMutatingUseContext, NonUseContext, PlaceContext,
};
#[derive(Eq, PartialEq, Clone)]
pub enum DefUse {
Def,
Use,
Drop,
}
pub fn categorize(context: PlaceContext) -> Option<DefUse> {
match context {
///////////////////////////////////////////////////////////////////////////
// DEFS
PlaceContext::MutatingUse(MutatingUseContext::Store) |
// We let Call define the result in both the success and
// unwind cases. This is not really correct, however it
// does not seem to be observable due to the way that we
// generate MIR. To do things properly, we would apply
// the def in call only to the input from the success
// path and not the unwind path. -nmatsakis
PlaceContext::MutatingUse(MutatingUseContext::Call) |
PlaceContext::MutatingUse(MutatingUseContext::AsmOutput) |
PlaceContext::MutatingUse(MutatingUseContext::Yield) |
// Storage live and storage dead aren't proper defines, but we can ignore
// values that come before them.
PlaceContext::NonUse(NonUseContext::StorageLive) |
PlaceContext::NonUse(NonUseContext::StorageDead) => Some(DefUse::Def),
///////////////////////////////////////////////////////////////////////////
// REGULAR USES
//
// These are uses that occur *outside* of a drop. For the
// purposes of NLL, these are special in that **all** the
// lifetimes appearing in the variable must be live for each regular use.
PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) |
PlaceContext::MutatingUse(MutatingUseContext::Projection) |
// Borrows only consider their local used at the point of the borrow.
// This won't affect the results since we use this analysis for generators
// and we only care about the result at suspension points. Borrows cannot
// cross suspension points so this behavior is unproblematic.
PlaceContext::MutatingUse(MutatingUseContext::Borrow) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow) |
PlaceContext::MutatingUse(MutatingUseContext::AddressOf) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) |
PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) |
PlaceContext::NonUse(NonUseContext::AscribeUserTy) |
PlaceContext::MutatingUse(MutatingUseContext::Retag) =>
Some(DefUse::Use),
///////////////////////////////////////////////////////////////////////////
// DROP USES
//
// These are uses that occur in a DROP (a MIR drop, not a
// call to `std::mem::drop()`). For the purposes of NLL,
// uses in drop are special because `#[may_dangle]`
// attributes can affect whether lifetimes must be live.
PlaceContext::MutatingUse(MutatingUseContext::Drop) =>
Some(DefUse::Drop),
// Debug info is neither def nor use.
PlaceContext::NonUse(NonUseContext::VarDebugInfo) => None,
PlaceContext::MutatingUse(MutatingUseContext::Deinit | MutatingUseContext::SetDiscriminant) => {
bug!("These statements are not allowed in this MIR phase")
}
}
}
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