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Make needs_drop less pessimistic on generators

This commit is contained in:
Jonas Schievink 2020-03-15 00:24:47 +01:00
parent 8d67f576b5
commit 50c1c295ee
4 changed files with 29 additions and 18 deletions

View file

@ -1047,10 +1047,7 @@ pub fn needs_drop_components(
// Foreign types can never have destructors.
ty::Foreign(..) => Ok(SmallVec::new()),
// Pessimistically assume that all generators will require destructors
// as we don't know if a destructor is a noop or not until after the MIR
// state transformation pass.
ty::Generator(..) | ty::Dynamic(..) | ty::Error => Err(AlwaysRequiresDrop),
ty::Dynamic(..) | ty::Error => Err(AlwaysRequiresDrop),
ty::Slice(ty) => needs_drop_components(ty, target_layout),
ty::Array(elem_ty, size) => {
@ -1083,7 +1080,8 @@ pub fn needs_drop_components(
| ty::Placeholder(..)
| ty::Opaque(..)
| ty::Infer(_)
| ty::Closure(..) => Ok(smallvec![ty]),
| ty::Closure(..)
| ty::Generator(..) => Ok(smallvec![ty]),
}
}

View file

@ -99,6 +99,23 @@ where
}
}
ty::Generator(def_id, substs, _) => {
let substs = substs.as_generator();
for upvar_ty in substs.upvar_tys(def_id, tcx) {
queue_type(self, upvar_ty);
}
let witness = substs.witness(def_id, tcx);
let interior_tys = match &witness.kind {
ty::GeneratorWitness(tys) => tcx.erase_late_bound_regions(tys),
_ => bug!(),
};
for interior_ty in interior_tys {
queue_type(self, interior_ty);
}
}
// Check for a `Drop` impl and whether this is a union or
// `ManuallyDrop`. If it's a struct or enum without a `Drop`
// impl then check whether the field types need `Drop`.

View file

@ -1,19 +1,16 @@
error[E0597]: `a` does not live long enough
--> $DIR/borrowing.rs:9:33
|
LL | let _b = {
| -- borrow later stored here
LL | let a = 3;
LL | Pin::new(&mut || yield &a).resume(())
| ----------^
| | |
| | borrowed value does not live long enough
| -- ^ borrowed value does not live long enough
| |
| value captured here by generator
| a temporary with access to the borrow is created here ...
LL |
LL | };
| -- ... and the borrow might be used here, when that temporary is dropped and runs the destructor for generator
| |
| `a` dropped here while still borrowed
|
= note: The temporary is part of an expression at the end of a block. Consider forcing this temporary to be dropped sooner, before the block's local variables are dropped. For example, you could save the expression's value in a new local variable `x` and then make `x` be the expression at the end of the block.
| - `a` dropped here while still borrowed
error[E0597]: `a` does not live long enough
--> $DIR/borrowing.rs:16:20

View file

@ -4,10 +4,9 @@ error[E0499]: cannot borrow `thing` as mutable more than once at a time
LL | gen.as_mut().resume(&mut thing);
| ---------- first mutable borrow occurs here
LL | gen.as_mut().resume(&mut thing);
| ^^^^^^^^^^ second mutable borrow occurs here
LL |
LL | }
| - first borrow might be used here, when `gen` is dropped and runs the destructor for generator
| ------ ^^^^^^^^^^ second mutable borrow occurs here
| |
| first borrow later used by call
error: aborting due to previous error