bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Simplify Len.

Browse source
This commit is contained in:
Camille GILLOT 2023-03-20 20:15:59 +00:00
parent 5fc23ad8e6
commit 3c48243b6f
15 changed files with 96 additions and 52 deletions
Download patch file Download diff file Expand all files Collapse all files

38
compiler/rustc_mir_transform/src/gvn.rs
View file

@ -776,10 +776,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
}
// Operations.
Rvalue::Len(ref mut place) => {
let place = self.simplify_place_value(place, location)?;
Value::Len(place)
}
Rvalue::Len(ref mut place) => return self.simplify_len(place, location),
Rvalue::Cast(kind, ref mut value, to) => {
let from = value.ty(self.local_decls, self.tcx);
let value = self.simplify_operand(value, location)?;
@ -1021,6 +1018,39 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
Some(result)
}
}
fn simplify_len(&mut self, place: &mut Place<'tcx>, location: Location) -> Option<VnIndex> {
// Trivial case: we are fetching a statically known length.
let place_ty = place.ty(self.local_decls, self.tcx).ty;
if let ty::Array(_, len) = place_ty.kind() {
return self.insert_constant(Const::from_ty_const(*len, self.tcx));
}
let mut inner = self.simplify_place_value(place, location)?;
// The length information is stored in the fat pointer.
// Reborrowing copies length information from one pointer to the other.
while let Value::Address { place: borrowed, .. } = self.get(inner)
&& let [PlaceElem::Deref] = borrowed.projection[..]
&& let Some(borrowed) = self.locals[borrowed.local]
{
inner = borrowed;
}
// We have an unsizing cast, which assigns the length to fat pointer metadata.
if let Value::Cast { kind, from, to, .. } = self.get(inner)
&& let CastKind::PointerCoercion(ty::adjustment::PointerCoercion::Unsize) = kind
&& let Some(from) = from.builtin_deref(true)
&& let ty::Array(_, len) = from.ty.kind()
&& let Some(to) = to.builtin_deref(true)
&& let ty::Slice(..) = to.ty.kind()
{
return self.insert_constant(Const::from_ty_const(*len, self.tcx));
}
// Fallback: a symbolic `Len`.
Some(self.insert(Value::Len(inner)))
}
}
fn op_to_prop_const<'tcx>(