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Explicit simplify_place.

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This commit is contained in:
Camille GILLOT 2023-09-26 16:39:39 +00:00
parent b2ff77cb78
commit 901be42bc0
1 changed files with 19 additions and 8 deletions
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27
compiler/rustc_mir_transform/src/gvn.rs
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@ -251,15 +251,25 @@ fn assign(&mut self, local: Local, value: VnIndex) {
}
}
/// Represent the *value* which would be read from `place`.
/// Represent the *value* which would be read from `place`, and point `place` to a preexisting
/// place with the same value (if that already exists).
#[instrument(level = "trace", skip(self), ret)]
fn simplify_place(&mut self, place: &mut Place<'tcx>, location: Location) -> Option<VnIndex> {
// Another place that holds the same value.
fn simplify_place_value(
&mut self,
place: &mut Place<'tcx>,
location: Location,
) -> Option<VnIndex> {
// Invariant: `place` and `place_ref` point to the same value, even if they point to
// different memory locations.
let mut place_ref = place.as_ref();
let mut value = self.locals[place.local]?;
// Invariant: `value` holds the value up-to the `index`th projection excluded.
let mut value = self.locals[place.local]?;
for (index, proj) in place.projection.iter().enumerate() {
if let Some(local) = self.try_as_local(value, location) {
// Both `local` and `Place { local: place.local, projection: projection[..index] }`
// hold the same value. Therefore, following place holds the value in the original
// `place`.
place_ref = PlaceRef { local, projection: &place.projection[index..] };
}
@ -301,7 +311,7 @@ fn simplify_place(&mut self, place: &mut Place<'tcx>, location: Location) -> Opt
}
if let Some(local) = self.try_as_local(value, location)
&& local != place.local
&& local != place.local // in case we had no projection to begin with.
{
*place = local.into();
self.reused_locals.insert(local);
@ -309,6 +319,7 @@ fn simplify_place(&mut self, place: &mut Place<'tcx>, location: Location) -> Opt
} else if place_ref.local != place.local
|| place_ref.projection.len() < place.projection.len()
{
// By the invariant on `place_ref`.
*place = place_ref.project_deeper(&[], self.tcx);
self.reused_locals.insert(place_ref.local);
self.any_replacement = true;
@ -326,7 +337,7 @@ fn simplify_operand(
match *operand {
Operand::Constant(ref constant) => Some(self.insert(Value::Constant(constant.const_))),
Operand::Copy(ref mut place) | Operand::Move(ref mut place) => {
let value = self.simplify_place(place, location)?;
let value = self.simplify_place_value(place, location)?;
if let Some(const_) = self.try_as_constant(value) {
*operand = Operand::Constant(Box::new(const_));
self.any_replacement = true;
@ -379,7 +390,7 @@ fn simplify_rvalue(
// Operations.
Rvalue::Len(ref mut place) => {
let place = self.simplify_place(place, location)?;
let place = self.simplify_place_value(place, location)?;
Value::Len(place)
}
Rvalue::Cast(kind, ref mut value, to) => {
@ -402,7 +413,7 @@ fn simplify_rvalue(
Value::UnaryOp(op, arg)
}
Rvalue::Discriminant(ref mut place) => {
let place = self.simplify_place(place, location)?;
let place = self.simplify_place_value(place, location)?;
Value::Discriminant(place)
}