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Auto merge of #110820 - cjgillot:faster-dcp, r=oli-obk

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Optimize dataflow-const-prop place-tracking infra

Optimization opportunities found while investigating https://github.com/rust-lang/rust/pull/110719

Computing places breadth-first ensures that we create short projections before deep projections, since the former are more likely to be propagated.

The most relevant is the pre-computation of flooded places. Callgrind showed `flood_*` methods and especially `preorder_preinvoke` were especially hot. This PR attempts to pre-compute the set of `ValueIndex` that `preorder_invoke` would visit.

Using this information, we make some `PlaceIndex` inaccessible when they contain no `ValueIndex`, allowing to skip computations for those places.

cc `@jachris` as original author
This commit is contained in:
bors 2023-05-10 20:54:31 +00:00
commit 9a767b6b9e
3 changed files with 183 additions and 141 deletions
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34
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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@ -79,22 +79,22 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
&self.map
}
fn handle_statement(&self, statement: &Statement<'tcx>, state: &mut State<Self::Value>) {
match statement.kind {
StatementKind::SetDiscriminant { box ref place, variant_index } => {
state.flood_discr(place.as_ref(), &self.map);
if self.map.find_discr(place.as_ref()).is_some() {
let enum_ty = place.ty(self.local_decls, self.tcx).ty;
if let Some(discr) = self.eval_discriminant(enum_ty, variant_index) {
state.assign_discr(
place.as_ref(),
ValueOrPlace::Value(FlatSet::Elem(discr)),
&self.map,
);
}
}
fn handle_set_discriminant(
&self,
place: Place<'tcx>,
variant_index: VariantIdx,
state: &mut State<Self::Value>,
) {
state.flood_discr(place.as_ref(), &self.map);
if self.map.find_discr(place.as_ref()).is_some() {
let enum_ty = place.ty(self.local_decls, self.tcx).ty;
if let Some(discr) = self.eval_discriminant(enum_ty, variant_index) {
state.assign_discr(
place.as_ref(),
ValueOrPlace::Value(FlatSet::Elem(discr)),
&self.map,
);
}
_ => self.super_statement(statement, state),
}
}
@ -208,8 +208,8 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
_ => unreachable!(),
}
.map(|result| ValueOrPlace::Value(self.wrap_immediate(result, *ty)))
.unwrap_or(ValueOrPlace::top()),
_ => ValueOrPlace::top(),
.unwrap_or(ValueOrPlace::TOP),
_ => ValueOrPlace::TOP,
},
Rvalue::BinaryOp(op, box (left, right)) => {
// Overflows must be ignored here.