bjoernager/rust
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Improve documentation, plus some small changes

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This commit is contained in:
Jannis Christopher Köhl 2022-10-19 15:56:58 +02:00
parent 931d99f61f
commit 274a49132b
4 changed files with 160 additions and 106 deletions
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24
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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@ -1,10 +1,14 @@
//! A constant propagation optimization pass based on dataflow analysis.
//!
//! Tracks places that have a scalar type.
use rustc_const_eval::interpret::{ConstValue, ImmTy, Immediate, InterpCx, Scalar};
use rustc_data_structures::fx::FxHashMap;
use rustc_middle::mir::visit::{MutVisitor, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_mir_dataflow::value_analysis::{
Map, ProjElem, State, ValueAnalysis, ValueOrPlace, ValueOrPlaceOrRef,
HasTop, Map, State, TrackElem, ValueAnalysis, ValueOrPlace, ValueOrPlaceOrRef,
};
use rustc_mir_dataflow::{lattice::FlatSet, Analysis, ResultsVisitor, SwitchIntEdgeEffects};
use rustc_span::{sym, DUMMY_SP};
@ -20,7 +24,7 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// Decide which places to track during the analysis.
let map = Map::from_filter(tcx, body, |ty| ty.is_scalar() && !ty.is_unsafe_ptr());
let map = Map::from_filter(tcx, body, Ty::is_scalar);
// Perform the actual dataflow analysis.
let analysis = ConstAnalysis::new(tcx, body, map);
@ -65,12 +69,10 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> {
state.flood_idx(target, self.map());
}
let value_target = target.and_then(|target| {
self.map().apply_elem(target, ProjElem::Field(0_u32.into()))
});
let overflow_target = target.and_then(|target| {
self.map().apply_elem(target, ProjElem::Field(1_u32.into()))
});
let value_target = target
.and_then(|target| self.map().apply(target, TrackElem::Field(0_u32.into())));
let overflow_target = target
.and_then(|target| self.map().apply(target, TrackElem::Field(1_u32.into())));
if value_target.is_some() || overflow_target.is_some() {
let (val, overflow) = self.binary_op(state, *op, left, right);
@ -211,6 +213,7 @@ struct ScalarTy<'tcx>(Scalar, Ty<'tcx>);
impl<'tcx> std::fmt::Debug for ScalarTy<'tcx> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
// This is used for dataflow visualization, so we return something more concise.
std::fmt::Display::fmt(&ConstantKind::Val(ConstValue::Scalar(self.0), self.1), f)
}
}
@ -341,13 +344,16 @@ impl<'mir, 'tcx, 'map> ResultsVisitor<'mir, 'tcx> for CollectAndPatch<'tcx, 'map
location: Location,
) {
match statement.kind {
StatementKind::Assign(box (_, Rvalue::Use(Operand::Constant(_)))) => {
// Don't overwrite the assignment if it already uses a constant (to keep the span).
}
StatementKind::Assign(box (place, _)) => match state.get(place.as_ref(), self.map) {
FlatSet::Top => (),
FlatSet::Elem(value) => {
self.assignments.insert(location, value);
}
FlatSet::Bottom => {
// This statement is not reachable. Do nothing, it will (hopefully) be removed.
// This assignment is either unreachable, or an uninitialized value is assigned.
}
},
_ => (),