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Handle discriminants in dataflow-const-prop.

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This commit is contained in:
Camille GILLOT 2023-01-21 22:28:54 +00:00
parent cd3649b2a5
commit 9a6c04f5d0
6 changed files with 311 additions and 65 deletions
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103
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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@ -13,6 +13,7 @@ use rustc_mir_dataflow::value_analysis::{Map, State, TrackElem, ValueAnalysis, V
use rustc_mir_dataflow::{lattice::FlatSet, Analysis, ResultsVisitor, SwitchIntEdgeEffects};
use rustc_span::DUMMY_SP;
use rustc_target::abi::Align;
use rustc_target::abi::VariantIdx;
use crate::MirPass;
@ -30,6 +31,7 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
#[instrument(skip_all level = "debug")]
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!(def_id = ?body.source.def_id());
if tcx.sess.mir_opt_level() < 4 && body.basic_blocks.len() > BLOCK_LIMIT {
debug!("aborted dataflow const prop due too many basic blocks");
return;
@ -63,14 +65,31 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
}
}
struct ConstAnalysis<'tcx> {
struct ConstAnalysis<'a, 'tcx> {
map: Map,
tcx: TyCtxt<'tcx>,
local_decls: &'a LocalDecls<'tcx>,
ecx: InterpCx<'tcx, 'tcx, DummyMachine>,
param_env: ty::ParamEnv<'tcx>,
}
impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> {
impl<'tcx> ConstAnalysis<'_, 'tcx> {
fn eval_disciminant(
&self,
enum_ty: Ty<'tcx>,
variant_index: VariantIdx,
) -> Option<ScalarTy<'tcx>> {
if !enum_ty.is_enum() {
return None;
}
let discr = enum_ty.discriminant_for_variant(self.tcx, variant_index)?;
let discr_layout = self.tcx.layout_of(self.param_env.and(discr.ty)).ok()?;
let discr_value = Scalar::try_from_uint(discr.val, discr_layout.size)?;
Some(ScalarTy(discr_value, discr.ty))
}
}
impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
type Value = FlatSet<ScalarTy<'tcx>>;
const NAME: &'static str = "ConstAnalysis";
@ -79,6 +98,25 @@ 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_disciminant(enum_ty, variant_index) {
state.assign_discr(
place.as_ref(),
ValueOrPlace::Value(FlatSet::Elem(discr)),
&self.map,
);
}
}
}
_ => self.super_statement(statement, state),
}
}
fn handle_assign(
&self,
target: Place<'tcx>,
@ -87,17 +125,22 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> {
) {
match rvalue {
Rvalue::Aggregate(kind, operands) => {
let target = self.map().find(target.as_ref());
if let Some(target) = target {
state.flood_idx_with(target, self.map(), FlatSet::Bottom);
let field_based = match **kind {
AggregateKind::Tuple | AggregateKind::Closure(..) => true,
AggregateKind::Adt(def_id, ..) => {
matches!(self.tcx.def_kind(def_id), DefKind::Struct)
state.flood_with(target.as_ref(), self.map(), FlatSet::Bottom);
if let Some(target_idx) = self.map().find(target.as_ref()) {
let (variant_target, variant_index) = match **kind {
AggregateKind::Tuple | AggregateKind::Closure(..) => {
(Some(target_idx), None)
}
_ => false,
AggregateKind::Adt(def_id, variant_index, ..) => {
match self.tcx.def_kind(def_id) {
DefKind::Struct => (Some(target_idx), None),
DefKind::Enum => (Some(target_idx), Some(variant_index)),
_ => (None, None),
}
}
_ => (None, None),
};
if field_based {
if let Some(target) = variant_target {
for (field_index, operand) in operands.iter().enumerate() {
if let Some(field) = self
.map()
@ -108,15 +151,20 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> {
}
}
}
if let Some(variant_index) = variant_index
&& let Some(discr_idx) = self.map().apply(target_idx, TrackElem::Discriminant)
{
let enum_ty = target.ty(self.local_decls, self.tcx).ty;
if let Some(discr_val) = self.eval_disciminant(enum_ty, variant_index) {
state.assign_idx(discr_idx, ValueOrPlace::Value(FlatSet::Elem(discr_val)), &self.map);
}
}
}
}
Rvalue::CheckedBinaryOp(op, box (left, right)) => {
state.flood(target.as_ref(), self.map());
let target = self.map().find(target.as_ref());
if let Some(target) = target {
// We should not track any projections other than
// what is overwritten below, but just in case...
state.flood_idx(target, self.map());
}
let value_target = target
.and_then(|target| self.map().apply(target, TrackElem::Field(0_u32.into())));
@ -195,6 +243,9 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> {
FlatSet::Bottom => ValueOrPlace::Value(FlatSet::Bottom),
FlatSet::Top => ValueOrPlace::Value(FlatSet::Top),
},
Rvalue::Discriminant(place) => {
ValueOrPlace::Value(state.get_discr(place.as_ref(), self.map()))
}
_ => self.super_rvalue(rvalue, state),
}
}
@ -268,12 +319,13 @@ impl<'tcx> std::fmt::Debug for ScalarTy<'tcx> {
}
}
impl<'tcx> ConstAnalysis<'tcx> {
pub fn new(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, map: Map) -> Self {
impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, map: Map) -> Self {
let param_env = tcx.param_env(body.source.def_id());
Self {
map,
tcx,
local_decls: &body.local_decls,
ecx: InterpCx::new(tcx, DUMMY_SP, param_env, DummyMachine),
param_env: param_env,
}
@ -466,6 +518,21 @@ impl<'tcx, 'map, 'a> Visitor<'tcx> for OperandCollector<'tcx, 'map, 'a> {
_ => (),
}
}
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
match rvalue {
Rvalue::Discriminant(place) => {
match self.state.get_discr(place.as_ref(), self.visitor.map) {
FlatSet::Top => (),
FlatSet::Elem(value) => {
self.visitor.before_effect.insert((location, *place), value);
}
FlatSet::Bottom => (),
}
}
_ => self.super_rvalue(rvalue, location),
}
}
}
struct DummyMachine;