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Auto merge of #115797 - cjgillot:const-prop-noclone, r=oli-obk

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Do not clone the Body for ConstProp

~Based on https://github.com/rust-lang/rust/pull/115748 for the `POST_MONO_CHECKS` flag.~
This commit is contained in:
bors 2023-09-13 16:30:07 +00:00
commit 5adddad28c
4 changed files with 114 additions and 136 deletions
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117
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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@ -7,10 +7,10 @@ use rustc_const_eval::interpret::{ImmTy, Immediate, InterpCx, OpTy, Projectable}
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def::DefKind;
use rustc_middle::mir::interpret::{AllocId, ConstAllocation, ConstValue, InterpResult, Scalar};
use rustc_middle::mir::visit::{MutVisitor, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_mir_dataflow::value_analysis::{
Map, PlaceIndex, State, TrackElem, ValueAnalysis, ValueAnalysisWrapper, ValueOrPlace,
};
@ -60,13 +60,10 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
.in_scope(|| analysis.wrap().into_engine(tcx, body).iterate_to_fixpoint());
// Collect results and patch the body afterwards.
let mut visitor = CollectAndPatch::new(tcx, &body.local_decls);
let mut visitor = Collector::new(tcx, &body.local_decls);
debug_span!("collect").in_scope(|| results.visit_reachable_with(body, &mut visitor));
debug_span!("patch").in_scope(|| {
for (block, bbdata) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
visitor.visit_basic_block_data(block, bbdata);
}
})
let mut patch = visitor.patch;
debug_span!("patch").in_scope(|| patch.visit_body_preserves_cfg(body));
}
}
@ -515,41 +512,55 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
}
}
struct CollectAndPatch<'tcx, 'locals> {
pub(crate) struct Patch<'tcx> {
tcx: TyCtxt<'tcx>,
local_decls: &'locals LocalDecls<'tcx>,
/// For a given MIR location, this stores the values of the operands used by that location. In
/// particular, this is before the effect, such that the operands of `_1 = _1 + _2` are
/// properly captured. (This may become UB soon, but it is currently emitted even by safe code.)
before_effect: FxHashMap<(Location, Place<'tcx>), ScalarInt>,
pub(crate) before_effect: FxHashMap<(Location, Place<'tcx>), ConstantKind<'tcx>>,
/// Stores the assigned values for assignments where the Rvalue is constant.
assignments: FxHashMap<Location, ScalarInt>,
pub(crate) assignments: FxHashMap<Location, ConstantKind<'tcx>>,
}
impl<'tcx, 'locals> CollectAndPatch<'tcx, 'locals> {
fn new(tcx: TyCtxt<'tcx>, local_decls: &'locals LocalDecls<'tcx>) -> Self {
Self {
tcx,
local_decls,
before_effect: FxHashMap::default(),
assignments: FxHashMap::default(),
}
impl<'tcx> Patch<'tcx> {
pub(crate) fn new(tcx: TyCtxt<'tcx>) -> Self {
Self { tcx, before_effect: FxHashMap::default(), assignments: FxHashMap::default() }
}
fn make_operand(&self, scalar: ScalarInt, ty: Ty<'tcx>) -> Operand<'tcx> {
Operand::Constant(Box::new(Constant {
span: DUMMY_SP,
user_ty: None,
literal: ConstantKind::Val(ConstValue::Scalar(scalar.into()), ty),
}))
fn make_operand(&self, literal: ConstantKind<'tcx>) -> Operand<'tcx> {
Operand::Constant(Box::new(Constant { span: DUMMY_SP, user_ty: None, literal }))
}
}
struct Collector<'tcx, 'locals> {
patch: Patch<'tcx>,
local_decls: &'locals LocalDecls<'tcx>,
}
impl<'tcx, 'locals> Collector<'tcx, 'locals> {
pub(crate) fn new(tcx: TyCtxt<'tcx>, local_decls: &'locals LocalDecls<'tcx>) -> Self {
Self { patch: Patch::new(tcx), local_decls }
}
fn try_make_constant(
&self,
place: Place<'tcx>,
state: &State<FlatSet<Scalar>>,
map: &Map,
) -> Option<ConstantKind<'tcx>> {
let FlatSet::Elem(Scalar::Int(value)) = state.get(place.as_ref(), &map) else {
return None;
};
let ty = place.ty(self.local_decls, self.patch.tcx).ty;
Some(ConstantKind::Val(ConstValue::Scalar(value.into()), ty))
}
}
impl<'mir, 'tcx>
ResultsVisitor<'mir, 'tcx, Results<'tcx, ValueAnalysisWrapper<ConstAnalysis<'_, 'tcx>>>>
for CollectAndPatch<'tcx, '_>
for Collector<'tcx, '_>
{
type FlowState = State<FlatSet<Scalar>>;
@ -581,10 +592,8 @@ impl<'mir, 'tcx>
// Don't overwrite the assignment if it already uses a constant (to keep the span).
}
StatementKind::Assign(box (place, _)) => {
if let FlatSet::Elem(Scalar::Int(value)) =
state.get(place.as_ref(), &results.analysis.0.map)
{
self.assignments.insert(location, value);
if let Some(value) = self.try_make_constant(place, state, &results.analysis.0.map) {
self.patch.assignments.insert(location, value);
}
}
_ => (),
@ -603,7 +612,7 @@ impl<'mir, 'tcx>
}
}
impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx, '_> {
impl<'tcx> MutVisitor<'tcx> for Patch<'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}
@ -612,8 +621,7 @@ impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx, '_> {
if let Some(value) = self.assignments.get(&location) {
match &mut statement.kind {
StatementKind::Assign(box (_, rvalue)) => {
let ty = rvalue.ty(self.local_decls, self.tcx);
*rvalue = Rvalue::Use(self.make_operand(*value, ty));
*rvalue = Rvalue::Use(self.make_operand(*value));
}
_ => bug!("found assignment info for non-assign statement"),
}
@ -626,8 +634,7 @@ impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx, '_> {
match operand {
Operand::Copy(place) | Operand::Move(place) => {
if let Some(value) = self.before_effect.get(&(location, *place)) {
let ty = place.ty(self.local_decls, self.tcx).ty;
*operand = self.make_operand(*value, ty);
*operand = self.make_operand(*value);
} else if !place.projection.is_empty() {
self.super_operand(operand, location)
}
@ -641,11 +648,11 @@ impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx, '_> {
elem: PlaceElem<'tcx>,
location: Location,
) -> Option<PlaceElem<'tcx>> {
if let PlaceElem::Index(local) = elem
&& let Some(value) = self.before_effect.get(&(location, local.into()))
&& let Ok(offset) = value.try_to_target_usize(self.tcx)
&& let Some(min_length) = offset.checked_add(1)
{
if let PlaceElem::Index(local) = elem {
let offset = self.before_effect.get(&(location, local.into()))?;
let offset = offset.try_to_scalar()?;
let offset = offset.to_target_usize(&self.tcx).ok()?;
let min_length = offset.checked_add(1)?;
Some(PlaceElem::ConstantIndex { offset, min_length, from_end: false })
} else {
None
@ -655,29 +662,35 @@ impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx, '_> {
struct OperandCollector<'tcx, 'map, 'locals, 'a> {
state: &'a State<FlatSet<Scalar>>,
visitor: &'a mut CollectAndPatch<'tcx, 'locals>,
visitor: &'a mut Collector<'tcx, 'locals>,
map: &'map Map,
}
impl<'tcx> Visitor<'tcx> for OperandCollector<'tcx, '_, '_, '_> {
fn visit_projection_elem(
&mut self,
_: PlaceRef<'tcx>,
elem: PlaceElem<'tcx>,
_: PlaceContext,
location: Location,
) {
if let PlaceElem::Index(local) = elem
&& let Some(value) = self.visitor.try_make_constant(local.into(), self.state, self.map)
{
self.visitor.patch.before_effect.insert((location, local.into()), value);
}
}
fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
if let Some(place) = operand.place() {
if let FlatSet::Elem(Scalar::Int(value)) = self.state.get(place.as_ref(), self.map) {
self.visitor.before_effect.insert((location, place), value);
if let Some(value) = self.visitor.try_make_constant(place, self.state, self.map) {
self.visitor.patch.before_effect.insert((location, place), value);
} else if !place.projection.is_empty() {
// Try to propagate into `Index` projections.
self.super_operand(operand, location)
}
}
}
fn visit_local(&mut self, local: Local, ctxt: PlaceContext, location: Location) {
if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy | NonMutatingUseContext::Move) = ctxt
&& let FlatSet::Elem(Scalar::Int(value)) = self.state.get(local.into(), self.map)
{
self.visitor.before_effect.insert((location, local.into()), value);
}
}
}
struct DummyMachine;