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Auto merge of #62012 - wesleywiser:const_prop_use_ecx, r=oli-obk
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Use ecx for const-prop local storage

r? @oli-obk
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@bors
bors committed Jun 24, 2019
2 parents 3cc3486 + c686130 commit 166c49d
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Showing 2 changed files with 116 additions and 25 deletions.
13 changes: 9 additions & 4 deletions src/librustc_mir/interpret/eval_context.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -319,7 +319,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpretCx<'mir, 'tcx, M> {
t: T,
) -> InterpResult<'tcx, T> {
match self.stack.last() {
Some(frame) => Ok(self.monomorphize_with_substs(t, frame.instance.substs)),
Some(frame) => Ok(self.monomorphize_with_substs(t, frame.instance.substs)?),
None => if t.needs_subst() {
err!(TooGeneric).into()
} else {
Expand All @@ -332,11 +332,16 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpretCx<'mir, 'tcx, M> {
&self,
t: T,
substs: SubstsRef<'tcx>
) -> T {
) -> InterpResult<'tcx, T> {
// miri doesn't care about lifetimes, and will choke on some crazy ones
// let's simply get rid of them
let substituted = t.subst(*self.tcx, substs);
self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), substituted)

if substituted.needs_subst() {
return err!(TooGeneric);
}

Ok(self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), substituted))
}

pub fn layout_of_local(
Expand All @@ -349,7 +354,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpretCx<'mir, 'tcx, M> {
None => {
let layout = crate::interpret::operand::from_known_layout(layout, || {
let local_ty = frame.body.local_decls[local].ty;
let local_ty = self.monomorphize_with_substs(local_ty, frame.instance.substs);
let local_ty = self.monomorphize_with_substs(local_ty, frame.instance.substs)?;
self.layout_of(local_ty)
})?;
// Layouts of locals are requested a lot, so we cache them.
Expand Down
128 changes: 107 additions & 21 deletions src/librustc_mir/transform/const_prop.rs
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
//! Propagates constants for early reporting of statically known
//! assertion failures
use std::cell::Cell;

use rustc::hir::def::DefKind;
use rustc::mir::{
AggregateKind, Constant, Location, Place, PlaceBase, Body, Operand, Rvalue,
Expand All @@ -21,7 +23,8 @@ use rustc::ty::layout::{
};

use crate::interpret::{
self, InterpretCx, ScalarMaybeUndef, Immediate, OpTy, ImmTy, MemoryKind,
self, InterpretCx, ScalarMaybeUndef, Immediate, OpTy,
ImmTy, MemoryKind, StackPopCleanup, LocalValue, LocalState,
};
use crate::const_eval::{
CompileTimeInterpreter, error_to_const_error, eval_promoted, mk_eval_cx,
Expand Down Expand Up @@ -56,21 +59,54 @@ impl MirPass for ConstProp {

trace!("ConstProp starting for {:?}", source.def_id());

// Steal some data we need from `body`.
let source_scope_local_data = std::mem::replace(
&mut body.source_scope_local_data,
ClearCrossCrate::Clear
);
let promoted = std::mem::replace(
&mut body.promoted,
IndexVec::new()
);

let dummy_body =
&Body::new(
body.basic_blocks().clone(),
Default::default(),
ClearCrossCrate::Clear,
Default::default(),
None,
body.local_decls.clone(),
Default::default(),
body.arg_count,
Default::default(),
tcx.def_span(source.def_id()),
Default::default(),
);

// FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold
// constants, instead of just checking for const-folding succeeding.
// That would require an uniform one-def no-mutation analysis
// and RPO (or recursing when needing the value of a local).
let mut optimization_finder = ConstPropagator::new(body, tcx, source);
let mut optimization_finder = ConstPropagator::new(
body,
dummy_body,
source_scope_local_data,
promoted,
tcx,
source
);
optimization_finder.visit_body(body);

// put back the data we stole from `mir`
let (source_scope_local_data, promoted) = optimization_finder.release_stolen_data();
std::mem::replace(
&mut body.source_scope_local_data,
optimization_finder.source_scope_local_data
source_scope_local_data
);
std::mem::replace(
&mut body.promoted,
optimization_finder.promoted
promoted
);

trace!("ConstProp done for {:?}", source.def_id());
Expand All @@ -84,7 +120,6 @@ struct ConstPropagator<'mir, 'tcx> {
ecx: InterpretCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
tcx: TyCtxt<'tcx>,
source: MirSource<'tcx>,
places: IndexVec<Local, Option<Const<'tcx>>>,
can_const_prop: IndexVec<Local, bool>,
param_env: ParamEnv<'tcx>,
source_scope_local_data: ClearCrossCrate<IndexVec<SourceScope, SourceScopeLocalData>>,
Expand Down Expand Up @@ -117,36 +152,87 @@ impl<'mir, 'tcx> HasTyCtxt<'tcx> for ConstPropagator<'mir, 'tcx> {

impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
fn new(
body: &mut Body<'tcx>,
body: &Body<'tcx>,
dummy_body: &'mir Body<'tcx>,
source_scope_local_data: ClearCrossCrate<IndexVec<SourceScope, SourceScopeLocalData>>,
promoted: IndexVec<Promoted, Body<'tcx>>,
tcx: TyCtxt<'tcx>,
source: MirSource<'tcx>,
) -> ConstPropagator<'mir, 'tcx> {
let param_env = tcx.param_env(source.def_id());
let ecx = mk_eval_cx(tcx, tcx.def_span(source.def_id()), param_env);
let def_id = source.def_id();
let param_env = tcx.param_env(def_id);
let span = tcx.def_span(def_id);
let mut ecx = mk_eval_cx(tcx, span, param_env);
let can_const_prop = CanConstProp::check(body);
let source_scope_local_data = std::mem::replace(
&mut body.source_scope_local_data,
ClearCrossCrate::Clear
);
let promoted = std::mem::replace(
&mut body.promoted,
IndexVec::new()
);

ecx.push_stack_frame(
Instance::new(def_id, &InternalSubsts::identity_for_item(tcx, def_id)),
span,
dummy_body,
None,
StackPopCleanup::None {
cleanup: false,
},
).expect("failed to push initial stack frame");

ConstPropagator {
ecx,
tcx,
source,
param_env,
can_const_prop,
places: IndexVec::from_elem(None, &body.local_decls),
source_scope_local_data,
//FIXME(wesleywiser) we can't steal this because `Visitor::super_visit_body()` needs it
local_decls: body.local_decls.clone(),
promoted,
}
}

fn release_stolen_data(
self,
) -> (
ClearCrossCrate<IndexVec<SourceScope, SourceScopeLocalData>>,
IndexVec<Promoted, Body<'tcx>>,
) {
(self.source_scope_local_data, self.promoted)
}

fn get_const(&self, local: Local) -> Option<Const<'tcx>> {
let l = &self.ecx.frame().locals[local];

// If the local is `Unitialized` or `Dead` then we haven't propagated a value into it.
//
// `InterpretCx::access_local()` mostly takes care of this for us however, for ZSTs,
// it will synthesize a value for us. In doing so, that will cause the
// `get_const(l).is_empty()` assert right before we call `set_const()` in `visit_statement`
// to fail.
if let LocalValue::Uninitialized | LocalValue::Dead = l.value {
return None;
}

self.ecx.access_local(self.ecx.frame(), local, None).ok()
}

fn set_const(&mut self, local: Local, c: Const<'tcx>) {
let frame = self.ecx.frame_mut();

if let Some(layout) = frame.locals[local].layout.get() {
debug_assert_eq!(c.layout, layout);
}

frame.locals[local] = LocalState {
value: LocalValue::Live(*c),
layout: Cell::new(Some(c.layout)),
};
}

fn remove_const(&mut self, local: Local) {
self.ecx.frame_mut().locals[local] = LocalState {
value: LocalValue::Uninitialized,
layout: Cell::new(None),
};
}

fn use_ecx<F, T>(
&mut self,
source_info: SourceInfo,
Expand Down Expand Up @@ -296,7 +382,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
trace!("eval_place(place={:?})", place);
place.iterate(|place_base, place_projection| {
let mut eval = match place_base {
PlaceBase::Local(loc) => self.places[*loc].clone()?,
PlaceBase::Local(loc) => self.get_const(*loc).clone()?,
PlaceBase::Static(box Static {kind: StaticKind::Promoted(promoted), ..}) => {
let generics = self.tcx.generics_of(self.source.def_id());
if generics.requires_monomorphization(self.tcx) {
Expand Down Expand Up @@ -699,8 +785,8 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
trace!("checking whether {:?} can be stored to {:?}", value, local);
if self.can_const_prop[local] {
trace!("storing {:?} to {:?}", value, local);
assert!(self.places[local].is_none());
self.places[local] = Some(value);
assert!(self.get_const(local).is_none());
self.set_const(local, value);

if self.should_const_prop() {
self.replace_with_const(
Expand Down Expand Up @@ -740,7 +826,7 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
place = &proj.base;
}
if let Place::Base(PlaceBase::Local(local)) = *place {
self.places[local] = None;
self.remove_const(local);
}
},
Operand::Constant(_) => {}
Expand Down

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