Check whether locals are too large instead of whether accesses into them are too large
This commit is contained in:
Oliver Scherer
parent
8611e526b7
commit
c3454c0007
1 changed files with 61 additions and 57 deletions
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@ -34,7 +34,9 @@ use crate::interpret::{
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};
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use crate::transform::{MirPass, MirSource};
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/// The maximum number of bytes that we'll allocate space for a return value.
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/// The maximum number of bytes that we'll allocate space for a local or the return value.
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/// Needed for #66397, because otherwise we eval into large places and that can cause OOM or just
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/// Severely regress performance.
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const MAX_ALLOC_LIMIT: u64 = 1024;
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/// Macro for machine-specific `InterpError` without allocation.
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@ -331,7 +333,10 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
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let param_env = tcx.param_env(def_id).with_reveal_all();
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let span = tcx.def_span(def_id);
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let can_const_prop = CanConstProp::check(body);
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// FIXME: `CanConstProp::check` computes the layout of all locals, return those layouts
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// so we can write them to `ecx.frame_mut().locals.layout, reducing the duplication in
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// `layout_of` query invocations.
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let can_const_prop = CanConstProp::check(tcx, param_env, body);
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let mut only_propagate_inside_block_locals = BitSet::new_empty(can_const_prop.len());
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for (l, mode) in can_const_prop.iter_enumerated() {
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if *mode == ConstPropMode::OnlyInsideOwnBlock {
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@ -612,15 +617,9 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
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fn const_prop(
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&mut self,
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rvalue: &Rvalue<'tcx>,
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place_layout: TyAndLayout<'tcx>,
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source_info: SourceInfo,
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place: Place<'tcx>,
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) -> Option<()> {
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// #66397: Don't try to eval into large places as that can cause an OOM
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if place_layout.size >= Size::from_bytes(MAX_ALLOC_LIMIT) {
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return None;
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}
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// Perform any special handling for specific Rvalue types.
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// Generally, checks here fall into one of two categories:
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// 1. Additional checking to provide useful lints to the user
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@ -893,7 +892,11 @@ struct CanConstProp {
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impl CanConstProp {
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/// Returns true if `local` can be propagated
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fn check(body: &Body<'_>) -> IndexVec<Local, ConstPropMode> {
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fn check(
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tcx: TyCtxt<'tcx>,
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param_env: ParamEnv<'tcx>,
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body: &Body<'tcx>,
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) -> IndexVec<Local, ConstPropMode> {
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let mut cpv = CanConstProp {
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can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls),
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found_assignment: BitSet::new_empty(body.local_decls.len()),
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@ -903,6 +906,16 @@ impl CanConstProp {
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),
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};
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for (local, val) in cpv.can_const_prop.iter_enumerated_mut() {
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let ty = body.local_decls[local].ty;
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match tcx.layout_of(param_env.and(ty)) {
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Ok(layout) if layout.size < Size::from_bytes(MAX_ALLOC_LIMIT) => {}
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// Either the layout fails to compute, then we can't use this local anyway
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// or the local is too large, then we don't want to.
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_ => {
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*val = ConstPropMode::NoPropagation;
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continue;
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}
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}
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// Cannot use args at all
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// Cannot use locals because if x < y { y - x } else { x - y } would
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// lint for x != y
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@ -1018,61 +1031,52 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
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let source_info = statement.source_info;
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self.source_info = Some(source_info);
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if let StatementKind::Assign(box (place, ref mut rval)) = statement.kind {
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let place_ty: Ty<'tcx> = place.ty(&self.local_decls, self.tcx).ty;
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if let Ok(place_layout) = self.tcx.layout_of(self.param_env.and(place_ty)) {
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let can_const_prop = self.can_const_prop[place.local];
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if let Some(()) = self.const_prop(rval, place_layout, source_info, place) {
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// This will return None if the above `const_prop` invocation only "wrote" a
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// type whose creation requires no write. E.g. a generator whose initial state
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// consists solely of uninitialized memory (so it doesn't capture any locals).
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if let Some(value) = self.get_const(place) {
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if self.should_const_prop(value) {
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trace!("replacing {:?} with {:?}", rval, value);
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self.replace_with_const(rval, value, source_info);
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if can_const_prop == ConstPropMode::FullConstProp
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|| can_const_prop == ConstPropMode::OnlyInsideOwnBlock
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{
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trace!("propagated into {:?}", place);
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}
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let can_const_prop = self.can_const_prop[place.local];
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if let Some(()) = self.const_prop(rval, source_info, place) {
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// This will return None if the above `const_prop` invocation only "wrote" a
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// type whose creation requires no write. E.g. a generator whose initial state
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// consists solely of uninitialized memory (so it doesn't capture any locals).
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if let Some(value) = self.get_const(place) {
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if self.should_const_prop(value) {
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trace!("replacing {:?} with {:?}", rval, value);
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self.replace_with_const(rval, value, source_info);
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if can_const_prop == ConstPropMode::FullConstProp
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|| can_const_prop == ConstPropMode::OnlyInsideOwnBlock
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{
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trace!("propagated into {:?}", place);
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}
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}
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match can_const_prop {
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ConstPropMode::OnlyInsideOwnBlock => {
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trace!(
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"found local restricted to its block. \
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}
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match can_const_prop {
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ConstPropMode::OnlyInsideOwnBlock => {
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trace!(
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"found local restricted to its block. \
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Will remove it from const-prop after block is finished. Local: {:?}",
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place.local
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);
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}
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ConstPropMode::OnlyPropagateInto | ConstPropMode::NoPropagation => {
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trace!("can't propagate into {:?}", place);
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if place.local != RETURN_PLACE {
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Self::remove_const(&mut self.ecx, place.local);
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}
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}
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ConstPropMode::FullConstProp => {}
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place.local
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);
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}
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} else {
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// Const prop failed, so erase the destination, ensuring that whatever happens
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// from here on, does not know about the previous value.
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// This is important in case we have
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// ```rust
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// let mut x = 42;
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// x = SOME_MUTABLE_STATIC;
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// // x must now be undefined
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// ```
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// FIXME: we overzealously erase the entire local, because that's easier to
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// implement.
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trace!(
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"propagation into {:?} failed.
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Nuking the entire site from orbit, it's the only way to be sure",
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place,
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);
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Self::remove_const(&mut self.ecx, place.local);
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ConstPropMode::OnlyPropagateInto | ConstPropMode::NoPropagation => {
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trace!("can't propagate into {:?}", place);
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if place.local != RETURN_PLACE {
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Self::remove_const(&mut self.ecx, place.local);
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}
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}
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ConstPropMode::FullConstProp => {}
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}
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} else {
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// Const prop failed, so erase the destination, ensuring that whatever happens
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// from here on, does not know about the previous value.
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// This is important in case we have
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// ```rust
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// let mut x = 42;
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// x = SOME_MUTABLE_STATIC;
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// // x must now be undefined
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// ```
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// FIXME: we overzealously erase the entire local, because that's easier to
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// implement.
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trace!(
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"cannot propagate into {:?}, because the type of the local is generic.",
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"propagation into {:?} failed.
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Nuking the entire site from orbit, it's the only way to be sure",
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place,
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);
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Self::remove_const(&mut self.ecx, place.local);
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