diff options
| -rw-r--r-- | compiler/rustc_mir_transform/src/const_prop.rs | 161 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/const_prop_lint.rs | 132 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/dataflow_const_prop.rs | 27 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/lib.rs | 1 |
4 files changed, 153 insertions, 168 deletions
diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs deleted file mode 100644 index eba62aae60f..00000000000 --- a/compiler/rustc_mir_transform/src/const_prop.rs +++ /dev/null @@ -1,161 +0,0 @@ -//! Propagates constants for early reporting of statically known -//! assertion failures - -use rustc_index::bit_set::BitSet; -use rustc_index::IndexVec; -use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor}; -use rustc_middle::mir::*; -use rustc_middle::ty::{ParamEnv, TyCtxt}; -use rustc_target::abi::Size; - -/// The maximum number of bytes that we'll allocate space for a local or the return value. -/// Needed for #66397, because otherwise we eval into large places and that can cause OOM or just -/// Severely regress performance. -const MAX_ALLOC_LIMIT: u64 = 1024; - -/// Macro for machine-specific `InterpError` without allocation. -/// (These will never be shown to the user, but they help diagnose ICEs.) -pub(crate) macro throw_machine_stop_str($($tt:tt)*) {{ - // We make a new local type for it. The type itself does not carry any information, - // but its vtable (for the `MachineStopType` trait) does. - #[derive(Debug)] - struct Zst; - // Printing this type shows the desired string. - impl std::fmt::Display for Zst { - fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { - write!(f, $($tt)*) - } - } - - impl rustc_middle::mir::interpret::MachineStopType for Zst { - fn diagnostic_message(&self) -> rustc_errors::DiagnosticMessage { - self.to_string().into() - } - - fn add_args( - self: Box<Self>, - _: &mut dyn FnMut(rustc_errors::DiagnosticArgName, rustc_errors::DiagnosticArgValue), - ) {} - } - throw_machine_stop!(Zst) -}} - -/// The mode that `ConstProp` is allowed to run in for a given `Local`. -#[derive(Clone, Copy, Debug, PartialEq)] -pub enum ConstPropMode { - /// The `Local` can be propagated into and reads of this `Local` can also be propagated. - FullConstProp, - /// The `Local` can only be propagated into and from its own block. - OnlyInsideOwnBlock, - /// The `Local` cannot be part of propagation at all. Any statement - /// referencing it either for reading or writing will not get propagated. - NoPropagation, -} - -pub struct CanConstProp { - can_const_prop: IndexVec<Local, ConstPropMode>, - // False at the beginning. Once set, no more assignments are allowed to that local. - found_assignment: BitSet<Local>, -} - -impl CanConstProp { - /// Returns true if `local` can be propagated - pub fn check<'tcx>( - tcx: TyCtxt<'tcx>, - param_env: ParamEnv<'tcx>, - body: &Body<'tcx>, - ) -> IndexVec<Local, ConstPropMode> { - let mut cpv = CanConstProp { - can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls), - found_assignment: BitSet::new_empty(body.local_decls.len()), - }; - for (local, val) in cpv.can_const_prop.iter_enumerated_mut() { - let ty = body.local_decls[local].ty; - match tcx.layout_of(param_env.and(ty)) { - Ok(layout) if layout.size < Size::from_bytes(MAX_ALLOC_LIMIT) => {} - // Either the layout fails to compute, then we can't use this local anyway - // or the local is too large, then we don't want to. - _ => { - *val = ConstPropMode::NoPropagation; - continue; - } - } - } - // Consider that arguments are assigned on entry. - for arg in body.args_iter() { - cpv.found_assignment.insert(arg); - } - cpv.visit_body(body); - cpv.can_const_prop - } -} - -impl<'tcx> Visitor<'tcx> for CanConstProp { - fn visit_place(&mut self, place: &Place<'tcx>, mut context: PlaceContext, loc: Location) { - use rustc_middle::mir::visit::PlaceContext::*; - - // Dereferencing just read the addess of `place.local`. - if place.projection.first() == Some(&PlaceElem::Deref) { - context = NonMutatingUse(NonMutatingUseContext::Copy); - } - - self.visit_local(place.local, context, loc); - self.visit_projection(place.as_ref(), context, loc); - } - - fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) { - use rustc_middle::mir::visit::PlaceContext::*; - match context { - // These are just stores, where the storing is not propagatable, but there may be later - // mutations of the same local via `Store` - | MutatingUse(MutatingUseContext::Call) - | MutatingUse(MutatingUseContext::AsmOutput) - | MutatingUse(MutatingUseContext::Deinit) - // Actual store that can possibly even propagate a value - | MutatingUse(MutatingUseContext::Store) - | MutatingUse(MutatingUseContext::SetDiscriminant) => { - if !self.found_assignment.insert(local) { - match &mut self.can_const_prop[local] { - // If the local can only get propagated in its own block, then we don't have - // to worry about multiple assignments, as we'll nuke the const state at the - // end of the block anyway, and inside the block we overwrite previous - // states as applicable. - ConstPropMode::OnlyInsideOwnBlock => {} - ConstPropMode::NoPropagation => {} - other @ ConstPropMode::FullConstProp => { - trace!( - "local {:?} can't be propagated because of multiple assignments. Previous state: {:?}", - local, other, - ); - *other = ConstPropMode::OnlyInsideOwnBlock; - } - } - } - } - // Reading constants is allowed an arbitrary number of times - NonMutatingUse(NonMutatingUseContext::Copy) - | NonMutatingUse(NonMutatingUseContext::Move) - | NonMutatingUse(NonMutatingUseContext::Inspect) - | NonMutatingUse(NonMutatingUseContext::PlaceMention) - | NonUse(_) => {} - - // These could be propagated with a smarter analysis or just some careful thinking about - // whether they'd be fine right now. - MutatingUse(MutatingUseContext::Yield) - | MutatingUse(MutatingUseContext::Drop) - | MutatingUse(MutatingUseContext::Retag) - // These can't ever be propagated under any scheme, as we can't reason about indirect - // mutation. - | NonMutatingUse(NonMutatingUseContext::SharedBorrow) - | NonMutatingUse(NonMutatingUseContext::FakeBorrow) - | NonMutatingUse(NonMutatingUseContext::AddressOf) - | MutatingUse(MutatingUseContext::Borrow) - | MutatingUse(MutatingUseContext::AddressOf) => { - trace!("local {:?} can't be propagated because it's used: {:?}", local, context); - self.can_const_prop[local] = ConstPropMode::NoPropagation; - } - MutatingUse(MutatingUseContext::Projection) - | NonMutatingUse(NonMutatingUseContext::Projection) => bug!("visit_place should not pass {context:?} for {local:?}"), - } - } -} diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs index 6212155a8fe..6f2ef8f9a4f 100644 --- a/compiler/rustc_mir_transform/src/const_prop_lint.rs +++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs @@ -9,17 +9,14 @@ use rustc_const_eval::interpret::{ use rustc_data_structures::fx::FxHashSet; use rustc_hir::def::DefKind; use rustc_hir::HirId; -use rustc_index::bit_set::BitSet; -use rustc_index::{Idx, IndexVec}; -use rustc_middle::mir::visit::Visitor; +use rustc_index::{bit_set::BitSet, Idx, IndexVec}; +use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor}; use rustc_middle::mir::*; use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout}; use rustc_middle::ty::{self, ConstInt, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitableExt}; use rustc_span::Span; use rustc_target::abi::{Abi, FieldIdx, HasDataLayout, Size, TargetDataLayout, VariantIdx}; -use crate::const_prop::CanConstProp; -use crate::const_prop::ConstPropMode; use crate::dataflow_const_prop::DummyMachine; use crate::errors::{AssertLint, AssertLintKind}; use crate::MirLint; @@ -849,3 +846,128 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> { } } } + +/// The maximum number of bytes that we'll allocate space for a local or the return value. +/// Needed for #66397, because otherwise we eval into large places and that can cause OOM or just +/// Severely regress performance. +const MAX_ALLOC_LIMIT: u64 = 1024; + +/// The mode that `ConstProp` is allowed to run in for a given `Local`. +#[derive(Clone, Copy, Debug, PartialEq)] +pub enum ConstPropMode { + /// The `Local` can be propagated into and reads of this `Local` can also be propagated. + FullConstProp, + /// The `Local` can only be propagated into and from its own block. + OnlyInsideOwnBlock, + /// The `Local` cannot be part of propagation at all. Any statement + /// referencing it either for reading or writing will not get propagated. + NoPropagation, +} + +pub struct CanConstProp { + can_const_prop: IndexVec<Local, ConstPropMode>, + // False at the beginning. Once set, no more assignments are allowed to that local. + found_assignment: BitSet<Local>, +} + +impl CanConstProp { + /// Returns true if `local` can be propagated + pub fn check<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ParamEnv<'tcx>, + body: &Body<'tcx>, + ) -> IndexVec<Local, ConstPropMode> { + let mut cpv = CanConstProp { + can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls), + found_assignment: BitSet::new_empty(body.local_decls.len()), + }; + for (local, val) in cpv.can_const_prop.iter_enumerated_mut() { + let ty = body.local_decls[local].ty; + match tcx.layout_of(param_env.and(ty)) { + Ok(layout) if layout.size < Size::from_bytes(MAX_ALLOC_LIMIT) => {} + // Either the layout fails to compute, then we can't use this local anyway + // or the local is too large, then we don't want to. + _ => { + *val = ConstPropMode::NoPropagation; + continue; + } + } + } + // Consider that arguments are assigned on entry. + for arg in body.args_iter() { + cpv.found_assignment.insert(arg); + } + cpv.visit_body(body); + cpv.can_const_prop + } +} + +impl<'tcx> Visitor<'tcx> for CanConstProp { + fn visit_place(&mut self, place: &Place<'tcx>, mut context: PlaceContext, loc: Location) { + use rustc_middle::mir::visit::PlaceContext::*; + + // Dereferencing just read the addess of `place.local`. + if place.projection.first() == Some(&PlaceElem::Deref) { + context = NonMutatingUse(NonMutatingUseContext::Copy); + } + + self.visit_local(place.local, context, loc); + self.visit_projection(place.as_ref(), context, loc); + } + + fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) { + use rustc_middle::mir::visit::PlaceContext::*; + match context { + // These are just stores, where the storing is not propagatable, but there may be later + // mutations of the same local via `Store` + | MutatingUse(MutatingUseContext::Call) + | MutatingUse(MutatingUseContext::AsmOutput) + | MutatingUse(MutatingUseContext::Deinit) + // Actual store that can possibly even propagate a value + | MutatingUse(MutatingUseContext::Store) + | MutatingUse(MutatingUseContext::SetDiscriminant) => { + if !self.found_assignment.insert(local) { + match &mut self.can_const_prop[local] { + // If the local can only get propagated in its own block, then we don't have + // to worry about multiple assignments, as we'll nuke the const state at the + // end of the block anyway, and inside the block we overwrite previous + // states as applicable. + ConstPropMode::OnlyInsideOwnBlock => {} + ConstPropMode::NoPropagation => {} + other @ ConstPropMode::FullConstProp => { + trace!( + "local {:?} can't be propagated because of multiple assignments. Previous state: {:?}", + local, other, + ); + *other = ConstPropMode::OnlyInsideOwnBlock; + } + } + } + } + // Reading constants is allowed an arbitrary number of times + NonMutatingUse(NonMutatingUseContext::Copy) + | NonMutatingUse(NonMutatingUseContext::Move) + | NonMutatingUse(NonMutatingUseContext::Inspect) + | NonMutatingUse(NonMutatingUseContext::PlaceMention) + | NonUse(_) => {} + + // These could be propagated with a smarter analysis or just some careful thinking about + // whether they'd be fine right now. + MutatingUse(MutatingUseContext::Yield) + | MutatingUse(MutatingUseContext::Drop) + | MutatingUse(MutatingUseContext::Retag) + // These can't ever be propagated under any scheme, as we can't reason about indirect + // mutation. + | NonMutatingUse(NonMutatingUseContext::SharedBorrow) + | NonMutatingUse(NonMutatingUseContext::FakeBorrow) + | NonMutatingUse(NonMutatingUseContext::AddressOf) + | MutatingUse(MutatingUseContext::Borrow) + | MutatingUse(MutatingUseContext::AddressOf) => { + trace!("local {:?} can't be propagated because it's used: {:?}", local, context); + self.can_const_prop[local] = ConstPropMode::NoPropagation; + } + MutatingUse(MutatingUseContext::Projection) + | NonMutatingUse(NonMutatingUseContext::Projection) => bug!("visit_place should not pass {context:?} for {local:?}"), + } + } +} diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs index 86e99a8a5b5..9dc7a50eca9 100644 --- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs +++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs @@ -21,7 +21,32 @@ use rustc_span::def_id::DefId; use rustc_span::DUMMY_SP; use rustc_target::abi::{Abi, FieldIdx, Size, VariantIdx, FIRST_VARIANT}; -use crate::const_prop::throw_machine_stop_str; +/// Macro for machine-specific `InterpError` without allocation. +/// (These will never be shown to the user, but they help diagnose ICEs.) +pub(crate) macro throw_machine_stop_str($($tt:tt)*) {{ + // We make a new local type for it. The type itself does not carry any information, + // but its vtable (for the `MachineStopType` trait) does. + #[derive(Debug)] + struct Zst; + // Printing this type shows the desired string. + impl std::fmt::Display for Zst { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + write!(f, $($tt)*) + } + } + + impl rustc_middle::mir::interpret::MachineStopType for Zst { + fn diagnostic_message(&self) -> rustc_errors::DiagnosticMessage { + self.to_string().into() + } + + fn add_args( + self: Box<Self>, + _: &mut dyn FnMut(rustc_errors::DiagnosticArgName, rustc_errors::DiagnosticArgValue), + ) {} + } + throw_machine_stop!(Zst) +}} // These constants are somewhat random guesses and have not been optimized. // If `tcx.sess.mir_opt_level() >= 4`, we ignore the limits (this can become very expensive). diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs index 7f0e6f90dbb..74b36eb5ee8 100644 --- a/compiler/rustc_mir_transform/src/lib.rs +++ b/compiler/rustc_mir_transform/src/lib.rs @@ -59,7 +59,6 @@ mod remove_place_mention; mod add_subtyping_projections; pub mod cleanup_post_borrowck; mod const_debuginfo; -mod const_prop; mod const_prop_lint; mod copy_prop; mod coroutine; |