Skip to content

Commit

Permalink
removed CanConstProp + Visitor
Browse files Browse the repository at this point in the history
  • Loading branch information
@Dajamante
Dajamante committed Jul 25, 2022
1 parent 68b433a commit e651829
Show file tree
Hide file tree
Showing 2 changed files with 7 additions and 125 deletions.
4 changes: 2 additions & 2 deletions compiler/rustc_mir_transform/src/const_prop.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -828,7 +828,7 @@ pub enum ConstPropMode {
NoPropagation,
}

struct CanConstProp {
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>,
Expand All @@ -838,7 +838,7 @@ struct CanConstProp {

impl CanConstProp {
/// Returns true if `local` can be propagated
fn check<'tcx>(
pub fn check<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
body: &Body<'tcx>,
Expand Down
128 changes: 5 additions & 123 deletions compiler/rustc_mir_transform/src/const_prop_lint.rs
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
//! Propagates constants for early reporting of statically known
//! assertion failures
use crate::const_prop::CanConstProp;
use crate::const_prop::ConstPropMachine;
use crate::const_prop::ConstPropMode;
use crate::MirLint;
Expand All @@ -13,11 +14,11 @@ use rustc_hir::def::DefKind;
use rustc_hir::HirId;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{
AssertKind, BinOp, Body, Constant, ConstantKind, Local, LocalDecl, LocalKind, Location,
Operand, Place, Rvalue, SourceInfo, SourceScope, SourceScopeData, Statement, StatementKind,
Terminator, TerminatorKind, UnOp, RETURN_PLACE,
AssertKind, BinOp, Body, Constant, ConstantKind, Local, LocalDecl, Location, Operand, Place,
Rvalue, SourceInfo, SourceScope, SourceScopeData, Statement, StatementKind, Terminator,
TerminatorKind, UnOp, RETURN_PLACE,
};
use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
use rustc_middle::ty::subst::{InternalSubsts, Subst};
Expand Down Expand Up @@ -522,125 +523,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
}
}

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>,
// Cache of locals' information
local_kinds: IndexVec<Local, LocalKind>,
}

impl CanConstProp {
/// Returns true if `local` can be propagated
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()),
local_kinds: IndexVec::from_fn_n(
|local| body.local_kind(local),
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;
}
}
// Cannot use args at all
// Cannot use locals because if x < y { y - x } else { x - y } would
// lint for x != y
// FIXME(oli-obk): lint variables until they are used in a condition
// FIXME(oli-obk): lint if return value is constant
if cpv.local_kinds[local] == LocalKind::Arg {
*val = ConstPropMode::OnlyPropagateInto;
trace!(
"local {:?} can't be const propagated because it's a function argument",
local
);
} else if cpv.local_kinds[local] == LocalKind::Var {
*val = ConstPropMode::OnlyInsideOwnBlock;
trace!(
"local {:?} will only be propagated inside its block, because it's a user variable",
local
);
}
}
cpv.visit_body(&body);
cpv.can_const_prop
}
}

impl Visitor<'_> for CanConstProp {
fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
use rustc_middle::mir::visit::PlaceContext::*;
match context {
// Projections are fine, because `&mut foo.x` will be caught by
// `MutatingUseContext::Borrow` elsewhere.
MutatingUse(MutatingUseContext::Projection)
// 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::SetDiscriminant)
| MutatingUse(MutatingUseContext::Store) => {
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 => {}
ConstPropMode::OnlyPropagateInto => {}
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::Projection)
| 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::ShallowBorrow)
| NonMutatingUse(NonMutatingUseContext::UniqueBorrow)
| NonMutatingUse(NonMutatingUseContext::AddressOf)
| MutatingUse(MutatingUseContext::Borrow)
| MutatingUse(MutatingUseContext::AddressOf) => {
trace!("local {:?} can't be propagaged because it's used: {:?}", local, context);
self.can_const_prop[local] = ConstPropMode::NoPropagation;
}
}
}
}

impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
fn visit_body(&mut self, body: &Body<'tcx>) {
for (bb, data) in body.basic_blocks().iter_enumerated() {
Expand Down

0 comments on commit e651829

Please sign in to comment.