bjoernager/rust
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Do not consider borrowed Freeze locals as SSA.

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This commit is contained in:
Camille GILLOT 2023-04-26 18:30:12 +00:00
parent 3490375570
commit 3c43b61b87
10 changed files with 69 additions and 43 deletions
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3
compiler/rustc_mir_transform/src/copy_prop.rs
View file

@ -33,9 +33,8 @@ impl<'tcx> MirPass<'tcx> for CopyProp {
}
fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
let borrowed_locals = borrowed_locals(body);
let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
let ssa = SsaLocals::new(body);
let fully_moved = fully_moved_locals(&ssa, body);
debug!(?fully_moved);

5
compiler/rustc_mir_transform/src/normalize_array_len.rs
View file

@ -7,7 +7,6 @@ use rustc_index::IndexVec;
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, TyCtxt};
use rustc_mir_dataflow::impls::borrowed_locals;
pub struct NormalizeArrayLen;
@ -24,9 +23,7 @@ impl<'tcx> MirPass<'tcx> for NormalizeArrayLen {
}
fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
let borrowed_locals = borrowed_locals(body);
let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
let ssa = SsaLocals::new(body);
let slice_lengths = compute_slice_length(tcx, &ssa, body);
debug!(?slice_lengths);

6
compiler/rustc_mir_transform/src/ref_prop.rs
View file

@ -4,7 +4,7 @@ use rustc_index::IndexVec;
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use rustc_mir_dataflow::impls::{borrowed_locals, MaybeStorageDead};
use rustc_mir_dataflow::impls::MaybeStorageDead;
use rustc_mir_dataflow::storage::always_storage_live_locals;
use rustc_mir_dataflow::Analysis;
@ -82,9 +82,7 @@ impl<'tcx> MirPass<'tcx> for ReferencePropagation {
}
fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
let borrowed_locals = borrowed_locals(body);
let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals);
let ssa = SsaLocals::new(body);
let mut replacer = compute_replacement(tcx, body, &ssa);
debug!(?replacer.targets, ?replacer.allowed_replacements, ?replacer.storage_to_remove);

49
compiler/rustc_mir_transform/src/ssa.rs
View file

@ -1,3 +1,16 @@
//! We denote as "SSA" the set of locals that verify the following properties:
//! 1/ They are only assigned-to once, either as a function parameter, or in an assign statement;
//! 2/ This single assignment dominates all uses;
//!
//! As a consequence of rule 2, we consider that borrowed locals are not SSA, even if they are
//! `Freeze`, as we do not track that the assignment dominates all uses of the borrow.
//!
//! We say a local has a stable address if its address has SSA-like properties:
//! 1/ It has a single `StorageLive` statement, or none at all (always-live);
//! 2/ All its uses dominate this `StorageLive` statement.
//!
//! We do not discard borrowed locals from this analysis, as we cannot take their address' address.
use either::Either;
use rustc_data_structures::graph::dominators::Dominators;
use rustc_index::bit_set::BitSet;
@ -5,7 +18,6 @@ use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::middle::resolve_bound_vars::Set1;
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::{ParamEnv, TyCtxt};
use rustc_mir_dataflow::storage::always_storage_live_locals;
#[derive(Debug)]
@ -62,12 +74,7 @@ impl SmallDominators {
}
impl SsaLocals {
pub fn new<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
body: &Body<'tcx>,
borrowed_locals: &BitSet<Local>,
) -> SsaLocals {
pub fn new<'tcx>(body: &Body<'tcx>) -> SsaLocals {
let assignment_order = Vec::with_capacity(body.local_decls.len());
let assignments = IndexVec::from_elem(Set1::Empty, &body.local_decls);
@ -80,13 +87,8 @@ impl SsaLocals {
let mut visitor =
SsaVisitor { assignments, assignment_order, dominators, direct_uses, storage_live };
for (local, decl) in body.local_decls.iter_enumerated() {
if matches!(body.local_kind(local), LocalKind::Arg) {
visitor.assignments[local] = Set1::One(LocationExtended::Arg);
}
if borrowed_locals.contains(local) && !decl.ty.is_freeze(tcx, param_env) {
visitor.assignments[local] = Set1::Many;
}
for local in body.args_iter() {
visitor.assignments[local] = Set1::One(LocationExtended::Arg);
}
for local in always_storage_live_locals(body).iter() {
@ -237,6 +239,8 @@ struct SsaVisitor {
impl<'tcx> Visitor<'tcx> for SsaVisitor {
fn visit_local(&mut self, local: Local, ctxt: PlaceContext, loc: Location) {
match ctxt {
PlaceContext::MutatingUse(MutatingUseContext::Projection)
| PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) => bug!(),
PlaceContext::MutatingUse(MutatingUseContext::Store) => {
self.assignments[local].insert(LocationExtended::Plain(loc));
if let Set1::One(_) = self.assignments[local] {
@ -246,13 +250,18 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
self.dominators.check_dominates(&mut self.storage_live[local], loc);
}
// Anything can happen with raw pointers, so remove them.
PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf)
// We do not verify that all uses of the borrow dominate the assignment to `local`,
// so we have to remove them too.
PlaceContext::NonMutatingUse(
NonMutatingUseContext::SharedBorrow
| NonMutatingUseContext::ShallowBorrow
| NonMutatingUseContext::UniqueBorrow
| NonMutatingUseContext::AddressOf,
)
| PlaceContext::MutatingUse(_) => {
self.assignments[local] = Set1::Many;
self.dominators.check_dominates(&mut self.storage_live[local], loc);
}
// Immutable borrows are taken into account in `SsaLocals::new` by
// removing non-freeze locals.
PlaceContext::NonMutatingUse(_) => {
self.dominators.check_dominates(&mut self.assignments[local], loc);
self.dominators.check_dominates(&mut self.storage_live[local], loc);
@ -270,15 +279,17 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor {
// Do not do anything for storage statements and debuginfo.
if ctxt.is_use() {
// Only change the context if it is a real use, not a "use" in debuginfo.
let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection);
let new_ctxt = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy);
self.visit_projection(place.as_ref(), new_ctxt, loc);
self.dominators.check_dominates(&mut self.assignments[place.local], loc);
self.dominators.check_dominates(&mut self.storage_live[place.local], loc);
}
return;
} else {
self.visit_projection(place.as_ref(), ctxt, loc);
self.visit_local(place.local, ctxt, loc);
}
self.super_place(place, ctxt, loc);
}
}