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Rollup merge of #119668 - cjgillot:transform-promote, r=oli-obk

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Simplify implementation of MIR promotion

Non-functional changes.
Best read ignoring whitespace.
This commit is contained in:
Guillaume Gomez 2024-01-09 13:23:17 +01:00 committed by GitHub
commit 72fdaf52e0
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 164 additions and 237 deletions
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1
compiler/rustc_const_eval/src/transform/mod.rs
View File

@ -1,3 +1,2 @@
pub mod check_consts;
pub mod promote_consts;
pub mod validate;

3
compiler/rustc_mir_transform/src/lib.rs
View File

@ -1,5 +1,6 @@
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
#![feature(assert_matches)]
#![feature(box_patterns)]
#![feature(cow_is_borrowed)]
#![feature(decl_macro)]
@ -94,6 +95,7 @@
mod normalize_array_len;
mod nrvo;
mod prettify;
mod promote_consts;
mod ref_prop;
mod remove_noop_landing_pads;
mod remove_storage_markers;
@ -115,7 +117,6 @@
mod unreachable_prop;
use rustc_const_eval::transform::check_consts::{self, ConstCx};
use rustc_const_eval::transform::promote_consts;
use rustc_const_eval::transform::validate;
use rustc_mir_dataflow::rustc_peek;

397
compiler/rustc_const_eval/src/transform/promote_consts.rs → compiler/rustc_mir_transform/src/promote_consts.rs
View File

@ -12,6 +12,7 @@
//! initialization and can otherwise silence errors, if
//! move analysis runs after promotion on broken MIR.
use either::{Left, Right};
use rustc_hir as hir;
use rustc_middle::mir;
use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
@ -22,10 +23,11 @@
use rustc_index::{Idx, IndexSlice, IndexVec};
use std::assert_matches::assert_matches;
use std::cell::Cell;
use std::{cmp, iter, mem};
use crate::transform::check_consts::{qualifs, ConstCx};
use rustc_const_eval::transform::check_consts::{qualifs, ConstCx};
/// A `MirPass` for promotion.
///
@ -64,7 +66,7 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
/// State of a temporary during collection and promotion.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum TempState {
enum TempState {
/// No references to this temp.
Undefined,
/// One direct assignment and any number of direct uses.
@ -78,18 +80,11 @@ pub enum TempState {
PromotedOut,
}
impl TempState {
pub fn is_promotable(&self) -> bool {
debug!("is_promotable: self={:?}", self);
matches!(self, TempState::Defined { .. })
}
}
/// A "root candidate" for promotion, which will become the
/// returned value in a promoted MIR, unless it's a subset
/// of a larger candidate.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub struct Candidate {
struct Candidate {
location: Location,
}
@ -123,46 +118,43 @@ fn visit_local(&mut self, index: Local, context: PlaceContext, location: Locatio
let temp = &mut self.temps[index];
debug!("visit_local: temp={:?}", temp);
if *temp == TempState::Undefined {
match context {
*temp = match *temp {
TempState::Undefined => match context {
PlaceContext::MutatingUse(MutatingUseContext::Store)
| PlaceContext::MutatingUse(MutatingUseContext::Call) => {
*temp = TempState::Defined { location, uses: 0, valid: Err(()) };
TempState::Defined { location, uses: 0, valid: Err(()) }
}
_ => TempState::Unpromotable,
},
TempState::Defined { ref mut uses, .. } => {
// We always allow borrows, even mutable ones, as we need
// to promote mutable borrows of some ZSTs e.g., `&mut []`.
let allowed_use = match context {
PlaceContext::MutatingUse(MutatingUseContext::Borrow)
| PlaceContext::NonMutatingUse(_) => true,
PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false,
};
debug!("visit_local: allowed_use={:?}", allowed_use);
if allowed_use {
*uses += 1;
return;
}
_ => { /* mark as unpromotable below */ }
TempState::Unpromotable
}
} else if let TempState::Defined { uses, .. } = temp {
// We always allow borrows, even mutable ones, as we need
// to promote mutable borrows of some ZSTs e.g., `&mut []`.
let allowed_use = match context {
PlaceContext::MutatingUse(MutatingUseContext::Borrow)
| PlaceContext::NonMutatingUse(_) => true,
PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false,
};
debug!("visit_local: allowed_use={:?}", allowed_use);
if allowed_use {
*uses += 1;
return;
}
/* mark as unpromotable below */
}
*temp = TempState::Unpromotable;
TempState::Unpromotable | TempState::PromotedOut => TempState::Unpromotable,
};
}
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
self.super_rvalue(rvalue, location);
match *rvalue {
Rvalue::Ref(..) => {
self.candidates.push(Candidate { location });
}
_ => {}
if let Rvalue::Ref(..) = *rvalue {
self.candidates.push(Candidate { location });
}
}
}
pub fn collect_temps_and_candidates<'tcx>(
fn collect_temps_and_candidates<'tcx>(
ccx: &ConstCx<'_, 'tcx>,
) -> (IndexVec<Local, TempState>, Vec<Candidate>) {
let mut collector = Collector {
@ -196,230 +188,165 @@ fn deref(&self) -> &Self::Target {
impl<'tcx> Validator<'_, 'tcx> {
fn validate_candidate(&mut self, candidate: Candidate) -> Result<(), Unpromotable> {
let loc = candidate.location;
let statement = &self.body[loc.block].statements[loc.statement_index];
match &statement.kind {
StatementKind::Assign(box (_, Rvalue::Ref(_, kind, place))) => {
// We can only promote interior borrows of promotable temps (non-temps
// don't get promoted anyway).
self.validate_local(place.local)?;
let Left(statement) = self.body.stmt_at(candidate.location) else { bug!() };
let Some((_, Rvalue::Ref(_, kind, place))) = statement.kind.as_assign() else { bug!() };
// The reference operation itself must be promotable.
// (Needs to come after `validate_local` to avoid ICEs.)
self.validate_ref(*kind, place)?;
// We can only promote interior borrows of promotable temps (non-temps
// don't get promoted anyway).
self.validate_local(place.local)?;
// We do not check all the projections (they do not get promoted anyway),
// but we do stay away from promoting anything involving a dereference.
if place.projection.contains(&ProjectionElem::Deref) {
return Err(Unpromotable);
}
// The reference operation itself must be promotable.
// (Needs to come after `validate_local` to avoid ICEs.)
self.validate_ref(*kind, place)?;
Ok(())
}
_ => bug!(),
// We do not check all the projections (they do not get promoted anyway),
// but we do stay away from promoting anything involving a dereference.
if place.projection.contains(&ProjectionElem::Deref) {
return Err(Unpromotable);
}
Ok(())
}
// FIXME(eddyb) maybe cache this?
fn qualif_local<Q: qualifs::Qualif>(&mut self, local: Local) -> bool {
if let TempState::Defined { location: loc, .. } = self.temps[local] {
let num_stmts = self.body[loc.block].statements.len();
let TempState::Defined { location: loc, .. } = self.temps[local] else {
return false;
};
if loc.statement_index < num_stmts {
let statement = &self.body[loc.block].statements[loc.statement_index];
match &statement.kind {
StatementKind::Assign(box (_, rhs)) => qualifs::in_rvalue::<Q, _>(
self.ccx,
&mut |l| self.qualif_local::<Q>(l),
rhs,
),
_ => {
span_bug!(
statement.source_info.span,
"{:?} is not an assignment",
statement
);
}
}
} else {
let terminator = self.body[loc.block].terminator();
match &terminator.kind {
TerminatorKind::Call { .. } => {
let return_ty = self.body.local_decls[local].ty;
Q::in_any_value_of_ty(self.ccx, return_ty)
}
kind => {
span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
}
}
let stmt_or_term = self.body.stmt_at(loc);
match stmt_or_term {
Left(statement) => {
let Some((_, rhs)) = statement.kind.as_assign() else {
span_bug!(statement.source_info.span, "{:?} is not an assignment", statement)
};
qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.qualif_local::<Q>(l), rhs)
}
Right(terminator) => {
assert_matches!(terminator.kind, TerminatorKind::Call { .. });
let return_ty = self.body.local_decls[local].ty;
Q::in_any_value_of_ty(self.ccx, return_ty)
}
} else {
false
}
}
fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> {
if let TempState::Defined { location: loc, uses, valid } = self.temps[local] {
// We cannot promote things that need dropping, since the promoted value
// would not get dropped.
if self.qualif_local::<qualifs::NeedsDrop>(local) {
return Err(Unpromotable);
}
valid.or_else(|_| {
let ok = {
let block = &self.body[loc.block];
let num_stmts = block.statements.len();
let TempState::Defined { location: loc, uses, valid } = self.temps[local] else {
return Err(Unpromotable);
};
if loc.statement_index < num_stmts {
let statement = &block.statements[loc.statement_index];
match &statement.kind {
StatementKind::Assign(box (_, rhs)) => self.validate_rvalue(rhs),
_ => {
span_bug!(
statement.source_info.span,
"{:?} is not an assignment",
statement
);
}
}
} else {
let terminator = block.terminator();
match &terminator.kind {
TerminatorKind::Call { func, args, .. } => {
self.validate_call(func, args)
}
TerminatorKind::Yield { .. } => Err(Unpromotable),
kind => {
span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
}
}
}
};
self.temps[local] = match ok {
Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) },
Err(_) => TempState::Unpromotable,
};
ok
})
} else {
Err(Unpromotable)
// We cannot promote things that need dropping, since the promoted value would not get
// dropped.
if self.qualif_local::<qualifs::NeedsDrop>(local) {
return Err(Unpromotable);
}
if valid.is_ok() {
return Ok(());
}
let ok = {
let stmt_or_term = self.body.stmt_at(loc);
match stmt_or_term {
Left(statement) => {
let Some((_, rhs)) = statement.kind.as_assign() else {
span_bug!(
statement.source_info.span,
"{:?} is not an assignment",
statement
)
};
self.validate_rvalue(rhs)
}
Right(terminator) => match &terminator.kind {
TerminatorKind::Call { func, args, .. } => self.validate_call(func, args),
TerminatorKind::Yield { .. } => Err(Unpromotable),
kind => {
span_bug!(terminator.source_info.span, "{:?} not promotable", kind);
}
},
}
};
self.temps[local] = match ok {
Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) },
Err(_) => TempState::Unpromotable,
};
ok
}
fn validate_place(&mut self, place: PlaceRef<'tcx>) -> Result<(), Unpromotable> {
match place.last_projection() {
None => self.validate_local(place.local),
Some((place_base, elem)) => {
// Validate topmost projection, then recurse.
match elem {
ProjectionElem::Deref => {
let mut promotable = false;
// When a static is used by-value, that gets desugared to `*STATIC_ADDR`,
// and we need to be able to promote this. So check if this deref matches
// that specific pattern.
let Some((place_base, elem)) = place.last_projection() else {
return self.validate_local(place.local);
};
// We need to make sure this is a `Deref` of a local with no further projections.
// Discussion can be found at
// https://github.com/rust-lang/rust/pull/74945#discussion_r463063247
if let Some(local) = place_base.as_local() {
if let TempState::Defined { location, .. } = self.temps[local] {
let def_stmt = self.body[location.block]
.statements
.get(location.statement_index);
if let Some(Statement {
kind:
StatementKind::Assign(box (
_,
Rvalue::Use(Operand::Constant(c)),
)),
..
}) = def_stmt
{
if let Some(did) = c.check_static_ptr(self.tcx) {
// Evaluating a promoted may not read statics except if it got
// promoted from a static (this is a CTFE check). So we
// can only promote static accesses inside statics.
if let Some(hir::ConstContext::Static(..)) = self.const_kind
{
if !self.tcx.is_thread_local_static(did) {
promotable = true;
}
}
}
}
}
}
if !promotable {
return Err(Unpromotable);
}
}
ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
return Err(Unpromotable);
}
// Validate topmost projection, then recurse.
match elem {
// Recurse directly.
ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subtype(_)
| ProjectionElem::Subslice { .. } => {}
ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subtype(_)
| ProjectionElem::Subslice { .. } => {}
// Never recurse.
ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => {
return Err(Unpromotable);
}
ProjectionElem::Index(local) => {
let mut promotable = false;
// Only accept if we can predict the index and are indexing an array.
let val = if let TempState::Defined { location: loc, .. } =
self.temps[local]
{
let block = &self.body[loc.block];
if loc.statement_index < block.statements.len() {
let statement = &block.statements[loc.statement_index];
match &statement.kind {
StatementKind::Assign(box (
_,
Rvalue::Use(Operand::Constant(c)),
)) => c.const_.try_eval_target_usize(self.tcx, self.param_env),
_ => None,
}
} else {
None
}
} else {
None
};
if let Some(idx) = val {
// Determine the type of the thing we are indexing.
let ty = place_base.ty(self.body, self.tcx).ty;
match ty.kind() {
ty::Array(_, len) => {
// It's an array; determine its length.
if let Some(len) =
len.try_eval_target_usize(self.tcx, self.param_env)
{
// If the index is in-bounds, go ahead.
if idx < len {
promotable = true;
}
}
}
_ => {}
}
}
if !promotable {
return Err(Unpromotable);
}
ProjectionElem::Deref => {
// When a static is used by-value, that gets desugared to `*STATIC_ADDR`,
// and we need to be able to promote this. So check if this deref matches
// that specific pattern.
self.validate_local(local)?;
}
ProjectionElem::Field(..) => {
let base_ty = place_base.ty(self.body, self.tcx).ty;
if base_ty.is_union() {
// No promotion of union field accesses.
return Err(Unpromotable);
}
}
// We need to make sure this is a `Deref` of a local with no further projections.
// Discussion can be found at
// https://github.com/rust-lang/rust/pull/74945#discussion_r463063247
if let Some(local) = place_base.as_local()
&& let TempState::Defined { location, .. } = self.temps[local]
&& let Left(def_stmt) = self.body.stmt_at(location)
&& let Some((_, Rvalue::Use(Operand::Constant(c)))) = def_stmt.kind.as_assign()
&& let Some(did) = c.check_static_ptr(self.tcx)
// Evaluating a promoted may not read statics except if it got
// promoted from a static (this is a CTFE check). So we
// can only promote static accesses inside statics.
&& let Some(hir::ConstContext::Static(..)) = self.const_kind
&& !self.tcx.is_thread_local_static(did)
{
// Recurse.
} else {
return Err(Unpromotable);
}
}
ProjectionElem::Index(local) => {
// Only accept if we can predict the index and are indexing an array.
if let TempState::Defined { location: loc, .. } = self.temps[local]
&& let Left(statement) = self.body.stmt_at(loc)
&& let Some((_, Rvalue::Use(Operand::Constant(c)))) = statement.kind.as_assign()
&& let Some(idx) = c.const_.try_eval_target_usize(self.tcx, self.param_env)
// Determine the type of the thing we are indexing.
&& let ty::Array(_, len) = place_base.ty(self.body, self.tcx).ty.kind()
// It's an array; determine its length.
&& let Some(len) = len.try_eval_target_usize(self.tcx, self.param_env)
// If the index is in-bounds, go ahead.
&& idx < len
{
self.validate_local(local)?;
// Recurse.
} else {
return Err(Unpromotable);
}
}
self.validate_place(place_base)
ProjectionElem::Field(..) => {
let base_ty = place_base.ty(self.body, self.tcx).ty;
if base_ty.is_union() {
// No promotion of union field accesses.
return Err(Unpromotable);
}
}
}
self.validate_place(place_base)
}
fn validate_operand(&mut self, operand: &Operand<'tcx>) -> Result<(), Unpromotable> {
@ -676,7 +603,7 @@ fn validate_call(
}
// FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`.
pub fn validate_candidates(
fn validate_candidates(
ccx: &ConstCx<'_, '_>,
temps: &mut IndexSlice<Local, TempState>,
candidates: &[Candidate],
@ -930,7 +857,7 @@ fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
}
}
pub fn promote_candidates<'tcx>(
fn promote_candidates<'tcx>(
body: &mut Body<'tcx>,
tcx: TyCtxt<'tcx>,
mut temps: IndexVec<Local, TempState>,