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initial working state

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This commit is contained in:
Bastian Kauschke 2020-09-10 09:06:30 +02:00
parent 2c69266c06
commit d327fa112b
8 changed files with 313 additions and 13 deletions
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15
compiler/rustc_middle/src/mir/abstract_const.rs Normal file
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@ -0,0 +1,15 @@
//! A subset of a mir body used for const evaluatability checking.
use crate::mir;
use crate::ty;
/// An index into an `AbstractConst`.
pub type NodeId = usize;
/// A node of an `AbstractConst`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable)]
pub enum Node<'tcx> {
Leaf(&'tcx ty::Const<'tcx>),
Binop(mir::BinOp, NodeId, NodeId),
UnaryOp(mir::UnOp, NodeId),
FunctionCall(NodeId, &'tcx [NodeId]),
}

1
compiler/rustc_middle/src/mir/mod.rs
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@ -40,6 +40,7 @@ use std::{iter, mem, option};
use self::predecessors::{PredecessorCache, Predecessors};
pub use self::query::*;
pub mod abstract_const;
pub mod coverage;
pub mod interpret;
pub mod mono;

19
compiler/rustc_middle/src/query/mod.rs
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@ -244,6 +244,25 @@ rustc_queries! {
no_hash
}
/// Try to build an abstract representation of the given constant.
query mir_abstract_const(
key: DefId
) -> Option<&'tcx [mir::abstract_const::Node<'tcx>]> {
desc {
|tcx| "building an abstract representation for {}", tcx.def_path_str(key),
}
}
/// Try to build an abstract representation of the given constant.
query mir_abstract_const_of_const_arg(
key: (LocalDefId, DefId)
) -> Option<&'tcx [mir::abstract_const::Node<'tcx>]> {
desc {
|tcx|
"building an abstract representation for the const argument {}",
tcx.def_path_str(key.0.to_def_id()),
}
}
query mir_drops_elaborated_and_const_checked(
key: ty::WithOptConstParam<LocalDefId>
) -> &'tcx Steal<mir::Body<'tcx>> {

6
compiler/rustc_mir/src/transform/mod.rs
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@ -329,7 +329,11 @@ fn mir_promoted(
// this point, before we steal the mir-const result.
// Also this means promotion can rely on all const checks having been done.
let _ = tcx.mir_const_qualif_opt_const_arg(def);
let _ = if let Some(param_did) = def.const_param_did {
tcx.mir_abstract_const_of_const_arg((def.did, param_did))
} else {
tcx.mir_abstract_const(def.did.to_def_id())
};
let mut body = tcx.mir_const(def).steal();
let mut required_consts = Vec::new();

1
compiler/rustc_trait_selection/src/lib.rs
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@ -12,6 +12,7 @@
#![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
#![feature(bool_to_option)]
#![feature(box_patterns)]
#![feature(drain_filter)]
#![feature(in_band_lifetimes)]
#![feature(crate_visibility_modifier)]

256
compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
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@ -1,10 +1,17 @@
#![allow(warnings)]
use rustc_hir::def::DefKind;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;
use rustc_infer::infer::InferCtxt;
use rustc_middle::mir::abstract_const::{Node, NodeId};
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{self, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::{self, TypeFoldable};
use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
use rustc_session::lint;
use rustc_span::def_id::DefId;
use rustc_span::def_id::{DefId, LocalDefId};
use rustc_span::Span;
pub fn is_const_evaluatable<'cx, 'tcx>(
@ -16,18 +23,23 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
) -> Result<(), ErrorHandled> {
debug!("is_const_evaluatable({:?}, {:?})", def, substs);
if infcx.tcx.features().const_evaluatable_checked {
// FIXME(const_evaluatable_checked): Actually look into generic constants to
// implement const equality.
for pred in param_env.caller_bounds() {
match pred.skip_binders() {
ty::PredicateAtom::ConstEvaluatable(b_def, b_substs) => {
debug!("is_const_evaluatable: caller_bound={:?}, {:?}", b_def, b_substs);
if b_def == def && b_substs == substs {
debug!("is_const_evaluatable: caller_bound ~~> ok");
return Ok(());
if let Some(ct) = AbstractConst::new(infcx.tcx, def, substs) {
for pred in param_env.caller_bounds() {
match pred.skip_binders() {
ty::PredicateAtom::ConstEvaluatable(b_def, b_substs) => {
debug!("is_const_evaluatable: caller_bound={:?}, {:?}", b_def, b_substs);
if b_def == def && b_substs == substs {
debug!("is_const_evaluatable: caller_bound ~~> ok");
return Ok(());
} else if AbstractConst::new(infcx.tcx, b_def, b_substs)
.map_or(false, |b_ct| try_unify(infcx.tcx, ct, b_ct))
{
debug!("is_const_evaluatable: abstract_const ~~> ok");
return Ok(());
}
}
_ => {} // don't care
}
_ => {} // don't care
}
}
}
@ -76,3 +88,223 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
debug!(?concrete, "is_const_evaluatable");
concrete.map(drop)
}
/// A tree representing an anonymous constant.
///
/// This is only able to represent a subset of `MIR`,
/// and should not leak any information about desugarings.
#[derive(Clone, Copy)]
pub struct AbstractConst<'tcx> {
pub inner: &'tcx [Node<'tcx>],
pub substs: SubstsRef<'tcx>,
}
impl AbstractConst<'tcx> {
pub fn new(
tcx: TyCtxt<'tcx>,
def: ty::WithOptConstParam<DefId>,
substs: SubstsRef<'tcx>,
) -> Option<AbstractConst<'tcx>> {
let inner = match (def.did.as_local(), def.const_param_did) {
(Some(did), Some(param_did)) => {
tcx.mir_abstract_const_of_const_arg((did, param_did))?
}
_ => tcx.mir_abstract_const(def.did)?,
};
Some(AbstractConst { inner, substs })
}
#[inline]
pub fn subtree(self, node: NodeId) -> AbstractConst<'tcx> {
AbstractConst { inner: &self.inner[..=node], substs: self.substs }
}
#[inline]
pub fn root(self) -> Node<'tcx> {
self.inner.last().copied().unwrap()
}
}
struct AbstractConstBuilder<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
body: &'a mir::Body<'tcx>,
nodes: Vec<Node<'tcx>>,
locals: IndexVec<mir::Local, NodeId>,
checked_op_locals: BitSet<mir::Local>,
}
impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> {
fn new(tcx: TyCtxt<'tcx>, body: &'a mir::Body<'tcx>) -> Option<AbstractConstBuilder<'a, 'tcx>> {
if body.is_cfg_cyclic() {
return None;
}
Some(AbstractConstBuilder {
tcx,
body,
nodes: vec![],
locals: IndexVec::from_elem(NodeId::MAX, &body.local_decls),
checked_op_locals: BitSet::new_empty(body.local_decls.len()),
})
}
fn add_node(&mut self, n: Node<'tcx>) -> NodeId {
let len = self.nodes.len();
self.nodes.push(n);
len
}
fn operand_to_node(&mut self, op: &mir::Operand<'tcx>) -> Option<NodeId> {
debug!("operand_to_node: op={:?}", op);
const ZERO_FIELD: mir::Field = mir::Field::from_usize(0);
match op {
mir::Operand::Copy(p) | mir::Operand::Move(p) => {
if let Some(p) = p.as_local() {
debug_assert!(!self.checked_op_locals.contains(p));
Some(self.locals[p])
} else if let &[mir::ProjectionElem::Field(ZERO_FIELD, _)] = p.projection.as_ref() {
// Only allow field accesses on the result of checked operations.
if self.checked_op_locals.contains(p.local) {
Some(self.locals[p.local])
} else {
None
}
} else {
None
}
}
mir::Operand::Constant(ct) => Some(self.add_node(Node::Leaf(ct.literal))),
}
}
fn check_binop(op: mir::BinOp) -> bool {
use mir::BinOp::*;
match op {
Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Shl | Shr | Eq | Lt | Le
| Ne | Ge | Gt => true,
Offset => false,
}
}
fn build(mut self) -> Option<&'tcx [Node<'tcx>]> {
let mut block = &self.body.basic_blocks()[mir::START_BLOCK];
loop {
debug!("AbstractConstBuilder: block={:?}", block);
for stmt in block.statements.iter() {
debug!("AbstractConstBuilder: stmt={:?}", stmt);
match stmt.kind {
StatementKind::Assign(box (ref place, ref rvalue)) => {
let local = place.as_local()?;
match *rvalue {
Rvalue::Use(ref operand) => {
self.locals[local] = self.operand_to_node(operand)?;
}
Rvalue::BinaryOp(op, ref lhs, ref rhs) if Self::check_binop(op) => {
let lhs = self.operand_to_node(lhs)?;
let rhs = self.operand_to_node(rhs)?;
self.locals[local] = self.add_node(Node::Binop(op, lhs, rhs));
if op.is_checkable() {
bug!("unexpected unchecked checkable binary operation");
}
}
Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs)
if Self::check_binop(op) =>
{
let lhs = self.operand_to_node(lhs)?;
let rhs = self.operand_to_node(rhs)?;
self.locals[local] = self.add_node(Node::Binop(op, lhs, rhs));
self.checked_op_locals.insert(local);
}
_ => return None,
}
}
_ => return None,
}
}
debug!("AbstractConstBuilder: terminator={:?}", block.terminator());
match block.terminator().kind {
TerminatorKind::Goto { target } => {
block = &self.body.basic_blocks()[target];
}
TerminatorKind::Return => {
warn!(?self.nodes);
return { Some(self.tcx.arena.alloc_from_iter(self.nodes)) };
}
TerminatorKind::Assert { ref cond, expected: false, target, .. } => {
let p = match cond {
mir::Operand::Copy(p) | mir::Operand::Move(p) => p,
mir::Operand::Constant(_) => bug!("Unexpected assert"),
};
const ONE_FIELD: mir::Field = mir::Field::from_usize(1);
debug!("proj: {:?}", p.projection);
if let &[mir::ProjectionElem::Field(ONE_FIELD, _)] = p.projection.as_ref() {
// Only allow asserts checking the result of a checked operation.
if self.checked_op_locals.contains(p.local) {
block = &self.body.basic_blocks()[target];
continue;
}
}
return None;
}
_ => return None,
}
}
}
}
/// Builds an abstract const, do not use this directly, but use `AbstractConst::new` instead.
pub(super) fn mir_abstract_const<'tcx>(
tcx: TyCtxt<'tcx>,
def: ty::WithOptConstParam<LocalDefId>,
) -> Option<&'tcx [Node<'tcx>]> {
if !tcx.features().const_evaluatable_checked {
None
} else {
let body = tcx.mir_const(def).borrow();
AbstractConstBuilder::new(tcx, &body)?.build()
}
}
pub fn try_unify<'tcx>(tcx: TyCtxt<'tcx>, a: AbstractConst<'tcx>, b: AbstractConst<'tcx>) -> bool {
match (a.root(), b.root()) {
(Node::Leaf(a_ct), Node::Leaf(b_ct)) => {
let a_ct = a_ct.subst(tcx, a.substs);
let b_ct = b_ct.subst(tcx, b.substs);
match (a_ct.val, b_ct.val) {
(ty::ConstKind::Param(a_param), ty::ConstKind::Param(b_param)) => {
a_param == b_param
}
(ty::ConstKind::Value(a_val), ty::ConstKind::Value(b_val)) => a_val == b_val,
// If we have `fn a<const N: usize>() -> [u8; N + 1]` and `fn b<const M: usize>() -> [u8; 1 + M]`
// we do not want to use `assert_eq!(a(), b())` to infer that `N` and `M` have to be `1`. This
// means that we can't do anything with inference variables here.
(ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => false,
// FIXME(const_evaluatable_checked): We may want to either actually try
// to evaluate `a_ct` and `b_ct` if they are are fully concrete or something like
// this, for now we just return false here.
_ => false,
}
}
(Node::Binop(a_op, al, ar), Node::Binop(b_op, bl, br)) if a_op == b_op => {
try_unify(tcx, a.subtree(al), b.subtree(bl))
&& try_unify(tcx, a.subtree(ar), b.subtree(br))
}
(Node::UnaryOp(a_op, av), Node::UnaryOp(b_op, bv)) if a_op == b_op => {
try_unify(tcx, a.subtree(av), b.subtree(bv))
}
(Node::FunctionCall(a_f, a_args), Node::FunctionCall(b_f, b_args))
if a_args.len() == b_args.len() =>
{
try_unify(tcx, a.subtree(a_f), b.subtree(b_f))
&& a_args
.iter()
.zip(b_args)
.all(|(&an, &bn)| try_unify(tcx, a.subtree(an), b.subtree(bn)))
}
_ => false,
}
}

14
compiler/rustc_trait_selection/src/traits/mod.rs
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@ -552,6 +552,20 @@ pub fn provide(providers: &mut ty::query::Providers) {
vtable_methods,
type_implements_trait,
subst_and_check_impossible_predicates,
mir_abstract_const: |tcx, def_id| {
let def_id = def_id.as_local()?; // We do not store failed AbstractConst's.
if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
tcx.mir_abstract_const_of_const_arg(def)
} else {
const_evaluatable::mir_abstract_const(tcx, ty::WithOptConstParam::unknown(def_id))
}
},
mir_abstract_const_of_const_arg: |tcx, (did, param_did)| {
const_evaluatable::mir_abstract_const(
tcx,
ty::WithOptConstParam { did, const_param_did: Some(param_did) },
)
},
..*providers
};
}

14
src/test/ui/const-generics/const_evaluatable_checked/less_than.rs Normal file
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@ -0,0 +1,14 @@
// run-pass
#![feature(const_generics, const_evaluatable_checked)]
#![allow(incomplete_features)]
struct Foo<const B: bool>;
fn test<const N: usize>() -> Foo<{ N > 10 }> where Foo<{ N > 10 }>: Sized {
Foo
}
fn main() {
let _: Foo<true> = test::<12>();
let _: Foo<false> = test::<9>();
}