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Consolidate type system const evaluation under traits::evaluate_const #132927

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Nov 12, 2024
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Consolidate type system const evaluation under traits::evaluate_const #132927

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2 changes: 1 addition & 1 deletion compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1491,7 +1491,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
}
} else if self.tcx.features().generic_const_exprs() {
ct.normalize_internal(self.tcx, self.param_env)
rustc_trait_selection::traits::evaluate_const(&self.infcx, ct, self.param_env)
} else {
ct
}
Expand Down
136 changes: 1 addition & 135 deletions compiler/rustc_infer/src/infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,10 +25,10 @@ use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_macros::extension;
pub use rustc_macros::{TypeFoldable, TypeVisitable};
use rustc_middle::bug;
use rustc_middle::infer::canonical::{CanonicalQueryInput, CanonicalVarValues};
use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableValue, ConstVidKey};
use rustc_middle::mir::ConstraintCategory;
use rustc_middle::mir::interpret::{ErrorHandled, EvalToValTreeResult};
use rustc_middle::traits::select;
pub use rustc_middle::ty::IntVarValue;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
Expand All @@ -40,7 +40,6 @@ use rustc_middle::ty::{
self, ConstVid, FloatVid, GenericArg, GenericArgKind, GenericArgs, GenericArgsRef,
GenericParamDefKind, InferConst, IntVid, Ty, TyCtxt, TyVid, TypingMode,
};
use rustc_middle::{bug, span_bug};
use rustc_span::Span;
use rustc_span::symbol::Symbol;
use rustc_type_ir::solve::Reveal;
Expand Down Expand Up @@ -1279,84 +1278,6 @@ impl<'tcx> InferCtxt<'tcx> {
u
}

pub fn try_const_eval_resolve(
&self,
param_env: ty::ParamEnv<'tcx>,
unevaluated: ty::UnevaluatedConst<'tcx>,
span: Span,
) -> Result<ty::Const<'tcx>, ErrorHandled> {
match self.const_eval_resolve(param_env, unevaluated, span) {
Ok(Ok(val)) => Ok(ty::Const::new_value(
self.tcx,
val,
self.tcx.type_of(unevaluated.def).instantiate(self.tcx, unevaluated.args),
)),
Ok(Err(bad_ty)) => {
let tcx = self.tcx;
let def_id = unevaluated.def;
span_bug!(
tcx.def_span(def_id),
"unable to construct a valtree for the unevaluated constant {:?}: type {bad_ty} is not valtree-compatible",
unevaluated
);
}
Err(err) => Err(err),
}
}

/// Resolves and evaluates a constant.
///
/// The constant can be located on a trait like `<A as B>::C`, in which case the given
/// generic parameters and environment are used to resolve the constant. Alternatively if the
/// constant has generic parameters in scope the instantiations are used to evaluate the value
/// of the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
/// constant `bar::<T>()` requires a instantiation for `T`, if the instantiation for `T` is
/// still too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
/// returned.
///
/// This handles inferences variables within both `param_env` and `args` by
/// performing the operation on their respective canonical forms.
#[instrument(skip(self), level = "debug")]
pub fn const_eval_resolve(
&self,
mut param_env: ty::ParamEnv<'tcx>,
unevaluated: ty::UnevaluatedConst<'tcx>,
span: Span,
) -> EvalToValTreeResult<'tcx> {
let mut args = self.resolve_vars_if_possible(unevaluated.args);
debug!(?args);

// Postpone the evaluation of constants whose args depend on inference
// variables
let tcx = self.tcx;
if args.has_non_region_infer() {
if let Some(ct) = tcx.thir_abstract_const(unevaluated.def)? {
let ct = tcx.expand_abstract_consts(ct.instantiate(tcx, args));
if let Err(e) = ct.error_reported() {
return Err(ErrorHandled::Reported(e.into(), span));
} else if ct.has_non_region_infer() || ct.has_non_region_param() {
return Err(ErrorHandled::TooGeneric(span));
} else {
args = replace_param_and_infer_args_with_placeholder(tcx, args);
}
} else {
args = GenericArgs::identity_for_item(tcx, unevaluated.def);
param_env = tcx.param_env(unevaluated.def);
}
}

let param_env_erased = tcx.erase_regions(param_env);
let args_erased = tcx.erase_regions(args);
debug!(?param_env_erased);
debug!(?args_erased);

let unevaluated = ty::UnevaluatedConst { def: unevaluated.def, args: args_erased };

// The return value is the evaluated value which doesn't contain any reference to inference
// variables, thus we don't need to instantiate back the original values.
tcx.const_eval_resolve_for_typeck(param_env_erased, unevaluated, span)
}

/// The returned function is used in a fast path. If it returns `true` the variable is
/// unchanged, `false` indicates that the status is unknown.
#[inline]
Expand Down Expand Up @@ -1622,61 +1543,6 @@ impl RegionVariableOrigin {
}
}

/// Replaces args that reference param or infer variables with suitable
/// placeholders. This function is meant to remove these param and infer
/// args when they're not actually needed to evaluate a constant.
fn replace_param_and_infer_args_with_placeholder<'tcx>(
tcx: TyCtxt<'tcx>,
args: GenericArgsRef<'tcx>,
) -> GenericArgsRef<'tcx> {
struct ReplaceParamAndInferWithPlaceholder<'tcx> {
tcx: TyCtxt<'tcx>,
idx: u32,
}

impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReplaceParamAndInferWithPlaceholder<'tcx> {
fn cx(&self) -> TyCtxt<'tcx> {
self.tcx
}

fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
if let ty::Infer(_) = t.kind() {
let idx = {
let idx = self.idx;
self.idx += 1;
idx
};
Ty::new_placeholder(self.tcx, ty::PlaceholderType {
universe: ty::UniverseIndex::ROOT,
bound: ty::BoundTy {
var: ty::BoundVar::from_u32(idx),
kind: ty::BoundTyKind::Anon,
},
})
} else {
t.super_fold_with(self)
}
}

fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
if let ty::ConstKind::Infer(_) = c.kind() {
ty::Const::new_placeholder(self.tcx, ty::PlaceholderConst {
universe: ty::UniverseIndex::ROOT,
bound: ty::BoundVar::from_u32({
let idx = self.idx;
self.idx += 1;
idx
}),
})
} else {
c.super_fold_with(self)
}
}
}

args.fold_with(&mut ReplaceParamAndInferWithPlaceholder { tcx, idx: 0 })
}

impl<'tcx> InferCtxt<'tcx> {
/// Given a [`hir::Block`], get the span of its last expression or
/// statement, peeling off any inner blocks.
Expand Down
20 changes: 9 additions & 11 deletions compiler/rustc_middle/src/mir/consts.rs
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Original file line number Diff line number Diff line change
@@ -1,17 +1,17 @@
use std::fmt::{self, Debug, Display, Formatter};

use either::Either;
use rustc_abi::{HasDataLayout, Size};
use rustc_hir::def_id::DefId;
use rustc_macros::{HashStable, Lift, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
use rustc_session::RemapFileNameExt;
use rustc_session::config::RemapPathScopeComponents;
use rustc_span::{DUMMY_SP, Span};
use rustc_type_ir::visit::TypeVisitableExt;

use crate::mir::interpret::{AllocId, ConstAllocation, ErrorHandled, Scalar, alloc_range};
use crate::mir::{Promoted, pretty_print_const_value};
use crate::ty::print::{pretty_print_const, with_no_trimmed_paths};
use crate::ty::{self, GenericArgsRef, ScalarInt, Ty, TyCtxt};
use crate::ty::{self, ConstKind, GenericArgsRef, ScalarInt, Ty, TyCtxt};

///////////////////////////////////////////////////////////////////////////
/// Evaluated Constants
Expand Down Expand Up @@ -319,15 +319,13 @@ impl<'tcx> Const<'tcx> {
) -> Result<ConstValue<'tcx>, ErrorHandled> {
match self {
Const::Ty(_, c) => {
// We want to consistently have a "clean" value for type system constants (i.e., no
// data hidden in the padding), so we always go through a valtree here.
match c.eval_valtree(tcx, param_env, span) {
Ok((ty, val)) => Ok(tcx.valtree_to_const_val((ty, val))),
Err(Either::Left(_bad_ty)) => Err(tcx
.dcx()
.delayed_bug("`mir::Const::eval` called on a non-valtree-compatible type")
.into()),
Err(Either::Right(e)) => Err(e),
if c.has_non_region_param() {
return Err(ErrorHandled::TooGeneric(span));
}

match c.kind() {
ConstKind::Value(ty, val) => Ok(tcx.valtree_to_const_val((ty, val))),
_ => Err(tcx.dcx().delayed_bug("Unevaluated `ty::Const` in MIR body").into()),
}
}
Const::Unevaluated(uneval, _) => {
Expand Down
59 changes: 2 additions & 57 deletions compiler/rustc_middle/src/ty/consts.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,3 @@
use either::Either;
use rustc_data_structures::intern::Interned;
use rustc_error_messages::MultiSpan;
use rustc_hir::def::{DefKind, Res};
Expand All @@ -9,7 +8,7 @@ use rustc_type_ir::{self as ir, TypeFlags, WithCachedTypeInfo};
use tracing::{debug, instrument};

use crate::middle::resolve_bound_vars as rbv;
use crate::mir::interpret::{ErrorHandled, LitToConstInput, Scalar};
use crate::mir::interpret::{LitToConstInput, Scalar};
use crate::ty::{self, GenericArgs, ParamEnv, ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt};

mod int;
Expand All @@ -18,7 +17,7 @@ mod valtree;

pub use int::*;
pub use kind::*;
use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
use rustc_span::{DUMMY_SP, ErrorGuaranteed};
pub use valtree::*;

pub type ConstKind<'tcx> = ir::ConstKind<TyCtxt<'tcx>>;
Expand Down Expand Up @@ -363,60 +362,6 @@ impl<'tcx> Const<'tcx> {
Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
}

/// Returns the evaluated constant as a valtree;
/// if that fails due to a valtree-incompatible type, indicate which type that is
/// by returning `Err(Left(bad_type))`.
#[inline]
pub fn eval_valtree(
self,
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
span: Span,
) -> Result<(Ty<'tcx>, ValTree<'tcx>), Either<Ty<'tcx>, ErrorHandled>> {
assert!(!self.has_escaping_bound_vars(), "escaping vars in {self:?}");
match self.kind() {
ConstKind::Unevaluated(unevaluated) => {
// FIXME(eddyb) maybe the `const_eval_*` methods should take
// `ty::ParamEnvAnd` instead of having them separate.
let (param_env, unevaluated) = unevaluated.prepare_for_eval(tcx, param_env);
// try to resolve e.g. associated constants to their definition on an impl, and then
// evaluate the const.
match tcx.const_eval_resolve_for_typeck(param_env, unevaluated, span) {
Ok(Ok(c)) => {
Ok((tcx.type_of(unevaluated.def).instantiate(tcx, unevaluated.args), c))
}
Ok(Err(bad_ty)) => Err(Either::Left(bad_ty)),
Err(err) => Err(Either::Right(err)),
}
}
ConstKind::Value(ty, val) => Ok((ty, val)),
ConstKind::Error(g) => Err(Either::Right(g.into())),
ConstKind::Param(_)
| ConstKind::Infer(_)
| ConstKind::Bound(_, _)
| ConstKind::Placeholder(_)
| ConstKind::Expr(_) => Err(Either::Right(ErrorHandled::TooGeneric(span))),
}
}

/// Normalizes the constant to a value or an error if possible.
#[inline]
pub fn normalize_internal(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Self {
match self.eval_valtree(tcx, param_env, DUMMY_SP) {
Ok((ty, val)) => Self::new_value(tcx, val, ty),
Err(Either::Left(_bad_ty)) => {
// This can happen when we run on ill-typed code.
Self::new_error(
tcx,
tcx.dcx()
.delayed_bug("`ty::Const::eval` called on a non-valtree-compatible type"),
)
}
Err(Either::Right(ErrorHandled::Reported(r, _span))) => Self::new_error(tcx, r.into()),
Err(Either::Right(ErrorHandled::TooGeneric(_span))) => self,
}
}

/// Panics if self.kind != ty::ConstKind::Value
pub fn to_valtree(self) -> (ty::ValTree<'tcx>, Ty<'tcx>) {
match self.kind() {
Expand Down
36 changes: 1 addition & 35 deletions compiler/rustc_middle/src/ty/consts/kind.rs
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Original file line number Diff line number Diff line change
@@ -1,46 +1,12 @@
use std::assert_matches::assert_matches;

use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable, extension};
use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};

use super::Const;
use crate::mir;
use crate::ty::abstract_const::CastKind;
use crate::ty::visit::TypeVisitableExt as _;
use crate::ty::{self, Ty, TyCtxt};

#[extension(pub(crate) trait UnevaluatedConstEvalExt<'tcx>)]
impl<'tcx> ty::UnevaluatedConst<'tcx> {
/// FIXME(RalfJung): I cannot explain what this does or why it makes sense, but not doing this
/// hurts performance.
#[inline]
fn prepare_for_eval(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> (ty::ParamEnv<'tcx>, Self) {
// HACK(eddyb) this erases lifetimes even though `const_eval_resolve`
// also does later, but we want to do it before checking for
// inference variables.
// Note that we erase regions *before* calling `with_reveal_all_normalized`,
// so that we don't try to invoke this query with
// any region variables.

// HACK(eddyb) when the query key would contain inference variables,
// attempt using identity args and `ParamEnv` instead, that will succeed
// when the expression doesn't depend on any parameters.
// FIXME(eddyb, skinny121) pass `InferCtxt` into here when it's available, so that
// we can call `infcx.const_eval_resolve` which handles inference variables.
if (param_env, self).has_non_region_infer() {
(tcx.param_env(self.def), ty::UnevaluatedConst {
def: self.def,
args: ty::GenericArgs::identity_for_item(tcx, self.def),
})
} else {
(tcx.erase_regions(param_env).with_reveal_all_normalized(tcx), tcx.erase_regions(self))
}
}
}

#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
#[derive(HashStable, TyEncodable, TyDecodable, TypeVisitable, TypeFoldable)]
pub enum ExprKind {
Expand Down
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