use std::convert::TryInto; use crate::mir::interpret::{AllocId, ConstValue, Scalar}; use crate::mir::Promoted; use crate::ty::subst::{InternalSubsts, SubstsRef}; use crate::ty::ParamEnv; use crate::ty::{self, TyCtxt, TypeVisitable}; use rustc_errors::ErrorGuaranteed; use rustc_hir::def_id::DefId; use rustc_macros::HashStable; use rustc_target::abi::Size; use super::ScalarInt; /// An unevaluated, potentially generic, constant. #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Lift)] #[derive(Hash, HashStable)] pub struct Unevaluated<'tcx, P = Option> { pub def: ty::WithOptConstParam, pub substs: SubstsRef<'tcx>, pub promoted: P, } impl<'tcx> Unevaluated<'tcx> { #[inline] pub fn shrink(self) -> Unevaluated<'tcx, ()> { debug_assert_eq!(self.promoted, None); Unevaluated { def: self.def, substs: self.substs, promoted: () } } } impl<'tcx> Unevaluated<'tcx, ()> { #[inline] pub fn expand(self) -> Unevaluated<'tcx> { Unevaluated { def: self.def, substs: self.substs, promoted: None } } } impl<'tcx, P: Default> Unevaluated<'tcx, P> { #[inline] pub fn new(def: ty::WithOptConstParam, substs: SubstsRef<'tcx>) -> Unevaluated<'tcx, P> { Unevaluated { def, substs, promoted: Default::default() } } } /// Represents a constant in Rust. #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)] #[derive(Hash, HashStable)] pub enum ConstKind<'tcx> { /// A const generic parameter. Param(ty::ParamConst), /// Infer the value of the const. Infer(InferConst<'tcx>), /// Bound const variable, used only when preparing a trait query. Bound(ty::DebruijnIndex, ty::BoundVar), /// A placeholder const - universally quantified higher-ranked const. Placeholder(ty::PlaceholderConst<'tcx>), /// Used in the HIR by using `Unevaluated` everywhere and later normalizing to one of the other /// variants when the code is monomorphic enough for that. Unevaluated(Unevaluated<'tcx>), /// Used to hold computed value. Value(ty::ValTree<'tcx>), /// A placeholder for a const which could not be computed; this is /// propagated to avoid useless error messages. Error(ty::DelaySpanBugEmitted), } #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))] static_assert_size!(ConstKind<'_>, 40); impl<'tcx> ConstKind<'tcx> { #[inline] pub fn try_to_value(self) -> Option> { if let ConstKind::Value(val) = self { Some(val) } else { None } } #[inline] pub fn try_to_scalar(self) -> Option> { self.try_to_value()?.try_to_scalar() } #[inline] pub fn try_to_scalar_int(self) -> Option { self.try_to_value()?.try_to_scalar_int() } #[inline] pub fn try_to_bits(self, size: Size) -> Option { self.try_to_scalar_int()?.to_bits(size).ok() } #[inline] pub fn try_to_bool(self) -> Option { self.try_to_scalar_int()?.try_into().ok() } #[inline] pub fn try_to_machine_usize(self, tcx: TyCtxt<'tcx>) -> Option { self.try_to_value()?.try_to_machine_usize(tcx) } } /// An inference variable for a const, for use in const generics. #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Hash)] #[derive(HashStable)] pub enum InferConst<'tcx> { /// Infer the value of the const. Var(ty::ConstVid<'tcx>), /// A fresh const variable. See `infer::freshen` for more details. Fresh(u32), } enum EvalMode { Typeck, Mir, } enum EvalResult<'tcx> { ValTree(ty::ValTree<'tcx>), ConstVal(ConstValue<'tcx>), } impl<'tcx> ConstKind<'tcx> { #[inline] /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the /// unevaluated constant. pub fn eval(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Self { self.try_eval_for_typeck(tcx, param_env).and_then(Result::ok).map_or(self, ConstKind::Value) } #[inline] /// Tries to evaluate the constant if it is `Unevaluated`. If that isn't possible or necessary /// return `None`. // FIXME(@lcnr): Completely rework the evaluation/normalization system for `ty::Const` once valtrees are merged. pub fn try_eval_for_mir( self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ) -> Option, ErrorGuaranteed>> { match self.try_eval_inner(tcx, param_env, EvalMode::Mir) { Some(Ok(EvalResult::ValTree(_))) => unreachable!(), Some(Ok(EvalResult::ConstVal(v))) => Some(Ok(v)), Some(Err(e)) => Some(Err(e)), None => None, } } #[inline] /// Tries to evaluate the constant if it is `Unevaluated`. If that isn't possible or necessary /// return `None`. // FIXME(@lcnr): Completely rework the evaluation/normalization system for `ty::Const` once valtrees are merged. pub fn try_eval_for_typeck( self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ) -> Option, ErrorGuaranteed>> { match self.try_eval_inner(tcx, param_env, EvalMode::Typeck) { Some(Ok(EvalResult::ValTree(v))) => Some(Ok(v)), Some(Ok(EvalResult::ConstVal(_))) => unreachable!(), Some(Err(e)) => Some(Err(e)), None => None, } } #[inline] fn try_eval_inner( self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, eval_mode: EvalMode, ) -> Option, ErrorGuaranteed>> { if let ConstKind::Unevaluated(unevaluated) = self { use crate::mir::interpret::ErrorHandled; // 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. let param_env_and = tcx .erase_regions(param_env) .with_reveal_all_normalized(tcx) .and(tcx.erase_regions(unevaluated)); // HACK(eddyb) when the query key would contain inference variables, // attempt using identity substs 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. let param_env_and = if param_env_and.needs_infer() { tcx.param_env(unevaluated.def.did).and(ty::Unevaluated { def: unevaluated.def, substs: InternalSubsts::identity_for_item(tcx, unevaluated.def.did), promoted: unevaluated.promoted, }) } else { param_env_and }; // FIXME(eddyb) maybe the `const_eval_*` methods should take // `ty::ParamEnvAnd` instead of having them separate. let (param_env, unevaluated) = param_env_and.into_parts(); // try to resolve e.g. associated constants to their definition on an impl, and then // evaluate the const. match eval_mode { EvalMode::Typeck => { match tcx.const_eval_resolve_for_typeck(param_env, unevaluated, None) { // NOTE(eddyb) `val` contains no lifetimes/types/consts, // and we use the original type, so nothing from `substs` // (which may be identity substs, see above), // can leak through `val` into the const we return. Ok(val) => Some(Ok(EvalResult::ValTree(val?))), Err(ErrorHandled::TooGeneric | ErrorHandled::Linted) => None, Err(ErrorHandled::Reported(e)) => Some(Err(e)), } } EvalMode::Mir => { match tcx.const_eval_resolve(param_env, unevaluated, None) { // NOTE(eddyb) `val` contains no lifetimes/types/consts, // and we use the original type, so nothing from `substs` // (which may be identity substs, see above), // can leak through `val` into the const we return. Ok(val) => Some(Ok(EvalResult::ConstVal(val))), Err(ErrorHandled::TooGeneric | ErrorHandled::Linted) => None, Err(ErrorHandled::Reported(e)) => Some(Err(e)), } } } } else { None } } }