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use super::{ErrorHandled, EvalToConstValueResult, GlobalId};
use crate::mir;
use crate::ty::fold::TypeFoldable;
use crate::ty::subst::InternalSubsts;
use crate::ty::{self, query::TyCtxtAt, TyCtxt};
use rustc_hir::def_id::DefId;
use rustc_span::{Span, DUMMY_SP};
impl<'tcx> TyCtxt<'tcx> {
/// Evaluates a constant without providing any substitutions. This is useful to evaluate consts
/// that can't take any generic arguments like statics, const items or enum discriminants. If a
/// generic parameter is used within the constant `ErrorHandled::ToGeneric` will be returned.
pub fn const_eval_poly(self, def_id: DefId) -> EvalToConstValueResult<'tcx> {
// In some situations def_id will have substitutions within scope, but they aren't allowed
// to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions
// into `const_eval` which will return `ErrorHandled::ToGeneric` if any of them are
// encountered.
let substs = InternalSubsts::identity_for_item(self, def_id);
let instance = ty::Instance::new(def_id, substs);
let cid = GlobalId { instance, promoted: None };
let param_env = self.param_env(def_id).with_reveal_all_normalized(self);
self.const_eval_global_id(param_env, cid, None)
}
/// Resolves and evaluates a constant.
///
/// The constant can be located on a trait like `<A as B>::C`, in which case the given
/// substitutions and environment are used to resolve the constant. Alternatively if the
/// constant has generic parameters in scope the substitutions 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 substitution for `T`, if the substitution for `T` is still
/// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
/// returned.
#[instrument(level = "debug", skip(self))]
pub fn const_eval_resolve(
self,
param_env: ty::ParamEnv<'tcx>,
ct: ty::Unevaluated<'tcx>,
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
// Cannot resolve `Unevaluated` constants that contain inference
// variables. We reject those here since `resolve_opt_const_arg`
// would fail otherwise.
//
// When trying to evaluate constants containing inference variables,
// use `Infcx::const_eval_resolve` instead.
if ct.substs.has_infer_types_or_consts() {
bug!("did not expect inference variables here");
}
match ty::Instance::resolve_opt_const_arg(self, param_env, ct.def, ct.substs) {
Ok(Some(instance)) => {
let cid = GlobalId { instance, promoted: ct.promoted };
self.const_eval_global_id(param_env, cid, span)
}
Ok(None) => Err(ErrorHandled::TooGeneric),
Err(error_reported) => Err(ErrorHandled::Reported(error_reported)),
}
}
pub fn const_eval_instance(
self,
param_env: ty::ParamEnv<'tcx>,
instance: ty::Instance<'tcx>,
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
self.const_eval_global_id(param_env, GlobalId { instance, promoted: None }, span)
}
/// Evaluate a constant.
pub fn const_eval_global_id(
self,
param_env: ty::ParamEnv<'tcx>,
cid: GlobalId<'tcx>,
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
let param_env = param_env.with_const();
// Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
// improve caching of queries.
let inputs = self.erase_regions(param_env.and(cid));
if let Some(span) = span {
self.at(span).eval_to_const_value_raw(inputs)
} else {
self.eval_to_const_value_raw(inputs)
}
}
/// Evaluate a static's initializer, returning the allocation of the initializer's memory.
#[inline(always)]
pub fn eval_static_initializer(
self,
def_id: DefId,
) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
self.at(DUMMY_SP).eval_static_initializer(def_id)
}
}
impl<'tcx> TyCtxtAt<'tcx> {
/// Evaluate a static's initializer, returning the allocation of the initializer's memory.
pub fn eval_static_initializer(
self,
def_id: DefId,
) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
trace!("eval_static_initializer: Need to compute {:?}", def_id);
assert!(self.is_static(def_id));
let instance = ty::Instance::mono(*self, def_id);
let gid = GlobalId { instance, promoted: None };
self.eval_to_allocation(gid, ty::ParamEnv::reveal_all())
}
/// Evaluate anything constant-like, returning the allocation of the final memory.
fn eval_to_allocation(
self,
gid: GlobalId<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Result<mir::ConstAllocation<'tcx>, ErrorHandled> {
let param_env = param_env.with_const();
trace!("eval_to_allocation: Need to compute {:?}", gid);
let raw_const = self.eval_to_allocation_raw(param_env.and(gid))?;
Ok(self.global_alloc(raw_const.alloc_id).unwrap_memory())
}
}
impl<'tcx> TyCtxt<'tcx> {
/// Destructure a type-level constant ADT or array into its variant index and its field values.
/// Panics if the destructuring fails, use `try_destructure_const` for fallible version.
pub fn destructure_const(
self,
param_env_and_val: ty::ParamEnvAnd<'tcx, ty::Const<'tcx>>,
) -> mir::DestructuredConst<'tcx> {
self.try_destructure_const(param_env_and_val).unwrap()
}
/// Destructure a mir constant ADT or array into its variant index and its field values.
/// Panics if the destructuring fails, use `try_destructure_const` for fallible version.
pub fn destructure_mir_constant(
self,
param_env: ty::ParamEnv<'tcx>,
constant: mir::ConstantKind<'tcx>,
) -> mir::DestructuredMirConstant<'tcx> {
self.try_destructure_mir_constant(param_env.and(constant)).unwrap()
}
}
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