1 use super::{ErrorHandled, EvalToConstValueResult, GlobalId};
4 use crate::ty::subst::InternalSubsts;
5 use crate::ty::{self, TyCtxt};
6 use rustc_hir::def_id::DefId;
9 impl<'tcx> TyCtxt<'tcx> {
10 /// Evaluates a constant without providing any substitutions. This is useful to evaluate consts
11 /// that can't take any generic arguments like statics, const items or enum discriminants. If a
12 /// generic parameter is used within the constant `ErrorHandled::ToGeneric` will be returned.
13 pub fn const_eval_poly(self, def_id: DefId) -> EvalToConstValueResult<'tcx> {
14 // In some situations def_id will have substitutions within scope, but they aren't allowed
15 // to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions
16 // into `const_eval` which will return `ErrorHandled::ToGeneric` if any of them are
18 let substs = InternalSubsts::identity_for_item(self, def_id);
19 let instance = ty::Instance::new(def_id, substs);
20 let cid = GlobalId { instance, promoted: None };
21 let param_env = self.param_env(def_id).with_reveal_all_normalized(self);
22 self.const_eval_global_id(param_env, cid, None)
25 /// Resolves and evaluates a constant.
27 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
28 /// substitutions and environment are used to resolve the constant. Alternatively if the
29 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
30 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
31 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
32 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
34 #[instrument(level = "debug", skip(self))]
35 pub fn const_eval_resolve(
37 param_env: ty::ParamEnv<'tcx>,
38 ct: ty::Unevaluated<'tcx>,
40 ) -> EvalToConstValueResult<'tcx> {
41 match ty::Instance::resolve_opt_const_arg(self, param_env, ct.def, ct.substs) {
42 Ok(Some(instance)) => {
43 let cid = GlobalId { instance, promoted: ct.promoted };
44 self.const_eval_global_id(param_env, cid, span)
46 Ok(None) => Err(ErrorHandled::TooGeneric),
47 Err(error_reported) => Err(ErrorHandled::Reported(error_reported)),
51 pub fn const_eval_instance(
53 param_env: ty::ParamEnv<'tcx>,
54 instance: ty::Instance<'tcx>,
56 ) -> EvalToConstValueResult<'tcx> {
57 self.const_eval_global_id(param_env, GlobalId { instance, promoted: None }, span)
60 /// Evaluate a constant.
61 pub fn const_eval_global_id(
63 param_env: ty::ParamEnv<'tcx>,
66 ) -> EvalToConstValueResult<'tcx> {
67 let param_env = param_env.with_const();
68 // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
69 // improve caching of queries.
70 let inputs = self.erase_regions(param_env.and(cid));
71 if let Some(span) = span {
72 self.at(span).eval_to_const_value_raw(inputs)
74 self.eval_to_const_value_raw(inputs)
78 /// Evaluate a static's initializer, returning the allocation of the initializer's memory.
79 pub fn eval_static_initializer(
82 ) -> Result<&'tcx mir::Allocation, ErrorHandled> {
83 trace!("eval_static_initializer: Need to compute {:?}", def_id);
84 assert!(self.is_static(def_id));
85 let instance = ty::Instance::mono(self, def_id);
86 let gid = GlobalId { instance, promoted: None };
87 self.eval_to_allocation(gid, ty::ParamEnv::reveal_all())
90 /// Evaluate anything constant-like, returning the allocation of the final memory.
91 fn eval_to_allocation(
94 param_env: ty::ParamEnv<'tcx>,
95 ) -> Result<&'tcx mir::Allocation, ErrorHandled> {
96 let param_env = param_env.with_const();
97 trace!("eval_to_allocation: Need to compute {:?}", gid);
98 let raw_const = self.eval_to_allocation_raw(param_env.and(gid))?;
99 Ok(self.global_alloc(raw_const.alloc_id).unwrap_memory())