compiler/rustc_middle/src/mir/interpret/queries.rs

   1 use super::{ErrorHandled, EvalToConstValueResult, GlobalId};
   2
   3 use crate::mir;
   4 use crate::ty::subst::{InternalSubsts, SubstsRef};
   5 use crate::ty::{self, TyCtxt};
   6 use rustc_hir::def_id::DefId;
   7 use rustc_span::Span;
   8
   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
  17         // encountered.
  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)
  23     }
  24
  25     /// Resolves and evaluates a constant.
  26     ///
  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
  33     /// returned.
  34     #[instrument(level = "debug", skip(self))]
  35     pub fn const_eval_resolve(
  36         self,
  37         param_env: ty::ParamEnv<'tcx>,
  38         def: ty::WithOptConstParam<DefId>,
  39         substs: SubstsRef<'tcx>,
  40         promoted: Option<mir::Promoted>,
  41         span: Option<Span>,
  42     ) -> EvalToConstValueResult<'tcx> {
  43         match ty::Instance::resolve_opt_const_arg(self, param_env, def, substs) {
  44             Ok(Some(instance)) => {
  45                 let cid = GlobalId { instance, promoted };
  46                 self.const_eval_global_id(param_env, cid, span)
  47             }
  48             Ok(None) => Err(ErrorHandled::TooGeneric),
  49             Err(error_reported) => Err(ErrorHandled::Reported(error_reported)),
  50         }
  51     }
  52
  53     pub fn const_eval_instance(
  54         self,
  55         param_env: ty::ParamEnv<'tcx>,
  56         instance: ty::Instance<'tcx>,
  57         span: Option<Span>,
  58     ) -> EvalToConstValueResult<'tcx> {
  59         self.const_eval_global_id(param_env, GlobalId { instance, promoted: None }, span)
  60     }
  61
  62     /// Evaluate a constant.
  63     pub fn const_eval_global_id(
  64         self,
  65         param_env: ty::ParamEnv<'tcx>,
  66         cid: GlobalId<'tcx>,
  67         span: Option<Span>,
  68     ) -> EvalToConstValueResult<'tcx> {
  69         // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
  70         // improve caching of queries.
  71         let inputs = self.erase_regions(param_env.and(cid));
  72         if let Some(span) = span {
  73             self.at(span).eval_to_const_value_raw(inputs)
  74         } else {
  75             self.eval_to_const_value_raw(inputs)
  76         }
  77     }
  78
  79     /// Evaluate a static's initializer, returning the allocation of the initializer's memory.
  80     pub fn eval_static_initializer(
  81         self,
  82         def_id: DefId,
  83     ) -> Result<&'tcx mir::Allocation, ErrorHandled> {
  84         trace!("eval_static_initializer: Need to compute {:?}", def_id);
  85         assert!(self.is_static(def_id));
  86         let instance = ty::Instance::mono(self, def_id);
  87         let gid = GlobalId { instance, promoted: None };
  88         self.eval_to_allocation(gid, ty::ParamEnv::reveal_all())
  89     }
  90
  91     /// Evaluate anything constant-like, returning the allocation of the final memory.
  92     fn eval_to_allocation(
  93         self,
  94         gid: GlobalId<'tcx>,
  95         param_env: ty::ParamEnv<'tcx>,
  96     ) -> Result<&'tcx mir::Allocation, ErrorHandled> {
  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())
 100     }
 101 }