compiler/rustc_middle/src/ty/consts.rs

   1 use crate::mir::interpret::ConstValue;
   2 use crate::mir::interpret::{LitToConstInput, Scalar};
   3 use crate::ty::{
   4     self, InlineConstSubsts, InlineConstSubstsParts, InternalSubsts, ParamEnv, ParamEnvAnd, Ty,
   5     TyCtxt, TypeFoldable,
   6 };
   7 use rustc_data_structures::intern::Interned;
   8 use rustc_errors::ErrorGuaranteed;
   9 use rustc_hir as hir;
  10 use rustc_hir::def_id::{DefId, LocalDefId};
  11 use rustc_macros::HashStable;
  12 use std::fmt;
  13
  14 mod int;
  15 mod kind;
  16 mod valtree;
  17
  18 pub use int::*;
  19 pub use kind::*;
  20 pub use valtree::*;
  21
  22 /// Use this rather than `ConstS`, whenever possible.
  23 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, HashStable)]
  24 #[rustc_pass_by_value]
  25 pub struct Const<'tcx>(pub Interned<'tcx, ConstS<'tcx>>);
  26
  27 impl<'tcx> fmt::Debug for Const<'tcx> {
  28     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  29         // This reflects what `Const` looked liked before `Interned` was
  30         // introduced. We print it like this to avoid having to update expected
  31         // output in a lot of tests.
  32         write!(f, "Const {{ ty: {:?}, val: {:?} }}", self.ty(), self.val())
  33     }
  34 }
  35
  36 /// Typed constant value.
  37 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
  38 pub struct ConstS<'tcx> {
  39     pub ty: Ty<'tcx>,
  40     pub val: ConstKind<'tcx>,
  41 }
  42
  43 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
  44 static_assert_size!(ConstS<'_>, 48);
  45
  46 impl<'tcx> Const<'tcx> {
  47     pub fn ty(self) -> Ty<'tcx> {
  48         self.0.ty
  49     }
  50
  51     pub fn val(self) -> ConstKind<'tcx> {
  52         self.0.val
  53     }
  54
  55     /// Literals and const generic parameters are eagerly converted to a constant, everything else
  56     /// becomes `Unevaluated`.
  57     pub fn from_anon_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
  58         Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id))
  59     }
  60
  61     #[instrument(skip(tcx), level = "debug")]
  62     pub fn from_opt_const_arg_anon_const(
  63         tcx: TyCtxt<'tcx>,
  64         def: ty::WithOptConstParam<LocalDefId>,
  65     ) -> Self {
  66         debug!("Const::from_anon_const(def={:?})", def);
  67
  68         let body_id = match tcx.hir().get_by_def_id(def.did) {
  69             hir::Node::AnonConst(ac) => ac.body,
  70             _ => span_bug!(
  71                 tcx.def_span(def.did.to_def_id()),
  72                 "from_anon_const can only process anonymous constants"
  73             ),
  74         };
  75
  76         let expr = &tcx.hir().body(body_id).value;
  77         debug!(?expr);
  78
  79         let ty = tcx.type_of(def.def_id_for_type_of());
  80
  81         match Self::try_eval_lit_or_param(tcx, ty, expr) {
  82             Some(v) => v,
  83             None => tcx.mk_const(ty::ConstS {
  84                 val: ty::ConstKind::Unevaluated(ty::Unevaluated {
  85                     def: def.to_global(),
  86                     substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
  87                     promoted: None,
  88                 }),
  89                 ty,
  90             }),
  91         }
  92     }
  93
  94     #[instrument(skip(tcx), level = "debug")]
  95     fn try_eval_lit_or_param(
  96         tcx: TyCtxt<'tcx>,
  97         ty: Ty<'tcx>,
  98         expr: &'tcx hir::Expr<'tcx>,
  99     ) -> Option<Self> {
 100         // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
 101         // currently have to be wrapped in curly brackets, so it's necessary to special-case.
 102         let expr = match &expr.kind {
 103             hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
 104                 block.expr.as_ref().unwrap()
 105             }
 106             _ => expr,
 107         };
 108
 109         let lit_input = match expr.kind {
 110             hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
 111             hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => match expr.kind {
 112                 hir::ExprKind::Lit(ref lit) => {
 113                     Some(LitToConstInput { lit: &lit.node, ty, neg: true })
 114                 }
 115                 _ => None,
 116             },
 117             _ => None,
 118         };
 119
 120         if let Some(lit_input) = lit_input {
 121             // If an error occurred, ignore that it's a literal and leave reporting the error up to
 122             // mir.
 123             match tcx.at(expr.span).lit_to_const(lit_input) {
 124                 Ok(c) => return Some(c),
 125                 Err(e) => {
 126                     tcx.sess.delay_span_bug(
 127                         expr.span,
 128                         &format!("Const::from_anon_const: couldn't lit_to_const {:?}", e),
 129                     );
 130                 }
 131             }
 132         }
 133
 134         use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
 135         match expr.kind {
 136             ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
 137                 // Find the name and index of the const parameter by indexing the generics of
 138                 // the parent item and construct a `ParamConst`.
 139                 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
 140                 let item_id = tcx.hir().get_parent_node(hir_id);
 141                 let item_def_id = tcx.hir().local_def_id(item_id);
 142                 let generics = tcx.generics_of(item_def_id.to_def_id());
 143                 let index = generics.param_def_id_to_index[&def_id];
 144                 let name = tcx.hir().name(hir_id);
 145                 Some(tcx.mk_const(ty::ConstS {
 146                     val: ty::ConstKind::Param(ty::ParamConst::new(index, name)),
 147                     ty,
 148                 }))
 149             }
 150             _ => None,
 151         }
 152     }
 153
 154     pub fn from_inline_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Self {
 155         debug!("Const::from_inline_const(def_id={:?})", def_id);
 156
 157         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 158
 159         let body_id = match tcx.hir().get(hir_id) {
 160             hir::Node::AnonConst(ac) => ac.body,
 161             _ => span_bug!(
 162                 tcx.def_span(def_id.to_def_id()),
 163                 "from_inline_const can only process anonymous constants"
 164             ),
 165         };
 166
 167         let expr = &tcx.hir().body(body_id).value;
 168
 169         let ty = tcx.typeck(def_id).node_type(hir_id);
 170
 171         let ret = match Self::try_eval_lit_or_param(tcx, ty, expr) {
 172             Some(v) => v,
 173             None => {
 174                 let typeck_root_def_id = tcx.typeck_root_def_id(def_id.to_def_id());
 175                 let parent_substs =
 176                     tcx.erase_regions(InternalSubsts::identity_for_item(tcx, typeck_root_def_id));
 177                 let substs =
 178                     InlineConstSubsts::new(tcx, InlineConstSubstsParts { parent_substs, ty })
 179                         .substs;
 180                 tcx.mk_const(ty::ConstS {
 181                     val: ty::ConstKind::Unevaluated(ty::Unevaluated {
 182                         def: ty::WithOptConstParam::unknown(def_id).to_global(),
 183                         substs,
 184                         promoted: None,
 185                     }),
 186                     ty,
 187                 })
 188             }
 189         };
 190         debug_assert!(!ret.has_free_regions());
 191         ret
 192     }
 193
 194     /// Interns the given value as a constant.
 195     #[inline]
 196     pub fn from_value(tcx: TyCtxt<'tcx>, val: ConstValue<'tcx>, ty: Ty<'tcx>) -> Self {
 197         tcx.mk_const(ConstS { val: ConstKind::Value(val), ty })
 198     }
 199
 200     #[inline]
 201     /// Interns the given scalar as a constant.
 202     pub fn from_scalar(tcx: TyCtxt<'tcx>, val: Scalar, ty: Ty<'tcx>) -> Self {
 203         Self::from_value(tcx, ConstValue::Scalar(val), ty)
 204     }
 205
 206     #[inline]
 207     /// Creates a constant with the given integer value and interns it.
 208     pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> Self {
 209         let size = tcx
 210             .layout_of(ty)
 211             .unwrap_or_else(|e| panic!("could not compute layout for {:?}: {:?}", ty, e))
 212             .size;
 213         Self::from_scalar(tcx, Scalar::from_uint(bits, size), ty.value)
 214     }
 215
 216     #[inline]
 217     /// Creates an interned zst constant.
 218     pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Self {
 219         Self::from_scalar(tcx, Scalar::ZST, ty)
 220     }
 221
 222     #[inline]
 223     /// Creates an interned bool constant.
 224     pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> Self {
 225         Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
 226     }
 227
 228     #[inline]
 229     /// Creates an interned usize constant.
 230     pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> Self {
 231         Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
 232     }
 233
 234     #[inline]
 235     /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
 236     /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
 237     /// contains const generic parameters or pointers).
 238     pub fn try_eval_bits(
 239         self,
 240         tcx: TyCtxt<'tcx>,
 241         param_env: ParamEnv<'tcx>,
 242         ty: Ty<'tcx>,
 243     ) -> Option<u128> {
 244         assert_eq!(self.ty(), ty);
 245         let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
 246         // if `ty` does not depend on generic parameters, use an empty param_env
 247         self.val().eval(tcx, param_env).try_to_bits(size)
 248     }
 249
 250     #[inline]
 251     pub fn try_eval_bool(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
 252         self.val().eval(tcx, param_env).try_to_bool()
 253     }
 254
 255     #[inline]
 256     pub fn try_eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u64> {
 257         self.val().eval(tcx, param_env).try_to_machine_usize(tcx)
 258     }
 259
 260     #[inline]
 261     /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
 262     /// unevaluated constant.
 263     pub fn eval(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Const<'tcx> {
 264         if let Some(val) = self.val().try_eval(tcx, param_env) {
 265             match val {
 266                 Ok(val) => Const::from_value(tcx, val, self.ty()),
 267                 Err(ErrorGuaranteed { .. }) => tcx.const_error(self.ty()),
 268             }
 269         } else {
 270             self
 271         }
 272     }
 273
 274     #[inline]
 275     /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
 276     pub fn eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
 277         self.try_eval_bits(tcx, param_env, ty)
 278             .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
 279     }
 280
 281     #[inline]
 282     /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
 283     pub fn eval_usize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
 284         self.try_eval_usize(tcx, param_env)
 285             .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
 286     }
 287 }
 288
 289 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Const<'tcx> {
 290     let default_def_id = match tcx.hir().get_by_def_id(def_id.expect_local()) {
 291         hir::Node::GenericParam(hir::GenericParam {
 292             kind: hir::GenericParamKind::Const { ty: _, default: Some(ac) },
 293             ..
 294         }) => tcx.hir().local_def_id(ac.hir_id),
 295         _ => span_bug!(
 296             tcx.def_span(def_id),
 297             "`const_param_default` expected a generic parameter with a constant"
 298         ),
 299     };
 300     Const::from_anon_const(tcx, default_def_id)
 301 }