1 use crate::mir::interpret::ConstValue;
2 use crate::mir::interpret::{LitToConstInput, Scalar};
3 use crate::ty::subst::InternalSubsts;
4 use crate::ty::{self, Ty, TyCtxt};
5 use crate::ty::{ParamEnv, ParamEnvAnd};
6 use rustc_errors::ErrorReported;
8 use rustc_hir::def_id::{DefId, LocalDefId};
9 use rustc_macros::HashStable;
19 /// Typed constant value.
20 #[derive(Copy, Clone, Debug, Hash, TyEncodable, TyDecodable, Eq, PartialEq, Ord, PartialOrd)]
22 pub struct Const<'tcx> {
25 pub val: ConstKind<'tcx>,
28 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
29 static_assert_size!(Const<'_>, 48);
31 impl<'tcx> Const<'tcx> {
32 /// Literals and const generic parameters are eagerly converted to a constant, everything else
33 /// becomes `Unevaluated`.
34 pub fn from_anon_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx Self {
35 Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id))
38 pub fn from_opt_const_arg_anon_const(
40 def: ty::WithOptConstParam<LocalDefId>,
42 debug!("Const::from_anon_const(def={:?})", def);
44 let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
46 let body_id = match tcx.hir().get(hir_id) {
47 hir::Node::AnonConst(ac) => ac.body,
49 tcx.def_span(def.did.to_def_id()),
50 "from_anon_const can only process anonymous constants"
54 let expr = &tcx.hir().body(body_id).value;
56 let ty = tcx.type_of(def.def_id_for_type_of());
58 let lit_input = match expr.kind {
59 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
60 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => match expr.kind {
61 hir::ExprKind::Lit(ref lit) => {
62 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
69 if let Some(lit_input) = lit_input {
70 // If an error occurred, ignore that it's a literal and leave reporting the error up to
72 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
75 tcx.sess.delay_span_bug(expr.span, "Const::from_anon_const: couldn't lit_to_const");
79 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
80 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
81 let expr = match &expr.kind {
82 hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
83 block.expr.as_ref().unwrap()
88 use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
89 let val = match expr.kind {
90 ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
91 // Find the name and index of the const parameter by indexing the generics of
92 // the parent item and construct a `ParamConst`.
93 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
94 let item_id = tcx.hir().get_parent_node(hir_id);
95 let item_def_id = tcx.hir().local_def_id(item_id);
96 let generics = tcx.generics_of(item_def_id.to_def_id());
97 let index = generics.param_def_id_to_index[&def_id];
98 let name = tcx.hir().name(hir_id);
99 ty::ConstKind::Param(ty::ParamConst::new(index, name))
101 _ => ty::ConstKind::Unevaluated(ty::Unevaluated {
102 def: def.to_global(),
103 substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
108 tcx.mk_const(ty::Const { val, ty })
111 /// Interns the given value as a constant.
113 pub fn from_value(tcx: TyCtxt<'tcx>, val: ConstValue<'tcx>, ty: Ty<'tcx>) -> &'tcx Self {
114 tcx.mk_const(Self { val: ConstKind::Value(val), ty })
118 /// Interns the given scalar as a constant.
119 pub fn from_scalar(tcx: TyCtxt<'tcx>, val: Scalar, ty: Ty<'tcx>) -> &'tcx Self {
120 Self::from_value(tcx, ConstValue::Scalar(val), ty)
124 /// Creates a constant with the given integer value and interns it.
125 pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> &'tcx Self {
128 .unwrap_or_else(|e| panic!("could not compute layout for {:?}: {:?}", ty, e))
130 Self::from_scalar(tcx, Scalar::from_uint(bits, size), ty.value)
134 /// Creates an interned zst constant.
135 pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> &'tcx Self {
136 Self::from_scalar(tcx, Scalar::ZST, ty)
140 /// Creates an interned bool constant.
141 pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> &'tcx Self {
142 Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
146 /// Creates an interned usize constant.
147 pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> &'tcx Self {
148 Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
152 /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
153 /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
154 /// contains const generic parameters or pointers).
155 pub fn try_eval_bits(
158 param_env: ParamEnv<'tcx>,
161 assert_eq!(self.ty, ty);
162 let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
163 // if `ty` does not depend on generic parameters, use an empty param_env
164 self.val.eval(tcx, param_env).try_to_bits(size)
168 pub fn try_eval_bool(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
169 self.val.eval(tcx, param_env).try_to_bool()
173 pub fn try_eval_usize(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u64> {
174 self.val.eval(tcx, param_env).try_to_machine_usize(tcx)
178 /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
179 /// unevaluated constant.
180 pub fn eval(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> &Const<'tcx> {
181 if let Some(val) = self.val.try_eval(tcx, param_env) {
183 Ok(val) => Const::from_value(tcx, val, self.ty),
184 Err(ErrorReported) => tcx.const_error(self.ty),
192 /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
193 pub fn eval_bits(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
194 self.try_eval_bits(tcx, param_env, ty)
195 .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
199 /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
200 pub fn eval_usize(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
201 self.try_eval_usize(tcx, param_env)
202 .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
206 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Const<'tcx> {
207 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
208 let default_def_id = match tcx.hir().get(hir_id) {
209 hir::Node::GenericParam(hir::GenericParam {
210 kind: hir::GenericParamKind::Const { ty: _, default: Some(ac) },
212 }) => tcx.hir().local_def_id(ac.hir_id),
214 tcx.def_span(def_id),
215 "`const_param_default` expected a generic parameter with a constant"
218 Const::from_anon_const(tcx, default_def_id)