1 use crate::mir::interpret::ConstValue;
2 use crate::mir::interpret::{LitToConstInput, Scalar};
4 self, InlineConstSubsts, InlineConstSubstsParts, InternalSubsts, ParamEnv, ParamEnvAnd, Ty,
7 use rustc_errors::ErrorReported;
9 use rustc_hir::def_id::{DefId, LocalDefId};
10 use rustc_macros::HashStable;
20 /// Typed constant value.
21 #[derive(Copy, Clone, Debug, Hash, TyEncodable, TyDecodable, Eq, PartialEq, Ord, PartialOrd)]
23 pub struct Const<'tcx> {
26 pub val: ConstKind<'tcx>,
29 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
30 static_assert_size!(Const<'_>, 48);
32 impl<'tcx> Const<'tcx> {
33 /// Literals and const generic parameters are eagerly converted to a constant, everything else
34 /// becomes `Unevaluated`.
35 pub fn from_anon_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx Self {
36 Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id))
39 pub fn from_opt_const_arg_anon_const(
41 def: ty::WithOptConstParam<LocalDefId>,
43 debug!("Const::from_anon_const(def={:?})", def);
45 let body_id = match tcx.hir().get_by_def_id(def.did) {
46 hir::Node::AnonConst(ac) => ac.body,
48 tcx.def_span(def.did.to_def_id()),
49 "from_anon_const can only process anonymous constants"
53 let expr = &tcx.hir().body(body_id).value;
55 let ty = tcx.type_of(def.def_id_for_type_of());
57 match Self::try_eval_lit_or_param(tcx, ty, expr) {
59 None => tcx.mk_const(ty::Const {
60 val: ty::ConstKind::Unevaluated(ty::Unevaluated {
62 substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
70 fn try_eval_lit_or_param(
73 expr: &'tcx hir::Expr<'tcx>,
74 ) -> Option<&'tcx Self> {
75 let lit_input = match expr.kind {
76 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
77 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => match expr.kind {
78 hir::ExprKind::Lit(ref lit) => {
79 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
86 if let Some(lit_input) = lit_input {
87 // If an error occurred, ignore that it's a literal and leave reporting the error up to
89 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
92 tcx.sess.delay_span_bug(expr.span, "Const::from_anon_const: couldn't lit_to_const");
96 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
97 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
98 let expr = match &expr.kind {
99 hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
100 block.expr.as_ref().unwrap()
105 use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
107 ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
108 // Find the name and index of the const parameter by indexing the generics of
109 // the parent item and construct a `ParamConst`.
110 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
111 let item_id = tcx.hir().get_parent_node(hir_id);
112 let item_def_id = tcx.hir().local_def_id(item_id);
113 let generics = tcx.generics_of(item_def_id.to_def_id());
114 let index = generics.param_def_id_to_index[&def_id];
115 let name = tcx.hir().name(hir_id);
116 Some(tcx.mk_const(ty::Const {
117 val: ty::ConstKind::Param(ty::ParamConst::new(index, name)),
125 pub fn from_inline_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx Self {
126 debug!("Const::from_inline_const(def_id={:?})", def_id);
128 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
130 let body_id = match tcx.hir().get(hir_id) {
131 hir::Node::AnonConst(ac) => ac.body,
133 tcx.def_span(def_id.to_def_id()),
134 "from_inline_const can only process anonymous constants"
138 let expr = &tcx.hir().body(body_id).value;
140 let ty = tcx.typeck(def_id).node_type(hir_id);
142 let ret = match Self::try_eval_lit_or_param(tcx, ty, expr) {
145 let typeck_root_def_id = tcx.typeck_root_def_id(def_id.to_def_id());
147 tcx.erase_regions(InternalSubsts::identity_for_item(tcx, typeck_root_def_id));
149 InlineConstSubsts::new(tcx, InlineConstSubstsParts { parent_substs, ty })
151 tcx.mk_const(ty::Const {
152 val: ty::ConstKind::Unevaluated(ty::Unevaluated {
153 def: ty::WithOptConstParam::unknown(def_id).to_global(),
161 debug_assert!(!ret.has_free_regions());
165 /// Interns the given value as a constant.
167 pub fn from_value(tcx: TyCtxt<'tcx>, val: ConstValue<'tcx>, ty: Ty<'tcx>) -> &'tcx Self {
168 tcx.mk_const(Self { val: ConstKind::Value(val), ty })
172 /// Interns the given scalar as a constant.
173 pub fn from_scalar(tcx: TyCtxt<'tcx>, val: Scalar, ty: Ty<'tcx>) -> &'tcx Self {
174 Self::from_value(tcx, ConstValue::Scalar(val), ty)
178 /// Creates a constant with the given integer value and interns it.
179 pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> &'tcx Self {
182 .unwrap_or_else(|e| panic!("could not compute layout for {:?}: {:?}", ty, e))
184 Self::from_scalar(tcx, Scalar::from_uint(bits, size), ty.value)
188 /// Creates an interned zst constant.
189 pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> &'tcx Self {
190 Self::from_scalar(tcx, Scalar::ZST, ty)
194 /// Creates an interned bool constant.
195 pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> &'tcx Self {
196 Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
200 /// Creates an interned usize constant.
201 pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> &'tcx Self {
202 Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
206 /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
207 /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
208 /// contains const generic parameters or pointers).
209 pub fn try_eval_bits(
212 param_env: ParamEnv<'tcx>,
215 assert_eq!(self.ty, ty);
216 let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
217 // if `ty` does not depend on generic parameters, use an empty param_env
218 self.val.eval(tcx, param_env).try_to_bits(size)
222 pub fn try_eval_bool(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
223 self.val.eval(tcx, param_env).try_to_bool()
227 pub fn try_eval_usize(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u64> {
228 self.val.eval(tcx, param_env).try_to_machine_usize(tcx)
232 /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
233 /// unevaluated constant.
234 pub fn eval(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> &Const<'tcx> {
235 if let Some(val) = self.val.try_eval(tcx, param_env) {
237 Ok(val) => Const::from_value(tcx, val, self.ty),
238 Err(ErrorReported) => tcx.const_error(self.ty),
246 /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
247 pub fn eval_bits(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
248 self.try_eval_bits(tcx, param_env, ty)
249 .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
253 /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
254 pub fn eval_usize(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
255 self.try_eval_usize(tcx, param_env)
256 .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
260 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Const<'tcx> {
261 let default_def_id = match tcx.hir().get_by_def_id(def_id.expect_local()) {
262 hir::Node::GenericParam(hir::GenericParam {
263 kind: hir::GenericParamKind::Const { ty: _, default: Some(ac) },
265 }) => tcx.hir().local_def_id(ac.hir_id),
267 tcx.def_span(def_id),
268 "`const_param_default` expected a generic parameter with a constant"
271 Const::from_anon_const(tcx, default_def_id)