compiler/rustc_mir_build/src/build/expr/as_constant.rs

   1 //! See docs in build/expr/mod.rs
   2
   3 use crate::build::{parse_float_into_constval, Builder};
   4 use rustc_ast as ast;
   5 use rustc_middle::mir;
   6 use rustc_middle::mir::interpret::{Allocation, LitToConstError, LitToConstInput, Scalar};
   7 use rustc_middle::mir::*;
   8 use rustc_middle::thir::*;
   9 use rustc_middle::ty::{
  10     self, CanonicalUserType, CanonicalUserTypeAnnotation, TyCtxt, UserTypeAnnotationIndex,
  11 };
  12 use rustc_span::DUMMY_SP;
  13 use rustc_target::abi::Size;
  14
  15 impl<'a, 'tcx> Builder<'a, 'tcx> {
  16     /// Compile `expr`, yielding a compile-time constant. Assumes that
  17     /// `expr` is a valid compile-time constant!
  18     pub(crate) fn as_constant(&mut self, expr: &Expr<'tcx>) -> ConstOperand<'tcx> {
  19         let this = self;
  20         let tcx = this.tcx;
  21         let Expr { ty, temp_lifetime: _, span, ref kind } = *expr;
  22         match kind {
  23             ExprKind::Scope { region_scope: _, lint_level: _, value } => {
  24                 this.as_constant(&this.thir[*value])
  25             }
  26             _ => as_constant_inner(
  27                 expr,
  28                 |user_ty| {
  29                     Some(this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
  30                         span,
  31                         user_ty: user_ty.clone(),
  32                         inferred_ty: ty,
  33                     }))
  34                 },
  35                 tcx,
  36             ),
  37         }
  38     }
  39 }
  40
  41 pub fn as_constant_inner<'tcx>(
  42     expr: &Expr<'tcx>,
  43     push_cuta: impl FnMut(&Box<CanonicalUserType<'tcx>>) -> Option<UserTypeAnnotationIndex>,
  44     tcx: TyCtxt<'tcx>,
  45 ) -> ConstOperand<'tcx> {
  46     let Expr { ty, temp_lifetime: _, span, ref kind } = *expr;
  47     match *kind {
  48         ExprKind::Literal { lit, neg } => {
  49             let const_ = match lit_to_mir_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg })
  50             {
  51                 Ok(c) => c,
  52                 Err(LitToConstError::Reported(guar)) => {
  53                     Const::Ty(ty::Const::new_error(tcx, guar, ty))
  54                 }
  55                 Err(LitToConstError::TypeError) => {
  56                     bug!("encountered type error in `lit_to_mir_constant`")
  57                 }
  58             };
  59
  60             ConstOperand { span, user_ty: None, const_ }
  61         }
  62         ExprKind::NonHirLiteral { lit, ref user_ty } => {
  63             let user_ty = user_ty.as_ref().and_then(push_cuta);
  64
  65             let const_ = Const::Val(ConstValue::Scalar(Scalar::Int(lit)), ty);
  66
  67             ConstOperand { span, user_ty, const_ }
  68         }
  69         ExprKind::ZstLiteral { ref user_ty } => {
  70             let user_ty = user_ty.as_ref().and_then(push_cuta);
  71
  72             let const_ = Const::Val(ConstValue::ZeroSized, ty);
  73
  74             ConstOperand { span, user_ty, const_ }
  75         }
  76         ExprKind::NamedConst { def_id, args, ref user_ty } => {
  77             let user_ty = user_ty.as_ref().and_then(push_cuta);
  78
  79             let uneval = mir::UnevaluatedConst::new(def_id, args);
  80             let const_ = Const::Unevaluated(uneval, ty);
  81
  82             ConstOperand { user_ty, span, const_ }
  83         }
  84         ExprKind::ConstParam { param, def_id: _ } => {
  85             let const_param = ty::Const::new_param(tcx, param, expr.ty);
  86             let const_ = Const::Ty(const_param);
  87
  88             ConstOperand { user_ty: None, span, const_ }
  89         }
  90         ExprKind::ConstBlock { did: def_id, args } => {
  91             let uneval = mir::UnevaluatedConst::new(def_id, args);
  92             let const_ = Const::Unevaluated(uneval, ty);
  93
  94             ConstOperand { user_ty: None, span, const_ }
  95         }
  96         ExprKind::StaticRef { alloc_id, ty, .. } => {
  97             let const_val = ConstValue::Scalar(Scalar::from_pointer(alloc_id.into(), &tcx));
  98             let const_ = Const::Val(const_val, ty);
  99
 100             ConstOperand { span, user_ty: None, const_ }
 101         }
 102         _ => span_bug!(span, "expression is not a valid constant {:?}", kind),
 103     }
 104 }
 105
 106 #[instrument(skip(tcx, lit_input))]
 107 fn lit_to_mir_constant<'tcx>(
 108     tcx: TyCtxt<'tcx>,
 109     lit_input: LitToConstInput<'tcx>,
 110 ) -> Result<Const<'tcx>, LitToConstError> {
 111     let LitToConstInput { lit, ty, neg } = lit_input;
 112     let trunc = |n| {
 113         let param_ty = ty::ParamEnv::reveal_all().and(ty);
 114         let width = tcx
 115             .layout_of(param_ty)
 116             .map_err(|_| {
 117                 LitToConstError::Reported(tcx.sess.span_delayed_bug(
 118                     DUMMY_SP,
 119                     format!("couldn't compute width of literal: {:?}", lit_input.lit),
 120                 ))
 121             })?
 122             .size;
 123         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
 124         let result = width.truncate(n);
 125         trace!("trunc result: {}", result);
 126         Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
 127     };
 128
 129     let value = match (lit, &ty.kind()) {
 130         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
 131             let s = s.as_str();
 132             let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes());
 133             let allocation = tcx.mk_const_alloc(allocation);
 134             ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
 135         }
 136         (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _))
 137             if matches!(inner_ty.kind(), ty::Slice(_)) =>
 138         {
 139             let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
 140             let allocation = tcx.mk_const_alloc(allocation);
 141             ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
 142         }
 143         (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
 144             let id = tcx.allocate_bytes(data);
 145             ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
 146         }
 147         (ast::LitKind::CStr(data, _), ty::Ref(_, inner_ty, _)) if matches!(inner_ty.kind(), ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().c_str()) =>
 148         {
 149             let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
 150             let allocation = tcx.mk_const_alloc(allocation);
 151             ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
 152         }
 153         (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
 154             ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
 155         }
 156         (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
 157             trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?
 158         }
 159         (ast::LitKind::Float(n, _), ty::Float(fty)) => parse_float_into_constval(*n, *fty, neg)
 160             .ok_or_else(|| {
 161                 LitToConstError::Reported(tcx.sess.span_delayed_bug(
 162                     DUMMY_SP,
 163                     format!("couldn't parse float literal: {:?}", lit_input.lit),
 164                 ))
 165             })?,
 166         (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
 167         (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
 168         (ast::LitKind::Err, _) => {
 169             return Err(LitToConstError::Reported(
 170                 tcx.sess.span_delayed_bug(DUMMY_SP, "encountered LitKind::Err during mir build"),
 171             ));
 172         }
 173         _ => return Err(LitToConstError::TypeError),
 174     };
 175
 176     Ok(Const::Val(value, ty))
 177 }