compiler/rustc_mir_build/src/thir/constant.rs

   1 use rustc_ast as ast;
   2 use rustc_middle::mir::interpret::{
   3     Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar,
   4 };
   5 use rustc_middle::ty::{self, ParamEnv, TyCtxt};
   6 use rustc_span::symbol::Symbol;
   7 use rustc_target::abi::Size;
   8
   9 crate fn lit_to_const<'tcx>(
  10     tcx: TyCtxt<'tcx>,
  11     lit_input: LitToConstInput<'tcx>,
  12 ) -> Result<&'tcx ty::Const<'tcx>, LitToConstError> {
  13     let LitToConstInput { lit, ty, neg } = lit_input;
  14
  15     let trunc = |n| {
  16         let param_ty = ParamEnv::reveal_all().and(ty);
  17         let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size;
  18         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
  19         let result = width.truncate(n);
  20         trace!("trunc result: {}", result);
  21         Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
  22     };
  23
  24     let lit = match (lit, &ty.kind()) {
  25         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
  26             let s = s.as_str();
  27             let allocation = Allocation::from_byte_aligned_bytes(s.as_bytes());
  28             let allocation = tcx.intern_const_alloc(allocation);
  29             ConstValue::Slice { data: allocation, start: 0, end: s.len() }
  30         }
  31         (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _))
  32             if matches!(inner_ty.kind(), ty::Slice(_)) =>
  33         {
  34             let allocation = Allocation::from_byte_aligned_bytes(data as &[u8]);
  35             let allocation = tcx.intern_const_alloc(allocation);
  36             ConstValue::Slice { data: allocation, start: 0, end: data.len() }
  37         }
  38         (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
  39             let id = tcx.allocate_bytes(data);
  40             ConstValue::Scalar(Scalar::Ptr(id.into()))
  41         }
  42         (ast::LitKind::Byte(n), ty::Uint(ast::UintTy::U8)) => {
  43             ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
  44         }
  45         (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
  46             trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?
  47         }
  48         (ast::LitKind::Float(n, _), ty::Float(fty)) => {
  49             parse_float(*n, *fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
  50         }
  51         (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
  52         (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
  53         (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
  54         _ => return Err(LitToConstError::TypeError),
  55     };
  56     Ok(ty::Const::from_value(tcx, lit, ty))
  57 }
  58
  59 fn parse_float<'tcx>(num: Symbol, fty: ast::FloatTy, neg: bool) -> Result<ConstValue<'tcx>, ()> {
  60     let num = num.as_str();
  61     use rustc_apfloat::ieee::{Double, Single};
  62     let scalar = match fty {
  63         ast::FloatTy::F32 => {
  64             num.parse::<f32>().map_err(|_| ())?;
  65             let mut f = num.parse::<Single>().unwrap_or_else(|e| {
  66                 panic!("apfloat::ieee::Single failed to parse `{}`: {:?}", num, e)
  67             });
  68             if neg {
  69                 f = -f;
  70             }
  71             Scalar::from_f32(f)
  72         }
  73         ast::FloatTy::F64 => {
  74             num.parse::<f64>().map_err(|_| ())?;
  75             let mut f = num.parse::<Double>().unwrap_or_else(|e| {
  76                 panic!("apfloat::ieee::Double failed to parse `{}`: {:?}", num, e)
  77             });
  78             if neg {
  79                 f = -f;
  80             }
  81             Scalar::from_f64(f)
  82         }
  83     };
  84
  85     Ok(ConstValue::Scalar(scalar))
  86 }