compiler/rustc_mir_build/src/thir/constant.rs

   1 use rustc_apfloat::Float;
   2 use rustc_ast as ast;
   3 use rustc_middle::mir::interpret::{
   4     Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar,
   5 };
   6 use rustc_middle::ty::{self, ParamEnv, TyCtxt};
   7 use rustc_span::symbol::Symbol;
   8 use rustc_target::abi::Size;
   9
  10 crate fn lit_to_const<'tcx>(
  11     tcx: TyCtxt<'tcx>,
  12     lit_input: LitToConstInput<'tcx>,
  13 ) -> Result<&'tcx ty::Const<'tcx>, LitToConstError> {
  14     let LitToConstInput { lit, ty, neg } = lit_input;
  15
  16     let trunc = |n| {
  17         let param_ty = ParamEnv::reveal_all().and(ty);
  18         let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size;
  19         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
  20         let result = width.truncate(n);
  21         trace!("trunc result: {}", result);
  22         Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
  23     };
  24
  25     let lit = match (lit, &ty.kind()) {
  26         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
  27             let s = s.as_str();
  28             let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes());
  29             let allocation = tcx.intern_const_alloc(allocation);
  30             ConstValue::Slice { data: allocation, start: 0, end: s.len() }
  31         }
  32         (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _))
  33             if matches!(inner_ty.kind(), ty::Slice(_)) =>
  34         {
  35             let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
  36             let allocation = tcx.intern_const_alloc(allocation);
  37             ConstValue::Slice { data: allocation, start: 0, end: data.len() }
  38         }
  39         (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
  40             let id = tcx.allocate_bytes(data);
  41             ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
  42         }
  43         (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
  44             ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
  45         }
  46         (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
  47             trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?
  48         }
  49         (ast::LitKind::Float(n, _), ty::Float(fty)) => parse_float(*n, *fty, neg),
  50         (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
  51         (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
  52         (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
  53         _ => return Err(LitToConstError::TypeError),
  54     };
  55     Ok(ty::Const::from_value(tcx, lit, ty))
  56 }
  57
  58 fn parse_float<'tcx>(num: Symbol, fty: ty::FloatTy, neg: bool) -> ConstValue<'tcx> {
  59     let num = num.as_str();
  60     use rustc_apfloat::ieee::{Double, Single};
  61     let scalar = match fty {
  62         ty::FloatTy::F32 => {
  63             let rust_f = num
  64                 .parse::<f32>()
  65                 .unwrap_or_else(|e| panic!("f32 failed to parse `{}`: {:?}", num, e));
  66             let mut f = num.parse::<Single>().unwrap_or_else(|e| {
  67                 panic!("apfloat::ieee::Single failed to parse `{}`: {:?}", num, e)
  68             });
  69             assert!(
  70                 u128::from(rust_f.to_bits()) == f.to_bits(),
  71                 "apfloat::ieee::Single gave different result for `{}`: \
  72                  {}({:#x}) vs Rust's {}({:#x})",
  73                 rust_f,
  74                 f,
  75                 f.to_bits(),
  76                 Single::from_bits(rust_f.to_bits().into()),
  77                 rust_f.to_bits()
  78             );
  79             if neg {
  80                 f = -f;
  81             }
  82             Scalar::from_f32(f)
  83         }
  84         ty::FloatTy::F64 => {
  85             let rust_f = num
  86                 .parse::<f64>()
  87                 .unwrap_or_else(|e| panic!("f64 failed to parse `{}`: {:?}", num, e));
  88             let mut f = num.parse::<Double>().unwrap_or_else(|e| {
  89                 panic!("apfloat::ieee::Double failed to parse `{}`: {:?}", num, e)
  90             });
  91             assert!(
  92                 u128::from(rust_f.to_bits()) == f.to_bits(),
  93                 "apfloat::ieee::Double gave different result for `{}`: \
  94                  {}({:#x}) vs Rust's {}({:#x})",
  95                 rust_f,
  96                 f,
  97                 f.to_bits(),
  98                 Double::from_bits(rust_f.to_bits().into()),
  99                 rust_f.to_bits()
 100             );
 101             if neg {
 102                 f = -f;
 103             }
 104             Scalar::from_f64(f)
 105         }
 106     };
 107
 108     ConstValue::Scalar(scalar)
 109 }