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Reduce Some Code Repetitions like (n << amt) >> amt #58569

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Feb 20, 2019
Merged

Reduce Some Code Repetitions like (n << amt) >> amt #58569

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10 changes: 4 additions & 6 deletions src/librustc_mir/interpret/operand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ use rustc::mir::interpret::{
GlobalId, AllocId, InboundsCheck,
ConstValue, Pointer, Scalar,
EvalResult, EvalErrorKind,
sign_extend, truncate,
};
use super::{
EvalContext, Machine, AllocMap, Allocation, AllocationExtra,
Expand Down Expand Up @@ -633,20 +634,17 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
Err(_) => return err!(InvalidDiscriminant(raw_discr.erase_tag())),
};
let real_discr = if discr_val.layout.ty.is_signed() {
let i = bits_discr as i128;
// going from layout tag type to typeck discriminant type
// requires first sign extending with the layout discriminant
let shift = 128 - discr_val.layout.size.bits();
let sexted = (i << shift) >> shift;
let sexted = sign_extend(bits_discr, discr_val.layout.size) as i128;
// and then zeroing with the typeck discriminant type
let discr_ty = rval.layout.ty
.ty_adt_def().expect("tagged layout corresponds to adt")
.repr
.discr_type();
let discr_ty = layout::Integer::from_attr(self, discr_ty);
let shift = 128 - discr_ty.size().bits();
let size = layout::Integer::from_attr(self, discr_ty).size();
let truncatee = sexted as u128;
(truncatee << shift) >> shift
truncate(truncatee, size)
} else {
bits_discr
};
Expand Down