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Rollup merge of #58569 - kenta7777:reduce-code-repetition, r=oli-obk

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Reduce Some Code Repetitions like `(n << amt) >> amt`

This Pull Request is related to [#49937](https://github.com/rust-lang/rust/issues/49937).
This Pull Request has reduced repetition of `(n << amt) >> amt`.
This commit is contained in:
kennytm 2019-02-20 01:13:47 +08:00
commit 95daca4aaf
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1 changed files with 4 additions and 6 deletions
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10
src/librustc_mir/interpret/operand.rs
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@ -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,
@ -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
};