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Rollup merge of #102076 - cuviper:transmute-discr-endian, r=jackh726

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rustc_transmute: fix big-endian discriminants

I noticed that some new tests were failing in Fedora on s390x only, which usually means there's a problem with big-endian, and sure enough there's a FIXME(``@jswrenn)`` for that in `rustc_transmute`. This patch implements the appropriate consideration for target endianness, rather than using native (host) endian.
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Dylan DPC 2022-09-22 18:25:54 +05:30 committed by GitHub
commit 7cac18e1be
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1 changed files with 16 additions and 6 deletions
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22
compiler/rustc_transmute/src/layout/tree.rs
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@ -404,7 +404,7 @@ pub(crate) mod rustc {
.unwrap();
trace!(?discr_layout, "computed discriminant layout");
variant_layout = variant_layout.extend(discr_layout).unwrap().0;
tree = tree.then(Self::from_disr(discr, tcx, layout_summary.discriminant_size));
tree = tree.then(Self::from_discr(discr, tcx, layout_summary.discriminant_size));
}
// Next come fields.
@ -444,11 +444,21 @@ pub(crate) mod rustc {
Ok(tree)
}
pub fn from_disr(discr: Discr<'tcx>, tcx: TyCtxt<'tcx>, size: usize) -> Self {
// FIXME(@jswrenn): I'm certain this is missing needed endian nuance.
let bytes = discr.val.to_ne_bytes();
let bytes = &bytes[..size];
Self::Seq(bytes.into_iter().copied().map(|b| Self::from_bits(b)).collect())
pub fn from_discr(discr: Discr<'tcx>, tcx: TyCtxt<'tcx>, size: usize) -> Self {
use rustc_target::abi::Endian;
let bytes: [u8; 16];
let bytes = match tcx.data_layout.endian {
Endian::Little => {
bytes = discr.val.to_le_bytes();
&bytes[..size]
}
Endian::Big => {
bytes = discr.val.to_be_bytes();
&bytes[bytes.len() - size..]
}
};
Self::Seq(bytes.iter().map(|&b| Self::from_bits(b)).collect())
}
}