2 files changed, 28 insertions, 13 deletions

diff --git a/compiler/rustc_transmute/src/layout/tree.rs b/compiler/rustc_transmute/src/layout/tree.rs
index 211c813b8..acd4fa63d 100644
--- a/compiler/rustc_transmute/src/layout/tree.rs
+++ b/compiler/rustc_transmute/src/layout/tree.rs
@@ -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())
         }
     }
 
diff --git a/compiler/rustc_transmute/src/lib.rs b/compiler/rustc_transmute/src/lib.rs
index 64cd70d36..f7cc94e53 100644
--- a/compiler/rustc_transmute/src/lib.rs
+++ b/compiler/rustc_transmute/src/lib.rs
@@ -80,11 +80,11 @@ mod rustc {
     }
 
     pub struct TransmuteTypeEnv<'cx, 'tcx> {
-        infcx: &'cx InferCtxt<'cx, 'tcx>,
+        infcx: &'cx InferCtxt<'tcx>,
     }
 
     impl<'cx, 'tcx> TransmuteTypeEnv<'cx, 'tcx> {
-        pub fn new(infcx: &'cx InferCtxt<'cx, 'tcx>) -> Self {
+        pub fn new(infcx: &'cx InferCtxt<'tcx>) -> Self {
             Self { infcx }
         }
 
@@ -115,7 +115,7 @@ mod rustc {
             tcx: TyCtxt<'tcx>,
             param_env: ParamEnv<'tcx>,
             c: Const<'tcx>,
-        ) -> Self {
+        ) -> Option<Self> {
             use rustc_middle::ty::ScalarInt;
             use rustc_middle::ty::TypeVisitable;
             use rustc_span::symbol::sym;
@@ -123,10 +123,15 @@ mod rustc {
             let c = c.eval(tcx, param_env);
 
             if let Some(err) = c.error_reported() {
-                return Self { alignment: true, lifetimes: true, safety: true, validity: true };
+                return Some(Self {
+                    alignment: true,
+                    lifetimes: true,
+                    safety: true,
+                    validity: true,
+                });
             }
 
-            let adt_def = c.ty().ty_adt_def().expect("The given `Const` must be an ADT.");
+            let adt_def = c.ty().ty_adt_def()?;
 
             assert_eq!(
                 tcx.require_lang_item(LangItem::TransmuteOpts, None),
@@ -148,12 +153,12 @@ mod rustc {
                 fields[field_idx].unwrap_leaf() == ScalarInt::TRUE
             };
 
-            Self {
+            Some(Self {
                 alignment: get_field(sym::alignment),
                 lifetimes: get_field(sym::lifetimes),
                 safety: get_field(sym::safety),
                 validity: get_field(sym::validity),
-            }
+            })
         }
     }
 }