Add `tag_for_variant` query

This query allows for sharing code between `rustc_const_eval` and
`rustc_transmutability`.

Also moves `DummyMachine` to `rustc_const_eval`.

1 files changed, 19 insertions, 25 deletions

diff --git a/compiler/rustc_transmute/src/layout/tree.rs b/compiler/rustc_transmute/src/layout/tree.rs
index 9a43d67d435..f6bc224c7e7 100644
--- a/compiler/rustc_transmute/src/layout/tree.rs
+++ b/compiler/rustc_transmute/src/layout/tree.rs
@@ -174,10 +174,10 @@ pub(crate) mod rustc {
     use crate::layout::rustc::{Def, Ref};
 
     use rustc_middle::ty::layout::LayoutError;
-    use rustc_middle::ty::util::Discr;
     use rustc_middle::ty::AdtDef;
     use rustc_middle::ty::GenericArgsRef;
     use rustc_middle::ty::ParamEnv;
+    use rustc_middle::ty::ScalarInt;
     use rustc_middle::ty::VariantDef;
     use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
     use rustc_span::ErrorGuaranteed;
@@ -331,14 +331,15 @@ pub(crate) mod rustc {
                             trace!(?adt_def, "treeifying enum");
                             let mut tree = Tree::uninhabited();
 
-                            for (idx, discr) in adt_def.discriminants(tcx) {
+                            for (idx, variant) in adt_def.variants().iter_enumerated() {
+                                let tag = tcx.tag_for_variant((ty, idx));
                                 tree = tree.or(Self::from_repr_c_variant(
                                     ty,
                                     *adt_def,
                                     args_ref,
                                     &layout_summary,
-                                    Some(discr),
-                                    adt_def.variant(idx),
+                                    tag,
+                                    variant,
                                     tcx,
                                 )?);
                             }
@@ -393,7 +394,7 @@ pub(crate) mod rustc {
             adt_def: AdtDef<'tcx>,
             args_ref: GenericArgsRef<'tcx>,
             layout_summary: &LayoutSummary,
-            discr: Option<Discr<'tcx>>,
+            tag: Option<ScalarInt>,
             variant_def: &'tcx VariantDef,
             tcx: TyCtxt<'tcx>,
         ) -> Result<Self, Err> {
@@ -403,9 +404,6 @@ pub(crate) mod rustc {
             let min_align = repr.align.unwrap_or(Align::ONE);
             let max_align = repr.pack.unwrap_or(Align::MAX);
 
-            let clamp =
-                |align: Align| align.clamp(min_align, max_align).bytes().try_into().unwrap();
-
             let variant_span = trace_span!(
                 "treeifying variant",
                 min_align = ?min_align,
@@ -419,17 +417,12 @@ pub(crate) mod rustc {
             )
             .unwrap();
 
-            // The layout of the variant is prefixed by the discriminant, if any.
-            if let Some(discr) = discr {
-                trace!(?discr, "treeifying discriminant");
-                let discr_layout = alloc::Layout::from_size_align(
-                    layout_summary.discriminant_size,
-                    clamp(layout_summary.discriminant_align),
-                )
-                .unwrap();
-                trace!(?discr_layout, "computed discriminant layout");
-                variant_layout = variant_layout.extend(discr_layout).unwrap().0;
-                tree = tree.then(Self::from_discr(discr, tcx, layout_summary.discriminant_size));
+            // The layout of the variant is prefixed by the tag, if any.
+            if let Some(tag) = tag {
+                let tag_layout =
+                    alloc::Layout::from_size_align(tag.size().bytes_usize(), 1).unwrap();
+                tree = tree.then(Self::from_tag(tag, tcx));
+                variant_layout = variant_layout.extend(tag_layout).unwrap().0;
             }
 
             // Next come fields.
@@ -469,18 +462,19 @@ pub(crate) mod rustc {
             Ok(tree)
         }
 
-        pub fn from_discr(discr: Discr<'tcx>, tcx: TyCtxt<'tcx>, size: usize) -> Self {
+        pub fn from_tag(tag: ScalarInt, tcx: TyCtxt<'tcx>) -> Self {
             use rustc_target::abi::Endian;
-
+            let size = tag.size();
+            let bits = tag.to_bits(size).unwrap();
             let bytes: [u8; 16];
             let bytes = match tcx.data_layout.endian {
                 Endian::Little => {
-                    bytes = discr.val.to_le_bytes();
-                    &bytes[..size]
+                    bytes = bits.to_le_bytes();
+                    &bytes[..size.bytes_usize()]
                 }
                 Endian::Big => {
-                    bytes = discr.val.to_be_bytes();
-                    &bytes[bytes.len() - size..]
+                    bytes = bits.to_be_bytes();
+                    &bytes[bytes.len() - size.bytes_usize()..]
                 }
             };
             Self::Seq(bytes.iter().map(|&b| Self::from_bits(b)).collect())