Interpret aggregates.

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -13,6 +13,7 @@ use rustc_middle::ty::cast::{CastTy, IntTy};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
 use rustc_span::source_map::{Span, DUMMY_SP};
+use rustc_target::abi::VariantIdx;
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     #[instrument(level = "trace", skip(self, bx))]
@@ -115,6 +116,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                             (dest, active_field_index)
                         }
                     }
+                    mir::AggregateKind::Generator(..) => {
+                        dest.codegen_set_discr(bx, VariantIdx::from_u32(0));
+                        (dest, None)
+                    }
                     _ => (dest, None),
                 };
                 for (i, operand) in operands.iter().enumerate() {

compiler/rustc_const_eval/src/interpret/place.rs

@@ -774,15 +774,6 @@ where
         variant_index: VariantIdx,
         dest: &PlaceTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx> {
-        // This must be an enum or generator.
-        match dest.layout.ty.kind() {
-            ty::Adt(adt, _) => assert!(adt.is_enum()),
-            ty::Generator(..) => {}
-            _ => span_bug!(
-                self.cur_span(),
-                "write_discriminant called on non-variant-type (neither enum nor generator)"
-            ),
-        }
         // Layout computation excludes uninhabited variants from consideration
         // therefore there's no way to represent those variants in the given layout.
         // Essentially, uninhabited variants do not have a tag that corresponds to their

compiler/rustc_const_eval/src/interpret/step.rs

@@ -7,6 +7,7 @@ use either::Either;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{InterpResult, Scalar};
 use rustc_middle::ty::layout::LayoutOf;
+use rustc_target::abi::VariantIdx;
 
 use super::{ImmTy, InterpCx, Machine};
 
@@ -199,13 +200,24 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
 
             Aggregate(box ref kind, ref operands) => {
-                assert!(matches!(kind, mir::AggregateKind::Array(..)));
+                self.write_uninit(&dest)?;
-
+                let (variant_index, variant_dest, active_field_index) = match *kind {
+                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
+                        let variant_dest = self.place_downcast(&dest, variant_index)?;
+                        (variant_index, variant_dest, active_field_index)
+                    }
+                    _ => (VariantIdx::from_u32(0), dest.clone(), None),
+                };
+                if active_field_index.is_some() {
+                    assert_eq!(operands.len(), 1);
+                }
                 for (field_index, operand) in operands.iter().enumerate() {
-                    let op = self.eval_operand(operand, None)?;
+                    let field_index = active_field_index.unwrap_or(field_index);
-                    let field_dest = self.place_field(&dest, field_index)?;
+                    let field_dest = self.place_field(&variant_dest, field_index)?;
+                    let op = self.eval_operand(operand, Some(field_dest.layout))?;
                     self.copy_op(&op, &field_dest, /*allow_transmute*/ false)?;
                 }
+                self.write_discriminant(variant_index, &dest)?;
             }
 
             Repeat(ref operand, _) => {

tests/mir-opt/const_allocation.main.ConstProp.after.64bit.mir

@@ -27,19 +27,19 @@ alloc1 (static: FOO, size: 16, align: 8) {
 alloc18 (size: 72, align: 8) {
     0x00 │ 00 00 00 00 __ __ __ __ ╾───────alloc5────────╼ │ ....░░░░╾──────╼
     0x10 │ 00 00 00 00 00 00 00 00 00 00 00 00 __ __ __ __ │ ............░░░░
-    0x20 │ ╾───────alloc9────────╼ 02 00 00 00 00 00 00 00 │ ╾──────╼........
+    0x20 │ ╾───────alloc8────────╼ 02 00 00 00 00 00 00 00 │ ╾──────╼........
-    0x30 │ 01 00 00 00 2a 00 00 00 ╾───────alloc14───────╼ │ ....*...╾──────╼
+    0x30 │ 01 00 00 00 2a 00 00 00 ╾───────alloc13───────╼ │ ....*...╾──────╼
     0x40 │ 03 00 00 00 00 00 00 00                         │ ........
 }
 
 alloc5 (size: 0, align: 8) {}
 
-alloc9 (size: 32, align: 8) {
+alloc8 (size: 32, align: 8) {
-    0x00 │ ╾───────alloc8────────╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
+    0x00 │ ╾───────alloc9────────╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
     0x10 │ ╾───────alloc10───────╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
 }
 
-alloc8 (size: 3, align: 1) {
+alloc9 (size: 3, align: 1) {
     66 6f 6f                                        │ foo
 }
 
@@ -47,13 +47,13 @@ alloc10 (size: 3, align: 1) {
     62 61 72                                        │ bar
 }
 
-alloc14 (size: 48, align: 8) {
+alloc13 (size: 48, align: 8) {
-    0x00 │ ╾───────alloc13───────╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
+    0x00 │ ╾───────alloc14───────╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
     0x10 │ ╾───────alloc15───────╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
     0x20 │ ╾───────alloc16───────╼ 04 00 00 00 00 00 00 00 │ ╾──────╼........
 }
 
-alloc13 (size: 3, align: 1) {
+alloc14 (size: 3, align: 1) {
     6d 65 68                                        │ meh
 }