Auto merge of #115705 - cjgillot:const-prop-aggregate, r=oli-obk

Read from non-scalar constants and statics in dataflow const-prop

DataflowConstProp is designed to handle scalar values. When MIR features an assignment from a non-scalar constant, we need to manually decompose it into the custom state space.

This PR tweaks interpreter callbacks to allow reusing `eval_mir_constant` without having a stack frame to get a span from.

r? `@oli-obk`
cc `@jachris`

3 files changed, 6 insertions, 5 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/discriminant.rs b/compiler/rustc_const_eval/src/interpret/discriminant.rs
index 6c35fb01a93..440ee06e7fe 100644
--- a/compiler/rustc_const_eval/src/interpret/discriminant.rs
+++ b/compiler/rustc_const_eval/src/interpret/discriminant.rs
@@ -247,9 +247,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         &self,
         layout: TyAndLayout<'tcx>,
         variant: VariantIdx,
-    ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
+    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
         let discr_layout = self.layout_of(layout.ty.discriminant_ty(*self.tcx))?;
-        Ok(match layout.ty.discriminant_for_variant(*self.tcx, variant) {
+        let discr_value = match layout.ty.discriminant_for_variant(*self.tcx, variant) {
             Some(discr) => {
                 // This type actually has discriminants.
                 assert_eq!(discr.ty, discr_layout.ty);
@@ -260,6 +260,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 assert_eq!(variant.as_u32(), 0);
                 Scalar::from_uint(variant.as_u32(), discr_layout.size)
             }
-        })
+        };
+        Ok(ImmTy::from_scalar(discr_value, discr_layout))
     }
 }
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 7feed74ceae..3b58f66353b 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -222,7 +222,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let place = self.deref_pointer(&args[0])?;
                 let variant = self.read_discriminant(&place)?;
                 let discr = self.discriminant_for_variant(place.layout, variant)?;
-                self.write_scalar(discr, dest)?;
+                self.write_immediate(*discr, dest)?;
             }
             sym::exact_div => {
                 let l = self.read_immediate(&args[0])?;
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 57f99bd8f61..cf1f7ff75e1 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -301,7 +301,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let op = self.eval_place_to_op(place, None)?;
                 let variant = self.read_discriminant(&op)?;
                 let discr = self.discriminant_for_variant(op.layout, variant)?;
-                self.write_scalar(discr, &dest)?;
+                self.write_immediate(*discr, &dest)?;
             }
         }