a bit of meta-related cleanup on Projectable

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -295,9 +295,9 @@ fn layout(&self) -> TyAndLayout<'tcx> {
     }
 
     #[inline(always)]
-    fn meta(&self) -> InterpResult<'tcx, MemPlaceMeta<Prov>> {
+    fn meta(&self) -> MemPlaceMeta<Prov> {
         debug_assert!(self.layout.is_sized()); // unsized ImmTy can only exist temporarily and should never reach this here
-        Ok(MemPlaceMeta::None)
+        MemPlaceMeta::None
     }
 
     fn offset_with_meta<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
@@ -326,14 +326,14 @@ fn layout(&self) -> TyAndLayout<'tcx> {
     }
 
     #[inline]
-    fn meta(&self) -> InterpResult<'tcx, MemPlaceMeta<Prov>> {
+    fn meta(&self) -> MemPlaceMeta<Prov> {
-        Ok(match self.as_mplace_or_imm() {
+        match self.as_mplace_or_imm() {
             Left(mplace) => mplace.meta,
             Right(_) => {
                 debug_assert!(self.layout.is_sized(), "unsized immediates are not a thing");
                 MemPlaceMeta::None
             }
-        })
+        }
     }
 
     fn offset_with_meta<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(

compiler/rustc_const_eval/src/interpret/place.rs

@@ -13,7 +13,7 @@
 use rustc_middle::ty;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_middle::ty::Ty;
-use rustc_target::abi::{self, Abi, Align, FieldIdx, HasDataLayout, Size, FIRST_VARIANT};
+use rustc_target::abi::{Abi, Align, FieldIdx, HasDataLayout, Size, FIRST_VARIANT};
 
 use super::{
     alloc_range, mir_assign_valid_types, AllocId, AllocRef, AllocRefMut, CheckInAllocMsg,
@@ -48,27 +48,6 @@ pub fn has_meta(self) -> bool {
             Self::None => false,
         }
     }
-
-    pub(crate) fn len<'tcx>(
-        &self,
-        layout: TyAndLayout<'tcx>,
-        cx: &impl HasDataLayout,
-    ) -> InterpResult<'tcx, u64> {
-        if layout.is_unsized() {
-            // We need to consult `meta` metadata
-            match layout.ty.kind() {
-                ty::Slice(..) | ty::Str => self.unwrap_meta().to_target_usize(cx),
-                _ => bug!("len not supported on unsized type {:?}", layout.ty),
-            }
-        } else {
-            // Go through the layout. There are lots of types that support a length,
-            // e.g., SIMD types. (But not all repr(simd) types even have FieldsShape::Array!)
-            match layout.fields {
-                abi::FieldsShape::Array { count, .. } => Ok(count),
-                _ => bug!("len not supported on sized type {:?}", layout.ty),
-            }
-        }
-    }
 }
 
 #[derive(Copy, Clone, Hash, PartialEq, Eq, Debug)]
@@ -224,8 +203,8 @@ fn layout(&self) -> TyAndLayout<'tcx> {
     }
 
     #[inline(always)]
-    fn meta(&self) -> InterpResult<'tcx, MemPlaceMeta<Prov>> {
+    fn meta(&self) -> MemPlaceMeta<Prov> {
-        Ok(self.meta)
+        self.meta
     }
 
     fn offset_with_meta<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
@@ -257,14 +236,14 @@ fn layout(&self) -> TyAndLayout<'tcx> {
     }
 
     #[inline]
-    fn meta(&self) -> InterpResult<'tcx, MemPlaceMeta<Prov>> {
+    fn meta(&self) -> MemPlaceMeta<Prov> {
-        Ok(match self.as_mplace_or_local() {
+        match self.as_mplace_or_local() {
             Left(mplace) => mplace.meta,
             Right(_) => {
                 debug_assert!(self.layout.is_sized(), "unsized locals should live in memory");
                 MemPlaceMeta::None
             }
-        })
+        }
     }
 
     fn offset_with_meta<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(

compiler/rustc_const_eval/src/interpret/projection.rs

@@ -25,13 +25,28 @@ pub trait Projectable<'tcx, Prov: Provenance>: Sized + std::fmt::Debug {
     fn layout(&self) -> TyAndLayout<'tcx>;
 
     /// Get the metadata of a wide value.
-    fn meta(&self) -> InterpResult<'tcx, MemPlaceMeta<Prov>>;
+    fn meta(&self) -> MemPlaceMeta<Prov>;
 
+    /// Get the length of a slice/string/array stored here.
     fn len<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
         &self,
         ecx: &InterpCx<'mir, 'tcx, M>,
     ) -> InterpResult<'tcx, u64> {
-        self.meta()?.len(self.layout(), ecx)
+        let layout = self.layout();
+        if layout.is_unsized() {
+            // We need to consult `meta` metadata
+            match layout.ty.kind() {
+                ty::Slice(..) | ty::Str => self.meta().unwrap_meta().to_target_usize(ecx),
+                _ => bug!("len not supported on unsized type {:?}", layout.ty),
+            }
+        } else {
+            // Go through the layout. There are lots of types that support a length,
+            // e.g., SIMD types. (But not all repr(simd) types even have FieldsShape::Array!)
+            match layout.fields {
+                abi::FieldsShape::Array { count, .. } => Ok(count),
+                _ => bug!("len not supported on sized type {:?}", layout.ty),
+            }
+        }
     }
 
     /// Offset the value by the given amount, replacing the layout and metadata.
@@ -43,6 +58,7 @@ fn offset_with_meta<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
         ecx: &InterpCx<'mir, 'tcx, M>,
     ) -> InterpResult<'tcx, Self>;
 
+    #[inline]
     fn offset<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
         &self,
         offset: Size,
@@ -53,6 +69,7 @@ fn offset<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
         self.offset_with_meta(offset, MemPlaceMeta::None, layout, ecx)
     }
 
+    #[inline]
     fn transmute<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>(
         &self,
         layout: TyAndLayout<'tcx>,
@@ -125,7 +142,7 @@ pub fn project_field<P: Projectable<'tcx, M::Provenance>>(
                 // But const-prop actually feeds us such nonsense MIR! (see test `const_prop/issue-86351.rs`)
                 throw_inval!(ConstPropNonsense);
             }
-            let base_meta = base.meta()?;
+            let base_meta = base.meta();
             // Re-use parent metadata to determine dynamic field layout.
             // With custom DSTS, this *will* execute user-defined code, but the same
             // happens at run-time so that's okay.
@@ -153,7 +170,7 @@ pub fn project_downcast<P: Projectable<'tcx, M::Provenance>>(
         base: &P,
         variant: VariantIdx,
     ) -> InterpResult<'tcx, P> {
-        assert!(!base.meta()?.has_meta());
+        assert!(!base.meta().has_meta());
         // Downcasts only change the layout.
         // (In particular, no check about whether this is even the active variant -- that's by design,
         // see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.)