adjust constValue::Slice to work for arbitrary slice types

4 files changed, 38 insertions, 27 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
index de78b4eb504..3d758cd01d3 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -151,19 +151,26 @@ pub(super) fn op_to_const<'tcx>(
             Immediate::Scalar(x) => ConstValue::Scalar(x),
             Immediate::ScalarPair(a, b) => {
                 debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
-                // FIXME: assert that this has an appropriate type.
-                // Currently we actually get here for non-[u8] slices during valtree construction!
-                let msg = "`op_to_const` on an immediate scalar pair must only be used on slice references to actually allocated memory";
+                // This codepath solely exists for `valtree_to_const_value` to not need to generate
+                // a `ConstValue::Indirect` for wide references, so it is tightly restricted to just
+                // that case.
+                let pointee_ty = imm.layout.ty.builtin_deref(false).unwrap().ty; // `false` = no raw ptrs
+                debug_assert!(
+                    matches!(
+                        ecx.tcx.struct_tail_without_normalization(pointee_ty).kind(),
+                        ty::Str | ty::Slice(..),
+                    ),
+                    "`ConstValue::Slice` is for slice-tailed types only, but got {}",
+                    imm.layout.ty,
+                );
+                let msg = "`op_to_const` on an immediate scalar pair must only be used on slice references to the beginning of an actual allocation";
                 // We know `offset` is relative to the allocation, so we can use `into_parts`.
-                // We use `ConstValue::Slice` so that we don't have to generate an allocation for
-                // `ConstValue::Indirect` here.
                 let (alloc_id, offset) = a.to_pointer(ecx).expect(msg).into_parts();
                 let alloc_id = alloc_id.expect(msg);
                 let data = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
-                let start = offset.bytes_usize();
-                let len = b.to_target_usize(ecx).expect(msg);
-                let len: usize = len.try_into().unwrap();
-                ConstValue::Slice { data, start, end: start + len }
+                assert!(offset == abi::Size::ZERO, "{}", msg);
+                let meta = b.to_target_usize(ecx).expect(msg);
+                ConstValue::Slice { data, meta }
             }
             Immediate::Uninit => bug!("`Uninit` is not a valid value for {}", op.layout.ty),
         },
diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
index 4c826239eca..bd897ffaafc 100644
--- a/compiler/rustc_const_eval/src/interpret/cast.rs
+++ b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -351,7 +351,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         match (&src_pointee_ty.kind(), &dest_pointee_ty.kind()) {
             (&ty::Array(_, length), &ty::Slice(_)) => {
-                let ptr = self.read_scalar(src)?;
+                let ptr = self.read_pointer(src)?;
                 // u64 cast is from usize to u64, which is always good
                 let val = Immediate::new_slice(
                     ptr,
@@ -367,6 +367,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     return self.write_immediate(*val, dest);
                 }
                 let (old_data, old_vptr) = val.to_scalar_pair();
+                let old_data = old_data.to_pointer(self)?;
                 let old_vptr = old_vptr.to_pointer(self)?;
                 let (ty, old_trait) = self.get_ptr_vtable(old_vptr)?;
                 if old_trait != data_a.principal() {
@@ -378,7 +379,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (_, &ty::Dynamic(data, _, ty::Dyn)) => {
                 // Initial cast from sized to dyn trait
                 let vtable = self.get_vtable_ptr(src_pointee_ty, data.principal())?;
-                let ptr = self.read_scalar(src)?;
+                let ptr = self.read_pointer(src)?;
                 let val = Immediate::new_dyn_trait(ptr, vtable, &*self.tcx);
                 self.write_immediate(val, dest)
             }
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index f08f1437918..775a834f2ee 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -62,7 +62,7 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
         sym::type_name => {
             ensure_monomorphic_enough(tcx, tp_ty)?;
             let alloc = alloc_type_name(tcx, tp_ty);
-            ConstValue::Slice { data: alloc, start: 0, end: alloc.inner().len() }
+            ConstValue::Slice { data: alloc, meta: alloc.inner().size().bytes() }
         }
         sym::needs_drop => {
             ensure_monomorphic_enough(tcx, tp_ty)?;
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index 788b50d7c4a..fdda98a50e8 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -43,24 +43,30 @@ impl<Prov: Provenance> From<Scalar<Prov>> for Immediate<Prov> {
 }
 
 impl<Prov: Provenance> Immediate<Prov> {
-    pub fn from_pointer(p: Pointer<Prov>, cx: &impl HasDataLayout) -> Self {
-        Immediate::Scalar(Scalar::from_pointer(p, cx))
+    pub fn from_pointer(ptr: Pointer<Prov>, cx: &impl HasDataLayout) -> Self {
+        Immediate::Scalar(Scalar::from_pointer(ptr, cx))
     }
 
-    pub fn from_maybe_pointer(p: Pointer<Option<Prov>>, cx: &impl HasDataLayout) -> Self {
-        Immediate::Scalar(Scalar::from_maybe_pointer(p, cx))
+    pub fn from_maybe_pointer(ptr: Pointer<Option<Prov>>, cx: &impl HasDataLayout) -> Self {
+        Immediate::Scalar(Scalar::from_maybe_pointer(ptr, cx))
     }
 
-    pub fn new_slice(val: Scalar<Prov>, len: u64, cx: &impl HasDataLayout) -> Self {
-        Immediate::ScalarPair(val, Scalar::from_target_usize(len, cx))
+    pub fn new_slice(ptr: Pointer<Option<Prov>>, len: u64, cx: &impl HasDataLayout) -> Self {
+        Immediate::ScalarPair(
+            Scalar::from_maybe_pointer(ptr, cx),
+            Scalar::from_target_usize(len, cx),
+        )
     }
 
     pub fn new_dyn_trait(
-        val: Scalar<Prov>,
+        val: Pointer<Option<Prov>>,
         vtable: Pointer<Option<Prov>>,
         cx: &impl HasDataLayout,
     ) -> Self {
-        Immediate::ScalarPair(val, Scalar::from_maybe_pointer(vtable, cx))
+        Immediate::ScalarPair(
+            Scalar::from_maybe_pointer(val, cx),
+            Scalar::from_maybe_pointer(vtable, cx),
+        )
     }
 
     #[inline]
@@ -722,16 +728,13 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
             mir::ConstValue::Scalar(x) => Operand::Immediate(adjust_scalar(x)?.into()),
             mir::ConstValue::ZeroSized => Operand::Immediate(Immediate::Uninit),
-            mir::ConstValue::Slice { data, start, end } => {
+            mir::ConstValue::Slice { data, meta } => {
                 // We rely on mutability being set correctly in `data` to prevent writes
                 // where none should happen.
-                let ptr = Pointer::new(
-                    self.tcx.reserve_and_set_memory_alloc(data),
-                    Size::from_bytes(start), // offset: `start`
-                );
+                let ptr = Pointer::new(self.tcx.reserve_and_set_memory_alloc(data), Size::ZERO);
                 Operand::Immediate(Immediate::new_slice(
-                    Scalar::from_pointer(self.global_base_pointer(ptr)?, &*self.tcx),
-                    u64::try_from(end.checked_sub(start).unwrap()).unwrap(), // len: `end - start`
+                    self.global_base_pointer(ptr)?.into(),
+                    meta,
                     self,
                 ))
             }