Use !null pattern type in libcore

Use `!null` pattern type in libcore

Author: oli-obk

compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -8,13 +8,38 @@
     rustc_attrs,
     rustc_private,
     transparent_unions,
+    pattern_types,
     auto_traits,
     freeze_impls,
     thread_local
 )]
 #![no_core]
 #![allow(dead_code, internal_features, ambiguous_wide_pointer_comparisons)]
 
+#[lang = "pointee_trait"]
+pub trait Pointee: PointeeSized {
+    #[lang = "metadata_type"]
+    // needed so that layout_of will return `TooGeneric` instead of `Unknown`
+    // when asked for the layout of `*const T`. Which is important for making
+    // transmutes between raw pointers (and especially pattern types of raw pointers)
+    // work.
+    type Metadata: Copy + Sync + Unpin + Freeze;
+}
+
+#[lang = "dyn_metadata"]
+pub struct DynMetadata<Dyn: PointeeSized> {
+    _vtable_ptr: NonNull<VTable>,
+    _phantom: PhantomData<Dyn>,
+}
+
+unsafe extern "C" {
+    /// Opaque type for accessing vtables.
+    ///
+    /// Private implementation detail of `DynMetadata::size_of` etc.
+    /// There is conceptually not actually any Abstract Machine memory behind this pointer.
+    type VTable;
+}
+
 #[lang = "pointee_sized"]
 pub trait PointeeSized {}
 
@@ -105,7 +130,7 @@ unsafe impl<'a, T: PointeeSized> Sync for &'a T {}
 unsafe impl<T: Sync, const N: usize> Sync for [T; N] {}
 
 #[lang = "freeze"]
-unsafe auto trait Freeze {}
+pub unsafe auto trait Freeze {}
 
 unsafe impl<T: PointeeSized> Freeze for PhantomData<T> {}
 unsafe impl<T: PointeeSized> Freeze for *const T {}
@@ -568,10 +593,24 @@ pub trait Deref {
     fn deref(&self) -> &Self::Target;
 }
 
+#[rustc_builtin_macro(pattern_type)]
+#[macro_export]
+macro_rules! pattern_type {
+    ($($arg:tt)*) => {
+        /* compiler built-in */
+    };
+}
+
+impl<T: PointeeSized, U: PointeeSized> CoerceUnsized<pattern_type!(*const U is !null)> for pattern_type!(*const T is !null) where
+    T: Unsize<U>
+{
+}
+
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<pattern_type!(U is !null)> for pattern_type!(T is !null) {}
+
 #[repr(transparent)]
-#[rustc_layout_scalar_valid_range_start(1)]
 #[rustc_nonnull_optimization_guaranteed]
-pub struct NonNull<T: PointeeSized>(pub *const T);
+pub struct NonNull<T: PointeeSized>(pub pattern_type!(*const T is !null));
 
 impl<T: PointeeSized, U: PointeeSized> CoerceUnsized<NonNull<U>> for NonNull<T> where T: Unsize<U> {}
 impl<T: PointeeSized, U: PointeeSized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: Unsize<U> {}
@@ -598,7 +637,16 @@ impl<T> Box<T> {
             let size = size_of::<T>();
             let ptr = libc::malloc(size);
             intrinsics::copy(&val as *const T as *const u8, ptr, size);
-            Box(Unique { pointer: NonNull(ptr as *const T), _marker: PhantomData }, Global)
+            Box(
+                Unique {
+                    pointer: NonNull(intrinsics::transmute::<
+                        *mut u8,
+                        pattern_type!(*const T is !null),
+                    >(ptr)),
+                    _marker: PhantomData,
+                },
+                Global,
+            )
         }
     }
 }
@@ -607,7 +655,9 @@ impl<T: ?Sized, A> Drop for Box<T, A> {
     fn drop(&mut self) {
         // inner value is dropped by compiler
         unsafe {
-            libc::free(self.0.pointer.0 as *mut u8);
+            libc::free(intrinsics::transmute::<pattern_type!(*const T is !null), *const T>(
+                self.0.pointer.0,
+            ) as *mut u8);
         }
     }
 }

compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs

@@ -6,6 +6,7 @@
     extern_types,
     thread_local,
     repr_simd,
+    pattern_types,
     rustc_private
 )]
 #![no_core]
@@ -159,7 +160,10 @@ extern "C" fn bool_struct_in_11(_arg0: bool_11) {}
 
 #[allow(unreachable_code)] // FIXME false positive
 fn main() {
-    take_unique(Unique { pointer: unsafe { NonNull(1 as *mut ()) }, _marker: PhantomData });
+    take_unique(Unique {
+        pointer: unsafe { NonNull(intrinsics::transmute(1 as *mut ())) },
+        _marker: PhantomData,
+    });
     take_f32(0.1);
 
     call_return_u128_pair();
@@ -225,7 +229,12 @@ fn main() {
         let noisy_unsized_drop = const { intrinsics::needs_drop::<NoisyDropUnsized>() };
         assert!(noisy_unsized_drop);
 
-        Unique { pointer: NonNull(1 as *mut &str), _marker: PhantomData } as Unique<dyn SomeTrait>;
+        Unique {
+            pointer: NonNull(intrinsics::transmute::<_, pattern_type!(*const &str is !null)>(
+                1 as *mut &str,
+            )),
+            _marker: PhantomData,
+        } as Unique<dyn SomeTrait>;
 
         struct MyDst<T: ?Sized>(T);
 

compiler/rustc_const_eval/src/interpret/visitor.rs

@@ -137,7 +137,12 @@ pub trait ValueVisitor<'tcx, M: Machine<'tcx>>: Sized {
 
                 // ... that contains a `NonNull`... (gladly, only a single field here)
                 assert_eq!(nonnull_ptr.layout().fields.count(), 1);
-                let raw_ptr = self.ecx().project_field(&nonnull_ptr, FieldIdx::ZERO)?; // the actual raw ptr
+                let pat_ty = self.ecx().project_field(&nonnull_ptr, FieldIdx::ZERO)?; // `*mut T is !null`
+                let base = match *pat_ty.layout().ty.kind() {
+                    ty::Pat(base, _) => self.ecx().layout_of(base)?,
+                    _ => unreachable!(),
+                };
+                let raw_ptr = pat_ty.transmute(base, self.ecx())?; // The actual raw pointer
 
                 // ... whose only field finally is a raw ptr we can dereference.
                 self.visit_box(ty, &raw_ptr)?;

compiler/rustc_middle/src/ty/layout.rs

@@ -17,7 +17,7 @@ use rustc_session::config::OptLevel;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 use rustc_target::callconv::FnAbi;
 use rustc_target::spec::{HasTargetSpec, HasX86AbiOpt, Target, X86Abi};
-use tracing::debug;
+use tracing::{debug, instrument, trace};
 use {rustc_abi as abi, rustc_hir as hir};
 
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
@@ -376,6 +376,7 @@ pub enum SizeSkeleton<'tcx> {
 }
 
 impl<'tcx> SizeSkeleton<'tcx> {
+    #[instrument(level = "trace", skip(tcx, typing_env), ret)]
     pub fn compute(
         ty: Ty<'tcx>,
         tcx: TyCtxt<'tcx>,
@@ -425,6 +426,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
                     },
                     || {},
                 );
+                trace!(?tail);
 
                 match tail.kind() {
                     ty::Param(_) | ty::Alias(ty::Projection | ty::Inherent, _) => {

compiler/rustc_mir_transform/src/elaborate_box_derefs.rs

@@ -10,7 +10,7 @@ use rustc_index::{IndexVec, indexvec};
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
 use rustc_middle::span_bug;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, PatternKind, Ty, TyCtxt};
 
 use crate::patch::MirPatch;
 
@@ -20,21 +20,27 @@ fn build_ptr_tys<'tcx>(
     pointee: Ty<'tcx>,
     unique_def: ty::AdtDef<'tcx>,
     nonnull_def: ty::AdtDef<'tcx>,
-) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
+) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
     let args = tcx.mk_args(&[pointee.into()]);
     let unique_ty = Ty::new_adt(tcx, unique_def, args);
     let nonnull_ty = Ty::new_adt(tcx, nonnull_def, args);
     let ptr_ty = Ty::new_imm_ptr(tcx, pointee);
+    let pat_ty = Ty::new_pat(tcx, ptr_ty, tcx.mk_pat(PatternKind::NotNull));
 
-    (unique_ty, nonnull_ty, ptr_ty)
+    (unique_ty, nonnull_ty, pat_ty, ptr_ty)
 }
 
 /// Constructs the projection needed to access a Box's pointer
 pub(super) fn build_projection<'tcx>(
     unique_ty: Ty<'tcx>,
     nonnull_ty: Ty<'tcx>,
-) -> [PlaceElem<'tcx>; 2] {
-    [PlaceElem::Field(FieldIdx::ZERO, unique_ty), PlaceElem::Field(FieldIdx::ZERO, nonnull_ty)]
+    pat_ty: Ty<'tcx>,
+) -> [PlaceElem<'tcx>; 3] {
+    [
+        PlaceElem::Field(FieldIdx::ZERO, unique_ty),
+        PlaceElem::Field(FieldIdx::ZERO, nonnull_ty),
+        PlaceElem::Field(FieldIdx::ZERO, pat_ty),
+    ]
 }
 
 struct ElaborateBoxDerefVisitor<'a, 'tcx> {
@@ -66,7 +72,7 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
         {
             let source_info = self.local_decls[place.local].source_info;
 
-            let (unique_ty, nonnull_ty, ptr_ty) =
+            let (unique_ty, nonnull_ty, pat_ty, ptr_ty) =
                 build_ptr_tys(tcx, boxed_ty, self.unique_def, self.nonnull_def);
 
             let ptr_local = self.patch.new_temp(ptr_ty, source_info.span);
@@ -78,7 +84,7 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
                     CastKind::Transmute,
                     Operand::Copy(
                         Place::from(place.local)
-                            .project_deeper(&build_projection(unique_ty, nonnull_ty), tcx),
+                            .project_deeper(&build_projection(unique_ty, nonnull_ty, pat_ty), tcx),
                     ),
                     ptr_ty,
                 ),
@@ -101,7 +107,7 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
             && let ty::Adt(box_adt, box_args) = Ty::new_box(tcx, pointee).kind()
         {
             let args = tcx.mk_args(&[pointee.into()]);
-            let (unique_ty, nonnull_ty, ptr_ty) =
+            let (unique_ty, nonnull_ty, pat_ty, ptr_ty) =
                 build_ptr_tys(tcx, pointee, self.unique_def, self.nonnull_def);
             let adt_kind = |def: ty::AdtDef<'tcx>, args| {
                 Box::new(AggregateKind::Adt(def.did(), VariantIdx::ZERO, args, None, None))
@@ -121,13 +127,20 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
                 Rvalue::Cast(CastKind::Transmute, mutptr_to_u8.clone(), ptr_ty),
             );
 
+            let pat_ptr = self.patch.new_temp(pat_ty, source_info.span);
+            self.patch.add_assign(
+                location,
+                pat_ptr.into(),
+                Rvalue::Cast(CastKind::Transmute, Operand::Move(constptr.into()), pat_ty),
+            );
+
             let nonnull = self.patch.new_temp(nonnull_ty, source_info.span);
             self.patch.add_assign(
                 location,
                 nonnull.into(),
                 Rvalue::Aggregate(
                     adt_kind(self.nonnull_def, args),
-                    indexvec![Operand::Move(constptr.into())],
+                    indexvec![Operand::Move(pat_ptr.into())],
                 ),
             );
 
@@ -199,10 +212,11 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateBoxDerefs {
                         let new_projections =
                             new_projections.get_or_insert_with(|| base.projection.to_vec());
 
-                        let (unique_ty, nonnull_ty, ptr_ty) =
+                        let (unique_ty, nonnull_ty, pat_ty, ptr_ty) =
                             build_ptr_tys(tcx, boxed_ty, unique_def, nonnull_def);
 
-                        new_projections.extend_from_slice(&build_projection(unique_ty, nonnull_ty));
+                        new_projections
+                            .extend_from_slice(&build_projection(unique_ty, nonnull_ty, pat_ty));
                         // While we can't project into `NonNull<_>` in a basic block
                         // due to MCP#807, this is debug info where it's fine.
                         new_projections.push(PlaceElem::Field(FieldIdx::ZERO, ptr_ty));

compiler/rustc_mir_transform/src/validate.rs

@@ -669,24 +669,25 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 let fail_out_of_bounds = |this: &mut Self, location| {
                     this.fail(location, format!("Out of bounds field {f:?} for {parent_ty:?}"));
                 };
+
+                let kind = match parent_ty.ty.kind() {
+                    &ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
+                        self.tcx.type_of(def_id).instantiate(self.tcx, args).kind()
+                    }
+                    kind => kind,
+                };
+
                 let check_equal = |this: &mut Self, location, f_ty| {
                     if !this.mir_assign_valid_types(ty, f_ty) {
                         this.fail(
                             location,
                             format!(
-                                "Field projection `{place_ref:?}.{f:?}` specified type `{ty}`, but actual type is `{f_ty}`"
+                                "Field projection `{place_ref:?}.{f:?}` specified type `{ty}`, but actual field type of `{kind:?}` is `{f_ty}`"
                             )
                         )
                     }
                 };
 
-                let kind = match parent_ty.ty.kind() {
-                    &ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
-                        self.tcx.type_of(def_id).instantiate(self.tcx, args).kind()
-                    }
-                    kind => kind,
-                };
-
                 match kind {
                     ty::Tuple(fields) => {
                         let Some(f_ty) = fields.get(f.as_usize()) else {