Make the alignment intrinsics return ptr::Alignment

Author: scottmcm

compiler/rustc_hir/src/lang_items.rs

@@ -168,6 +168,7 @@ language_item_table! {
     MetaSized,               sym::meta_sized,          meta_sized_trait,           Target::Trait,          GenericRequirement::Exact(0);
     PointeeSized,            sym::pointee_sized,       pointee_sized_trait,        Target::Trait,          GenericRequirement::Exact(0);
     Unsize,                  sym::unsize,              unsize_trait,               Target::Trait,          GenericRequirement::Minimum(1);
+    Alignment,               sym::Alignment,           alignment_type,             Target::Struct,         GenericRequirement::Exact(0);
     AlignOf,                 sym::mem_align_const,     align_const,                Target::AssocConst,     GenericRequirement::Exact(0);
     SizeOf,                  sym::mem_size_const,      size_const,                 Target::AssocConst,     GenericRequirement::Exact(0);
     OffsetOf,                sym::offset_of,           offset_of,                  Target::Fn,             GenericRequirement::Exact(1);

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -291,10 +291,10 @@ pub(crate) fn check_intrinsic_type(
         sym::amdgpu_dispatch_ptr => (0, 0, vec![], Ty::new_imm_ptr(tcx, tcx.types.unit)),
         sym::unreachable => (0, 0, vec![], tcx.types.never),
         sym::breakpoint => (0, 0, vec![], tcx.types.unit),
-        sym::size_of | sym::align_of | sym::variant_count => (1, 0, vec![], tcx.types.usize),
-        sym::size_of_val | sym::align_of_val => {
-            (1, 0, vec![Ty::new_imm_ptr(tcx, param(0))], tcx.types.usize)
-        }
+        sym::size_of | sym::variant_count => (1, 0, vec![], tcx.types.usize),
+        sym::align_of => (1, 0, vec![], tcx.ty_alignment(span)),
+        sym::size_of_val => (1, 0, vec![Ty::new_imm_ptr(tcx, param(0))], tcx.types.usize),
+        sym::align_of_val => (1, 0, vec![Ty::new_imm_ptr(tcx, param(0))], tcx.ty_alignment(span)),
         sym::offset_of => (1, 0, vec![tcx.types.u32, tcx.types.u32], tcx.types.usize),
         sym::rustc_peek => (1, 0, vec![param(0)], param(0)),
         sym::caller_location => (0, 0, vec![], tcx.caller_location_ty()),

compiler/rustc_middle/src/ty/context.rs

@@ -1079,6 +1079,13 @@ impl<'tcx> TyCtxt<'tcx> {
         self.type_of(ordering_enum).no_bound_vars().unwrap()
     }
 
+    /// Gets a `Ty` representing the [`LangItem::Alignment`]
+    #[track_caller]
+    pub fn ty_alignment(self, span: Span) -> Ty<'tcx> {
+        let alignment = self.require_lang_item(hir::LangItem::Alignment, span);
+        self.type_of(alignment).no_bound_vars().unwrap()
+    }
+
     /// Obtain the given diagnostic item's `DefId`. Use `is_diagnostic_item` if you just want to
     /// compare against another `DefId`, since `is_diagnostic_item` is cheaper.
     pub fn get_diagnostic_item(self, name: Symbol) -> Option<DefId> {

compiler/rustc_mir_transform/src/check_alignment.rs

@@ -55,14 +55,23 @@ fn insert_alignment_check<'tcx>(
     stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((thin_ptr, rvalue)))));
 
     // Transmute the pointer to a usize (equivalent to `ptr.addr()`).
-    let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Copy(thin_ptr), tcx.types.usize);
+    let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Move(thin_ptr), tcx.types.usize);
     let addr = local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
     stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((addr, rvalue)))));
 
     // Get the alignment of the pointee
     let align_def_id = tcx.require_lang_item(LangItem::AlignOf, source_info.span);
+    let alignment_usize =
+        local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
     let alignment =
         Operand::unevaluated_constant(tcx, align_def_id, &[pointee_ty.into()], source_info.span);
+    stmts.push(Statement::new(
+        source_info,
+        StatementKind::Assign(Box::new((
+            alignment_usize,
+            Rvalue::Cast(CastKind::Transmute, alignment.clone(), tcx.types.usize),
+        ))),
+    ));
 
     // Subtract 1 from the alignment to get the alignment mask
     let alignment_mask =
@@ -76,7 +85,7 @@ fn insert_alignment_check<'tcx>(
         source_info,
         StatementKind::Assign(Box::new((
             alignment_mask,
-            Rvalue::BinaryOp(BinOp::Sub, Box::new((alignment.clone(), one))),
+            Rvalue::BinaryOp(BinOp::SubUnchecked, Box::new((Operand::Move(alignment_usize), one))),
         ))),
     ));
 
@@ -139,10 +148,10 @@ fn insert_alignment_check<'tcx>(
     // Emit a check that asserts on the alignment and otherwise triggers a
     // AssertKind::MisalignedPointerDereference.
     PointerCheck {
-        cond: Operand::Copy(is_ok),
+        cond: Operand::Move(is_ok),
         assert_kind: Box::new(AssertKind::MisalignedPointerDereference {
             required: alignment,
-            found: Operand::Copy(addr),
+            found: Operand::Move(addr),
         }),
     }
 }

library/alloc/src/alloc.rs

@@ -484,8 +484,8 @@ unsafe impl const Allocator for Global {
 #[lang = "exchange_malloc"]
 #[inline]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
-unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
-    let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
+unsafe fn exchange_malloc(size: usize, align: Alignment) -> *mut u8 {
+    let layout = unsafe { Layout::from_size_alignment_unchecked(size, align) };
     match Global.allocate(layout) {
         Ok(ptr) => ptr.as_mut_ptr(),
         Err(_) => handle_alloc_error(layout),

library/core/src/intrinsics/mod.rs

@@ -2789,7 +2789,7 @@ pub const fn size_of<T>() -> usize;
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic_const_stable_indirect]
 #[rustc_intrinsic]
-pub const fn align_of<T>() -> usize;
+pub const fn align_of<T>() -> ptr::Alignment;
 
 /// The offset of a field inside a type.
 ///
@@ -2849,7 +2849,7 @@ pub const unsafe fn size_of_val<T: ?Sized>(ptr: *const T) -> usize;
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic]
 #[rustc_intrinsic_const_stable_indirect]
-pub const unsafe fn align_of_val<T: ?Sized>(ptr: *const T) -> usize;
+pub const unsafe fn align_of_val<T: ?Sized>(ptr: *const T) -> ptr::Alignment;
 
 /// Compute the type information of a concrete type.
 /// It can only be called at compile time, the backends do

library/core/src/mem/mod.rs

@@ -450,7 +450,7 @@ pub const unsafe fn size_of_val_raw<T: ?Sized>(val: *const T) -> usize {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[deprecated(note = "use `align_of` instead", since = "1.2.0", suggestion = "align_of")]
 pub fn min_align_of<T>() -> usize {
-    <T as SizedTypeProperties>::ALIGN
+    align_of::<T>()
 }
 
 /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to in
@@ -473,8 +473,7 @@ pub fn min_align_of<T>() -> usize {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[deprecated(note = "use `align_of_val` instead", since = "1.2.0", suggestion = "align_of_val")]
 pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
-    // SAFETY: val is a reference, so it's a valid raw pointer
-    unsafe { intrinsics::align_of_val(val) }
+    align_of_val(val)
 }
 
 /// Returns the [ABI]-required minimum alignment of a type in bytes.
@@ -497,7 +496,7 @@ pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
 #[rustc_const_stable(feature = "const_align_of", since = "1.24.0")]
 #[rustc_diagnostic_item = "mem_align_of"]
 pub const fn align_of<T>() -> usize {
-    <T as SizedTypeProperties>::ALIGN
+    Alignment::of::<T>().as_usize()
 }
 
 /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to in
@@ -517,8 +516,7 @@ pub const fn align_of<T>() -> usize {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_stable(feature = "const_align_of_val", since = "1.85.0")]
 pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
-    // SAFETY: val is a reference, so it's a valid raw pointer
-    unsafe { intrinsics::align_of_val(val) }
+    Alignment::of_val(val).as_usize()
 }
 
 /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to in
@@ -565,7 +563,7 @@ pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
 #[unstable(feature = "layout_for_ptr", issue = "69835")]
 pub const unsafe fn align_of_val_raw<T: ?Sized>(val: *const T) -> usize {
     // SAFETY: the caller must provide a valid raw pointer
-    unsafe { intrinsics::align_of_val(val) }
+    unsafe { Alignment::of_val_raw(val) }.as_usize()
 }
 
 /// Returns `true` if dropping values of type `T` matters.
@@ -1256,14 +1254,8 @@ pub trait SizedTypeProperties: Sized {
     #[doc(hidden)]
     #[unstable(feature = "sized_type_properties", issue = "none")]
     #[lang = "mem_align_const"]
-    const ALIGN: usize = intrinsics::align_of::<Self>();
-
-    #[doc(hidden)]
-    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
-    const ALIGNMENT: Alignment = {
-        // This can't panic since type alignment is always a power of two.
-        Alignment::new(Self::ALIGN).unwrap()
-    };
+    // #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    const ALIGNMENT: Alignment = intrinsics::align_of::<Self>();
 
     /// `true` if this type requires no storage.
     /// `false` if its [size](size_of) is greater than zero.
@@ -1300,7 +1292,7 @@ pub trait SizedTypeProperties: Sized {
         // SAFETY: if the type is instantiated, rustc already ensures that its
         // layout is valid. Use the unchecked constructor to avoid inserting a
         // panicking codepath that needs to be optimized out.
-        unsafe { Layout::from_size_align_unchecked(Self::SIZE, Self::ALIGN) }
+        unsafe { Layout::from_size_alignment_unchecked(Self::SIZE, Self::ALIGNMENT) }
     };
 
     /// The largest safe length for a `[Self]`.

library/core/src/ptr/alignment.rs

@@ -3,15 +3,18 @@
 use crate::marker::MetaSized;
 use crate::num::NonZero;
 use crate::ub_checks::assert_unsafe_precondition;
-use crate::{cmp, fmt, hash, mem, num};
+use crate::{cmp, fmt, hash, intrinsics, mem, num};
 
 /// A type storing a `usize` which is a power of two, and thus
 /// represents a possible alignment in the Rust abstract machine.
 ///
 /// Note that particularly large alignments, while representable in this type,
 /// are likely not to be supported by actual allocators and linkers.
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+// No special behaviour, but used as the return type from an intrinsic
+#[lang = "Alignment"]
 #[derive(Copy, Clone, PartialEq, Eq)]
+// This being transparent is critical for its use in `__rust_alloc` and friends
 #[repr(transparent)]
 pub struct Alignment {
     // This field is never used directly (nor is the enum),
@@ -73,9 +76,8 @@ impl Alignment {
     #[must_use]
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
     pub const fn of_val<T: MetaSized>(val: &T) -> Self {
-        let align = mem::align_of_val(val);
-        // SAFETY: `align_of_val` returns valid alignment
-        unsafe { Alignment::new_unchecked(align) }
+        // SAFETY: val is a reference, so it's a valid raw pointer
+        unsafe { Alignment::of_val_raw(val) }
     }
 
     /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to.
@@ -122,9 +124,7 @@ impl Alignment {
     // #[unstable(feature = "layout_for_ptr", issue = "69835")]
     pub const unsafe fn of_val_raw<T: MetaSized>(val: *const T) -> Self {
         // SAFETY: precondition propagated to the caller
-        let align = unsafe { mem::align_of_val_raw(val) };
-        // SAFETY: `align_of_val_raw` returns valid alignment
-        unsafe { Alignment::new_unchecked(align) }
+        unsafe { intrinsics::align_of_val(val) }
     }
 
     /// Creates an `Alignment` from a `usize`, or returns `None` if it's

tests/auxiliary/minicore.rs

@@ -268,6 +268,12 @@ trait Drop {
     fn drop(&mut self);
 }
 
+pub mod ptr {
+    #[lang = "Alignment"]
+    #[repr(transparent)]
+    pub struct Alignment(usize);
+}
+
 pub mod mem {
     #[rustc_nounwind]
     #[rustc_intrinsic]
@@ -276,9 +282,10 @@ pub mod mem {
     #[rustc_nounwind]
     #[rustc_intrinsic]
     pub const fn size_of<T>() -> usize;
+
     #[rustc_nounwind]
     #[rustc_intrinsic]
-    pub const fn align_of<T>() -> usize;
+    pub const fn align_of<T>() -> crate::ptr::Alignment;
 }
 
 #[lang = "c_void"]

tests/mir-opt/alignment_checks.rs

@@ -14,6 +14,6 @@ pub unsafe fn sized_ptr(ptr: *const u32) -> u32 {
     // CHECK: _2 = copy _1 as usize (Transmute);
     // CHECK: _3 = BitAnd(copy _2, const 3_usize);
     // CHECK: _4 = Eq(copy _3, const 0_usize);
-    // CHECK: assert(copy _4,
+    // CHECK: assert(move _4,
     *ptr
 }