Auto merge of #152681 - scottmcm:also-simplify-of-sized-val, r=<try>

Also simplify `size/align_of_val<T: Sized>` to `size/align_of<T>` instead

Author: bors

compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -645,6 +645,12 @@ pub union MaybeUninit<T> {
     pub value: ManuallyDrop<T>,
 }
 
+pub mod ptr {
+    #[lang = "Alignment"]
+    #[repr(transparent)]
+    pub struct Alignment(pub usize);
+}
+
 pub mod intrinsics {
     #[rustc_intrinsic]
     pub fn abort() -> !;
@@ -653,9 +659,9 @@ pub mod intrinsics {
     #[rustc_intrinsic]
     pub unsafe fn size_of_val<T: ?crate::Sized>(val: *const T) -> usize;
     #[rustc_intrinsic]
-    pub const fn align_of<T>() -> usize;
+    pub const fn align_of<T>() -> crate::ptr::Alignment;
     #[rustc_intrinsic]
-    pub unsafe fn align_of_val<T: ?crate::Sized>(val: *const T) -> usize;
+    pub unsafe fn align_of_val<T: ?crate::Sized>(val: *const T) -> crate::ptr::Alignment;
     #[rustc_intrinsic]
     pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);
     #[rustc_intrinsic]
@@ -723,15 +729,15 @@ pub const fn size_of<T>() -> usize {
 }
 
 pub const fn align_of<T>() -> usize {
-    <T as SizedTypeProperties>::ALIGN
+    <T as SizedTypeProperties>::ALIGN.0
 }
 
 trait SizedTypeProperties: Sized {
     #[lang = "mem_size_const"]
     const SIZE: usize = intrinsics::size_of::<Self>();
 
     #[lang = "mem_align_const"]
-    const ALIGN: usize = intrinsics::align_of::<Self>();
+    const ALIGN: crate::ptr::Alignment = intrinsics::align_of::<Self>();
 }
 impl<T> SizedTypeProperties for T {}
 

compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs

@@ -216,7 +216,7 @@ fn main() {
         assert_eq!(intrinsics::size_of_val(&0u32) as u8, 4);
 
         assert_eq!(align_of::<u16>() as u8, 2);
-        assert_eq!(intrinsics::align_of_val(&a) as u8, align_of::<&str>() as u8);
+        assert_eq!(intrinsics::align_of_val(&a).0 as u8, align_of::<&str>() as u8);
 
         let u8_needs_drop = const { intrinsics::needs_drop::<u8>() };
         assert!(!u8_needs_drop);

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -602,7 +602,8 @@ fn codegen_regular_intrinsic_call<'tcx>(
                 None
             };
             let (_size, align) = crate::unsize::size_and_align_of(fx, layout, meta);
-            ret.write_cvalue(fx, CValue::by_val(align, usize_layout));
+            let alignment_layout = fx.layout_of(fx.tcx.ty_alignment(source_info.span));
+            ret.write_cvalue(fx, CValue::by_val(align, alignment_layout));
         }
 
         sym::vtable_size => {

compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -651,6 +651,12 @@ pub union MaybeUninit<T> {
     pub value: ManuallyDrop<T>,
 }
 
+pub mod ptr {
+    #[lang = "Alignment"]
+    #[repr(transparent)]
+    pub struct Alignment(pub usize);
+}
+
 pub mod intrinsics {
     #[rustc_intrinsic]
     pub const fn black_box<T>(_dummy: T) -> T;
@@ -661,9 +667,9 @@ pub mod intrinsics {
     #[rustc_intrinsic]
     pub unsafe fn size_of_val<T: ?::Sized>(val: *const T) -> usize;
     #[rustc_intrinsic]
-    pub const fn align_of<T>() -> usize;
+    pub const fn align_of<T>() -> crate::ptr::Alignment;
     #[rustc_intrinsic]
-    pub unsafe fn align_of_val<T: ?::Sized>(val: *const T) -> usize;
+    pub unsafe fn align_of_val<T: ?::Sized>(val: *const T) -> crate::ptr::Alignment;
     #[rustc_intrinsic]
     pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);
     #[rustc_intrinsic]
@@ -704,15 +710,15 @@ pub const fn size_of<T>() -> usize {
 }
 
 pub const fn align_of<T>() -> usize {
-    <T as SizedTypeProperties>::ALIGN
+    <T as SizedTypeProperties>::ALIGN.0
 }
 
 trait SizedTypeProperties: Sized {
     #[lang = "mem_size_const"]
     const SIZE: usize = intrinsics::size_of::<Self>();
 
     #[lang = "mem_align_const"]
-    const ALIGN: usize = intrinsics::align_of::<Self>();
+    const ALIGN: crate::ptr::Alignment = intrinsics::align_of::<Self>();
 }
 
 impl<T> SizedTypeProperties for T {}

compiler/rustc_codegen_gcc/example/mini_core_hello_world.rs

@@ -196,7 +196,7 @@ fn main() {
         assert_eq!(intrinsics::size_of_val(&0u32) as u8, 4);
 
         assert_eq!(align_of::<u16>() as u8, 2);
-        assert_eq!(intrinsics::align_of_val(&a) as u8, align_of::<&str>() as u8);
+        assert_eq!(intrinsics::align_of_val(&a).0 as u8, align_of::<&str>() as u8);
 
         let u8_needs_drop = const { intrinsics::needs_drop::<u8>() };
         assert!(!u8_needs_drop);

compiler/rustc_hir/src/lang_items.rs

@@ -156,6 +156,7 @@ 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

@@ -292,10 +292,10 @@ 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),
         }),
     }
 }

compiler/rustc_mir_transform/src/instsimplify.rs

@@ -56,7 +56,7 @@ impl<'tcx> crate::MirPass<'tcx> for InstSimplify {
 
             let terminator = block.terminator.as_mut().unwrap();
             ctx.simplify_primitive_clone(terminator, &mut block.statements);
-            ctx.simplify_align_of_slice_val(terminator, &mut block.statements);
+            ctx.simplify_size_or_align_of_val(terminator, &mut block.statements);
             ctx.simplify_intrinsic_assert(terminator);
             ctx.simplify_nounwind_call(terminator);
             simplify_duplicate_switch_targets(terminator);
@@ -246,13 +246,18 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
         terminator.kind = TerminatorKind::Goto { target: *destination_block };
     }
 
-    // Convert `align_of_val::<[T]>(ptr)` to `align_of::<T>()`, since the
-    // alignment of a slice doesn't actually depend on metadata at all
-    // and the element type is always `Sized`.
-    //
-    // This is here so it can run after inlining, where it's more useful.
-    // (LowerIntrinsics is done in cleanup, before the optimization passes.)
-    fn simplify_align_of_slice_val(
+    /// Simplify `size_of_val` and `align_of_val` if we don't actually need
+    /// to look at the value in order to calculate the result:
+    /// - For `Sized` types we can always do this for both,
+    /// - For `align_of_val::<[T]>` we can return `align_of::<T>()`, since it
+    ///   doesn't depend on the slice's length and the elements are sized.
+    ///
+    /// This is here so it can run after inlining, where it's more useful.
+    /// (LowerIntrinsics is done in cleanup, before the optimization passes.)
+    ///
+    /// Note that we intentionally just produce the lang item constants so this
+    /// works on generic types and avoids any risk of layout calculation cycles.
+    fn simplify_size_or_align_of_val(
         &self,
         terminator: &mut Terminator<'tcx>,
         statements: &mut Vec<Statement<'tcx>>,
@@ -263,19 +268,35 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
         } = &terminator.kind
             && args.len() == 1
             && let Some((fn_def_id, generics)) = func.const_fn_def()
-            && self.tcx.is_intrinsic(fn_def_id, sym::align_of_val)
-            && let ty::Slice(elem_ty) = *generics.type_at(0).kind()
         {
-            let align_def_id = self.tcx.require_lang_item(LangItem::AlignOf, source_info.span);
-            let align_const = Operand::unevaluated_constant(
+            let lang_item = if self.tcx.is_intrinsic(fn_def_id, sym::size_of_val) {
+                LangItem::SizeOf
+            } else if self.tcx.is_intrinsic(fn_def_id, sym::align_of_val) {
+                LangItem::AlignOf
+            } else {
+                return;
+            };
+            let generic_ty = generics.type_at(0);
+            let ty = if generic_ty.is_sized(self.tcx, self.typing_env) {
+                generic_ty
+            } else if let LangItem::AlignOf = lang_item
+                && let ty::Slice(elem_ty) = *generic_ty.kind()
+            {
+                elem_ty
+            } else {
+                return;
+            };
+
+            let const_def_id = self.tcx.require_lang_item(lang_item, source_info.span);
+            let const_op = Operand::unevaluated_constant(
                 self.tcx,
-                align_def_id,
-                &[elem_ty.into()],
+                const_def_id,
+                &[ty.into()],
                 source_info.span,
             );
             statements.push(Statement::new(
                 source_info,
-                StatementKind::Assign(Box::new((*destination, Rvalue::Use(align_const)))),
+                StatementKind::Assign(Box::new((*destination, Rvalue::Use(const_op)))),
             ));
             terminator.kind = TerminatorKind::Goto { target: *destination_block };
         }