Introduce NullOp::AlignOf

compiler/rustc_codegen_cranelift/src/base.rs

@@ -726,15 +726,20 @@ fn codegen_stmt<'tcx>(
                     let ptr = fx.bcx.inst_results(call)[0];
                     lval.write_cvalue(fx, CValue::by_val(ptr, box_layout));
                 }
-                Rvalue::NullaryOp(NullOp::SizeOf, ty) => {
+                Rvalue::NullaryOp(null_op, ty) => {
                     assert!(
                         lval.layout()
                             .ty
                             .is_sized(fx.tcx.at(stmt.source_info.span), ParamEnv::reveal_all())
                     );
-                    let ty_size = fx.layout_of(fx.monomorphize(ty)).size.bytes();
+                    let layout = fx.layout_of(fx.monomorphize(ty));
+                    let val = match null_op {
+                        NullOp::SizeOf => layout.size.bytes(),
+                        NullOp::AlignOf => layout.align.abi.bytes(),
+                        NullOp::Box => unreachable!(),
+                    };
                     let val =
-                        CValue::const_val(fx, fx.layout_of(fx.tcx.types.usize), ty_size.into());
+                        CValue::const_val(fx, fx.layout_of(fx.tcx.types.usize), val.into());
                     lval.write_cvalue(fx, val);
                 }
                 Rvalue::Aggregate(ref kind, ref operands) => match kind.as_ref() {

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -823,7 +823,7 @@ pub(crate) fn codegen_intrinsic_call<'tcx>(
             dest.write_cvalue(fx, val);
         };
 
-        pref_align_of | min_align_of | needs_drop | type_id | type_name | variant_count, () {
+        pref_align_of | needs_drop | type_id | type_name | variant_count, () {
             let const_val =
                 fx.tcx.const_eval_instance(ParamEnv::reveal_all(), instance, None).unwrap();
             let val = crate::constant::codegen_const_value(

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -104,7 +104,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 }
             }
             sym::pref_align_of
-            | sym::min_align_of
             | sym::needs_drop
             | sym::type_id
             | sym::type_name

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -487,20 +487,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 )
             }
 
-            mir::Rvalue::NullaryOp(mir::NullOp::SizeOf, ty) => {
-                let ty = self.monomorphize(ty);
-                assert!(bx.cx().type_is_sized(ty));
-                let val = bx.cx().const_usize(bx.cx().layout_of(ty).size.bytes());
-                let tcx = self.cx.tcx();
-                (
-                    bx,
-                    OperandRef {
-                        val: OperandValue::Immediate(val),
-                        layout: self.cx.layout_of(tcx.types.usize),
-                    },
-                )
-            }
-
             mir::Rvalue::NullaryOp(mir::NullOp::Box, content_ty) => {
                 let content_ty = self.monomorphize(content_ty);
                 let content_layout = bx.cx().layout_of(content_ty);
@@ -525,6 +511,27 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 let operand = OperandRef { val: OperandValue::Immediate(val), layout: box_layout };
                 (bx, operand)
             }
+
+            mir::Rvalue::NullaryOp(null_op, ty) => {
+                let ty = self.monomorphize(ty);
+                assert!(bx.cx().type_is_sized(ty));
+                let layout = bx.cx().layout_of(ty);
+                let val = match null_op {
+                    mir::NullOp::SizeOf => layout.size.bytes(),
+                    mir::NullOp::AlignOf => layout.align.abi.bytes(),
+                    mir::NullOp::Box => unreachable!(),
+                };
+                let val = bx.cx().const_usize(val);
+                let tcx = self.cx.tcx();
+                (
+                    bx,
+                    OperandRef {
+                        val: OperandValue::Immediate(val),
+                        layout: self.cx.layout_of(tcx.types.usize),
+                    },
+                )
+            }
+
             mir::Rvalue::ThreadLocalRef(def_id) => {
                 assert!(bx.cx().tcx().is_static(def_id));
                 let static_ = bx.get_static(def_id);

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -160,17 +160,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
             }
 
-            sym::min_align_of
-            | sym::pref_align_of
+            sym::pref_align_of
             | sym::needs_drop
             | sym::type_id
             | sym::type_name
             | sym::variant_count => {
                 let gid = GlobalId { instance, promoted: None };
                 let ty = match intrinsic_name {
-                    sym::min_align_of | sym::pref_align_of | sym::variant_count => {
-                        self.tcx.types.usize
-                    }
+                    sym::pref_align_of | sym::variant_count => self.tcx.types.usize,
                     sym::needs_drop => self.tcx.types.bool,
                     sym::type_id => self.tcx.types.u64,
                     sym::type_name => self.tcx.mk_static_str(),

compiler/rustc_const_eval/src/interpret/step.rs

@@ -270,18 +270,23 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 M::box_alloc(self, &dest)?;
             }
 
-            NullaryOp(mir::NullOp::SizeOf, ty) => {
+            NullaryOp(null_op, ty) => {
                 let ty = self.subst_from_current_frame_and_normalize_erasing_regions(ty);
                 let layout = self.layout_of(ty)?;
                 if layout.is_unsized() {
                     // FIXME: This should be a span_bug (#80742)
                     self.tcx.sess.delay_span_bug(
                         self.frame().current_span(),
-                        &format!("SizeOf nullary MIR operator called for unsized type {}", ty),
+                        &format!("Nullary MIR operator called for unsized type {}", ty),
                     );
                     throw_inval!(SizeOfUnsizedType(ty));
                 }
-                self.write_scalar(Scalar::from_machine_usize(layout.size.bytes(), self), &dest)?;
+                let val = match null_op {
+                    mir::NullOp::SizeOf => layout.size.bytes(),
+                    mir::NullOp::AlignOf => layout.align.abi.bytes(),
+                    mir::NullOp::Box => unreachable!(),
+                };
+                self.write_scalar(Scalar::from_machine_usize(val, self), &dest)?;
             }
 
             Cast(cast_kind, ref operand, cast_ty) => {

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -648,7 +648,7 @@ impl Visitor<'tcx> for Checker<'mir, 'tcx> {
                 }
             }
 
-            Rvalue::NullaryOp(NullOp::SizeOf, _) => {}
+            Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {}
             Rvalue::NullaryOp(NullOp::Box, _) => self.check_op(ops::HeapAllocation),
 
             Rvalue::UnaryOp(_, ref operand) => {

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -520,6 +520,7 @@ impl<'tcx> Validator<'_, 'tcx> {
             Rvalue::NullaryOp(op, _) => match op {
                 NullOp::Box => return Err(Unpromotable),
                 NullOp::SizeOf => {}
+                NullOp::AlignOf => {}
             },
 
             Rvalue::UnaryOp(op, operand) => {

compiler/rustc_middle/src/mir/mod.rs

@@ -2278,6 +2278,8 @@ impl BinOp {
 pub enum NullOp {
     /// Returns the size of a value of that type
     SizeOf,
+    /// Returns the minimum alignment of a type
+    AlignOf,
     /// Creates a new uninitialized box for a value of that type
     Box,
 }

compiler/rustc_middle/src/mir/tcx.rs

@@ -196,7 +196,7 @@ impl<'tcx> Rvalue<'tcx> {
             Rvalue::UnaryOp(UnOp::Not | UnOp::Neg, ref operand) => operand.ty(local_decls, tcx),
             Rvalue::Discriminant(ref place) => place.ty(local_decls, tcx).ty.discriminant_ty(tcx),
             Rvalue::NullaryOp(NullOp::Box, t) => tcx.mk_box(t),
-            Rvalue::NullaryOp(NullOp::SizeOf, _) => tcx.types.usize,
+            Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => tcx.types.usize,
             Rvalue::Aggregate(ref ak, ref ops) => match **ak {
                 AggregateKind::Array(ty) => tcx.mk_array(ty, ops.len() as u64),
                 AggregateKind::Tuple => tcx.mk_tup(ops.iter().map(|op| op.ty(local_decls, tcx))),

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -342,7 +342,7 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
             | Rvalue::AddressOf(..)
             | Rvalue::Discriminant(..)
             | Rvalue::Len(..)
-            | Rvalue::NullaryOp(NullOp::SizeOf, _)
+            | Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _)
             | Rvalue::NullaryOp(NullOp::Box, _) => {
                 // This returns an rvalue with uninitialized contents. We can't
                 // move out of it here because it is an rvalue - assignments always

compiler/rustc_mir_transform/src/lower_intrinsics.rs

@@ -92,14 +92,19 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                         // since their semantics depend on the value of overflow-checks flag used
                         // during codegen. Issue #35310.
                     }
-                    sym::size_of => {
+                    sym::size_of | sym::min_align_of => {
                         if let Some((destination, target)) = *destination {
                             let tp_ty = substs.type_at(0);
+                            let null_op = match intrinsic_name {
+                                sym::size_of => NullOp::SizeOf,
+                                sym::min_align_of => NullOp::AlignOf,
+                                _ => bug!("unexpected intrinsic"),
+                            };
                             block.statements.push(Statement {
                                 source_info: terminator.source_info,
                                 kind: StatementKind::Assign(Box::new((
                                     destination,
-                                    Rvalue::NullaryOp(NullOp::SizeOf, tp_ty),
+                                    Rvalue::NullaryOp(null_op, tp_ty),
                                 ))),
                             });
                             terminator.kind = TerminatorKind::Goto { target };

src/test/mir-opt/lower_intrinsics.align_of.LowerIntrinsics.diff

@@ -0,0 +1,24 @@
+- // MIR for `align_of` before LowerIntrinsics
++ // MIR for `align_of` after LowerIntrinsics
+
+  fn align_of() -> usize {
+      let mut _0: usize;                   // return place in scope 0 at $DIR/lower_intrinsics.rs:18:25: 18:30
+
+      bb0: {
+-         _0 = std::intrinsics::min_align_of::<T>() -> bb1; // scope 0 at $DIR/lower_intrinsics.rs:19:5: 19:42
+-                                          // mir::Constant
+-                                          // + span: $DIR/lower_intrinsics.rs:19:5: 19:40
+-                                          // + literal: Const { ty: extern "rust-intrinsic" fn() -> usize {std::intrinsics::min_align_of::<T>}, val: Value(Scalar(<ZST>)) }
++         _0 = AlignOf(T);                 // scope 0 at $DIR/lower_intrinsics.rs:19:5: 19:42
++         goto -> bb1;                     // scope 0 at $DIR/lower_intrinsics.rs:19:5: 19:42
+      }
+
+      bb1: {
+          return;                          // scope 0 at $DIR/lower_intrinsics.rs:20:2: 20:2
+      }
+
+      bb2 (cleanup): {
+          resume;                          // scope 0 at $DIR/lower_intrinsics.rs:18:1: 20:2
+      }
+  }
+