Auto merge of #88839 - nbdd0121:alignof, r=nagisa

Introduce NullOp::AlignOf

This PR introduces `Rvalue::NullaryOp(NullOp::AlignOf, ty)`, which will be lowered from `align_of`, similar to `size_of` lowering to `Rvalue::NullaryOp(NullOp::SizeOf, ty)`.

The changes are originally part of #88700 but since it's not dependent on other changes and could have performance impact on its own, it's separated into its own PR.

12 files changed, 53 insertions, 32 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
index 46a7485e4ef..d29558a4e1f 100644
--- a/compiler/rustc_codegen_cranelift/src/base.rs
+++ b/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() {
diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
index 8b62b44df8a..48183b2d4f6 100644
--- a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
+++ b/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(
diff --git a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
index 75999225c03..f943157dc66 100644
--- a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
+++ b/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
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index f65af17535a..7403c21a906 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -486,20 +486,6 @@ 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);
@@ -524,6 +510,27 @@ 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);
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 1e91ad07ba9..b032ee96ce7 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/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(),
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 09bd07660a3..6e35b33188c 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/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) => {
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index d02b4286c17..02b317b8981 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/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) => {
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
index 6822ad2d7b5..8c24c9fa976 100644
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ b/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) => {
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index ebdf354b905..e8d30034dc4 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -2277,6 +2277,8 @@ 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,
 }
diff --git a/compiler/rustc_middle/src/mir/tcx.rs b/compiler/rustc_middle/src/mir/tcx.rs
index 74d303cee5d..b48e8a868ef 100644
--- a/compiler/rustc_middle/src/mir/tcx.rs
+++ b/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))),
diff --git a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs b/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
index cea465ea1ed..407ba739463 100644
--- a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
+++ b/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
diff --git a/compiler/rustc_mir_transform/src/lower_intrinsics.rs b/compiler/rustc_mir_transform/src/lower_intrinsics.rs
index 2f89b041c27..5848163af72 100644
--- a/compiler/rustc_mir_transform/src/lower_intrinsics.rs
+++ b/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 };