Elaborate ShallowInitBox too.

cjgillot · cjgillot · commit 51275e82c9db · 2025-10-22T00:52:52.000Z
diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -829,13 +829,6 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:
                         fx.bcx.ins().nop();
                     }
                 }
-                Rvalue::ShallowInitBox(ref operand, content_ty) => {
-                    let content_ty = fx.monomorphize(content_ty);
-                    let box_layout = fx.layout_of(Ty::new_box(fx.tcx, content_ty));
-                    let operand = codegen_operand(fx, operand);
-                    let operand = operand.load_scalar(fx);
-                    lval.write_cvalue(fx, CValue::by_val(operand, box_layout));
-                }
                 Rvalue::NullaryOp(ref null_op, ty) => {
                     assert!(lval.layout().ty.is_sized(fx.tcx, fx.typing_env()));
                     let layout = fx.layout_of(fx.monomorphize(ty));
@@ -924,6 +917,7 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:
                     lval.write_cvalue_transmute(fx, operand);
                 }
                 Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in codegen"),
+                Rvalue::ShallowInitBox(..) => bug!("`ShallowInitBox` in codegen"),
             }
         }
         StatementKind::StorageLive(_)
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -724,22 +724,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     }
                 }
             }
-            mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {
-                let operand = self.codegen_operand(bx, operand);
-                let val = operand.immediate();
-
-                let content_ty = self.monomorphize(content_ty);
-                let box_layout = bx.cx().layout_of(Ty::new_box(bx.tcx(), content_ty));
-
-                OperandRef { val: OperandValue::Immediate(val), layout: box_layout }
-            }
             mir::Rvalue::WrapUnsafeBinder(ref operand, binder_ty) => {
                 let operand = self.codegen_operand(bx, operand);
                 let binder_ty = self.monomorphize(binder_ty);
                 let layout = bx.cx().layout_of(binder_ty);
                 OperandRef { val: operand.val, layout }
             }
             mir::Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in codegen"),
+            mir::Rvalue::ShallowInitBox(..) => bug!("`ShallowInitBox` in codegen"),
         }
     }
 
diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -480,6 +480,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
             Rvalue::Discriminant(place) => state.get_discr(place.as_ref(), &self.map),
             Rvalue::Use(operand) => return self.handle_operand(operand, state),
             Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in runtime MIR"),
+            Rvalue::ShallowInitBox(..) => bug!("`ShallowInitBox` in runtime MIR"),
             Rvalue::Ref(..) | Rvalue::RawPtr(..) => {
                 // We don't track such places.
                 return ValueOrPlace::TOP;
@@ -489,7 +490,6 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
             | Rvalue::Cast(..)
             | Rvalue::BinaryOp(..)
             | Rvalue::Aggregate(..)
-            | Rvalue::ShallowInitBox(..)
             | Rvalue::WrapUnsafeBinder(..) => {
                 // No modification is possible through these r-values.
                 return ValueOrPlace::TOP;
diff --git a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
@@ -1,26 +1,29 @@
 //! This pass transforms derefs of Box into a deref of the pointer inside Box.
 //!
 //! Box is not actually a pointer so it is incorrect to dereference it directly.
+//!
+//! `ShallowInitBox` being a device for drop elaboration to understand deferred assignment to box
+//! contents, we do not need this any more on runtime MIR.
 
-use rustc_abi::FieldIdx;
-use rustc_hir::def_id::DefId;
+use rustc_abi::{FieldIdx, VariantIdx};
+use rustc_index::IndexVec;
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
 use rustc_middle::span_bug;
-use rustc_middle::ty::{Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 
 use crate::patch::MirPatch;
 
 /// Constructs the types used when accessing a Box's pointer
 fn build_ptr_tys<'tcx>(
     tcx: TyCtxt<'tcx>,
     pointee: Ty<'tcx>,
-    unique_did: DefId,
-    nonnull_did: DefId,
+    unique_def: ty::AdtDef<'tcx>,
+    nonnull_def: ty::AdtDef<'tcx>,
 ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
     let args = tcx.mk_args(&[pointee.into()]);
-    let unique_ty = tcx.type_of(unique_did).instantiate(tcx, args);
-    let nonnull_ty = tcx.type_of(nonnull_did).instantiate(tcx, args);
+    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);
 
     (unique_ty, nonnull_ty, ptr_ty)
@@ -36,8 +39,8 @@ pub(super) fn build_projection<'tcx>(
 
 struct ElaborateBoxDerefVisitor<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
-    unique_did: DefId,
-    nonnull_did: DefId,
+    unique_def: ty::AdtDef<'tcx>,
+    nonnull_def: ty::AdtDef<'tcx>,
     local_decls: &'a mut LocalDecls<'tcx>,
     patch: MirPatch<'tcx>,
 }
@@ -64,7 +67,7 @@ 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) =
-                build_ptr_tys(tcx, boxed_ty, self.unique_did, self.nonnull_did);
+                build_ptr_tys(tcx, boxed_ty, self.unique_def, self.nonnull_def);
 
             let ptr_local = self.patch.new_temp(ptr_ty, source_info.span);
 
@@ -86,6 +89,68 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
 
         self.super_place(place, context, location);
     }
+
+    fn visit_statement(&mut self, stmt: &mut Statement<'tcx>, location: Location) {
+        self.super_statement(stmt, location);
+
+        let tcx = self.tcx;
+        let source_info = stmt.source_info;
+
+        if let StatementKind::Assign(box (_, ref mut rvalue)) = stmt.kind
+            && let Rvalue::ShallowInitBox(ref mut mutptr_to_u8, pointee) = *rvalue
+            && 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) =
+                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))
+            };
+            let zst = |ty| {
+                Operand::Constant(Box::new(ConstOperand {
+                    span: source_info.span,
+                    user_ty: None,
+                    const_: Const::zero_sized(ty),
+                }))
+            };
+
+            let constptr = self.patch.new_temp(ptr_ty, source_info.span);
+            self.patch.add_assign(
+                location,
+                constptr.into(),
+                Rvalue::Cast(CastKind::Transmute, mutptr_to_u8.clone(), ptr_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::from_raw(vec![Operand::Move(constptr.into())]),
+                ),
+            );
+
+            let unique = self.patch.new_temp(unique_ty, source_info.span);
+            let phantomdata_ty =
+                self.unique_def.non_enum_variant().fields[FieldIdx::ONE].ty(tcx, args);
+            self.patch.add_assign(
+                location,
+                unique.into(),
+                Rvalue::Aggregate(
+                    adt_kind(self.unique_def, args),
+                    IndexVec::from_raw(vec![Operand::Move(nonnull.into()), zst(phantomdata_ty)]),
+                ),
+            );
+
+            let global_alloc_ty =
+                box_adt.non_enum_variant().fields[FieldIdx::ONE].ty(tcx, box_args);
+            *rvalue = Rvalue::Aggregate(
+                adt_kind(*box_adt, box_args),
+                IndexVec::from_raw(vec![Operand::Move(unique.into()), zst(global_alloc_ty)]),
+            );
+        }
+    }
 }
 
 pub(super) struct ElaborateBoxDerefs;
@@ -97,18 +162,22 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateBoxDerefs {
 
         let unique_did = tcx.adt_def(def_id).non_enum_variant().fields[FieldIdx::ZERO].did;
 
-        let Some(nonnull_def) = tcx.type_of(unique_did).instantiate_identity().ty_adt_def() else {
+        let Some(unique_def) = tcx.type_of(unique_did).instantiate_identity().ty_adt_def() else {
             span_bug!(tcx.def_span(unique_did), "expected Box to contain Unique")
         };
 
-        let nonnull_did = nonnull_def.non_enum_variant().fields[FieldIdx::ZERO].did;
+        let nonnull_did = unique_def.non_enum_variant().fields[FieldIdx::ZERO].did;
+
+        let Some(nonnull_def) = tcx.type_of(nonnull_did).instantiate_identity().ty_adt_def() else {
+            span_bug!(tcx.def_span(nonnull_did), "expected Unique to contain Nonnull")
+        };
 
         let patch = MirPatch::new(body);
 
         let local_decls = &mut body.local_decls;
 
         let mut visitor =
-            ElaborateBoxDerefVisitor { tcx, unique_did, nonnull_did, local_decls, patch };
+            ElaborateBoxDerefVisitor { tcx, unique_def, nonnull_def, local_decls, patch };
 
         for (block, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
             visitor.visit_basic_block_data(block, data);
@@ -131,7 +200,7 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateBoxDerefs {
                             new_projections.get_or_insert_with(|| base.projection.to_vec());
 
                         let (unique_ty, nonnull_ty, ptr_ty) =
-                            build_ptr_tys(tcx, boxed_ty, unique_did, nonnull_did);
+                            build_ptr_tys(tcx, boxed_ty, unique_def, nonnull_def);
 
                         new_projections.extend_from_slice(&build_projection(unique_ty, nonnull_ty));
                         // While we can't project into `NonNull<_>` in a basic block
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
@@ -1073,8 +1073,10 @@ impl<'body, 'a, 'tcx> VnState<'body, 'a, 'tcx> {
             }
 
             // Unsupported values.
-            Rvalue::ThreadLocalRef(..) | Rvalue::ShallowInitBox(..) => return None,
-            Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in runtime MIR"),
+            Rvalue::ThreadLocalRef(..) => return None,
+            Rvalue::CopyForDeref(_) | Rvalue::ShallowInitBox(..) => {
+                bug!("forbidden in runtime MIR: {rvalue:?}")
+            }
         };
         let ty = rvalue.ty(self.local_decls, self.tcx);
         Some(self.insert(ty, value))
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
@@ -656,7 +656,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
     ) {
         match elem {
             ProjectionElem::Deref
-                if self.body.phase >= MirPhase::Runtime(RuntimePhase::PostCleanup) =>
+                if self.body.phase >= MirPhase::Runtime(RuntimePhase::Initial) =>
             {
                 let base_ty = place_ref.ty(&self.body.local_decls, self.tcx).ty;
 
@@ -1047,7 +1047,11 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     assert!(!adt_def.is_union());
                     let variant = &adt_def.variants()[idx];
                     if variant.fields.len() != fields.len() {
-                        self.fail(location, "adt has the wrong number of initialized fields");
+                        self.fail(location, format!(
+                            "adt {def_id:?} has the wrong number of initialized fields, expected {}, found {}",
+                            fields.len(),
+                            variant.fields.len(),
+                        ));
                     }
                     for (src, dest) in std::iter::zip(fields, &variant.fields) {
                         let dest_ty = self
@@ -1250,6 +1254,10 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 }
             }
             Rvalue::ShallowInitBox(operand, _) => {
+                if self.body.phase >= MirPhase::Runtime(RuntimePhase::Initial) {
+                    self.fail(location, format!("ShallowInitBox after ElaborateBoxDerefs"))
+                }
+
                 let a = operand.ty(&self.body.local_decls, self.tcx);
                 check_kinds!(a, "Cannot shallow init type {:?}", ty::RawPtr(..));
             }
diff --git a/tests/mir-opt/box_expr.rs b/tests/mir-opt/box_expr.rs
@@ -6,7 +6,10 @@
 // EMIT_MIR box_expr.main.ElaborateDrops.diff
 fn main() {
     // CHECK-LABEL: fn main(
-    // CHECK:   [[box:_.*]] = ShallowInitBox(
+    // CHECK:   [[ptr:_.*]] = move {{_.*}} as *const S (Transmute);
+    // CHECK:   [[nonnull:_.*]] = NonNull::<S> { pointer: move [[ptr]] };
+    // CHECK:   [[unique:_.*]] = Unique::<S> { pointer: move [[nonnull]], _marker: const PhantomData::<S> };
+    // CHECK:   [[box:_.*]] = Box::<S>(move [[unique]], const std::alloc::Global);
     // CHECK:   [[ptr:_.*]] = copy (([[box]].0: std::ptr::Unique<S>).0: std::ptr::NonNull<S>) as *const S (Transmute);
     // CHECK:   (*[[ptr]]) = S::new() -> [return: [[ret:bb.*]], unwind: [[unwind:bb.*]]];
     // CHECK: [[ret]]: {
diff --git a/tests/mir-opt/const_prop/boxes.main.GVN.panic-abort.diff b/tests/mir-opt/const_prop/boxes.main.GVN.panic-abort.diff
@@ -11,7 +11,10 @@
       let mut _6: *mut u8;
       let mut _7: std::boxed::Box<i32>;
       let mut _8: *const i32;
-      let mut _9: *const i32;
+      let mut _9: std::ptr::NonNull<i32>;
+      let mut _10: std::ptr::Unique<i32>;
+      let mut _11: *const i32;
+      let mut _12: *const i32;
       scope 1 {
           debug x => _1;
       }
@@ -31,13 +34,21 @@
   
       bb1: {
           StorageLive(_7);
-          _7 = ShallowInitBox(move _6, i32);
-          _8 = copy ((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
-          (*_8) = const 42_i32;
+-         _8 = move _6 as *const i32 (Transmute);
+-         _9 = NonNull::<i32> { pointer: move _8 };
+-         _10 = Unique::<i32> { pointer: move _9, _marker: const PhantomData::<i32> };
++         _8 = copy _6 as *const i32 (PtrToPtr);
++         _9 = NonNull::<i32> { pointer: copy _8 };
++         _10 = Unique::<i32> { pointer: copy _9, _marker: const PhantomData::<i32> };
+          _7 = Box::<i32>(move _10, const std::alloc::Global);
+-         _11 = copy ((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
+-         (*_11) = const 42_i32;
++         _11 = copy _8;
++         (*_8) = const 42_i32;
           _3 = move _7;
           StorageDead(_7);
-          _9 = copy ((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
-          _2 = copy (*_9);
+          _12 = copy ((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
+          _2 = copy (*_12);
 -         _1 = Add(move _2, const 0_i32);
 -         StorageDead(_2);
 +         _1 = copy _2;
diff --git a/tests/mir-opt/const_prop/boxes.main.GVN.panic-unwind.diff b/tests/mir-opt/const_prop/boxes.main.GVN.panic-unwind.diff
@@ -11,7 +11,10 @@
       let mut _6: *mut u8;
       let mut _7: std::boxed::Box<i32>;
       let mut _8: *const i32;
-      let mut _9: *const i32;
+      let mut _9: std::ptr::NonNull<i32>;
+      let mut _10: std::ptr::Unique<i32>;
+      let mut _11: *const i32;
+      let mut _12: *const i32;
       scope 1 {
           debug x => _1;
       }
@@ -31,13 +34,21 @@
   
       bb1: {
           StorageLive(_7);
-          _7 = ShallowInitBox(move _6, i32);
-          _8 = copy ((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
-          (*_8) = const 42_i32;
+-         _8 = move _6 as *const i32 (Transmute);
+-         _9 = NonNull::<i32> { pointer: move _8 };
+-         _10 = Unique::<i32> { pointer: move _9, _marker: const PhantomData::<i32> };
++         _8 = copy _6 as *const i32 (PtrToPtr);
++         _9 = NonNull::<i32> { pointer: copy _8 };
++         _10 = Unique::<i32> { pointer: copy _9, _marker: const PhantomData::<i32> };
+          _7 = Box::<i32>(move _10, const std::alloc::Global);
+-         _11 = copy ((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
+-         (*_11) = const 42_i32;
++         _11 = copy _8;
++         (*_8) = const 42_i32;
           _3 = move _7;
           StorageDead(_7);
-          _9 = copy ((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
-          _2 = copy (*_9);
+          _12 = copy ((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>) as *const i32 (Transmute);
+          _2 = copy (*_12);
 -         _1 = Add(move _2, const 0_i32);
 -         StorageDead(_2);
 +         _1 = copy _2;
diff --git a/tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.32bit.panic-abort.diff b/tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.32bit.panic-abort.diff
diff --git a/tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.64bit.panic-abort.diff b/tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.64bit.panic-abort.diff

Original file line number	Diff line number	Diff line change
`@@ -829,13 +829,6 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:`
`829`	`829`	`fx.bcx.ins().nop();`
`830`	`830`	`}`
`831`	`831`	`}`
`832`		`- Rvalue::ShallowInitBox(ref operand, content_ty) => {`
`833`		`- let content_ty = fx.monomorphize(content_ty);`
`834`		`- let box_layout = fx.layout_of(Ty::new_box(fx.tcx, content_ty));`
`835`		`- let operand = codegen_operand(fx, operand);`
`836`		`- let operand = operand.load_scalar(fx);`
`837`		`- lval.write_cvalue(fx, CValue::by_val(operand, box_layout));`
`838`		`- }`
`839`	`832`	`Rvalue::NullaryOp(ref null_op, ty) => {`
`840`	`833`	`assert!(lval.layout().ty.is_sized(fx.tcx, fx.typing_env()));`
`841`	`834`	`let layout = fx.layout_of(fx.monomorphize(ty));`
`@@ -924,6 +917,7 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:`
`924`	`917`	`lval.write_cvalue_transmute(fx, operand);`
`925`	`918`	`}`
`926`	`919`	Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in codegen"),
	`920`	+ Rvalue::ShallowInitBox(..) => bug!("`ShallowInitBox` in codegen"),
`927`	`921`	`}`
`928`	`922`	`}`
`929`	`923`	`StatementKind::StorageLive(_)`
Original file line number	Diff line number	Diff line change
`@@ -724,22 +724,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {`
`724`	`724`	`}`
`725`	`725`	`}`
`726`	`726`	`}`
`727`		`- mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {`
`728`		`- let operand = self.codegen_operand(bx, operand);`
`729`		`- let val = operand.immediate();`
`730`		`-`
`731`		`- let content_ty = self.monomorphize(content_ty);`
`732`		`- let box_layout = bx.cx().layout_of(Ty::new_box(bx.tcx(), content_ty));`
`733`		`-`
`734`		`- OperandRef { val: OperandValue::Immediate(val), layout: box_layout }`
`735`		`- }`
`736`	`727`	`mir::Rvalue::WrapUnsafeBinder(ref operand, binder_ty) => {`
`737`	`728`	`let operand = self.codegen_operand(bx, operand);`
`738`	`729`	`let binder_ty = self.monomorphize(binder_ty);`
`739`	`730`	`let layout = bx.cx().layout_of(binder_ty);`
`740`	`731`	`OperandRef { val: operand.val, layout }`
`741`	`732`	`}`
`742`	`733`	mir::Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in codegen"),
	`734`	+ mir::Rvalue::ShallowInitBox(..) => bug!("`ShallowInitBox` in codegen"),
`743`	`735`	`}`
`744`	`736`	`}`
`745`	`737`