Auto merge of #95576 - DrMeepster:box_erasure, r=oli-obk

Remove dereferencing of Box from codegen

Through #94043, #94414, #94873, and #95328, I've been fixing issues caused by Box being treated like a pointer when it is not a pointer. However, these PRs just introduced special cases for Box. This PR removes those special cases and instead transforms a deref of Box into a deref of the pointer it contains.

Hopefully, this is the end of the Box<T, A> ICEs.

2 files changed, 8 insertions, 30 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 08be4c0a7b6..2e655ae94cc 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -118,22 +118,20 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
     }
 
     pub fn deref<Cx: LayoutTypeMethods<'tcx>>(self, cx: &Cx) -> PlaceRef<'tcx, V> {
+        if self.layout.ty.is_box() {
+            bug!("dereferencing {:?} in codegen", self.layout.ty);
+        }
+
         let projected_ty = self
             .layout
             .ty
             .builtin_deref(true)
             .unwrap_or_else(|| bug!("deref of non-pointer {:?}", self))
             .ty;
+
         let (llptr, llextra) = match self.val {
             OperandValue::Immediate(llptr) => (llptr, None),
-            OperandValue::Pair(llptr, llextra) => {
-                // if the box's allocator isn't a ZST, then "llextra" is actually the allocator
-                if self.layout.ty.is_box() && !self.layout.field(cx, 1).is_zst() {
-                    (llptr, None)
-                } else {
-                    (llptr, Some(llextra))
-                }
-            }
+            OperandValue::Pair(llptr, llextra) => (llptr, Some(llextra)),
             OperandValue::Ref(..) => bug!("Deref of by-Ref operand {:?}", self),
         };
         let layout = cx.layout_of(projected_ty);
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
index 3185b952ab8..5b88635982f 100644
--- a/compiler/rustc_codegen_ssa/src/mir/place.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/place.rs
@@ -446,16 +446,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         mir::PlaceRef { projection: &place_ref.projection[..elem.0], ..place_ref },
                     );
 
-                    // a box with a non-zst allocator should not be directly dereferenced
-                    if cg_base.layout.ty.is_box() && !cg_base.layout.field(cx, 1).is_zst() {
-                        // Extract `Box<T>` -> `Unique<T>` -> `NonNull<T>` -> `*const T`
-                        let ptr =
-                            cg_base.extract_field(bx, 0).extract_field(bx, 0).extract_field(bx, 0);
-
-                        ptr.deref(bx.cx())
-                    } else {
-                        cg_base.deref(bx.cx())
-                    }
+                    cg_base.deref(bx.cx())
                 } else {
                     bug!("using operand local {:?} as place", place_ref);
                 }
@@ -463,18 +454,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         };
         for elem in place_ref.projection[base..].iter() {
             cg_base = match *elem {
-                mir::ProjectionElem::Deref => {
-                    // a box with a non-zst allocator should not be directly dereferenced
-                    if cg_base.layout.ty.is_box() && !cg_base.layout.field(cx, 1).is_zst() {
-                        // Project `Box<T>` -> `Unique<T>` -> `NonNull<T>` -> `*const T`
-                        let ptr =
-                            cg_base.project_field(bx, 0).project_field(bx, 0).project_field(bx, 0);
-
-                        bx.load_operand(ptr).deref(bx.cx())
-                    } else {
-                        bx.load_operand(cg_base).deref(bx.cx())
-                    }
-                }
+                mir::ProjectionElem::Deref => bx.load_operand(cg_base).deref(bx.cx()),
                 mir::ProjectionElem::Field(ref field, _) => {
                     cg_base.project_field(bx, field.index())
                 }