get rid of ExprKind::Box

Author: RalfJung

compiler/rustc_middle/src/thir.rs

@@ -284,10 +284,6 @@ pub enum ExprKind<'tcx> {
         lint_level: LintLevel,
         value: ExprId,
     },
-    /// A `box <value>` expression.
-    Box {
-        value: ExprId,
-    },
     /// An `if` expression.
     If {
         if_then_scope: region::Scope,

compiler/rustc_middle/src/thir/visit.rs

@@ -50,7 +50,6 @@ pub fn walk_expr<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
         Scope { value, region_scope: _, lint_level: _ } => {
             visitor.visit_expr(&visitor.thir()[value])
         }
-        Box { value } => visitor.visit_expr(&visitor.thir()[value]),
         If { cond, then, else_opt, if_then_scope: _ } => {
             visitor.visit_expr(&visitor.thir()[cond]);
             visitor.visit_expr(&visitor.thir()[then]);

compiler/rustc_mir_build/src/builder/expr/as_place.rs

@@ -554,7 +554,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | ExprKind::Unary { .. }
             | ExprKind::Binary { .. }
             | ExprKind::LogicalOp { .. }
-            | ExprKind::Box { .. }
             | ExprKind::Cast { .. }
             | ExprKind::Use { .. }
             | ExprKind::NeverToAny { .. }

compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs

@@ -1,7 +1,6 @@
 //! See docs in `build/expr/mod.rs`.
 
 use rustc_abi::FieldIdx;
-use rustc_hir::lang_items::LangItem;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::bug;
 use rustc_middle::middle::region;
@@ -121,65 +120,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 }
                 block.and(Rvalue::UnaryOp(op, arg))
             }
-            ExprKind::Box { value } => {
-                let value_ty = this.thir[value].ty;
-                let tcx = this.tcx;
-                let source_info = this.source_info(expr_span);
-
-                let size = tcx.require_lang_item(LangItem::SizeOf, expr_span);
-                let size = Operand::unevaluated_constant(tcx, size, &[value_ty.into()], expr_span);
-
-                let align = tcx.require_lang_item(LangItem::AlignOf, expr_span);
-                let align =
-                    Operand::unevaluated_constant(tcx, align, &[value_ty.into()], expr_span);
-
-                // malloc some memory of suitable size and align:
-                let exchange_malloc = Operand::function_handle(
-                    tcx,
-                    tcx.require_lang_item(LangItem::ExchangeMalloc, expr_span),
-                    [],
-                    expr_span,
-                );
-                let storage = this.temp(Ty::new_mut_ptr(tcx, tcx.types.u8), expr_span);
-                let success = this.cfg.start_new_block();
-                this.cfg.terminate(
-                    block,
-                    source_info,
-                    TerminatorKind::Call {
-                        func: exchange_malloc,
-                        args: [
-                            Spanned { node: size, span: DUMMY_SP },
-                            Spanned { node: align, span: DUMMY_SP },
-                        ]
-                        .into(),
-                        destination: storage,
-                        target: Some(success),
-                        unwind: UnwindAction::Continue,
-                        call_source: CallSource::Misc,
-                        fn_span: expr_span,
-                    },
-                );
-                this.diverge_from(block);
-                block = success;
-
-                let result = this.local_decls.push(LocalDecl::new(expr.ty, expr_span));
-                this.cfg
-                    .push(block, Statement::new(source_info, StatementKind::StorageLive(result)));
-                if let Some(scope) = scope.temp_lifetime {
-                    // schedule a shallow free of that memory, lest we unwind:
-                    this.schedule_drop_storage_and_value(expr_span, scope, result);
-                }
-
-                // Transmute `*mut u8` to the box (thus far, uninitialized):
-                let box_ = Rvalue::ShallowInitBox(Operand::Move(storage), value_ty);
-                this.cfg.push_assign(block, source_info, Place::from(result), box_);
-
-                // initialize the box contents:
-                block = this
-                    .expr_into_dest(this.tcx.mk_place_deref(Place::from(result)), block, value)
-                    .into_block();
-                block.and(Rvalue::Use(Operand::Move(Place::from(result))))
-            }
             ExprKind::Cast { source } => {
                 let source_expr = &this.thir[source];
 

compiler/rustc_mir_build/src/builder/expr/category.rs

@@ -64,7 +64,6 @@ impl Category {
             | ExprKind::Closure { .. }
             | ExprKind::Unary { .. }
             | ExprKind::Binary { .. }
-            | ExprKind::Box { .. }
             | ExprKind::Cast { .. }
             | ExprKind::PointerCoercion { .. }
             | ExprKind::Repeat { .. }

compiler/rustc_mir_build/src/builder/expr/into.rs

@@ -876,7 +876,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // these are the cases that are more naturally handled by some other mode
             ExprKind::Unary { .. }
             | ExprKind::Binary { .. }
-            | ExprKind::Box { .. }
             | ExprKind::Cast { .. }
             | ExprKind::PointerCoercion { .. }
             | ExprKind::Repeat { .. }

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -474,7 +474,6 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
             | ExprKind::LoopMatch { .. }
             | ExprKind::Let { .. }
             | ExprKind::Match { .. }
-            | ExprKind::Box { .. }
             | ExprKind::If { .. }
             | ExprKind::InlineAsm { .. }
             | ExprKind::OffsetOf { .. }

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -353,7 +353,6 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             | Binary { .. }
             | Block { .. }
             | Borrow { .. }
-            | Box { .. }
             | Call { .. }
             | ByUse { .. }
             | Closure { .. }

compiler/rustc_mir_build/src/thir/print.rs

@@ -205,11 +205,6 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
                 self.print_expr(*value, depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl);
             }
-            Box { value } => {
-                print_indented!(self, "Box {", depth_lvl);
-                self.print_expr(*value, depth_lvl + 1);
-                print_indented!(self, "}", depth_lvl);
-            }
             If { if_then_scope, cond, then, else_opt } => {
                 print_indented!(self, "If {", depth_lvl);
                 print_indented!(self, format!("if_then_scope: {:?}", if_then_scope), depth_lvl + 1);

compiler/rustc_ty_utils/messages.ftl

@@ -12,8 +12,6 @@ ty_utils_block_not_supported = blocks are not supported in generic constants
 
 ty_utils_borrow_not_supported = borrowing is not supported in generic constants
 
-ty_utils_box_not_supported = allocations are not allowed in generic constants
-
 ty_utils_by_use_not_supported = .use is not allowed in generic constants
 
 ty_utils_closure_and_return_not_supported = closures and function keywords are not supported in generic constants