src/librustc_mir/build/expr/into.rs

   1 //! See docs in build/expr/mod.rs
   2
   3 use crate::build::expr::category::{Category, RvalueFunc};
   4 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
   5 use crate::hair::*;
   6 use rustc::mir::*;
   7 use rustc::ty;
   8
   9 use rustc_target::spec::abi::Abi;
  10
  11 impl<'a, 'tcx> Builder<'a, 'tcx> {
  12     /// Compile `expr`, storing the result into `destination`, which
  13     /// is assumed to be uninitialized.
  14     pub fn into_expr(
  15         &mut self,
  16         destination: &Place<'tcx>,
  17         mut block: BasicBlock,
  18         expr: Expr<'tcx>,
  19     ) -> BlockAnd<()> {
  20         debug!(
  21             "into_expr(destination={:?}, block={:?}, expr={:?})",
  22             destination, block, expr
  23         );
  24
  25         // since we frequently have to reference `self` from within a
  26         // closure, where `self` would be shadowed, it's easier to
  27         // just use the name `this` uniformly
  28         let this = self;
  29         let expr_span = expr.span;
  30         let source_info = this.source_info(expr_span);
  31
  32         let expr_is_block_or_scope = match expr.kind {
  33             ExprKind::Block { .. } => true,
  34             ExprKind::Scope { .. } => true,
  35             _ => false,
  36         };
  37
  38         if !expr_is_block_or_scope {
  39             this.block_context.push(BlockFrame::SubExpr);
  40         }
  41
  42         let block_and = match expr.kind {
  43             ExprKind::Scope {
  44                 region_scope,
  45                 lint_level,
  46                 value,
  47             } => {
  48                 let region_scope = (region_scope, source_info);
  49                 this.in_scope(region_scope, lint_level, |this| {
  50                     this.into(destination, block, value)
  51                 })
  52             }
  53             ExprKind::Block { body: ast_block } => {
  54                 this.ast_block(destination, block, ast_block, source_info)
  55             }
  56             ExprKind::Match { scrutinee, arms } => {
  57                 this.match_expr(destination, expr_span, block, scrutinee, arms)
  58             }
  59             ExprKind::NeverToAny { source } => {
  60                 let source = this.hir.mirror(source);
  61                 let is_call = match source.kind {
  62                     ExprKind::Call { .. } => true,
  63                     _ => false,
  64                 };
  65
  66                 unpack!(block = this.as_local_rvalue(block, source));
  67
  68                 // This is an optimization. If the expression was a call then we already have an
  69                 // unreachable block. Don't bother to terminate it and create a new one.
  70                 if is_call {
  71                     block.unit()
  72                 } else {
  73                     this.cfg
  74                         .terminate(block, source_info, TerminatorKind::Unreachable);
  75                     let end_block = this.cfg.start_new_block();
  76                     end_block.unit()
  77                 }
  78             }
  79             ExprKind::LogicalOp { op, lhs, rhs } => {
  80                 // And:
  81                 //
  82                 // [block: If(lhs)] -true-> [else_block: If(rhs)] -true-> [true_block]
  83                 //        |                          | (false)
  84                 //        +----------false-----------+------------------> [false_block]
  85                 //
  86                 // Or:
  87                 //
  88                 // [block: If(lhs)] -false-> [else_block: If(rhs)] -true-> [true_block]
  89                 //        | (true)                   | (false)
  90                 //  [true_block]               [false_block]
  91
  92                 let (true_block, false_block, mut else_block, join_block) = (
  93                     this.cfg.start_new_block(),
  94                     this.cfg.start_new_block(),
  95                     this.cfg.start_new_block(),
  96                     this.cfg.start_new_block(),
  97                 );
  98
  99                 let lhs = unpack!(block = this.as_local_operand(block, lhs));
 100                 let blocks = match op {
 101                     LogicalOp::And => (else_block, false_block),
 102                     LogicalOp::Or => (true_block, else_block),
 103                 };
 104                 let term = TerminatorKind::if_(this.hir.tcx(), lhs, blocks.0, blocks.1);
 105                 this.cfg.terminate(block, source_info, term);
 106
 107                 let rhs = unpack!(else_block = this.as_local_operand(else_block, rhs));
 108                 let term = TerminatorKind::if_(this.hir.tcx(), rhs, true_block, false_block);
 109                 this.cfg.terminate(else_block, source_info, term);
 110
 111                 this.cfg.push_assign_constant(
 112                     true_block,
 113                     source_info,
 114                     destination,
 115                     Constant {
 116                         span: expr_span,
 117                         user_ty: None,
 118                         literal: this.hir.true_literal(),
 119                     },
 120                 );
 121
 122                 this.cfg.push_assign_constant(
 123                     false_block,
 124                     source_info,
 125                     destination,
 126                     Constant {
 127                         span: expr_span,
 128                         user_ty: None,
 129                         literal: this.hir.false_literal(),
 130                     },
 131                 );
 132
 133                 this.cfg.terminate(
 134                     true_block,
 135                     source_info,
 136                     TerminatorKind::Goto { target: join_block },
 137                 );
 138                 this.cfg.terminate(
 139                     false_block,
 140                     source_info,
 141                     TerminatorKind::Goto { target: join_block },
 142                 );
 143
 144                 join_block.unit()
 145             }
 146             ExprKind::Loop { body } => {
 147                 // [block]
 148                 //    |
 149                 //   [loop_block] -> [body_block] -/eval. body/-> [body_block_end]
 150                 //    |        ^                                         |
 151                 // false link  |                                         |
 152                 //    |        +-----------------------------------------+
 153                 //    +-> [diverge_cleanup]
 154                 // The false link is required to make sure borrowck considers unwinds through the
 155                 // body, even when the exact code in the body cannot unwind
 156
 157                 let loop_block = this.cfg.start_new_block();
 158                 let exit_block = this.cfg.start_new_block();
 159
 160                 // start the loop
 161                 this.cfg.terminate(
 162                     block,
 163                     source_info,
 164                     TerminatorKind::Goto { target: loop_block },
 165                 );
 166
 167                 this.in_breakable_scope(
 168                     Some(loop_block),
 169                     exit_block,
 170                     destination.clone(),
 171                     move |this| {
 172                         // conduct the test, if necessary
 173                         let body_block = this.cfg.start_new_block();
 174                         let diverge_cleanup = this.diverge_cleanup();
 175                         this.cfg.terminate(
 176                             loop_block,
 177                             source_info,
 178                             TerminatorKind::FalseUnwind {
 179                                 real_target: body_block,
 180                                 unwind: Some(diverge_cleanup),
 181                             },
 182                         );
 183
 184                         // The “return” value of the loop body must always be an unit. We therefore
 185                         // introduce a unit temporary as the destination for the loop body.
 186                         let tmp = this.get_unit_temp();
 187                         // Execute the body, branching back to the test.
 188                         let body_block_end = unpack!(this.into(&tmp, body_block, body));
 189                         this.cfg.terminate(
 190                             body_block_end,
 191                             source_info,
 192                             TerminatorKind::Goto { target: loop_block },
 193                         );
 194                     },
 195                 );
 196                 exit_block.unit()
 197             }
 198             ExprKind::Call { ty, fun, args, from_hir_call } => {
 199                 let intrinsic = match ty.sty {
 200                     ty::FnDef(def_id, _) => {
 201                         let f = ty.fn_sig(this.hir.tcx());
 202                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 203                             Some(this.hir.tcx().item_name(def_id).as_str())
 204                         } else {
 205                             None
 206                         }
 207                     }
 208                     _ => None,
 209                 };
 210                 let intrinsic = intrinsic.as_ref().map(|s| &s[..]);
 211                 let fun = unpack!(block = this.as_local_operand(block, fun));
 212                 if intrinsic == Some("move_val_init") {
 213                     // `move_val_init` has "magic" semantics - the second argument is
 214                     // always evaluated "directly" into the first one.
 215
 216                     let mut args = args.into_iter();
 217                     let ptr = args.next().expect("0 arguments to `move_val_init`");
 218                     let val = args.next().expect("1 argument to `move_val_init`");
 219                     assert!(args.next().is_none(), ">2 arguments to `move_val_init`");
 220
 221                     let ptr = this.hir.mirror(ptr);
 222                     let ptr_ty = ptr.ty;
 223                     // Create an *internal* temp for the pointer, so that unsafety
 224                     // checking won't complain about the raw pointer assignment.
 225                     let ptr_temp = this.local_decls.push(LocalDecl {
 226                         mutability: Mutability::Mut,
 227                         ty: ptr_ty,
 228                         user_ty: UserTypeProjections::none(),
 229                         name: None,
 230                         source_info,
 231                         visibility_scope: source_info.scope,
 232                         internal: true,
 233                         is_user_variable: None,
 234                         is_block_tail: None,
 235                     });
 236                     let ptr_temp = Place::from(ptr_temp);
 237                     let block = unpack!(this.into(&ptr_temp, block, ptr));
 238                     this.into(&ptr_temp.deref(), block, val)
 239                 } else {
 240                     let args: Vec<_> = args
 241                         .into_iter()
 242                         .map(|arg| unpack!(block = this.as_local_operand(block, arg)))
 243                         .collect();
 244
 245                     let success = this.cfg.start_new_block();
 246                     let cleanup = this.diverge_cleanup();
 247                     this.cfg.terminate(
 248                         block,
 249                         source_info,
 250                         TerminatorKind::Call {
 251                             func: fun,
 252                             args,
 253                             cleanup: Some(cleanup),
 254                             // FIXME(varkor): replace this with an uninhabitedness-based check.
 255                             // This requires getting access to the current module to call
 256                             // `tcx.is_ty_uninhabited_from`, which is currently tricky to do.
 257                             destination: if expr.ty.is_never() {
 258                                 None
 259                             } else {
 260                                 Some((destination.clone(), success))
 261                             },
 262                             from_hir_call,
 263                         },
 264                     );
 265                     success.unit()
 266                 }
 267             }
 268             ExprKind::Use { source } => {
 269                 this.into(destination, block, source)
 270             }
 271
 272             // These cases don't actually need a destination
 273             ExprKind::Assign { .. }
 274             | ExprKind::AssignOp { .. }
 275             | ExprKind::Continue { .. }
 276             | ExprKind::Break { .. }
 277             | ExprKind::InlineAsm { .. }
 278             | ExprKind::Return { .. } => {
 279                 unpack!(block = this.stmt_expr(block, expr, None));
 280                 this.cfg.push_assign_unit(block, source_info, destination);
 281                 block.unit()
 282             }
 283
 284             // Avoid creating a temporary
 285             ExprKind::VarRef { .. } |
 286             ExprKind::SelfRef |
 287             ExprKind::StaticRef { .. } |
 288             ExprKind::PlaceTypeAscription { .. } |
 289             ExprKind::ValueTypeAscription { .. } => {
 290                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 291
 292                 let place = unpack!(block = this.as_place(block, expr));
 293                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 294                 this.cfg
 295                     .push_assign(block, source_info, destination, rvalue);
 296                 block.unit()
 297             }
 298             ExprKind::Index { .. } | ExprKind::Deref { .. } | ExprKind::Field { .. } => {
 299                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 300
 301                 // Create a "fake" temporary variable so that we check that the
 302                 // value is Sized. Usually, this is caught in type checking, but
 303                 // in the case of box expr there is no such check.
 304                 if !destination.projection.is_empty() {
 305                     this.local_decls
 306                         .push(LocalDecl::new_temp(expr.ty, expr.span));
 307                 }
 308
 309                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 310
 311                 let place = unpack!(block = this.as_place(block, expr));
 312                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 313                 this.cfg
 314                     .push_assign(block, source_info, destination, rvalue);
 315                 block.unit()
 316             }
 317
 318             // these are the cases that are more naturally handled by some other mode
 319             ExprKind::Unary { .. }
 320             | ExprKind::Binary { .. }
 321             | ExprKind::Box { .. }
 322             | ExprKind::Cast { .. }
 323             | ExprKind::Pointer { .. }
 324             | ExprKind::Repeat { .. }
 325             | ExprKind::Borrow { .. }
 326             | ExprKind::Array { .. }
 327             | ExprKind::Tuple { .. }
 328             | ExprKind::Adt { .. }
 329             | ExprKind::Closure { .. }
 330             | ExprKind::Literal { .. }
 331             | ExprKind::Yield { .. } => {
 332                 debug_assert!(match Category::of(&expr.kind).unwrap() {
 333                     // should be handled above
 334                     Category::Rvalue(RvalueFunc::Into) => false,
 335
 336                     // must be handled above or else we get an
 337                     // infinite loop in the builder; see
 338                     // e.g., `ExprKind::VarRef` above
 339                     Category::Place => false,
 340
 341                     _ => true,
 342                 });
 343
 344                 let rvalue = unpack!(block = this.as_local_rvalue(block, expr));
 345                 this.cfg.push_assign(block, source_info, destination, rvalue);
 346                 block.unit()
 347             }
 348         };
 349
 350         if !expr_is_block_or_scope {
 351             let popped = this.block_context.pop();
 352             assert!(popped.is_some());
 353         }
 354
 355         block_and
 356     }
 357 }