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                         ty: this.hir.bool_ty(),
 118                         user_ty: None,
 119                         literal: this.hir.true_literal(),
 120                     },
 121                 );
 122
 123                 this.cfg.push_assign_constant(
 124                     false_block,
 125                     source_info,
 126                     destination,
 127                     Constant {
 128                         span: expr_span,
 129                         ty: this.hir.bool_ty(),
 130                         user_ty: None,
 131                         literal: this.hir.false_literal(),
 132                     },
 133                 );
 134
 135                 this.cfg.terminate(
 136                     true_block,
 137                     source_info,
 138                     TerminatorKind::Goto { target: join_block },
 139                 );
 140                 this.cfg.terminate(
 141                     false_block,
 142                     source_info,
 143                     TerminatorKind::Goto { target: join_block },
 144                 );
 145
 146                 join_block.unit()
 147             }
 148             ExprKind::Loop { body } => {
 149                 // [block]
 150                 //    |
 151                 //   [loop_block] -> [body_block] -/eval. body/-> [body_block_end]
 152                 //    |        ^                                         |
 153                 // false link  |                                         |
 154                 //    |        +-----------------------------------------+
 155                 //    +-> [diverge_cleanup]
 156                 // The false link is required to make sure borrowck considers unwinds through the
 157                 // body, even when the exact code in the body cannot unwind
 158
 159                 let loop_block = this.cfg.start_new_block();
 160                 let exit_block = this.cfg.start_new_block();
 161
 162                 // start the loop
 163                 this.cfg.terminate(
 164                     block,
 165                     source_info,
 166                     TerminatorKind::Goto { target: loop_block },
 167                 );
 168
 169                 this.in_breakable_scope(
 170                     Some(loop_block),
 171                     exit_block,
 172                     destination.clone(),
 173                     move |this| {
 174                         // conduct the test, if necessary
 175                         let body_block = this.cfg.start_new_block();
 176                         let diverge_cleanup = this.diverge_cleanup();
 177                         this.cfg.terminate(
 178                             loop_block,
 179                             source_info,
 180                             TerminatorKind::FalseUnwind {
 181                                 real_target: body_block,
 182                                 unwind: Some(diverge_cleanup),
 183                             },
 184                         );
 185
 186                         // The “return” value of the loop body must always be an unit. We therefore
 187                         // introduce a unit temporary as the destination for the loop body.
 188                         let tmp = this.get_unit_temp();
 189                         // Execute the body, branching back to the test.
 190                         let body_block_end = unpack!(this.into(&tmp, body_block, body));
 191                         this.cfg.terminate(
 192                             body_block_end,
 193                             source_info,
 194                             TerminatorKind::Goto { target: loop_block },
 195                         );
 196                     },
 197                 );
 198                 exit_block.unit()
 199             }
 200             ExprKind::Call { ty, fun, args, from_hir_call } => {
 201                 let intrinsic = match ty.sty {
 202                     ty::FnDef(def_id, _) => {
 203                         let f = ty.fn_sig(this.hir.tcx());
 204                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 205                             Some(this.hir.tcx().item_name(def_id).as_str())
 206                         } else {
 207                             None
 208                         }
 209                     }
 210                     _ => None,
 211                 };
 212                 let intrinsic = intrinsic.as_ref().map(|s| &s[..]);
 213                 let fun = unpack!(block = this.as_local_operand(block, fun));
 214                 if intrinsic == Some("move_val_init") {
 215                     // `move_val_init` has "magic" semantics - the second argument is
 216                     // always evaluated "directly" into the first one.
 217
 218                     let mut args = args.into_iter();
 219                     let ptr = args.next().expect("0 arguments to `move_val_init`");
 220                     let val = args.next().expect("1 argument to `move_val_init`");
 221                     assert!(args.next().is_none(), ">2 arguments to `move_val_init`");
 222
 223                     let ptr = this.hir.mirror(ptr);
 224                     let ptr_ty = ptr.ty;
 225                     // Create an *internal* temp for the pointer, so that unsafety
 226                     // checking won't complain about the raw pointer assignment.
 227                     let ptr_temp = this.local_decls.push(LocalDecl {
 228                         mutability: Mutability::Mut,
 229                         ty: ptr_ty,
 230                         user_ty: UserTypeProjections::none(),
 231                         name: None,
 232                         source_info,
 233                         visibility_scope: source_info.scope,
 234                         internal: true,
 235                         is_user_variable: None,
 236                         is_block_tail: None,
 237                     });
 238                     let ptr_temp = Place::from(ptr_temp);
 239                     let block = unpack!(this.into(&ptr_temp, block, ptr));
 240                     this.into(&ptr_temp.deref(), block, val)
 241                 } else {
 242                     let args: Vec<_> = args
 243                         .into_iter()
 244                         .map(|arg| unpack!(block = this.as_local_operand(block, arg)))
 245                         .collect();
 246
 247                     let success = this.cfg.start_new_block();
 248                     let cleanup = this.diverge_cleanup();
 249                     this.cfg.terminate(
 250                         block,
 251                         source_info,
 252                         TerminatorKind::Call {
 253                             func: fun,
 254                             args,
 255                             cleanup: Some(cleanup),
 256                             // FIXME(varkor): replace this with an uninhabitedness-based check.
 257                             // This requires getting access to the current module to call
 258                             // `tcx.is_ty_uninhabited_from`, which is currently tricky to do.
 259                             destination: if expr.ty.is_never() {
 260                                 None
 261                             } else {
 262                                 Some((destination.clone(), success))
 263                             },
 264                             from_hir_call,
 265                         },
 266                     );
 267                     success.unit()
 268                 }
 269             }
 270             ExprKind::Use { source } => {
 271                 this.into(destination, block, source)
 272             }
 273
 274             // These cases don't actually need a destination
 275             ExprKind::Assign { .. }
 276             | ExprKind::AssignOp { .. }
 277             | ExprKind::Continue { .. }
 278             | ExprKind::Break { .. }
 279             | ExprKind::InlineAsm { .. }
 280             | ExprKind::Return { .. } => {
 281                 unpack!(block = this.stmt_expr(block, expr, None));
 282                 this.cfg.push_assign_unit(block, source_info, destination);
 283                 block.unit()
 284             }
 285
 286             // Avoid creating a temporary
 287             ExprKind::VarRef { .. } |
 288             ExprKind::SelfRef |
 289             ExprKind::StaticRef { .. } |
 290             ExprKind::PlaceTypeAscription { .. } |
 291             ExprKind::ValueTypeAscription { .. } => {
 292                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 293
 294                 let place = unpack!(block = this.as_place(block, expr));
 295                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 296                 this.cfg
 297                     .push_assign(block, source_info, destination, rvalue);
 298                 block.unit()
 299             }
 300             ExprKind::Index { .. } | ExprKind::Deref { .. } | ExprKind::Field { .. } => {
 301                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 302
 303                 // Create a "fake" temporary variable so that we check that the
 304                 // value is Sized. Usually, this is caught in type checking, but
 305                 // in the case of box expr there is no such check.
 306                 if destination.projection.is_some() {
 307                     this.local_decls
 308                         .push(LocalDecl::new_temp(expr.ty, expr.span));
 309                 }
 310
 311                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 312
 313                 let place = unpack!(block = this.as_place(block, expr));
 314                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 315                 this.cfg
 316                     .push_assign(block, source_info, destination, rvalue);
 317                 block.unit()
 318             }
 319
 320             // these are the cases that are more naturally handled by some other mode
 321             ExprKind::Unary { .. }
 322             | ExprKind::Binary { .. }
 323             | ExprKind::Box { .. }
 324             | ExprKind::Cast { .. }
 325             | ExprKind::Pointer { .. }
 326             | ExprKind::Repeat { .. }
 327             | ExprKind::Borrow { .. }
 328             | ExprKind::Array { .. }
 329             | ExprKind::Tuple { .. }
 330             | ExprKind::Adt { .. }
 331             | ExprKind::Closure { .. }
 332             | ExprKind::Literal { .. }
 333             | ExprKind::Yield { .. } => {
 334                 debug_assert!(match Category::of(&expr.kind).unwrap() {
 335                     // should be handled above
 336                     Category::Rvalue(RvalueFunc::Into) => false,
 337
 338                     // must be handled above or else we get an
 339                     // infinite loop in the builder; see
 340                     // e.g., `ExprKind::VarRef` above
 341                     Category::Place => false,
 342
 343                     _ => true,
 344                 });
 345
 346                 let rvalue = unpack!(block = this.as_local_rvalue(block, expr));
 347                 this.cfg.push_assign(block, source_info, destination, rvalue);
 348                 block.unit()
 349             }
 350         };
 351
 352         if !expr_is_block_or_scope {
 353             let popped = this.block_context.pop();
 354             assert!(popped.is_some());
 355         }
 356
 357         block_and
 358     }
 359 }