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: dest = (rhs)]
  83                 //        | (false)
  84                 //  [shortcurcuit_block: dest = false]
  85                 //
  86                 // Or:
  87                 //
  88                 // [block: If(lhs)] -false-> [else_block: dest = (rhs)]
  89                 //        | (true)
  90                 //  [shortcurcuit_block: dest = true]
  91
  92                 let (shortcircuit_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                 );
  97
  98                 let lhs = unpack!(block = this.as_local_operand(block, lhs));
  99                 let blocks = match op {
 100                     LogicalOp::And => (else_block, shortcircuit_block),
 101                     LogicalOp::Or => (shortcircuit_block, else_block),
 102                 };
 103                 let term = TerminatorKind::if_(this.hir.tcx(), lhs, blocks.0, blocks.1);
 104                 this.cfg.terminate(block, source_info, term);
 105
 106                 this.cfg.push_assign_constant(
 107                     shortcircuit_block,
 108                     source_info,
 109                     destination,
 110                     Constant {
 111                         span: expr_span,
 112                         ty: this.hir.bool_ty(),
 113                         user_ty: None,
 114                         literal: match op {
 115                             LogicalOp::And => this.hir.false_literal(),
 116                             LogicalOp::Or => this.hir.true_literal(),
 117                         },
 118                     },
 119                 );
 120                 this.cfg.terminate(
 121                     shortcircuit_block,
 122                     source_info,
 123                     TerminatorKind::Goto { target: join_block },
 124                 );
 125
 126                 let rhs = unpack!(else_block = this.as_local_operand(else_block, rhs));
 127                 this.cfg.push_assign(
 128                     else_block,
 129                     source_info,
 130                     destination,
 131                     Rvalue::Use(rhs),
 132                 );
 133                 this.cfg.terminate(
 134                     else_block,
 135                     source_info,
 136                     TerminatorKind::Goto { target: join_block },
 137                 );
 138
 139                 join_block.unit()
 140             }
 141             ExprKind::Loop {
 142                 condition: opt_cond_expr,
 143                 body,
 144             } => {
 145                 // [block] --> [loop_block] -/eval. cond./-> [loop_block_end] -1-> [exit_block]
 146                 //                  ^                               |
 147                 //                  |                               0
 148                 //                  |                               |
 149                 //                  |                               v
 150                 //           [body_block_end] <-/eval. body/-- [body_block]
 151                 //
 152                 // If `opt_cond_expr` is `None`, then the graph is somewhat simplified:
 153                 //
 154                 // [block]
 155                 //    |
 156                 //   [loop_block] -> [body_block] -/eval. body/-> [body_block_end]
 157                 //    |        ^                                         |
 158                 // false link  |                                         |
 159                 //    |        +-----------------------------------------+
 160                 //    +-> [diverge_cleanup]
 161                 // The false link is required to make sure borrowck considers unwinds through the
 162                 // body, even when the exact code in the body cannot unwind
 163
 164                 let loop_block = this.cfg.start_new_block();
 165                 let exit_block = this.cfg.start_new_block();
 166
 167                 // start the loop
 168                 this.cfg.terminate(
 169                     block,
 170                     source_info,
 171                     TerminatorKind::Goto { target: loop_block },
 172                 );
 173
 174                 this.in_breakable_scope(
 175                     Some(loop_block),
 176                     exit_block,
 177                     destination.clone(),
 178                     move |this| {
 179                         // conduct the test, if necessary
 180                         let body_block;
 181                         if let Some(cond_expr) = opt_cond_expr {
 182                             let loop_block_end;
 183                             let cond = unpack!(
 184                                 loop_block_end = this.as_local_operand(loop_block, cond_expr)
 185                             );
 186                             body_block = this.cfg.start_new_block();
 187                             let term =
 188                                 TerminatorKind::if_(this.hir.tcx(), cond, body_block, exit_block);
 189                             this.cfg.terminate(loop_block_end, source_info, term);
 190
 191                             // if the test is false, there's no `break` to assign `destination`, so
 192                             // we have to do it; this overwrites any `break`-assigned value but it's
 193                             // always `()` anyway
 194                             this.cfg
 195                                 .push_assign_unit(exit_block, source_info, destination);
 196                         } else {
 197                             body_block = this.cfg.start_new_block();
 198                             let diverge_cleanup = this.diverge_cleanup();
 199                             this.cfg.terminate(
 200                                 loop_block,
 201                                 source_info,
 202                                 TerminatorKind::FalseUnwind {
 203                                     real_target: body_block,
 204                                     unwind: Some(diverge_cleanup),
 205                                 },
 206                             )
 207                         }
 208
 209                         // The “return” value of the loop body must always be an unit. We therefore
 210                         // introduce a unit temporary as the destination for the loop body.
 211                         let tmp = this.get_unit_temp();
 212                         // Execute the body, branching back to the test.
 213                         let body_block_end = unpack!(this.into(&tmp, body_block, body));
 214                         this.cfg.terminate(
 215                             body_block_end,
 216                             source_info,
 217                             TerminatorKind::Goto { target: loop_block },
 218                         );
 219                     },
 220                 );
 221                 exit_block.unit()
 222             }
 223             ExprKind::Call { ty, fun, args, from_hir_call } => {
 224                 let intrinsic = match ty.sty {
 225                     ty::FnDef(def_id, _) => {
 226                         let f = ty.fn_sig(this.hir.tcx());
 227                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 228                             Some(this.hir.tcx().item_name(def_id).as_str())
 229                         } else {
 230                             None
 231                         }
 232                     }
 233                     _ => None,
 234                 };
 235                 let intrinsic = intrinsic.as_ref().map(|s| &s[..]);
 236                 let fun = unpack!(block = this.as_local_operand(block, fun));
 237                 if intrinsic == Some("move_val_init") {
 238                     // `move_val_init` has "magic" semantics - the second argument is
 239                     // always evaluated "directly" into the first one.
 240
 241                     let mut args = args.into_iter();
 242                     let ptr = args.next().expect("0 arguments to `move_val_init`");
 243                     let val = args.next().expect("1 argument to `move_val_init`");
 244                     assert!(args.next().is_none(), ">2 arguments to `move_val_init`");
 245
 246                     let ptr = this.hir.mirror(ptr);
 247                     let ptr_ty = ptr.ty;
 248                     // Create an *internal* temp for the pointer, so that unsafety
 249                     // checking won't complain about the raw pointer assignment.
 250                     let ptr_temp = this.local_decls.push(LocalDecl {
 251                         mutability: Mutability::Mut,
 252                         ty: ptr_ty,
 253                         user_ty: UserTypeProjections::none(),
 254                         name: None,
 255                         source_info,
 256                         visibility_scope: source_info.scope,
 257                         internal: true,
 258                         is_user_variable: None,
 259                         is_block_tail: None,
 260                     });
 261                     let ptr_temp = Place::Base(PlaceBase::Local(ptr_temp));
 262                     let block = unpack!(this.into(&ptr_temp, block, ptr));
 263                     this.into(&ptr_temp.deref(), block, val)
 264                 } else {
 265                     let args: Vec<_> = args
 266                         .into_iter()
 267                         .map(|arg| unpack!(block = this.as_local_operand(block, arg)))
 268                         .collect();
 269
 270                     let success = this.cfg.start_new_block();
 271                     let cleanup = this.diverge_cleanup();
 272                     this.cfg.terminate(
 273                         block,
 274                         source_info,
 275                         TerminatorKind::Call {
 276                             func: fun,
 277                             args,
 278                             cleanup: Some(cleanup),
 279                             // FIXME(varkor): replace this with an uninhabitedness-based check.
 280                             // This requires getting access to the current module to call
 281                             // `tcx.is_ty_uninhabited_from`, which is currently tricky to do.
 282                             destination: if expr.ty.is_never() {
 283                                 None
 284                             } else {
 285                                 Some((destination.clone(), success))
 286                             },
 287                             from_hir_call,
 288                         },
 289                     );
 290                     success.unit()
 291                 }
 292             }
 293             ExprKind::Use { source } => {
 294                 this.into(destination, block, source)
 295             }
 296
 297             // These cases don't actually need a destination
 298             ExprKind::Assign { .. }
 299             | ExprKind::AssignOp { .. }
 300             | ExprKind::Continue { .. }
 301             | ExprKind::Break { .. }
 302             | ExprKind::InlineAsm { .. }
 303             | ExprKind::Return { .. } => {
 304                 unpack!(block = this.stmt_expr(block, expr, None));
 305                 this.cfg.push_assign_unit(block, source_info, destination);
 306                 block.unit()
 307             }
 308
 309             // Avoid creating a temporary
 310             ExprKind::VarRef { .. } |
 311             ExprKind::SelfRef |
 312             ExprKind::StaticRef { .. } |
 313             ExprKind::PlaceTypeAscription { .. } |
 314             ExprKind::ValueTypeAscription { .. } => {
 315                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 316
 317                 let place = unpack!(block = this.as_place(block, expr));
 318                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 319                 this.cfg
 320                     .push_assign(block, source_info, destination, rvalue);
 321                 block.unit()
 322             }
 323             ExprKind::Index { .. } | ExprKind::Deref { .. } | ExprKind::Field { .. } => {
 324                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 325
 326                 // Create a "fake" temporary variable so that we check that the
 327                 // value is Sized. Usually, this is caught in type checking, but
 328                 // in the case of box expr there is no such check.
 329                 if let Place::Projection(..) = destination {
 330                     this.local_decls
 331                         .push(LocalDecl::new_temp(expr.ty, expr.span));
 332                 }
 333
 334                 debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
 335
 336                 let place = unpack!(block = this.as_place(block, expr));
 337                 let rvalue = Rvalue::Use(this.consume_by_copy_or_move(place));
 338                 this.cfg
 339                     .push_assign(block, source_info, destination, rvalue);
 340                 block.unit()
 341             }
 342
 343             // these are the cases that are more naturally handled by some other mode
 344             ExprKind::Unary { .. }
 345             | ExprKind::Binary { .. }
 346             | ExprKind::Box { .. }
 347             | ExprKind::Cast { .. }
 348             | ExprKind::Pointer { .. }
 349             | ExprKind::Repeat { .. }
 350             | ExprKind::Borrow { .. }
 351             | ExprKind::Array { .. }
 352             | ExprKind::Tuple { .. }
 353             | ExprKind::Adt { .. }
 354             | ExprKind::Closure { .. }
 355             | ExprKind::Literal { .. }
 356             | ExprKind::Yield { .. } => {
 357                 debug_assert!(match Category::of(&expr.kind).unwrap() {
 358                     // should be handled above
 359                     Category::Rvalue(RvalueFunc::Into) => false,
 360
 361                     // must be handled above or else we get an
 362                     // infinite loop in the builder; see
 363                     // e.g., `ExprKind::VarRef` above
 364                     Category::Place => false,
 365
 366                     _ => true,
 367                 });
 368
 369                 let rvalue = unpack!(block = this.as_local_rvalue(block, expr));
 370                 this.cfg.push_assign(block, source_info, destination, rvalue);
 371                 block.unit()
 372             }
 373         };
 374
 375         if !expr_is_block_or_scope {
 376             let popped = this.block_context.pop();
 377             assert!(popped.is_some());
 378         }
 379
 380         block_and
 381     }
 382 }