src/librustc_mir_build/build/mod.rs

   1 use crate::build;
   2 use crate::build::scope::DropKind;
   3 use crate::thir::cx::Cx;
   4 use crate::thir::{BindingMode, LintLevel, PatKind};
   5 use rustc_attr::{self as attr, UnwindAttr};
   6 use rustc_errors::ErrorReported;
   7 use rustc_hir as hir;
   8 use rustc_hir::def_id::{DefId, LocalDefId};
   9 use rustc_hir::lang_items::LangItem;
  10 use rustc_hir::{GeneratorKind, HirIdMap, Node};
  11 use rustc_index::vec::{Idx, IndexVec};
  12 use rustc_infer::infer::TyCtxtInferExt;
  13 use rustc_middle::middle::region;
  14 use rustc_middle::mir::*;
  15 use rustc_middle::ty::subst::Subst;
  16 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
  17 use rustc_span::symbol::kw;
  18 use rustc_span::Span;
  19 use rustc_target::spec::abi::Abi;
  20 use rustc_target::spec::PanicStrategy;
  21
  22 use super::lints;
  23
  24 crate fn mir_built<'tcx>(
  25     tcx: TyCtxt<'tcx>,
  26     def: ty::WithOptConstParam<LocalDefId>,
  27 ) -> &'tcx ty::steal::Steal<Body<'tcx>> {
  28     if let Some(def) = def.try_upgrade(tcx) {
  29         return tcx.mir_built(def);
  30     }
  31
  32     tcx.alloc_steal_mir(mir_build(tcx, def))
  33 }
  34
  35 /// Construct the MIR for a given `DefId`.
  36 fn mir_build(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
  37     let id = tcx.hir().local_def_id_to_hir_id(def.did);
  38
  39     // Figure out what primary body this item has.
  40     let (body_id, return_ty_span, span_with_body) = match tcx.hir().get(id) {
  41         Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(_, decl, body_id, _, _), .. }) => {
  42             (*body_id, decl.output.span(), None)
  43         }
  44         Node::Item(hir::Item {
  45             kind: hir::ItemKind::Fn(hir::FnSig { decl, .. }, _, body_id),
  46             span,
  47             ..
  48         })
  49         | Node::ImplItem(hir::ImplItem {
  50             kind: hir::ImplItemKind::Fn(hir::FnSig { decl, .. }, body_id),
  51             span,
  52             ..
  53         })
  54         | Node::TraitItem(hir::TraitItem {
  55             kind: hir::TraitItemKind::Fn(hir::FnSig { decl, .. }, hir::TraitFn::Provided(body_id)),
  56             span,
  57             ..
  58         }) => {
  59             // Use the `Span` of the `Item/ImplItem/TraitItem` as the body span,
  60             // since the def span of a function does not include the body
  61             (*body_id, decl.output.span(), Some(*span))
  62         }
  63         Node::Item(hir::Item {
  64             kind: hir::ItemKind::Static(ty, _, body_id) | hir::ItemKind::Const(ty, body_id),
  65             ..
  66         })
  67         | Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(ty, body_id), .. })
  68         | Node::TraitItem(hir::TraitItem {
  69             kind: hir::TraitItemKind::Const(ty, Some(body_id)),
  70             ..
  71         }) => (*body_id, ty.span, None),
  72         Node::AnonConst(hir::AnonConst { body, hir_id, .. }) => (*body, tcx.hir().span(*hir_id), None),
  73
  74         _ => span_bug!(tcx.hir().span(id), "can't build MIR for {:?}", def.did),
  75     };
  76
  77     // If we don't have a specialized span for the body, just use the
  78     // normal def span.
  79     let span_with_body = span_with_body.unwrap_or_else(|| tcx.hir().span(id));
  80
  81     tcx.infer_ctxt().enter(|infcx| {
  82         let cx = Cx::new(&infcx, def, id);
  83         let body = if let Some(ErrorReported) = cx.typeck_results().tainted_by_errors {
  84             build::construct_error(cx, body_id)
  85         } else if cx.body_owner_kind.is_fn_or_closure() {
  86             // fetch the fully liberated fn signature (that is, all bound
  87             // types/lifetimes replaced)
  88             let fn_sig = cx.typeck_results().liberated_fn_sigs()[id];
  89             let fn_def_id = tcx.hir().local_def_id(id);
  90
  91             let safety = match fn_sig.unsafety {
  92                 hir::Unsafety::Normal => Safety::Safe,
  93                 hir::Unsafety::Unsafe => Safety::FnUnsafe,
  94             };
  95
  96             let body = tcx.hir().body(body_id);
  97             let ty = tcx.type_of(fn_def_id);
  98             let mut abi = fn_sig.abi;
  99             let implicit_argument = match ty.kind {
 100                 ty::Closure(..) => {
 101                     // HACK(eddyb) Avoid having RustCall on closures,
 102                     // as it adds unnecessary (and wrong) auto-tupling.
 103                     abi = Abi::Rust;
 104                     vec![ArgInfo(liberated_closure_env_ty(tcx, id, body_id), None, None, None)]
 105                 }
 106                 ty::Generator(..) => {
 107                     let gen_ty = tcx.typeck_body(body_id).node_type(id);
 108
 109                     // The resume argument may be missing, in that case we need to provide it here.
 110                     // It will always be `()` in this case.
 111                     if body.params.is_empty() {
 112                         vec![
 113                             ArgInfo(gen_ty, None, None, None),
 114                             ArgInfo(tcx.mk_unit(), None, None, None),
 115                         ]
 116                     } else {
 117                         vec![ArgInfo(gen_ty, None, None, None)]
 118                     }
 119                 }
 120                 _ => vec![],
 121             };
 122
 123             let explicit_arguments = body.params.iter().enumerate().map(|(index, arg)| {
 124                 let owner_id = tcx.hir().body_owner(body_id);
 125                 let opt_ty_info;
 126                 let self_arg;
 127                 if let Some(ref fn_decl) = tcx.hir().fn_decl_by_hir_id(owner_id) {
 128                     opt_ty_info = fn_decl.inputs.get(index).map(|ty| ty.span);
 129                     self_arg = if index == 0 && fn_decl.implicit_self.has_implicit_self() {
 130                         match fn_decl.implicit_self {
 131                             hir::ImplicitSelfKind::Imm => Some(ImplicitSelfKind::Imm),
 132                             hir::ImplicitSelfKind::Mut => Some(ImplicitSelfKind::Mut),
 133                             hir::ImplicitSelfKind::ImmRef => Some(ImplicitSelfKind::ImmRef),
 134                             hir::ImplicitSelfKind::MutRef => Some(ImplicitSelfKind::MutRef),
 135                             _ => None,
 136                         }
 137                     } else {
 138                         None
 139                     };
 140                 } else {
 141                     opt_ty_info = None;
 142                     self_arg = None;
 143                 }
 144
 145                 // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
 146                 // (as it's created inside the body itself, not passed in from outside).
 147                 let ty = if fn_sig.c_variadic && index == fn_sig.inputs().len() {
 148                     let va_list_did = tcx.require_lang_item(LangItem::VaList, Some(arg.span));
 149
 150                     tcx.type_of(va_list_did).subst(tcx, &[tcx.lifetimes.re_erased.into()])
 151                 } else {
 152                     fn_sig.inputs()[index]
 153                 };
 154
 155                 ArgInfo(ty, opt_ty_info, Some(&arg), self_arg)
 156             });
 157
 158             let arguments = implicit_argument.into_iter().chain(explicit_arguments);
 159
 160             let (yield_ty, return_ty) = if body.generator_kind.is_some() {
 161                 let gen_ty = tcx.typeck_body(body_id).node_type(id);
 162                 let gen_sig = match gen_ty.kind {
 163                     ty::Generator(_, gen_substs, ..) => gen_substs.as_generator().sig(),
 164                     _ => span_bug!(tcx.hir().span(id), "generator w/o generator type: {:?}", ty),
 165                 };
 166                 (Some(gen_sig.yield_ty), gen_sig.return_ty)
 167             } else {
 168                 (None, fn_sig.output())
 169             };
 170
 171             let mut mir = build::construct_fn(
 172                 cx,
 173                 id,
 174                 arguments,
 175                 safety,
 176                 abi,
 177                 return_ty,
 178                 return_ty_span,
 179                 body,
 180                 span_with_body
 181             );
 182             mir.yield_ty = yield_ty;
 183             mir
 184         } else {
 185             // Get the revealed type of this const. This is *not* the adjusted
 186             // type of its body, which may be a subtype of this type. For
 187             // example:
 188             //
 189             // fn foo(_: &()) {}
 190             // static X: fn(&'static ()) = foo;
 191             //
 192             // The adjusted type of the body of X is `for<'a> fn(&'a ())` which
 193             // is not the same as the type of X. We need the type of the return
 194             // place to be the type of the constant because NLL typeck will
 195             // equate them.
 196
 197             let return_ty = cx.typeck_results().node_type(id);
 198
 199             build::construct_const(cx, body_id, return_ty, return_ty_span)
 200         };
 201
 202         lints::check(tcx, &body, def.did);
 203
 204         // The borrow checker will replace all the regions here with its own
 205         // inference variables. There's no point having non-erased regions here.
 206         // The exception is `body.user_type_annotations`, which is used unmodified
 207         // by borrow checking.
 208         debug_assert!(
 209             !(body.local_decls.has_free_regions()
 210                 || body.basic_blocks().has_free_regions()
 211                 || body.var_debug_info.has_free_regions()
 212                 || body.yield_ty.has_free_regions()),
 213             "Unexpected free regions in MIR: {:?}",
 214             body,
 215         );
 216
 217         body
 218     })
 219 }
 220
 221 ///////////////////////////////////////////////////////////////////////////
 222 // BuildMir -- walks a crate, looking for fn items and methods to build MIR from
 223
 224 fn liberated_closure_env_ty(
 225     tcx: TyCtxt<'_>,
 226     closure_expr_id: hir::HirId,
 227     body_id: hir::BodyId,
 228 ) -> Ty<'_> {
 229     let closure_ty = tcx.typeck_body(body_id).node_type(closure_expr_id);
 230
 231     let (closure_def_id, closure_substs) = match closure_ty.kind {
 232         ty::Closure(closure_def_id, closure_substs) => (closure_def_id, closure_substs),
 233         _ => bug!("closure expr does not have closure type: {:?}", closure_ty),
 234     };
 235
 236     let closure_env_ty = tcx.closure_env_ty(closure_def_id, closure_substs).unwrap();
 237     tcx.erase_late_bound_regions(&closure_env_ty)
 238 }
 239
 240 #[derive(Debug, PartialEq, Eq)]
 241 enum BlockFrame {
 242     /// Evaluation is currently within a statement.
 243     ///
 244     /// Examples include:
 245     /// 1. `EXPR;`
 246     /// 2. `let _ = EXPR;`
 247     /// 3. `let x = EXPR;`
 248     Statement {
 249         /// If true, then statement discards result from evaluating
 250         /// the expression (such as examples 1 and 2 above).
 251         ignores_expr_result: bool,
 252     },
 253
 254     /// Evaluation is currently within the tail expression of a block.
 255     ///
 256     /// Example: `{ STMT_1; STMT_2; EXPR }`
 257     TailExpr {
 258         /// If true, then the surrounding context of the block ignores
 259         /// the result of evaluating the block's tail expression.
 260         ///
 261         /// Example: `let _ = { STMT_1; EXPR };`
 262         tail_result_is_ignored: bool,
 263
 264         /// `Span` of the tail expression.
 265         span: Span,
 266     },
 267
 268     /// Generic mark meaning that the block occurred as a subexpression
 269     /// where the result might be used.
 270     ///
 271     /// Examples: `foo(EXPR)`, `match EXPR { ... }`
 272     SubExpr,
 273 }
 274
 275 impl BlockFrame {
 276     fn is_tail_expr(&self) -> bool {
 277         match *self {
 278             BlockFrame::TailExpr { .. } => true,
 279
 280             BlockFrame::Statement { .. } | BlockFrame::SubExpr => false,
 281         }
 282     }
 283     fn is_statement(&self) -> bool {
 284         match *self {
 285             BlockFrame::Statement { .. } => true,
 286
 287             BlockFrame::TailExpr { .. } | BlockFrame::SubExpr => false,
 288         }
 289     }
 290 }
 291
 292 #[derive(Debug)]
 293 struct BlockContext(Vec<BlockFrame>);
 294
 295 struct Builder<'a, 'tcx> {
 296     hir: Cx<'a, 'tcx>,
 297     cfg: CFG<'tcx>,
 298
 299     fn_span: Span,
 300     arg_count: usize,
 301     generator_kind: Option<GeneratorKind>,
 302
 303     /// The current set of scopes, updated as we traverse;
 304     /// see the `scope` module for more details.
 305     scopes: scope::Scopes<'tcx>,
 306
 307     /// The block-context: each time we build the code within an thir::Block,
 308     /// we push a frame here tracking whether we are building a statement or
 309     /// if we are pushing the tail expression of the block. This is used to
 310     /// embed information in generated temps about whether they were created
 311     /// for a block tail expression or not.
 312     ///
 313     /// It would be great if we could fold this into `self.scopes`
 314     /// somehow, but right now I think that is very tightly tied to
 315     /// the code generation in ways that we cannot (or should not)
 316     /// start just throwing new entries onto that vector in order to
 317     /// distinguish the context of EXPR1 from the context of EXPR2 in
 318     /// `{ STMTS; EXPR1 } + EXPR2`.
 319     block_context: BlockContext,
 320
 321     /// The current unsafe block in scope, even if it is hidden by
 322     /// a `PushUnsafeBlock`.
 323     unpushed_unsafe: Safety,
 324
 325     /// The number of `push_unsafe_block` levels in scope.
 326     push_unsafe_count: usize,
 327
 328     /// The vector of all scopes that we have created thus far;
 329     /// we track this for debuginfo later.
 330     source_scopes: IndexVec<SourceScope, SourceScopeData>,
 331     source_scope: SourceScope,
 332
 333     /// The guard-context: each time we build the guard expression for
 334     /// a match arm, we push onto this stack, and then pop when we
 335     /// finish building it.
 336     guard_context: Vec<GuardFrame>,
 337
 338     /// Maps `HirId`s of variable bindings to the `Local`s created for them.
 339     /// (A match binding can have two locals; the 2nd is for the arm's guard.)
 340     var_indices: HirIdMap<LocalsForNode>,
 341     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 342     canonical_user_type_annotations: ty::CanonicalUserTypeAnnotations<'tcx>,
 343     upvar_mutbls: Vec<Mutability>,
 344     unit_temp: Option<Place<'tcx>>,
 345
 346     var_debug_info: Vec<VarDebugInfo<'tcx>>,
 347
 348     /// Cached block with the `RESUME` terminator; this is created
 349     /// when first set of cleanups are built.
 350     cached_resume_block: Option<BasicBlock>,
 351     /// Cached block with the `RETURN` terminator.
 352     cached_return_block: Option<BasicBlock>,
 353     /// Cached block with the `UNREACHABLE` terminator.
 354     cached_unreachable_block: Option<BasicBlock>,
 355 }
 356
 357 impl<'a, 'tcx> Builder<'a, 'tcx> {
 358     fn is_bound_var_in_guard(&self, id: hir::HirId) -> bool {
 359         self.guard_context.iter().any(|frame| frame.locals.iter().any(|local| local.id == id))
 360     }
 361
 362     fn var_local_id(&self, id: hir::HirId, for_guard: ForGuard) -> Local {
 363         self.var_indices[&id].local_id(for_guard)
 364     }
 365 }
 366
 367 impl BlockContext {
 368     fn new() -> Self {
 369         BlockContext(vec![])
 370     }
 371     fn push(&mut self, bf: BlockFrame) {
 372         self.0.push(bf);
 373     }
 374     fn pop(&mut self) -> Option<BlockFrame> {
 375         self.0.pop()
 376     }
 377
 378     /// Traverses the frames on the `BlockContext`, searching for either
 379     /// the first block-tail expression frame with no intervening
 380     /// statement frame.
 381     ///
 382     /// Notably, this skips over `SubExpr` frames; this method is
 383     /// meant to be used in the context of understanding the
 384     /// relationship of a temp (created within some complicated
 385     /// expression) with its containing expression, and whether the
 386     /// value of that *containing expression* (not the temp!) is
 387     /// ignored.
 388     fn currently_in_block_tail(&self) -> Option<BlockTailInfo> {
 389         for bf in self.0.iter().rev() {
 390             match bf {
 391                 BlockFrame::SubExpr => continue,
 392                 BlockFrame::Statement { .. } => break,
 393                 &BlockFrame::TailExpr { tail_result_is_ignored, span } => {
 394                     return Some(BlockTailInfo { tail_result_is_ignored, span });
 395                 }
 396             }
 397         }
 398
 399         None
 400     }
 401
 402     /// Looks at the topmost frame on the BlockContext and reports
 403     /// whether its one that would discard a block tail result.
 404     ///
 405     /// Unlike `currently_within_ignored_tail_expression`, this does
 406     /// *not* skip over `SubExpr` frames: here, we want to know
 407     /// whether the block result itself is discarded.
 408     fn currently_ignores_tail_results(&self) -> bool {
 409         match self.0.last() {
 410             // no context: conservatively assume result is read
 411             None => false,
 412
 413             // sub-expression: block result feeds into some computation
 414             Some(BlockFrame::SubExpr) => false,
 415
 416             // otherwise: use accumulated is_ignored state.
 417             Some(
 418                 BlockFrame::TailExpr { tail_result_is_ignored: ignored, .. }
 419                 | BlockFrame::Statement { ignores_expr_result: ignored },
 420             ) => *ignored,
 421         }
 422     }
 423 }
 424
 425 #[derive(Debug)]
 426 enum LocalsForNode {
 427     /// In the usual case, a `HirId` for an identifier maps to at most
 428     /// one `Local` declaration.
 429     One(Local),
 430
 431     /// The exceptional case is identifiers in a match arm's pattern
 432     /// that are referenced in a guard of that match arm. For these,
 433     /// we have `2` Locals.
 434     ///
 435     /// * `for_arm_body` is the Local used in the arm body (which is
 436     ///   just like the `One` case above),
 437     ///
 438     /// * `ref_for_guard` is the Local used in the arm's guard (which
 439     ///   is a reference to a temp that is an alias of
 440     ///   `for_arm_body`).
 441     ForGuard { ref_for_guard: Local, for_arm_body: Local },
 442 }
 443
 444 #[derive(Debug)]
 445 struct GuardFrameLocal {
 446     id: hir::HirId,
 447 }
 448
 449 impl GuardFrameLocal {
 450     fn new(id: hir::HirId, _binding_mode: BindingMode) -> Self {
 451         GuardFrameLocal { id }
 452     }
 453 }
 454
 455 #[derive(Debug)]
 456 struct GuardFrame {
 457     /// These are the id's of names that are bound by patterns of the
 458     /// arm of *this* guard.
 459     ///
 460     /// (Frames higher up the stack will have the id's bound in arms
 461     /// further out, such as in a case like:
 462     ///
 463     /// match E1 {
 464     ///      P1(id1) if (... (match E2 { P2(id2) if ... => B2 })) => B1,
 465     /// }
 466     ///
 467     /// here, when building for FIXME.
 468     locals: Vec<GuardFrameLocal>,
 469 }
 470
 471 /// `ForGuard` indicates whether we are talking about:
 472 ///   1. The variable for use outside of guard expressions, or
 473 ///   2. The temp that holds reference to (1.), which is actually what the
 474 ///      guard expressions see.
 475 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 476 enum ForGuard {
 477     RefWithinGuard,
 478     OutsideGuard,
 479 }
 480
 481 impl LocalsForNode {
 482     fn local_id(&self, for_guard: ForGuard) -> Local {
 483         match (self, for_guard) {
 484             (&LocalsForNode::One(local_id), ForGuard::OutsideGuard)
 485             | (
 486                 &LocalsForNode::ForGuard { ref_for_guard: local_id, .. },
 487                 ForGuard::RefWithinGuard,
 488             )
 489             | (&LocalsForNode::ForGuard { for_arm_body: local_id, .. }, ForGuard::OutsideGuard) => {
 490                 local_id
 491             }
 492
 493             (&LocalsForNode::One(_), ForGuard::RefWithinGuard) => {
 494                 bug!("anything with one local should never be within a guard.")
 495             }
 496         }
 497     }
 498 }
 499
 500 struct CFG<'tcx> {
 501     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 502 }
 503
 504 rustc_index::newtype_index! {
 505     struct ScopeId { .. }
 506 }
 507
 508 ///////////////////////////////////////////////////////////////////////////
 509 /// The `BlockAnd` "monad" packages up the new basic block along with a
 510 /// produced value (sometimes just unit, of course). The `unpack!`
 511 /// macro (and methods below) makes working with `BlockAnd` much more
 512 /// convenient.
 513
 514 #[must_use = "if you don't use one of these results, you're leaving a dangling edge"]
 515 struct BlockAnd<T>(BasicBlock, T);
 516
 517 trait BlockAndExtension {
 518     fn and<T>(self, v: T) -> BlockAnd<T>;
 519     fn unit(self) -> BlockAnd<()>;
 520 }
 521
 522 impl BlockAndExtension for BasicBlock {
 523     fn and<T>(self, v: T) -> BlockAnd<T> {
 524         BlockAnd(self, v)
 525     }
 526
 527     fn unit(self) -> BlockAnd<()> {
 528         BlockAnd(self, ())
 529     }
 530 }
 531
 532 /// Update a block pointer and return the value.
 533 /// Use it like `let x = unpack!(block = self.foo(block, foo))`.
 534 macro_rules! unpack {
 535     ($x:ident = $c:expr) => {{
 536         let BlockAnd(b, v) = $c;
 537         $x = b;
 538         v
 539     }};
 540
 541     ($c:expr) => {{
 542         let BlockAnd(b, ()) = $c;
 543         b
 544     }};
 545 }
 546
 547 fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> bool {
 548     // Validate `#[unwind]` syntax regardless of platform-specific panic strategy.
 549     let attrs = &tcx.get_attrs(fn_def_id.to_def_id());
 550     let unwind_attr = attr::find_unwind_attr(&tcx.sess, attrs);
 551
 552     // We never unwind, so it's not relevant to stop an unwind.
 553     if tcx.sess.panic_strategy() != PanicStrategy::Unwind {
 554         return false;
 555     }
 556
 557     // This is a special case: some functions have a C abi but are meant to
 558     // unwind anyway. Don't stop them.
 559     match unwind_attr {
 560         None => false, // FIXME(#58794); should be `!(abi == Abi::Rust || abi == Abi::RustCall)`
 561         Some(UnwindAttr::Allowed) => false,
 562         Some(UnwindAttr::Aborts) => true,
 563     }
 564 }
 565
 566 ///////////////////////////////////////////////////////////////////////////
 567 /// the main entry point for building MIR for a function
 568
 569 struct ArgInfo<'tcx>(
 570     Ty<'tcx>,
 571     Option<Span>,
 572     Option<&'tcx hir::Param<'tcx>>,
 573     Option<ImplicitSelfKind>,
 574 );
 575
 576 fn construct_fn<'a, 'tcx, A>(
 577     hir: Cx<'a, 'tcx>,
 578     fn_id: hir::HirId,
 579     arguments: A,
 580     safety: Safety,
 581     abi: Abi,
 582     return_ty: Ty<'tcx>,
 583     return_ty_span: Span,
 584     body: &'tcx hir::Body<'tcx>,
 585     span_with_body: Span
 586 ) -> Body<'tcx>
 587 where
 588     A: Iterator<Item = ArgInfo<'tcx>>,
 589 {
 590     let arguments: Vec<_> = arguments.collect();
 591
 592     let tcx = hir.tcx();
 593     let tcx_hir = tcx.hir();
 594     let span = tcx_hir.span(fn_id);
 595
 596     let fn_def_id = tcx_hir.local_def_id(fn_id);
 597
 598     let mut builder = Builder::new(
 599         hir,
 600         span_with_body,
 601         arguments.len(),
 602         safety,
 603         return_ty,
 604         return_ty_span,
 605         body.generator_kind,
 606     );
 607
 608     let call_site_scope =
 609         region::Scope { id: body.value.hir_id.local_id, data: region::ScopeData::CallSite };
 610     let arg_scope =
 611         region::Scope { id: body.value.hir_id.local_id, data: region::ScopeData::Arguments };
 612     let mut block = START_BLOCK;
 613     let source_info = builder.source_info(span);
 614     let call_site_s = (call_site_scope, source_info);
 615     unpack!(
 616         block = builder.in_scope(call_site_s, LintLevel::Inherited, |builder| {
 617             if should_abort_on_panic(tcx, fn_def_id, abi) {
 618                 builder.schedule_abort();
 619             }
 620
 621             let arg_scope_s = (arg_scope, source_info);
 622             // `return_block` is called when we evaluate a `return` expression, so
 623             // we just use `START_BLOCK` here.
 624             unpack!(
 625                 block = builder.in_breakable_scope(
 626                     None,
 627                     START_BLOCK,
 628                     Place::return_place(),
 629                     |builder| {
 630                         builder.in_scope(arg_scope_s, LintLevel::Inherited, |builder| {
 631                             builder.args_and_body(
 632                                 block,
 633                                 fn_def_id.to_def_id(),
 634                                 &arguments,
 635                                 arg_scope,
 636                                 &body.value,
 637                             )
 638                         })
 639                     },
 640                 )
 641             );
 642             // Attribute epilogue to function's closing brace
 643             let fn_end = span_with_body.shrink_to_hi();
 644             let source_info = builder.source_info(fn_end);
 645             let return_block = builder.return_block();
 646             builder.cfg.goto(block, source_info, return_block);
 647             builder.cfg.terminate(return_block, source_info, TerminatorKind::Return);
 648             // Attribute any unreachable codepaths to the function's closing brace
 649             if let Some(unreachable_block) = builder.cached_unreachable_block {
 650                 builder.cfg.terminate(unreachable_block, source_info, TerminatorKind::Unreachable);
 651             }
 652             return_block.unit()
 653         })
 654     );
 655     assert_eq!(block, builder.return_block());
 656
 657     let spread_arg = if abi == Abi::RustCall {
 658         // RustCall pseudo-ABI untuples the last argument.
 659         Some(Local::new(arguments.len()))
 660     } else {
 661         None
 662     };
 663     debug!("fn_id {:?} has attrs {:?}", fn_def_id, tcx.get_attrs(fn_def_id.to_def_id()));
 664
 665     let mut body = builder.finish();
 666     body.spread_arg = spread_arg;
 667     body
 668 }
 669
 670 fn construct_const<'a, 'tcx>(
 671     hir: Cx<'a, 'tcx>,
 672     body_id: hir::BodyId,
 673     const_ty: Ty<'tcx>,
 674     const_ty_span: Span,
 675 ) -> Body<'tcx> {
 676     let tcx = hir.tcx();
 677     let owner_id = tcx.hir().body_owner(body_id);
 678     let span = tcx.hir().span(owner_id);
 679     let mut builder = Builder::new(hir, span, 0, Safety::Safe, const_ty, const_ty_span, None);
 680
 681     let mut block = START_BLOCK;
 682     let ast_expr = &tcx.hir().body(body_id).value;
 683     let expr = builder.hir.mirror(ast_expr);
 684     unpack!(block = builder.into_expr(Place::return_place(), block, expr));
 685
 686     let source_info = builder.source_info(span);
 687     builder.cfg.terminate(block, source_info, TerminatorKind::Return);
 688
 689     // Constants can't `return` so a return block should not be created.
 690     assert_eq!(builder.cached_return_block, None);
 691
 692     // Constants may be match expressions in which case an unreachable block may
 693     // be created, so terminate it properly.
 694     if let Some(unreachable_block) = builder.cached_unreachable_block {
 695         builder.cfg.terminate(unreachable_block, source_info, TerminatorKind::Unreachable);
 696     }
 697
 698     builder.finish()
 699 }
 700
 701 /// Construct MIR for a item that has had errors in type checking.
 702 ///
 703 /// This is required because we may still want to run MIR passes on an item
 704 /// with type errors, but normal MIR construction can't handle that in general.
 705 fn construct_error<'a, 'tcx>(hir: Cx<'a, 'tcx>, body_id: hir::BodyId) -> Body<'tcx> {
 706     let tcx = hir.tcx();
 707     let owner_id = tcx.hir().body_owner(body_id);
 708     let span = tcx.hir().span(owner_id);
 709     let ty = tcx.ty_error();
 710     let num_params = match hir.body_owner_kind {
 711         hir::BodyOwnerKind::Fn => tcx.hir().fn_decl_by_hir_id(owner_id).unwrap().inputs.len(),
 712         hir::BodyOwnerKind::Closure => {
 713             if tcx.hir().body(body_id).generator_kind().is_some() {
 714                 // Generators have an implicit `self` parameter *and* a possibly
 715                 // implicit resume parameter.
 716                 2
 717             } else {
 718                 // The implicit self parameter adds another local in MIR.
 719                 1 + tcx.hir().fn_decl_by_hir_id(owner_id).unwrap().inputs.len()
 720             }
 721         }
 722         hir::BodyOwnerKind::Const => 0,
 723         hir::BodyOwnerKind::Static(_) => 0,
 724     };
 725     let mut builder = Builder::new(hir, span, num_params, Safety::Safe, ty, span, None);
 726     let source_info = builder.source_info(span);
 727     // Some MIR passes will expect the number of parameters to match the
 728     // function declaration.
 729     for _ in 0..num_params {
 730         builder.local_decls.push(LocalDecl::with_source_info(ty, source_info));
 731     }
 732     builder.cfg.terminate(START_BLOCK, source_info, TerminatorKind::Unreachable);
 733     let mut body = builder.finish();
 734     if tcx.hir().body(body_id).generator_kind.is_some() {
 735         body.yield_ty = Some(ty);
 736     }
 737     body
 738 }
 739
 740 impl<'a, 'tcx> Builder<'a, 'tcx> {
 741     fn new(
 742         hir: Cx<'a, 'tcx>,
 743         span: Span,
 744         arg_count: usize,
 745         safety: Safety,
 746         return_ty: Ty<'tcx>,
 747         return_span: Span,
 748         generator_kind: Option<GeneratorKind>,
 749     ) -> Builder<'a, 'tcx> {
 750         let lint_level = LintLevel::Explicit(hir.root_lint_level);
 751         let mut builder = Builder {
 752             hir,
 753             cfg: CFG { basic_blocks: IndexVec::new() },
 754             fn_span: span,
 755             arg_count,
 756             generator_kind,
 757             scopes: Default::default(),
 758             block_context: BlockContext::new(),
 759             source_scopes: IndexVec::new(),
 760             source_scope: OUTERMOST_SOURCE_SCOPE,
 761             guard_context: vec![],
 762             push_unsafe_count: 0,
 763             unpushed_unsafe: safety,
 764             local_decls: IndexVec::from_elem_n(LocalDecl::new(return_ty, return_span), 1),
 765             canonical_user_type_annotations: IndexVec::new(),
 766             upvar_mutbls: vec![],
 767             var_indices: Default::default(),
 768             unit_temp: None,
 769             var_debug_info: vec![],
 770             cached_resume_block: None,
 771             cached_return_block: None,
 772             cached_unreachable_block: None,
 773         };
 774
 775         assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
 776         assert_eq!(
 777             builder.new_source_scope(span, lint_level, Some(safety)),
 778             OUTERMOST_SOURCE_SCOPE
 779         );
 780         builder.source_scopes[OUTERMOST_SOURCE_SCOPE].parent_scope = None;
 781
 782         builder
 783     }
 784
 785     fn finish(self) -> Body<'tcx> {
 786         for (index, block) in self.cfg.basic_blocks.iter().enumerate() {
 787             if block.terminator.is_none() {
 788                 span_bug!(self.fn_span, "no terminator on block {:?}", index);
 789             }
 790         }
 791
 792         Body::new(
 793             self.cfg.basic_blocks,
 794             self.source_scopes,
 795             self.local_decls,
 796             self.canonical_user_type_annotations,
 797             self.arg_count,
 798             self.var_debug_info,
 799             self.fn_span,
 800             self.generator_kind,
 801         )
 802     }
 803
 804     fn args_and_body(
 805         &mut self,
 806         mut block: BasicBlock,
 807         fn_def_id: DefId,
 808         arguments: &[ArgInfo<'tcx>],
 809         argument_scope: region::Scope,
 810         ast_body: &'tcx hir::Expr<'tcx>,
 811     ) -> BlockAnd<()> {
 812         // Allocate locals for the function arguments
 813         for &ArgInfo(ty, _, arg_opt, _) in arguments.iter() {
 814             let source_info =
 815                 SourceInfo::outermost(arg_opt.map_or(self.fn_span, |arg| arg.pat.span));
 816             let arg_local = self.local_decls.push(LocalDecl::with_source_info(ty, source_info));
 817
 818             // If this is a simple binding pattern, give debuginfo a nice name.
 819             if let Some(arg) = arg_opt {
 820                 if let Some(ident) = arg.pat.simple_ident() {
 821                     self.var_debug_info.push(VarDebugInfo {
 822                         name: ident.name,
 823                         source_info,
 824                         place: arg_local.into(),
 825                     });
 826                 }
 827             }
 828         }
 829
 830         let tcx = self.hir.tcx();
 831         let tcx_hir = tcx.hir();
 832         let hir_typeck_results = self.hir.typeck_results();
 833
 834         // In analyze_closure() in upvar.rs we gathered a list of upvars used by a
 835         // indexed closure and we stored in a map called closure_captures in TypeckResults
 836         // with the closure's DefId. Here, we run through that vec of UpvarIds for
 837         // the given closure and use the necessary information to create upvar
 838         // debuginfo and to fill `self.upvar_mutbls`.
 839         if let Some(upvars) = hir_typeck_results.closure_captures.get(&fn_def_id) {
 840             let closure_env_arg = Local::new(1);
 841             let mut closure_env_projs = vec![];
 842             let mut closure_ty = self.local_decls[closure_env_arg].ty;
 843             if let ty::Ref(_, ty, _) = closure_ty.kind {
 844                 closure_env_projs.push(ProjectionElem::Deref);
 845                 closure_ty = ty;
 846             }
 847             let upvar_substs = match closure_ty.kind {
 848                 ty::Closure(_, substs) => ty::UpvarSubsts::Closure(substs),
 849                 ty::Generator(_, substs, _) => ty::UpvarSubsts::Generator(substs),
 850                 _ => span_bug!(self.fn_span, "upvars with non-closure env ty {:?}", closure_ty),
 851             };
 852             let upvar_tys = upvar_substs.upvar_tys();
 853             let upvars_with_tys = upvars.iter().zip(upvar_tys);
 854             self.upvar_mutbls = upvars_with_tys
 855                 .enumerate()
 856                 .map(|(i, ((&var_id, &upvar_id), ty))| {
 857                     let capture = hir_typeck_results.upvar_capture(upvar_id);
 858
 859                     let mut mutability = Mutability::Not;
 860                     let mut name = kw::Invalid;
 861                     if let Some(Node::Binding(pat)) = tcx_hir.find(var_id) {
 862                         if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
 863                             name = ident.name;
 864                             match hir_typeck_results
 865                                 .extract_binding_mode(tcx.sess, pat.hir_id, pat.span)
 866                             {
 867                                 Some(ty::BindByValue(hir::Mutability::Mut)) => {
 868                                     mutability = Mutability::Mut;
 869                                 }
 870                                 Some(_) => mutability = Mutability::Not,
 871                                 _ => {}
 872                             }
 873                         }
 874                     }
 875
 876                     let mut projs = closure_env_projs.clone();
 877                     projs.push(ProjectionElem::Field(Field::new(i), ty));
 878                     match capture {
 879                         ty::UpvarCapture::ByValue => {}
 880                         ty::UpvarCapture::ByRef(..) => {
 881                             projs.push(ProjectionElem::Deref);
 882                         }
 883                     };
 884
 885                     self.var_debug_info.push(VarDebugInfo {
 886                         name,
 887                         source_info: SourceInfo::outermost(tcx_hir.span(var_id)),
 888                         place: Place {
 889                             local: closure_env_arg,
 890                             projection: tcx.intern_place_elems(&projs),
 891                         },
 892                     });
 893
 894                     mutability
 895                 })
 896                 .collect();
 897         }
 898
 899         let mut scope = None;
 900         // Bind the argument patterns
 901         for (index, arg_info) in arguments.iter().enumerate() {
 902             // Function arguments always get the first Local indices after the return place
 903             let local = Local::new(index + 1);
 904             let place = Place::from(local);
 905             let &ArgInfo(_, opt_ty_info, arg_opt, ref self_binding) = arg_info;
 906
 907             // Make sure we drop (parts of) the argument even when not matched on.
 908             self.schedule_drop(
 909                 arg_opt.as_ref().map_or(ast_body.span, |arg| arg.pat.span),
 910                 argument_scope,
 911                 local,
 912                 DropKind::Value,
 913             );
 914
 915             if let Some(arg) = arg_opt {
 916                 let pattern = self.hir.pattern_from_hir(&arg.pat);
 917                 let original_source_scope = self.source_scope;
 918                 let span = pattern.span;
 919                 self.set_correct_source_scope_for_arg(arg.hir_id, original_source_scope, span);
 920                 match *pattern.kind {
 921                     // Don't introduce extra copies for simple bindings
 922                     PatKind::Binding {
 923                         mutability,
 924                         var,
 925                         mode: BindingMode::ByValue,
 926                         subpattern: None,
 927                         ..
 928                     } => {
 929                         self.local_decls[local].mutability = mutability;
 930                         self.local_decls[local].source_info.scope = self.source_scope;
 931                         self.local_decls[local].local_info = if let Some(kind) = self_binding {
 932                             Some(box LocalInfo::User(ClearCrossCrate::Set(
 933                                 BindingForm::ImplicitSelf(*kind),
 934                             )))
 935                         } else {
 936                             let binding_mode = ty::BindingMode::BindByValue(mutability);
 937                             Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
 938                                 VarBindingForm {
 939                                     binding_mode,
 940                                     opt_ty_info,
 941                                     opt_match_place: Some((Some(place), span)),
 942                                     pat_span: span,
 943                                 },
 944                             ))))
 945                         };
 946                         self.var_indices.insert(var, LocalsForNode::One(local));
 947                     }
 948                     _ => {
 949                         scope = self.declare_bindings(
 950                             scope,
 951                             ast_body.span,
 952                             &pattern,
 953                             matches::ArmHasGuard(false),
 954                             Some((Some(&place), span)),
 955                         );
 956                         unpack!(block = self.place_into_pattern(block, pattern, place, false));
 957                     }
 958                 }
 959                 self.source_scope = original_source_scope;
 960             }
 961         }
 962
 963         // Enter the argument pattern bindings source scope, if it exists.
 964         if let Some(source_scope) = scope {
 965             self.source_scope = source_scope;
 966         }
 967
 968         let body = self.hir.mirror(ast_body);
 969         self.into(Place::return_place(), block, body)
 970     }
 971
 972     fn set_correct_source_scope_for_arg(
 973         &mut self,
 974         arg_hir_id: hir::HirId,
 975         original_source_scope: SourceScope,
 976         pattern_span: Span,
 977     ) {
 978         let tcx = self.hir.tcx();
 979         let current_root = tcx.maybe_lint_level_root_bounded(arg_hir_id, self.hir.root_lint_level);
 980         let parent_root = tcx.maybe_lint_level_root_bounded(
 981             self.source_scopes[original_source_scope]
 982                 .local_data
 983                 .as_ref()
 984                 .assert_crate_local()
 985                 .lint_root,
 986             self.hir.root_lint_level,
 987         );
 988         if current_root != parent_root {
 989             self.source_scope =
 990                 self.new_source_scope(pattern_span, LintLevel::Explicit(current_root), None);
 991         }
 992     }
 993
 994     fn get_unit_temp(&mut self) -> Place<'tcx> {
 995         match self.unit_temp {
 996             Some(tmp) => tmp,
 997             None => {
 998                 let ty = self.hir.unit_ty();
 999                 let fn_span = self.fn_span;
1000                 let tmp = self.temp(ty, fn_span);
1001                 self.unit_temp = Some(tmp);
1002                 tmp
1003             }
1004         }
1005     }
1006
1007     fn return_block(&mut self) -> BasicBlock {
1008         match self.cached_return_block {
1009             Some(rb) => rb,
1010             None => {
1011                 let rb = self.cfg.start_new_block();
1012                 self.cached_return_block = Some(rb);
1013                 rb
1014             }
1015         }
1016     }
1017 }
1018
1019 ///////////////////////////////////////////////////////////////////////////
1020 // Builder methods are broken up into modules, depending on what kind
1021 // of thing is being lowered. Note that they use the `unpack` macro
1022 // above extensively.
1023
1024 mod block;
1025 mod cfg;
1026 mod expr;
1027 mod into;
1028 mod matches;
1029 mod misc;
1030 mod scope;