compiler/rustc_mir_build/src/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::hir::place::PlaceBase as HirPlaceBase;
  14 use rustc_middle::middle::region;
  15 use rustc_middle::mir::*;
  16 use rustc_middle::ty::subst::Subst;
  17 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
  18 use rustc_span::symbol::kw;
  19 use rustc_span::Span;
  20 use rustc_target::spec::abi::Abi;
  21 use rustc_target::spec::PanicStrategy;
  22
  23 use super::lints;
  24
  25 crate fn mir_built<'tcx>(
  26     tcx: TyCtxt<'tcx>,
  27     def: ty::WithOptConstParam<LocalDefId>,
  28 ) -> &'tcx rustc_data_structures::steal::Steal<Body<'tcx>> {
  29     if let Some(def) = def.try_upgrade(tcx) {
  30         return tcx.mir_built(def);
  31     }
  32
  33     let mut body = mir_build(tcx, def);
  34     if def.const_param_did.is_some() {
  35         assert!(matches!(body.source.instance, ty::InstanceDef::Item(_)));
  36         body.source = MirSource::from_instance(ty::InstanceDef::Item(def.to_global()));
  37     }
  38
  39     tcx.alloc_steal_mir(body)
  40 }
  41
  42 /// Construct the MIR for a given `DefId`.
  43 fn mir_build(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_> {
  44     let id = tcx.hir().local_def_id_to_hir_id(def.did);
  45
  46     // Figure out what primary body this item has.
  47     let (body_id, return_ty_span, span_with_body) = match tcx.hir().get(id) {
  48         Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(_, decl, body_id, _, _), .. }) => {
  49             (*body_id, decl.output.span(), None)
  50         }
  51         Node::Item(hir::Item {
  52             kind: hir::ItemKind::Fn(hir::FnSig { decl, .. }, _, body_id),
  53             span,
  54             ..
  55         })
  56         | Node::ImplItem(hir::ImplItem {
  57             kind: hir::ImplItemKind::Fn(hir::FnSig { decl, .. }, body_id),
  58             span,
  59             ..
  60         })
  61         | Node::TraitItem(hir::TraitItem {
  62             kind: hir::TraitItemKind::Fn(hir::FnSig { decl, .. }, hir::TraitFn::Provided(body_id)),
  63             span,
  64             ..
  65         }) => {
  66             // Use the `Span` of the `Item/ImplItem/TraitItem` as the body span,
  67             // since the def span of a function does not include the body
  68             (*body_id, decl.output.span(), Some(*span))
  69         }
  70         Node::Item(hir::Item {
  71             kind: hir::ItemKind::Static(ty, _, body_id) | hir::ItemKind::Const(ty, body_id),
  72             ..
  73         })
  74         | Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(ty, body_id), .. })
  75         | Node::TraitItem(hir::TraitItem {
  76             kind: hir::TraitItemKind::Const(ty, Some(body_id)),
  77             ..
  78         }) => (*body_id, ty.span, None),
  79         Node::AnonConst(hir::AnonConst { body, hir_id, .. }) => {
  80             (*body, tcx.hir().span(*hir_id), None)
  81         }
  82
  83         _ => span_bug!(tcx.hir().span(id), "can't build MIR for {:?}", def.did),
  84     };
  85
  86     // If we don't have a specialized span for the body, just use the
  87     // normal def span.
  88     let span_with_body = span_with_body.unwrap_or_else(|| tcx.hir().span(id));
  89
  90     tcx.infer_ctxt().enter(|infcx| {
  91         let cx = Cx::new(&infcx, def, id);
  92         let body = if let Some(ErrorReported) = cx.typeck_results().tainted_by_errors {
  93             build::construct_error(cx, body_id)
  94         } else if cx.body_owner_kind.is_fn_or_closure() {
  95             // fetch the fully liberated fn signature (that is, all bound
  96             // types/lifetimes replaced)
  97             let fn_sig = cx.typeck_results().liberated_fn_sigs()[id];
  98             let fn_def_id = tcx.hir().local_def_id(id);
  99
 100             let safety = match fn_sig.unsafety {
 101                 hir::Unsafety::Normal => Safety::Safe,
 102                 hir::Unsafety::Unsafe => Safety::FnUnsafe,
 103             };
 104
 105             let body = tcx.hir().body(body_id);
 106             let ty = tcx.type_of(fn_def_id);
 107             let mut abi = fn_sig.abi;
 108             let implicit_argument = match ty.kind() {
 109                 ty::Closure(..) => {
 110                     // HACK(eddyb) Avoid having RustCall on closures,
 111                     // as it adds unnecessary (and wrong) auto-tupling.
 112                     abi = Abi::Rust;
 113                     vec![ArgInfo(liberated_closure_env_ty(tcx, id, body_id), None, None, None)]
 114                 }
 115                 ty::Generator(..) => {
 116                     let gen_ty = tcx.typeck_body(body_id).node_type(id);
 117
 118                     // The resume argument may be missing, in that case we need to provide it here.
 119                     // It will always be `()` in this case.
 120                     if body.params.is_empty() {
 121                         vec![
 122                             ArgInfo(gen_ty, None, None, None),
 123                             ArgInfo(tcx.mk_unit(), None, None, None),
 124                         ]
 125                     } else {
 126                         vec![ArgInfo(gen_ty, None, None, None)]
 127                     }
 128                 }
 129                 _ => vec![],
 130             };
 131
 132             let explicit_arguments = body.params.iter().enumerate().map(|(index, arg)| {
 133                 let owner_id = tcx.hir().body_owner(body_id);
 134                 let opt_ty_info;
 135                 let self_arg;
 136                 if let Some(ref fn_decl) = tcx.hir().fn_decl_by_hir_id(owner_id) {
 137                     opt_ty_info = fn_decl.inputs.get(index).map(|ty| ty.span);
 138                     self_arg = if index == 0 && fn_decl.implicit_self.has_implicit_self() {
 139                         match fn_decl.implicit_self {
 140                             hir::ImplicitSelfKind::Imm => Some(ImplicitSelfKind::Imm),
 141                             hir::ImplicitSelfKind::Mut => Some(ImplicitSelfKind::Mut),
 142                             hir::ImplicitSelfKind::ImmRef => Some(ImplicitSelfKind::ImmRef),
 143                             hir::ImplicitSelfKind::MutRef => Some(ImplicitSelfKind::MutRef),
 144                             _ => None,
 145                         }
 146                     } else {
 147                         None
 148                     };
 149                 } else {
 150                     opt_ty_info = None;
 151                     self_arg = None;
 152                 }
 153
 154                 // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
 155                 // (as it's created inside the body itself, not passed in from outside).
 156                 let ty = if fn_sig.c_variadic && index == fn_sig.inputs().len() {
 157                     let va_list_did = tcx.require_lang_item(LangItem::VaList, Some(arg.span));
 158
 159                     tcx.type_of(va_list_did).subst(tcx, &[tcx.lifetimes.re_erased.into()])
 160                 } else {
 161                     fn_sig.inputs()[index]
 162                 };
 163
 164                 ArgInfo(ty, opt_ty_info, Some(&arg), self_arg)
 165             });
 166
 167             let arguments = implicit_argument.into_iter().chain(explicit_arguments);
 168
 169             let (yield_ty, return_ty) = if body.generator_kind.is_some() {
 170                 let gen_ty = tcx.typeck_body(body_id).node_type(id);
 171                 let gen_sig = match gen_ty.kind() {
 172                     ty::Generator(_, gen_substs, ..) => gen_substs.as_generator().sig(),
 173                     _ => span_bug!(tcx.hir().span(id), "generator w/o generator type: {:?}", ty),
 174                 };
 175                 (Some(gen_sig.yield_ty), gen_sig.return_ty)
 176             } else {
 177                 (None, fn_sig.output())
 178             };
 179
 180             let mut mir = build::construct_fn(
 181                 cx,
 182                 id,
 183                 arguments,
 184                 safety,
 185                 abi,
 186                 return_ty,
 187                 return_ty_span,
 188                 body,
 189                 span_with_body,
 190             );
 191             mir.yield_ty = yield_ty;
 192             mir
 193         } else {
 194             // Get the revealed type of this const. This is *not* the adjusted
 195             // type of its body, which may be a subtype of this type. For
 196             // example:
 197             //
 198             // fn foo(_: &()) {}
 199             // static X: fn(&'static ()) = foo;
 200             //
 201             // The adjusted type of the body of X is `for<'a> fn(&'a ())` which
 202             // is not the same as the type of X. We need the type of the return
 203             // place to be the type of the constant because NLL typeck will
 204             // equate them.
 205
 206             let return_ty = cx.typeck_results().node_type(id);
 207
 208             build::construct_const(cx, body_id, return_ty, return_ty_span)
 209         };
 210
 211         lints::check(tcx, &body);
 212
 213         // The borrow checker will replace all the regions here with its own
 214         // inference variables. There's no point having non-erased regions here.
 215         // The exception is `body.user_type_annotations`, which is used unmodified
 216         // by borrow checking.
 217         debug_assert!(
 218             !(body.local_decls.has_free_regions()
 219                 || body.basic_blocks().has_free_regions()
 220                 || body.var_debug_info.has_free_regions()
 221                 || body.yield_ty.has_free_regions()),
 222             "Unexpected free regions in MIR: {:?}",
 223             body,
 224         );
 225
 226         body
 227     })
 228 }
 229
 230 ///////////////////////////////////////////////////////////////////////////
 231 // BuildMir -- walks a crate, looking for fn items and methods to build MIR from
 232
 233 fn liberated_closure_env_ty(
 234     tcx: TyCtxt<'_>,
 235     closure_expr_id: hir::HirId,
 236     body_id: hir::BodyId,
 237 ) -> Ty<'_> {
 238     let closure_ty = tcx.typeck_body(body_id).node_type(closure_expr_id);
 239
 240     let (closure_def_id, closure_substs) = match *closure_ty.kind() {
 241         ty::Closure(closure_def_id, closure_substs) => (closure_def_id, closure_substs),
 242         _ => bug!("closure expr does not have closure type: {:?}", closure_ty),
 243     };
 244
 245     let closure_env_ty = tcx.closure_env_ty(closure_def_id, closure_substs).unwrap();
 246     tcx.erase_late_bound_regions(closure_env_ty)
 247 }
 248
 249 #[derive(Debug, PartialEq, Eq)]
 250 enum BlockFrame {
 251     /// Evaluation is currently within a statement.
 252     ///
 253     /// Examples include:
 254     /// 1. `EXPR;`
 255     /// 2. `let _ = EXPR;`
 256     /// 3. `let x = EXPR;`
 257     Statement {
 258         /// If true, then statement discards result from evaluating
 259         /// the expression (such as examples 1 and 2 above).
 260         ignores_expr_result: bool,
 261     },
 262
 263     /// Evaluation is currently within the tail expression of a block.
 264     ///
 265     /// Example: `{ STMT_1; STMT_2; EXPR }`
 266     TailExpr {
 267         /// If true, then the surrounding context of the block ignores
 268         /// the result of evaluating the block's tail expression.
 269         ///
 270         /// Example: `let _ = { STMT_1; EXPR };`
 271         tail_result_is_ignored: bool,
 272
 273         /// `Span` of the tail expression.
 274         span: Span,
 275     },
 276
 277     /// Generic mark meaning that the block occurred as a subexpression
 278     /// where the result might be used.
 279     ///
 280     /// Examples: `foo(EXPR)`, `match EXPR { ... }`
 281     SubExpr,
 282 }
 283
 284 impl BlockFrame {
 285     fn is_tail_expr(&self) -> bool {
 286         match *self {
 287             BlockFrame::TailExpr { .. } => true,
 288
 289             BlockFrame::Statement { .. } | BlockFrame::SubExpr => false,
 290         }
 291     }
 292     fn is_statement(&self) -> bool {
 293         match *self {
 294             BlockFrame::Statement { .. } => true,
 295
 296             BlockFrame::TailExpr { .. } | BlockFrame::SubExpr => false,
 297         }
 298     }
 299 }
 300
 301 #[derive(Debug)]
 302 struct BlockContext(Vec<BlockFrame>);
 303
 304 struct Builder<'a, 'tcx> {
 305     hir: Cx<'a, 'tcx>,
 306     cfg: CFG<'tcx>,
 307
 308     def_id: DefId,
 309     fn_span: Span,
 310     arg_count: usize,
 311     generator_kind: Option<GeneratorKind>,
 312
 313     /// The current set of scopes, updated as we traverse;
 314     /// see the `scope` module for more details.
 315     scopes: scope::Scopes<'tcx>,
 316
 317     /// The block-context: each time we build the code within an thir::Block,
 318     /// we push a frame here tracking whether we are building a statement or
 319     /// if we are pushing the tail expression of the block. This is used to
 320     /// embed information in generated temps about whether they were created
 321     /// for a block tail expression or not.
 322     ///
 323     /// It would be great if we could fold this into `self.scopes`
 324     /// somehow, but right now I think that is very tightly tied to
 325     /// the code generation in ways that we cannot (or should not)
 326     /// start just throwing new entries onto that vector in order to
 327     /// distinguish the context of EXPR1 from the context of EXPR2 in
 328     /// `{ STMTS; EXPR1 } + EXPR2`.
 329     block_context: BlockContext,
 330
 331     /// The current unsafe block in scope, even if it is hidden by
 332     /// a `PushUnsafeBlock`.
 333     unpushed_unsafe: Safety,
 334
 335     /// The number of `push_unsafe_block` levels in scope.
 336     push_unsafe_count: usize,
 337
 338     /// The vector of all scopes that we have created thus far;
 339     /// we track this for debuginfo later.
 340     source_scopes: IndexVec<SourceScope, SourceScopeData<'tcx>>,
 341     source_scope: SourceScope,
 342
 343     /// The guard-context: each time we build the guard expression for
 344     /// a match arm, we push onto this stack, and then pop when we
 345     /// finish building it.
 346     guard_context: Vec<GuardFrame>,
 347
 348     /// Maps `HirId`s of variable bindings to the `Local`s created for them.
 349     /// (A match binding can have two locals; the 2nd is for the arm's guard.)
 350     var_indices: HirIdMap<LocalsForNode>,
 351     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 352     canonical_user_type_annotations: ty::CanonicalUserTypeAnnotations<'tcx>,
 353     upvar_mutbls: Vec<Mutability>,
 354     unit_temp: Option<Place<'tcx>>,
 355
 356     var_debug_info: Vec<VarDebugInfo<'tcx>>,
 357 }
 358
 359 impl<'a, 'tcx> Builder<'a, 'tcx> {
 360     fn is_bound_var_in_guard(&self, id: hir::HirId) -> bool {
 361         self.guard_context.iter().any(|frame| frame.locals.iter().any(|local| local.id == id))
 362     }
 363
 364     fn var_local_id(&self, id: hir::HirId, for_guard: ForGuard) -> Local {
 365         self.var_indices[&id].local_id(for_guard)
 366     }
 367 }
 368
 369 impl BlockContext {
 370     fn new() -> Self {
 371         BlockContext(vec![])
 372     }
 373     fn push(&mut self, bf: BlockFrame) {
 374         self.0.push(bf);
 375     }
 376     fn pop(&mut self) -> Option<BlockFrame> {
 377         self.0.pop()
 378     }
 379
 380     /// Traverses the frames on the `BlockContext`, searching for either
 381     /// the first block-tail expression frame with no intervening
 382     /// statement frame.
 383     ///
 384     /// Notably, this skips over `SubExpr` frames; this method is
 385     /// meant to be used in the context of understanding the
 386     /// relationship of a temp (created within some complicated
 387     /// expression) with its containing expression, and whether the
 388     /// value of that *containing expression* (not the temp!) is
 389     /// ignored.
 390     fn currently_in_block_tail(&self) -> Option<BlockTailInfo> {
 391         for bf in self.0.iter().rev() {
 392             match bf {
 393                 BlockFrame::SubExpr => continue,
 394                 BlockFrame::Statement { .. } => break,
 395                 &BlockFrame::TailExpr { tail_result_is_ignored, span } => {
 396                     return Some(BlockTailInfo { tail_result_is_ignored, span });
 397                 }
 398             }
 399         }
 400
 401         None
 402     }
 403
 404     /// Looks at the topmost frame on the BlockContext and reports
 405     /// whether its one that would discard a block tail result.
 406     ///
 407     /// Unlike `currently_within_ignored_tail_expression`, this does
 408     /// *not* skip over `SubExpr` frames: here, we want to know
 409     /// whether the block result itself is discarded.
 410     fn currently_ignores_tail_results(&self) -> bool {
 411         match self.0.last() {
 412             // no context: conservatively assume result is read
 413             None => false,
 414
 415             // sub-expression: block result feeds into some computation
 416             Some(BlockFrame::SubExpr) => false,
 417
 418             // otherwise: use accumulated is_ignored state.
 419             Some(
 420                 BlockFrame::TailExpr { tail_result_is_ignored: ignored, .. }
 421                 | BlockFrame::Statement { ignores_expr_result: ignored },
 422             ) => *ignored,
 423         }
 424     }
 425 }
 426
 427 #[derive(Debug)]
 428 enum LocalsForNode {
 429     /// In the usual case, a `HirId` for an identifier maps to at most
 430     /// one `Local` declaration.
 431     One(Local),
 432
 433     /// The exceptional case is identifiers in a match arm's pattern
 434     /// that are referenced in a guard of that match arm. For these,
 435     /// we have `2` Locals.
 436     ///
 437     /// * `for_arm_body` is the Local used in the arm body (which is
 438     ///   just like the `One` case above),
 439     ///
 440     /// * `ref_for_guard` is the Local used in the arm's guard (which
 441     ///   is a reference to a temp that is an alias of
 442     ///   `for_arm_body`).
 443     ForGuard { ref_for_guard: Local, for_arm_body: Local },
 444 }
 445
 446 #[derive(Debug)]
 447 struct GuardFrameLocal {
 448     id: hir::HirId,
 449 }
 450
 451 impl GuardFrameLocal {
 452     fn new(id: hir::HirId, _binding_mode: BindingMode) -> Self {
 453         GuardFrameLocal { id }
 454     }
 455 }
 456
 457 #[derive(Debug)]
 458 struct GuardFrame {
 459     /// These are the id's of names that are bound by patterns of the
 460     /// arm of *this* guard.
 461     ///
 462     /// (Frames higher up the stack will have the id's bound in arms
 463     /// further out, such as in a case like:
 464     ///
 465     /// match E1 {
 466     ///      P1(id1) if (... (match E2 { P2(id2) if ... => B2 })) => B1,
 467     /// }
 468     ///
 469     /// here, when building for FIXME.
 470     locals: Vec<GuardFrameLocal>,
 471 }
 472
 473 /// `ForGuard` indicates whether we are talking about:
 474 ///   1. The variable for use outside of guard expressions, or
 475 ///   2. The temp that holds reference to (1.), which is actually what the
 476 ///      guard expressions see.
 477 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 478 enum ForGuard {
 479     RefWithinGuard,
 480     OutsideGuard,
 481 }
 482
 483 impl LocalsForNode {
 484     fn local_id(&self, for_guard: ForGuard) -> Local {
 485         match (self, for_guard) {
 486             (&LocalsForNode::One(local_id), ForGuard::OutsideGuard)
 487             | (
 488                 &LocalsForNode::ForGuard { ref_for_guard: local_id, .. },
 489                 ForGuard::RefWithinGuard,
 490             )
 491             | (&LocalsForNode::ForGuard { for_arm_body: local_id, .. }, ForGuard::OutsideGuard) => {
 492                 local_id
 493             }
 494
 495             (&LocalsForNode::One(_), ForGuard::RefWithinGuard) => {
 496                 bug!("anything with one local should never be within a guard.")
 497             }
 498         }
 499     }
 500 }
 501
 502 struct CFG<'tcx> {
 503     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 504 }
 505
 506 rustc_index::newtype_index! {
 507     struct ScopeId { .. }
 508 }
 509
 510 ///////////////////////////////////////////////////////////////////////////
 511 /// The `BlockAnd` "monad" packages up the new basic block along with a
 512 /// produced value (sometimes just unit, of course). The `unpack!`
 513 /// macro (and methods below) makes working with `BlockAnd` much more
 514 /// convenient.
 515
 516 #[must_use = "if you don't use one of these results, you're leaving a dangling edge"]
 517 struct BlockAnd<T>(BasicBlock, T);
 518
 519 trait BlockAndExtension {
 520     fn and<T>(self, v: T) -> BlockAnd<T>;
 521     fn unit(self) -> BlockAnd<()>;
 522 }
 523
 524 impl BlockAndExtension for BasicBlock {
 525     fn and<T>(self, v: T) -> BlockAnd<T> {
 526         BlockAnd(self, v)
 527     }
 528
 529     fn unit(self) -> BlockAnd<()> {
 530         BlockAnd(self, ())
 531     }
 532 }
 533
 534 /// Update a block pointer and return the value.
 535 /// Use it like `let x = unpack!(block = self.foo(block, foo))`.
 536 macro_rules! unpack {
 537     ($x:ident = $c:expr) => {{
 538         let BlockAnd(b, v) = $c;
 539         $x = b;
 540         v
 541     }};
 542
 543     ($c:expr) => {{
 544         let BlockAnd(b, ()) = $c;
 545         b
 546     }};
 547 }
 548
 549 fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> bool {
 550     // Validate `#[unwind]` syntax regardless of platform-specific panic strategy.
 551     let attrs = &tcx.get_attrs(fn_def_id.to_def_id());
 552     let unwind_attr = attr::find_unwind_attr(&tcx.sess, attrs);
 553
 554     // We never unwind, so it's not relevant to stop an unwind.
 555     if tcx.sess.panic_strategy() != PanicStrategy::Unwind {
 556         return false;
 557     }
 558
 559     // This is a special case: some functions have a C abi but are meant to
 560     // unwind anyway. Don't stop them.
 561     match unwind_attr {
 562         None => false, // FIXME(#58794); should be `!(abi == Abi::Rust || abi == Abi::RustCall)`
 563         Some(UnwindAttr::Allowed) => false,
 564         Some(UnwindAttr::Aborts) => true,
 565     }
 566 }
 567
 568 ///////////////////////////////////////////////////////////////////////////
 569 /// the main entry point for building MIR for a function
 570
 571 struct ArgInfo<'tcx>(
 572     Ty<'tcx>,
 573     Option<Span>,
 574     Option<&'tcx hir::Param<'tcx>>,
 575     Option<ImplicitSelfKind>,
 576 );
 577
 578 fn construct_fn<'a, 'tcx, A>(
 579     hir: Cx<'a, 'tcx>,
 580     fn_id: hir::HirId,
 581     arguments: A,
 582     safety: Safety,
 583     abi: Abi,
 584     return_ty: Ty<'tcx>,
 585     return_ty_span: Span,
 586     body: &'tcx hir::Body<'tcx>,
 587     span_with_body: Span,
 588 ) -> Body<'tcx>
 589 where
 590     A: Iterator<Item = ArgInfo<'tcx>>,
 591 {
 592     let arguments: Vec<_> = arguments.collect();
 593
 594     let tcx = hir.tcx();
 595     let tcx_hir = tcx.hir();
 596     let span = tcx_hir.span(fn_id);
 597
 598     let fn_def_id = tcx_hir.local_def_id(fn_id);
 599
 600     let mut builder = Builder::new(
 601         hir,
 602         fn_def_id.to_def_id(),
 603         span_with_body,
 604         arguments.len(),
 605         safety,
 606         return_ty,
 607         return_ty_span,
 608         body.generator_kind,
 609     );
 610
 611     let call_site_scope =
 612         region::Scope { id: body.value.hir_id.local_id, data: region::ScopeData::CallSite };
 613     let arg_scope =
 614         region::Scope { id: body.value.hir_id.local_id, data: region::ScopeData::Arguments };
 615     let source_info = builder.source_info(span);
 616     let call_site_s = (call_site_scope, source_info);
 617     unpack!(builder.in_scope(call_site_s, LintLevel::Inherited, |builder| {
 618         let arg_scope_s = (arg_scope, source_info);
 619         // Attribute epilogue to function's closing brace
 620         let fn_end = span_with_body.shrink_to_hi();
 621         let return_block =
 622             unpack!(builder.in_breakable_scope(None, Place::return_place(), fn_end, |builder| {
 623                 Some(builder.in_scope(arg_scope_s, LintLevel::Inherited, |builder| {
 624                     builder.args_and_body(
 625                         START_BLOCK,
 626                         fn_def_id.to_def_id(),
 627                         &arguments,
 628                         arg_scope,
 629                         &body.value,
 630                     )
 631                 }))
 632             }));
 633         let source_info = builder.source_info(fn_end);
 634         builder.cfg.terminate(return_block, source_info, TerminatorKind::Return);
 635         let should_abort = should_abort_on_panic(tcx, fn_def_id, abi);
 636         builder.build_drop_trees(should_abort);
 637         return_block.unit()
 638     }));
 639
 640     let spread_arg = if abi == Abi::RustCall {
 641         // RustCall pseudo-ABI untuples the last argument.
 642         Some(Local::new(arguments.len()))
 643     } else {
 644         None
 645     };
 646     debug!("fn_id {:?} has attrs {:?}", fn_def_id, tcx.get_attrs(fn_def_id.to_def_id()));
 647
 648     let mut body = builder.finish();
 649     body.spread_arg = spread_arg;
 650     body
 651 }
 652
 653 fn construct_const<'a, 'tcx>(
 654     hir: Cx<'a, 'tcx>,
 655     body_id: hir::BodyId,
 656     const_ty: Ty<'tcx>,
 657     const_ty_span: Span,
 658 ) -> Body<'tcx> {
 659     let tcx = hir.tcx();
 660     let owner_id = tcx.hir().body_owner(body_id);
 661     let def_id = tcx.hir().local_def_id(owner_id);
 662     let span = tcx.hir().span(owner_id);
 663     let mut builder =
 664         Builder::new(hir, def_id.to_def_id(), span, 0, Safety::Safe, const_ty, const_ty_span, None);
 665
 666     let mut block = START_BLOCK;
 667     let ast_expr = &tcx.hir().body(body_id).value;
 668     let expr = builder.hir.mirror(ast_expr);
 669     unpack!(block = builder.into_expr(Place::return_place(), block, expr));
 670
 671     let source_info = builder.source_info(span);
 672     builder.cfg.terminate(block, source_info, TerminatorKind::Return);
 673
 674     builder.build_drop_trees(false);
 675
 676     builder.finish()
 677 }
 678
 679 /// Construct MIR for a item that has had errors in type checking.
 680 ///
 681 /// This is required because we may still want to run MIR passes on an item
 682 /// with type errors, but normal MIR construction can't handle that in general.
 683 fn construct_error<'a, 'tcx>(hir: Cx<'a, 'tcx>, body_id: hir::BodyId) -> Body<'tcx> {
 684     let tcx = hir.tcx();
 685     let owner_id = tcx.hir().body_owner(body_id);
 686     let def_id = tcx.hir().local_def_id(owner_id);
 687     let span = tcx.hir().span(owner_id);
 688     let ty = tcx.ty_error();
 689     let num_params = match hir.body_owner_kind {
 690         hir::BodyOwnerKind::Fn => tcx.hir().fn_decl_by_hir_id(owner_id).unwrap().inputs.len(),
 691         hir::BodyOwnerKind::Closure => {
 692             if tcx.hir().body(body_id).generator_kind().is_some() {
 693                 // Generators have an implicit `self` parameter *and* a possibly
 694                 // implicit resume parameter.
 695                 2
 696             } else {
 697                 // The implicit self parameter adds another local in MIR.
 698                 1 + tcx.hir().fn_decl_by_hir_id(owner_id).unwrap().inputs.len()
 699             }
 700         }
 701         hir::BodyOwnerKind::Const => 0,
 702         hir::BodyOwnerKind::Static(_) => 0,
 703     };
 704     let mut builder =
 705         Builder::new(hir, def_id.to_def_id(), span, num_params, Safety::Safe, ty, span, None);
 706     let source_info = builder.source_info(span);
 707     // Some MIR passes will expect the number of parameters to match the
 708     // function declaration.
 709     for _ in 0..num_params {
 710         builder.local_decls.push(LocalDecl::with_source_info(ty, source_info));
 711     }
 712     builder.cfg.terminate(START_BLOCK, source_info, TerminatorKind::Unreachable);
 713     let mut body = builder.finish();
 714     if tcx.hir().body(body_id).generator_kind.is_some() {
 715         body.yield_ty = Some(ty);
 716     }
 717     body
 718 }
 719
 720 impl<'a, 'tcx> Builder<'a, 'tcx> {
 721     fn new(
 722         hir: Cx<'a, 'tcx>,
 723         def_id: DefId,
 724         span: Span,
 725         arg_count: usize,
 726         safety: Safety,
 727         return_ty: Ty<'tcx>,
 728         return_span: Span,
 729         generator_kind: Option<GeneratorKind>,
 730     ) -> Builder<'a, 'tcx> {
 731         let lint_level = LintLevel::Explicit(hir.root_lint_level);
 732         let mut builder = Builder {
 733             hir,
 734             def_id,
 735             cfg: CFG { basic_blocks: IndexVec::new() },
 736             fn_span: span,
 737             arg_count,
 738             generator_kind,
 739             scopes: scope::Scopes::new(),
 740             block_context: BlockContext::new(),
 741             source_scopes: IndexVec::new(),
 742             source_scope: OUTERMOST_SOURCE_SCOPE,
 743             guard_context: vec![],
 744             push_unsafe_count: 0,
 745             unpushed_unsafe: safety,
 746             local_decls: IndexVec::from_elem_n(LocalDecl::new(return_ty, return_span), 1),
 747             canonical_user_type_annotations: IndexVec::new(),
 748             upvar_mutbls: vec![],
 749             var_indices: Default::default(),
 750             unit_temp: None,
 751             var_debug_info: vec![],
 752         };
 753
 754         assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
 755         assert_eq!(
 756             builder.new_source_scope(span, lint_level, Some(safety)),
 757             OUTERMOST_SOURCE_SCOPE
 758         );
 759         builder.source_scopes[OUTERMOST_SOURCE_SCOPE].parent_scope = None;
 760
 761         builder
 762     }
 763
 764     fn finish(self) -> Body<'tcx> {
 765         for (index, block) in self.cfg.basic_blocks.iter().enumerate() {
 766             if block.terminator.is_none() {
 767                 span_bug!(self.fn_span, "no terminator on block {:?}", index);
 768             }
 769         }
 770
 771         Body::new(
 772             MirSource::item(self.def_id),
 773             self.cfg.basic_blocks,
 774             self.source_scopes,
 775             self.local_decls,
 776             self.canonical_user_type_annotations,
 777             self.arg_count,
 778             self.var_debug_info,
 779             self.fn_span,
 780             self.generator_kind,
 781         )
 782     }
 783
 784     fn args_and_body(
 785         &mut self,
 786         mut block: BasicBlock,
 787         fn_def_id: DefId,
 788         arguments: &[ArgInfo<'tcx>],
 789         argument_scope: region::Scope,
 790         ast_body: &'tcx hir::Expr<'tcx>,
 791     ) -> BlockAnd<()> {
 792         // Allocate locals for the function arguments
 793         for &ArgInfo(ty, _, arg_opt, _) in arguments.iter() {
 794             let source_info =
 795                 SourceInfo::outermost(arg_opt.map_or(self.fn_span, |arg| arg.pat.span));
 796             let arg_local = self.local_decls.push(LocalDecl::with_source_info(ty, source_info));
 797
 798             // If this is a simple binding pattern, give debuginfo a nice name.
 799             if let Some(arg) = arg_opt {
 800                 if let Some(ident) = arg.pat.simple_ident() {
 801                     self.var_debug_info.push(VarDebugInfo {
 802                         name: ident.name,
 803                         source_info,
 804                         value: VarDebugInfoContents::Place(arg_local.into()),
 805                     });
 806                 }
 807             }
 808         }
 809
 810         let tcx = self.hir.tcx();
 811         let tcx_hir = tcx.hir();
 812         let hir_typeck_results = self.hir.typeck_results();
 813
 814         // In analyze_closure() in upvar.rs we gathered a list of upvars used by a
 815         // indexed closure and we stored in a map called closure_captures in TypeckResults
 816         // with the closure's DefId. Here, we run through that vec of UpvarIds for
 817         // the given closure and use the necessary information to create upvar
 818         // debuginfo and to fill `self.upvar_mutbls`.
 819         if hir_typeck_results.closure_min_captures.get(&fn_def_id).is_some() {
 820             let closure_env_arg = Local::new(1);
 821             let mut closure_env_projs = vec![];
 822             let mut closure_ty = self.local_decls[closure_env_arg].ty;
 823             if let ty::Ref(_, ty, _) = closure_ty.kind() {
 824                 closure_env_projs.push(ProjectionElem::Deref);
 825                 closure_ty = ty;
 826             }
 827             let upvar_substs = match closure_ty.kind() {
 828                 ty::Closure(_, substs) => ty::UpvarSubsts::Closure(substs),
 829                 ty::Generator(_, substs, _) => ty::UpvarSubsts::Generator(substs),
 830                 _ => span_bug!(self.fn_span, "upvars with non-closure env ty {:?}", closure_ty),
 831             };
 832             let capture_tys = upvar_substs.upvar_tys();
 833             let captures_with_tys =
 834                 hir_typeck_results.closure_min_captures_flattened(fn_def_id).zip(capture_tys);
 835
 836             self.upvar_mutbls = captures_with_tys
 837                 .enumerate()
 838                 .map(|(i, (captured_place, ty))| {
 839                     let capture = captured_place.info.capture_kind;
 840                     let var_id = match captured_place.place.base {
 841                         HirPlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
 842                         _ => bug!("Expected an upvar"),
 843                     };
 844
 845                     let mutability = captured_place.mutability;
 846
 847                     // FIXME(project-rfc-2229#8): Store more precise information
 848                     let mut name = kw::Empty;
 849                     if let Some(Node::Binding(pat)) = tcx_hir.find(var_id) {
 850                         if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
 851                             name = ident.name;
 852                         }
 853                     }
 854
 855                     let mut projs = closure_env_projs.clone();
 856                     projs.push(ProjectionElem::Field(Field::new(i), ty));
 857                     match capture {
 858                         ty::UpvarCapture::ByValue(_) => {}
 859                         ty::UpvarCapture::ByRef(..) => {
 860                             projs.push(ProjectionElem::Deref);
 861                         }
 862                     };
 863
 864                     self.var_debug_info.push(VarDebugInfo {
 865                         name,
 866                         source_info: SourceInfo::outermost(tcx_hir.span(var_id)),
 867                         value: VarDebugInfoContents::Place(Place {
 868                             local: closure_env_arg,
 869                             projection: tcx.intern_place_elems(&projs),
 870                         }),
 871                     });
 872
 873                     mutability
 874                 })
 875                 .collect();
 876         }
 877
 878         let mut scope = None;
 879         // Bind the argument patterns
 880         for (index, arg_info) in arguments.iter().enumerate() {
 881             // Function arguments always get the first Local indices after the return place
 882             let local = Local::new(index + 1);
 883             let place = Place::from(local);
 884             let &ArgInfo(_, opt_ty_info, arg_opt, ref self_binding) = arg_info;
 885
 886             // Make sure we drop (parts of) the argument even when not matched on.
 887             self.schedule_drop(
 888                 arg_opt.as_ref().map_or(ast_body.span, |arg| arg.pat.span),
 889                 argument_scope,
 890                 local,
 891                 DropKind::Value,
 892             );
 893
 894             if let Some(arg) = arg_opt {
 895                 let pattern = self.hir.pattern_from_hir(&arg.pat);
 896                 let original_source_scope = self.source_scope;
 897                 let span = pattern.span;
 898                 self.set_correct_source_scope_for_arg(arg.hir_id, original_source_scope, span);
 899                 match *pattern.kind {
 900                     // Don't introduce extra copies for simple bindings
 901                     PatKind::Binding {
 902                         mutability,
 903                         var,
 904                         mode: BindingMode::ByValue,
 905                         subpattern: None,
 906                         ..
 907                     } => {
 908                         self.local_decls[local].mutability = mutability;
 909                         self.local_decls[local].source_info.scope = self.source_scope;
 910                         self.local_decls[local].local_info = if let Some(kind) = self_binding {
 911                             Some(box LocalInfo::User(ClearCrossCrate::Set(
 912                                 BindingForm::ImplicitSelf(*kind),
 913                             )))
 914                         } else {
 915                             let binding_mode = ty::BindingMode::BindByValue(mutability);
 916                             Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
 917                                 VarBindingForm {
 918                                     binding_mode,
 919                                     opt_ty_info,
 920                                     opt_match_place: Some((Some(place), span)),
 921                                     pat_span: span,
 922                                 },
 923                             ))))
 924                         };
 925                         self.var_indices.insert(var, LocalsForNode::One(local));
 926                     }
 927                     _ => {
 928                         scope = self.declare_bindings(
 929                             scope,
 930                             ast_body.span,
 931                             &pattern,
 932                             matches::ArmHasGuard(false),
 933                             Some((Some(&place), span)),
 934                         );
 935                         unpack!(block = self.place_into_pattern(block, pattern, place, false));
 936                     }
 937                 }
 938                 self.source_scope = original_source_scope;
 939             }
 940         }
 941
 942         // Enter the argument pattern bindings source scope, if it exists.
 943         if let Some(source_scope) = scope {
 944             self.source_scope = source_scope;
 945         }
 946
 947         let body = self.hir.mirror(ast_body);
 948         self.into(Place::return_place(), block, body)
 949     }
 950
 951     fn set_correct_source_scope_for_arg(
 952         &mut self,
 953         arg_hir_id: hir::HirId,
 954         original_source_scope: SourceScope,
 955         pattern_span: Span,
 956     ) {
 957         let tcx = self.hir.tcx();
 958         let current_root = tcx.maybe_lint_level_root_bounded(arg_hir_id, self.hir.root_lint_level);
 959         let parent_root = tcx.maybe_lint_level_root_bounded(
 960             self.source_scopes[original_source_scope]
 961                 .local_data
 962                 .as_ref()
 963                 .assert_crate_local()
 964                 .lint_root,
 965             self.hir.root_lint_level,
 966         );
 967         if current_root != parent_root {
 968             self.source_scope =
 969                 self.new_source_scope(pattern_span, LintLevel::Explicit(current_root), None);
 970         }
 971     }
 972
 973     fn get_unit_temp(&mut self) -> Place<'tcx> {
 974         match self.unit_temp {
 975             Some(tmp) => tmp,
 976             None => {
 977                 let ty = self.hir.unit_ty();
 978                 let fn_span = self.fn_span;
 979                 let tmp = self.temp(ty, fn_span);
 980                 self.unit_temp = Some(tmp);
 981                 tmp
 982             }
 983         }
 984     }
 985 }
 986
 987 ///////////////////////////////////////////////////////////////////////////
 988 // Builder methods are broken up into modules, depending on what kind
 989 // of thing is being lowered. Note that they use the `unpack` macro
 990 // above extensively.
 991
 992 mod block;
 993 mod cfg;
 994 mod expr;
 995 mod into;
 996 mod matches;
 997 mod misc;
 998 mod scope;