src/librustc_mir/build/mod.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11
  12 use build;
  13 use hair::cx::Cx;
  14 use hair::LintLevel;
  15 use rustc::hir;
  16 use rustc::hir::def_id::{DefId, LocalDefId};
  17 use rustc::middle::region;
  18 use rustc::mir::*;
  19 use rustc::mir::visit::{MutVisitor, TyContext};
  20 use rustc::ty::{self, Ty, TyCtxt};
  21 use rustc::ty::subst::Substs;
  22 use rustc::util::nodemap::NodeMap;
  23 use rustc_const_eval::pattern::{BindingMode, PatternKind};
  24 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
  25 use shim;
  26 use std::mem;
  27 use std::u32;
  28 use syntax::abi::Abi;
  29 use syntax::ast;
  30 use syntax::symbol::keywords;
  31 use syntax_pos::Span;
  32 use transform::MirSource;
  33 use util as mir_util;
  34
  35 /// Construct the MIR for a given def-id.
  36 pub fn mir_build<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Mir<'tcx> {
  37     let id = tcx.hir.as_local_node_id(def_id).unwrap();
  38     let unsupported = || {
  39         span_bug!(tcx.hir.span(id), "can't build MIR for {:?}", def_id);
  40     };
  41
  42     // Figure out what primary body this item has.
  43     let body_id = match tcx.hir.get(id) {
  44         hir::map::NodeItem(item) => {
  45             match item.node {
  46                 hir::ItemConst(_, body) |
  47                 hir::ItemStatic(_, _, body) |
  48                 hir::ItemFn(.., body) => body,
  49                 _ => unsupported()
  50             }
  51         }
  52         hir::map::NodeTraitItem(item) => {
  53             match item.node {
  54                 hir::TraitItemKind::Const(_, Some(body)) |
  55                 hir::TraitItemKind::Method(_,
  56                     hir::TraitMethod::Provided(body)) => body,
  57                 _ => unsupported()
  58             }
  59         }
  60         hir::map::NodeImplItem(item) => {
  61             match item.node {
  62                 hir::ImplItemKind::Const(_, body) |
  63                 hir::ImplItemKind::Method(_, body) => body,
  64                 _ => unsupported()
  65             }
  66         }
  67         hir::map::NodeExpr(expr) => {
  68             // FIXME(eddyb) Closures should have separate
  69             // function definition IDs and expression IDs.
  70             // Type-checking should not let closures get
  71             // this far in a constant position.
  72             // Assume that everything other than closures
  73             // is a constant "initializer" expression.
  74             match expr.node {
  75                 hir::ExprClosure(_, _, body, _, _) => body,
  76                 _ => hir::BodyId { node_id: expr.id },
  77             }
  78         }
  79         hir::map::NodeVariant(variant) =>
  80             return create_constructor_shim(tcx, id, &variant.node.data),
  81         hir::map::NodeStructCtor(ctor) =>
  82             return create_constructor_shim(tcx, id, ctor),
  83         _ => unsupported(),
  84     };
  85
  86     tcx.infer_ctxt().enter(|infcx| {
  87         let cx = Cx::new(&infcx, id);
  88         let mut mir = if cx.tables().tainted_by_errors {
  89             build::construct_error(cx, body_id)
  90         } else if let hir::BodyOwnerKind::Fn = cx.body_owner_kind {
  91             // fetch the fully liberated fn signature (that is, all bound
  92             // types/lifetimes replaced)
  93             let fn_hir_id = tcx.hir.node_to_hir_id(id);
  94             let fn_sig = cx.tables().liberated_fn_sigs()[fn_hir_id].clone();
  95
  96             let ty = tcx.type_of(tcx.hir.local_def_id(id));
  97             let mut abi = fn_sig.abi;
  98             let implicit_argument = match ty.sty {
  99                 ty::TyClosure(..) => {
 100                     // HACK(eddyb) Avoid having RustCall on closures,
 101                     // as it adds unnecessary (and wrong) auto-tupling.
 102                     abi = Abi::Rust;
 103                     Some((closure_self_ty(tcx, id, body_id), None))
 104                 }
 105                 ty::TyGenerator(..) => {
 106                     let gen_ty =  tcx.body_tables(body_id).node_id_to_type(fn_hir_id);
 107                     Some((gen_ty, None))
 108                 }
 109                 _ => None,
 110             };
 111
 112             // FIXME: safety in closures
 113             let safety = match fn_sig.unsafety {
 114                 hir::Unsafety::Normal => Safety::Safe,
 115                 hir::Unsafety::Unsafe => Safety::FnUnsafe,
 116             };
 117
 118             let body = tcx.hir.body(body_id);
 119             let explicit_arguments =
 120                 body.arguments
 121                     .iter()
 122                     .enumerate()
 123                     .map(|(index, arg)| {
 124                         (fn_sig.inputs()[index], Some(&*arg.pat))
 125                     });
 126
 127             let arguments = implicit_argument.into_iter().chain(explicit_arguments);
 128
 129             let (yield_ty, return_ty) = if body.is_generator {
 130                 let gen_sig = cx.tables().generator_sigs()[fn_hir_id].clone().unwrap();
 131                 (Some(gen_sig.yield_ty), gen_sig.return_ty)
 132             } else {
 133                 (None, fn_sig.output())
 134             };
 135
 136             build::construct_fn(cx, id, arguments, safety, abi,
 137                                 return_ty, yield_ty, body)
 138         } else {
 139             build::construct_const(cx, body_id)
 140         };
 141
 142         // Convert the Mir to global types.
 143         let mut globalizer = GlobalizeMir {
 144             tcx,
 145             span: mir.span
 146         };
 147         globalizer.visit_mir(&mut mir);
 148         let mir = unsafe {
 149             mem::transmute::<Mir, Mir<'tcx>>(mir)
 150         };
 151
 152         mir_util::dump_mir(tcx, None, "mir_map", &0,
 153                            MirSource::item(def_id), &mir, |_, _| Ok(()) );
 154
 155         mir
 156     })
 157 }
 158
 159 /// A pass to lift all the types and substitutions in a Mir
 160 /// to the global tcx. Sadly, we don't have a "folder" that
 161 /// can change 'tcx so we have to transmute afterwards.
 162 struct GlobalizeMir<'a, 'gcx: 'a> {
 163     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 164     span: Span
 165 }
 166
 167 impl<'a, 'gcx: 'tcx, 'tcx> MutVisitor<'tcx> for GlobalizeMir<'a, 'gcx> {
 168     fn visit_ty(&mut self, ty: &mut Ty<'tcx>, _: TyContext) {
 169         if let Some(lifted) = self.tcx.lift(ty) {
 170             *ty = lifted;
 171         } else {
 172             span_bug!(self.span,
 173                       "found type `{:?}` with inference types/regions in MIR",
 174                       ty);
 175         }
 176     }
 177
 178     fn visit_region(&mut self, region: &mut ty::Region<'tcx>, _: Location) {
 179         if let Some(lifted) = self.tcx.lift(region) {
 180             *region = lifted;
 181         } else {
 182             span_bug!(self.span,
 183                       "found region `{:?}` with inference types/regions in MIR",
 184                       region);
 185         }
 186     }
 187
 188     fn visit_const(&mut self, constant: &mut &'tcx ty::Const<'tcx>, _: Location) {
 189         if let Some(lifted) = self.tcx.lift(constant) {
 190             *constant = lifted;
 191         } else {
 192             span_bug!(self.span,
 193                       "found constant `{:?}` with inference types/regions in MIR",
 194                       constant);
 195         }
 196     }
 197
 198     fn visit_substs(&mut self, substs: &mut &'tcx Substs<'tcx>, _: Location) {
 199         if let Some(lifted) = self.tcx.lift(substs) {
 200             *substs = lifted;
 201         } else {
 202             span_bug!(self.span,
 203                       "found substs `{:?}` with inference types/regions in MIR",
 204                       substs);
 205         }
 206     }
 207 }
 208
 209 fn create_constructor_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 210                                      ctor_id: ast::NodeId,
 211                                      v: &'tcx hir::VariantData)
 212                                      -> Mir<'tcx>
 213 {
 214     let span = tcx.hir.span(ctor_id);
 215     if let hir::VariantData::Tuple(ref fields, ctor_id) = *v {
 216         tcx.infer_ctxt().enter(|infcx| {
 217             let mut mir = shim::build_adt_ctor(&infcx, ctor_id, fields, span);
 218
 219             // Convert the Mir to global types.
 220             let tcx = infcx.tcx.global_tcx();
 221             let mut globalizer = GlobalizeMir {
 222                 tcx,
 223                 span: mir.span
 224             };
 225             globalizer.visit_mir(&mut mir);
 226             let mir = unsafe {
 227                 mem::transmute::<Mir, Mir<'tcx>>(mir)
 228             };
 229
 230             mir_util::dump_mir(tcx, None, "mir_map", &0,
 231                                MirSource::item(tcx.hir.local_def_id(ctor_id)),
 232                                &mir, |_, _| Ok(()) );
 233
 234             mir
 235         })
 236     } else {
 237         span_bug!(span, "attempting to create MIR for non-tuple variant {:?}", v);
 238     }
 239 }
 240
 241 ///////////////////////////////////////////////////////////////////////////
 242 // BuildMir -- walks a crate, looking for fn items and methods to build MIR from
 243
 244 pub fn closure_self_ty<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
 245                                        closure_expr_id: ast::NodeId,
 246                                        body_id: hir::BodyId)
 247                                        -> Ty<'tcx> {
 248     let closure_expr_hir_id = tcx.hir.node_to_hir_id(closure_expr_id);
 249     let closure_ty = tcx.body_tables(body_id).node_id_to_type(closure_expr_hir_id);
 250
 251     let closure_def_id = tcx.hir.local_def_id(closure_expr_id);
 252     let region = ty::ReFree(ty::FreeRegion {
 253         scope: closure_def_id,
 254         bound_region: ty::BoundRegion::BrEnv,
 255     });
 256     let region = tcx.mk_region(region);
 257
 258     match tcx.closure_kind(closure_def_id) {
 259         ty::ClosureKind::Fn =>
 260             tcx.mk_ref(region,
 261                        ty::TypeAndMut { ty: closure_ty,
 262                                         mutbl: hir::MutImmutable }),
 263         ty::ClosureKind::FnMut =>
 264             tcx.mk_ref(region,
 265                        ty::TypeAndMut { ty: closure_ty,
 266                                         mutbl: hir::MutMutable }),
 267         ty::ClosureKind::FnOnce =>
 268             closure_ty
 269     }
 270 }
 271
 272 struct Builder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 273     hir: Cx<'a, 'gcx, 'tcx>,
 274     cfg: CFG<'tcx>,
 275
 276     fn_span: Span,
 277     arg_count: usize,
 278
 279     /// the current set of scopes, updated as we traverse;
 280     /// see the `scope` module for more details
 281     scopes: Vec<scope::Scope<'tcx>>,
 282
 283     /// The current unsafe block in scope, even if it is hidden by
 284     /// a PushUnsafeBlock
 285     unpushed_unsafe: Safety,
 286
 287     /// The number of `push_unsafe_block` levels in scope
 288     push_unsafe_count: usize,
 289
 290     /// the current set of breakables; see the `scope` module for more
 291     /// details
 292     breakable_scopes: Vec<scope::BreakableScope<'tcx>>,
 293
 294     /// the vector of all scopes that we have created thus far;
 295     /// we track this for debuginfo later
 296     visibility_scopes: IndexVec<VisibilityScope, VisibilityScopeData>,
 297     visibility_scope_info: IndexVec<VisibilityScope, VisibilityScopeInfo>,
 298     visibility_scope: VisibilityScope,
 299
 300     /// Maps node ids of variable bindings to the `Local`s created for them.
 301     var_indices: NodeMap<Local>,
 302     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
 303     unit_temp: Option<Lvalue<'tcx>>,
 304
 305     /// cached block with the RESUME terminator; this is created
 306     /// when first set of cleanups are built.
 307     cached_resume_block: Option<BasicBlock>,
 308     /// cached block with the RETURN terminator
 309     cached_return_block: Option<BasicBlock>,
 310     /// cached block with the UNREACHABLE terminator
 311     cached_unreachable_block: Option<BasicBlock>,
 312 }
 313
 314 struct CFG<'tcx> {
 315     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 316 }
 317
 318 newtype_index!(ScopeId);
 319
 320 ///////////////////////////////////////////////////////////////////////////
 321 /// The `BlockAnd` "monad" packages up the new basic block along with a
 322 /// produced value (sometimes just unit, of course). The `unpack!`
 323 /// macro (and methods below) makes working with `BlockAnd` much more
 324 /// convenient.
 325
 326 #[must_use] // if you don't use one of these results, you're leaving a dangling edge
 327 struct BlockAnd<T>(BasicBlock, T);
 328
 329 trait BlockAndExtension {
 330     fn and<T>(self, v: T) -> BlockAnd<T>;
 331     fn unit(self) -> BlockAnd<()>;
 332 }
 333
 334 impl BlockAndExtension for BasicBlock {
 335     fn and<T>(self, v: T) -> BlockAnd<T> {
 336         BlockAnd(self, v)
 337     }
 338
 339     fn unit(self) -> BlockAnd<()> {
 340         BlockAnd(self, ())
 341     }
 342 }
 343
 344 /// Update a block pointer and return the value.
 345 /// Use it like `let x = unpack!(block = self.foo(block, foo))`.
 346 macro_rules! unpack {
 347     ($x:ident = $c:expr) => {
 348         {
 349             let BlockAnd(b, v) = $c;
 350             $x = b;
 351             v
 352         }
 353     };
 354
 355     ($c:expr) => {
 356         {
 357             let BlockAnd(b, ()) = $c;
 358             b
 359         }
 360     };
 361 }
 362
 363 ///////////////////////////////////////////////////////////////////////////
 364 /// the main entry point for building MIR for a function
 365
 366 fn construct_fn<'a, 'gcx, 'tcx, A>(hir: Cx<'a, 'gcx, 'tcx>,
 367                                    fn_id: ast::NodeId,
 368                                    arguments: A,
 369                                    safety: Safety,
 370                                    abi: Abi,
 371                                    return_ty: Ty<'gcx>,
 372                                    yield_ty: Option<Ty<'gcx>>,
 373                                    body: &'gcx hir::Body)
 374                                    -> Mir<'tcx>
 375     where A: Iterator<Item=(Ty<'gcx>, Option<&'gcx hir::Pat>)>
 376 {
 377     let arguments: Vec<_> = arguments.collect();
 378
 379     let tcx = hir.tcx();
 380     let span = tcx.hir.span(fn_id);
 381     let mut builder = Builder::new(hir.clone(),
 382         span,
 383         arguments.len(),
 384         safety,
 385         return_ty);
 386
 387     let call_site_scope = region::Scope::CallSite(body.value.hir_id.local_id);
 388     let arg_scope = region::Scope::Arguments(body.value.hir_id.local_id);
 389     let mut block = START_BLOCK;
 390     let source_info = builder.source_info(span);
 391     let call_site_s = (call_site_scope, source_info);
 392     unpack!(block = builder.in_scope(call_site_s, LintLevel::Inherited, block, |builder| {
 393         let arg_scope_s = (arg_scope, source_info);
 394         unpack!(block = builder.in_scope(arg_scope_s, LintLevel::Inherited, block, |builder| {
 395             builder.args_and_body(block, &arguments, arg_scope, &body.value)
 396         }));
 397         // Attribute epilogue to function's closing brace
 398         let fn_end = span.with_lo(span.hi());
 399         let source_info = builder.source_info(fn_end);
 400         let return_block = builder.return_block();
 401         builder.cfg.terminate(block, source_info,
 402                               TerminatorKind::Goto { target: return_block });
 403         builder.cfg.terminate(return_block, source_info,
 404                               TerminatorKind::Return);
 405         // Attribute any unreachable codepaths to the function's closing brace
 406         if let Some(unreachable_block) = builder.cached_unreachable_block {
 407             builder.cfg.terminate(unreachable_block, source_info,
 408                                   TerminatorKind::Unreachable);
 409         }
 410         return_block.unit()
 411     }));
 412     assert_eq!(block, builder.return_block());
 413
 414     let mut spread_arg = None;
 415     if abi == Abi::RustCall {
 416         // RustCall pseudo-ABI untuples the last argument.
 417         spread_arg = Some(Local::new(arguments.len()));
 418     }
 419
 420     // Gather the upvars of a closure, if any.
 421     let upvar_decls: Vec<_> = tcx.with_freevars(fn_id, |freevars| {
 422         freevars.iter().map(|fv| {
 423             let var_id = fv.var_id();
 424             let var_hir_id = tcx.hir.node_to_hir_id(var_id);
 425             let closure_expr_id = tcx.hir.local_def_id(fn_id);
 426             let capture = hir.tables().upvar_capture(ty::UpvarId {
 427                 var_id: var_hir_id,
 428                 closure_expr_id: LocalDefId::from_def_id(closure_expr_id),
 429             });
 430             let by_ref = match capture {
 431                 ty::UpvarCapture::ByValue => false,
 432                 ty::UpvarCapture::ByRef(..) => true
 433             };
 434             let mut decl = UpvarDecl {
 435                 debug_name: keywords::Invalid.name(),
 436                 by_ref,
 437             };
 438             if let Some(hir::map::NodeBinding(pat)) = tcx.hir.find(var_id) {
 439                 if let hir::PatKind::Binding(_, _, ref ident, _) = pat.node {
 440                     decl.debug_name = ident.node;
 441                 }
 442             }
 443             decl
 444         }).collect()
 445     });
 446
 447     let mut mir = builder.finish(upvar_decls, yield_ty);
 448     mir.spread_arg = spread_arg;
 449     mir
 450 }
 451
 452 fn construct_const<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
 453                                    body_id: hir::BodyId)
 454                                    -> Mir<'tcx> {
 455     let tcx = hir.tcx();
 456     let ast_expr = &tcx.hir.body(body_id).value;
 457     let ty = hir.tables().expr_ty_adjusted(ast_expr);
 458     let owner_id = tcx.hir.body_owner(body_id);
 459     let span = tcx.hir.span(owner_id);
 460     let mut builder = Builder::new(hir.clone(), span, 0, Safety::Safe, ty);
 461
 462     let mut block = START_BLOCK;
 463     let expr = builder.hir.mirror(ast_expr);
 464     unpack!(block = builder.into_expr(&Lvalue::Local(RETURN_POINTER), block, expr));
 465
 466     let source_info = builder.source_info(span);
 467     builder.cfg.terminate(block, source_info, TerminatorKind::Return);
 468
 469     // Constants can't `return` so a return block should not be created.
 470     assert_eq!(builder.cached_return_block, None);
 471
 472     builder.finish(vec![], None)
 473 }
 474
 475 fn construct_error<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
 476                                    body_id: hir::BodyId)
 477                                    -> Mir<'tcx> {
 478     let owner_id = hir.tcx().hir.body_owner(body_id);
 479     let span = hir.tcx().hir.span(owner_id);
 480     let ty = hir.tcx().types.err;
 481     let mut builder = Builder::new(hir, span, 0, Safety::Safe, ty);
 482     let source_info = builder.source_info(span);
 483     builder.cfg.terminate(START_BLOCK, source_info, TerminatorKind::Unreachable);
 484     builder.finish(vec![], None)
 485 }
 486
 487 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 488     fn new(hir: Cx<'a, 'gcx, 'tcx>,
 489            span: Span,
 490            arg_count: usize,
 491            safety: Safety,
 492            return_ty: Ty<'tcx>)
 493            -> Builder<'a, 'gcx, 'tcx> {
 494         let lint_level = LintLevel::Explicit(hir.root_lint_level);
 495         let mut builder = Builder {
 496             hir,
 497             cfg: CFG { basic_blocks: IndexVec::new() },
 498             fn_span: span,
 499             arg_count,
 500             scopes: vec![],
 501             visibility_scopes: IndexVec::new(),
 502             visibility_scope: ARGUMENT_VISIBILITY_SCOPE,
 503             visibility_scope_info: IndexVec::new(),
 504             push_unsafe_count: 0,
 505             unpushed_unsafe: safety,
 506             breakable_scopes: vec![],
 507             local_decls: IndexVec::from_elem_n(LocalDecl::new_return_pointer(return_ty,
 508                                                                              span), 1),
 509             var_indices: NodeMap(),
 510             unit_temp: None,
 511             cached_resume_block: None,
 512             cached_return_block: None,
 513             cached_unreachable_block: None,
 514         };
 515
 516         assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
 517         assert_eq!(
 518             builder.new_visibility_scope(span, lint_level, Some(safety)),
 519             ARGUMENT_VISIBILITY_SCOPE);
 520         builder.visibility_scopes[ARGUMENT_VISIBILITY_SCOPE].parent_scope = None;
 521
 522         builder
 523     }
 524
 525     fn finish(self,
 526               upvar_decls: Vec<UpvarDecl>,
 527               yield_ty: Option<Ty<'tcx>>)
 528               -> Mir<'tcx> {
 529         for (index, block) in self.cfg.basic_blocks.iter().enumerate() {
 530             if block.terminator.is_none() {
 531                 span_bug!(self.fn_span, "no terminator on block {:?}", index);
 532             }
 533         }
 534
 535         Mir::new(self.cfg.basic_blocks,
 536                  self.visibility_scopes,
 537                  ClearOnDecode::Set(self.visibility_scope_info),
 538                  IndexVec::new(),
 539                  yield_ty,
 540                  self.local_decls,
 541                  self.arg_count,
 542                  upvar_decls,
 543                  self.fn_span
 544         )
 545     }
 546
 547     fn args_and_body(&mut self,
 548                      mut block: BasicBlock,
 549                      arguments: &[(Ty<'gcx>, Option<&'gcx hir::Pat>)],
 550                      argument_scope: region::Scope,
 551                      ast_body: &'gcx hir::Expr)
 552                      -> BlockAnd<()>
 553     {
 554         // Allocate locals for the function arguments
 555         for &(ty, pattern) in arguments.iter() {
 556             // If this is a simple binding pattern, give the local a nice name for debuginfo.
 557             let mut name = None;
 558             if let Some(pat) = pattern {
 559                 if let hir::PatKind::Binding(_, _, ref ident, _) = pat.node {
 560                     name = Some(ident.node);
 561                 }
 562             }
 563
 564             self.local_decls.push(LocalDecl {
 565                 mutability: Mutability::Not,
 566                 ty,
 567                 source_info: SourceInfo {
 568                     scope: ARGUMENT_VISIBILITY_SCOPE,
 569                     span: pattern.map_or(self.fn_span, |pat| pat.span)
 570                 },
 571                 lexical_scope: ARGUMENT_VISIBILITY_SCOPE,
 572                 name,
 573                 internal: false,
 574                 is_user_variable: false,
 575             });
 576         }
 577
 578         let mut scope = None;
 579         // Bind the argument patterns
 580         for (index, &(ty, pattern)) in arguments.iter().enumerate() {
 581             // Function arguments always get the first Local indices after the return pointer
 582             let local = Local::new(index + 1);
 583             let lvalue = Lvalue::Local(local);
 584
 585             if let Some(pattern) = pattern {
 586                 let pattern = self.hir.pattern_from_hir(pattern);
 587
 588                 match *pattern.kind {
 589                     // Don't introduce extra copies for simple bindings
 590                     PatternKind::Binding { mutability, var, mode: BindingMode::ByValue, .. } => {
 591                         self.local_decls[local].mutability = mutability;
 592                         self.var_indices.insert(var, local);
 593                     }
 594                     _ => {
 595                         scope = self.declare_bindings(scope, ast_body.span,
 596                                                       LintLevel::Inherited, &pattern);
 597                         unpack!(block = self.lvalue_into_pattern(block, pattern, &lvalue));
 598                     }
 599                 }
 600             }
 601
 602             // Make sure we drop (parts of) the argument even when not matched on.
 603             self.schedule_drop(pattern.as_ref().map_or(ast_body.span, |pat| pat.span),
 604                                argument_scope, &lvalue, ty);
 605
 606         }
 607
 608         // Enter the argument pattern bindings visibility scope, if it exists.
 609         if let Some(visibility_scope) = scope {
 610             self.visibility_scope = visibility_scope;
 611         }
 612
 613         let body = self.hir.mirror(ast_body);
 614         self.into(&Lvalue::Local(RETURN_POINTER), block, body)
 615     }
 616
 617     fn get_unit_temp(&mut self) -> Lvalue<'tcx> {
 618         match self.unit_temp {
 619             Some(ref tmp) => tmp.clone(),
 620             None => {
 621                 let ty = self.hir.unit_ty();
 622                 let fn_span = self.fn_span;
 623                 let tmp = self.temp(ty, fn_span);
 624                 self.unit_temp = Some(tmp.clone());
 625                 tmp
 626             }
 627         }
 628     }
 629
 630     fn return_block(&mut self) -> BasicBlock {
 631         match self.cached_return_block {
 632             Some(rb) => rb,
 633             None => {
 634                 let rb = self.cfg.start_new_block();
 635                 self.cached_return_block = Some(rb);
 636                 rb
 637             }
 638         }
 639     }
 640
 641     fn unreachable_block(&mut self) -> BasicBlock {
 642         match self.cached_unreachable_block {
 643             Some(ub) => ub,
 644             None => {
 645                 let ub = self.cfg.start_new_block();
 646                 self.cached_unreachable_block = Some(ub);
 647                 ub
 648             }
 649         }
 650     }
 651 }
 652
 653 ///////////////////////////////////////////////////////////////////////////
 654 // Builder methods are broken up into modules, depending on what kind
 655 // of thing is being translated. Note that they use the `unpack` macro
 656 // above extensively.
 657
 658 mod block;
 659 mod cfg;
 660 mod expr;
 661 mod into;
 662 mod matches;
 663 mod misc;
 664 mod scope;