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