compiler/rustc_mir/src/transform/inline.rs

   1 //! Inlining pass for MIR functions
   2
   3 use rustc_attr::InlineAttr;
   4 use rustc_hir as hir;
   5 use rustc_index::bit_set::BitSet;
   6 use rustc_index::vec::Idx;
   7 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
   8 use rustc_middle::mir::visit::*;
   9 use rustc_middle::mir::*;
  10 use rustc_middle::ty::subst::Subst;
  11 use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
  12 use rustc_span::{hygiene::ExpnKind, ExpnData, Span};
  13 use rustc_target::spec::abi::Abi;
  14
  15 use super::simplify::{remove_dead_blocks, CfgSimplifier};
  16 use crate::transform::MirPass;
  17 use std::iter;
  18 use std::ops::{Range, RangeFrom};
  19
  20 crate mod cycle;
  21
  22 const INSTR_COST: usize = 5;
  23 const CALL_PENALTY: usize = 25;
  24 const LANDINGPAD_PENALTY: usize = 50;
  25 const RESUME_PENALTY: usize = 45;
  26
  27 const UNKNOWN_SIZE_COST: usize = 10;
  28
  29 pub struct Inline;
  30
  31 #[derive(Copy, Clone, Debug)]
  32 struct CallSite<'tcx> {
  33     callee: Instance<'tcx>,
  34     fn_sig: ty::PolyFnSig<'tcx>,
  35     block: BasicBlock,
  36     target: Option<BasicBlock>,
  37     source_info: SourceInfo,
  38 }
  39
  40 /// Returns true if MIR inlining is enabled in the current compilation session.
  41 crate fn is_enabled(tcx: TyCtxt<'_>) -> bool {
  42     if let Some(enabled) = tcx.sess.opts.debugging_opts.inline_mir {
  43         return enabled;
  44     }
  45
  46     tcx.sess.mir_opt_level() >= 3
  47 }
  48
  49 impl<'tcx> MirPass<'tcx> for Inline {
  50     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  51         if !is_enabled(tcx) {
  52             return;
  53         }
  54
  55         let span = trace_span!("inline", body = %tcx.def_path_str(body.source.def_id()));
  56         let _guard = span.enter();
  57         if inline(tcx, body) {
  58             debug!("running simplify cfg on {:?}", body.source);
  59             CfgSimplifier::new(body).simplify();
  60             remove_dead_blocks(tcx, body);
  61         }
  62     }
  63 }
  64
  65 fn inline(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  66     let def_id = body.source.def_id();
  67     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  68
  69     // Only do inlining into fn bodies.
  70     if !tcx.hir().body_owner_kind(hir_id).is_fn_or_closure() {
  71         return false;
  72     }
  73     if body.source.promoted.is_some() {
  74         return false;
  75     }
  76
  77     let mut this = Inliner {
  78         tcx,
  79         param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()),
  80         codegen_fn_attrs: tcx.codegen_fn_attrs(body.source.def_id()),
  81         hir_id,
  82         history: Vec::new(),
  83         changed: false,
  84     };
  85     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  86     this.process_blocks(body, blocks);
  87     this.changed
  88 }
  89
  90 struct Inliner<'tcx> {
  91     tcx: TyCtxt<'tcx>,
  92     param_env: ParamEnv<'tcx>,
  93     /// Caller codegen attributes.
  94     codegen_fn_attrs: &'tcx CodegenFnAttrs,
  95     /// Caller HirID.
  96     hir_id: hir::HirId,
  97     /// Stack of inlined Instances.
  98     history: Vec<ty::Instance<'tcx>>,
  99     /// Indicates that the caller body has been modified.
 100     changed: bool,
 101 }
 102
 103 impl Inliner<'tcx> {
 104     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 105         for bb in blocks {
 106             let bb_data = &caller_body[bb];
 107             if bb_data.is_cleanup {
 108                 continue;
 109             }
 110
 111             let callsite = match self.resolve_callsite(caller_body, bb, bb_data) {
 112                 None => continue,
 113                 Some(it) => it,
 114             };
 115
 116             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 117             let _guard = span.enter();
 118
 119             match self.try_inlining(caller_body, &callsite) {
 120                 Err(reason) => {
 121                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 122                     continue;
 123                 }
 124                 Ok(new_blocks) => {
 125                     debug!("inlined {}", callsite.callee);
 126                     self.changed = true;
 127                     self.history.push(callsite.callee);
 128                     self.process_blocks(caller_body, new_blocks);
 129                     self.history.pop();
 130                 }
 131             }
 132         }
 133     }
 134
 135     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 136     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 137     /// place.
 138     fn try_inlining(
 139         &self,
 140         caller_body: &mut Body<'tcx>,
 141         callsite: &CallSite<'tcx>,
 142     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 143         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 144         self.check_codegen_attributes(callsite, callee_attrs)?;
 145         self.check_mir_is_available(caller_body, &callsite.callee)?;
 146         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 147         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 148
 149         if !self.tcx.consider_optimizing(|| {
 150             format!("Inline {:?} into {}", callee_body.span, callsite.callee)
 151         }) {
 152             return Err("optimization fuel exhausted");
 153         }
 154
 155         let callee_body = callsite.callee.subst_mir_and_normalize_erasing_regions(
 156             self.tcx,
 157             self.param_env,
 158             callee_body.clone(),
 159         );
 160
 161         let old_blocks = caller_body.basic_blocks().next_index();
 162         self.inline_call(caller_body, &callsite, callee_body);
 163         let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 164
 165         Ok(new_blocks)
 166     }
 167
 168     fn check_mir_is_available(
 169         &self,
 170         caller_body: &Body<'tcx>,
 171         callee: &Instance<'tcx>,
 172     ) -> Result<(), &'static str> {
 173         if callee.def_id() == caller_body.source.def_id() {
 174             return Err("self-recursion");
 175         }
 176
 177         match callee.def {
 178             InstanceDef::Item(_) => {
 179                 // If there is no MIR available (either because it was not in metadata or
 180                 // because it has no MIR because it's an extern function), then the inliner
 181                 // won't cause cycles on this.
 182                 if !self.tcx.is_mir_available(callee.def_id()) {
 183                     return Err("item MIR unavailable");
 184                 }
 185             }
 186             // These have no own callable MIR.
 187             InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
 188                 return Err("instance without MIR (intrinsic / virtual)");
 189             }
 190             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
 191             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
 192             // do not need to catch this here, we can wait until the inliner decides to continue
 193             // inlining a second time.
 194             InstanceDef::VtableShim(_)
 195             | InstanceDef::ReifyShim(_)
 196             | InstanceDef::FnPtrShim(..)
 197             | InstanceDef::ClosureOnceShim { .. }
 198             | InstanceDef::DropGlue(..)
 199             | InstanceDef::CloneShim(..) => return Ok(()),
 200         }
 201
 202         if self.tcx.is_constructor(callee.def_id()) {
 203             trace!("constructors always have MIR");
 204             // Constructor functions cannot cause a query cycle.
 205             return Ok(());
 206         }
 207
 208         if let Some(callee_def_id) = callee.def_id().as_local() {
 209             let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
 210             // Avoid inlining into generators,
 211             // since their `optimized_mir` is used for layout computation, which can
 212             // create a cycle, even when no attempt is made to inline the function
 213             // in the other direction.
 214             if caller_body.generator.is_some() {
 215                 return Err("local generator (query cycle avoidance)");
 216             }
 217
 218             // Avoid a cycle here by only using `instance_mir` only if we have
 219             // a lower `HirId` than the callee. This ensures that the callee will
 220             // not inline us. This trick only works without incremental compilation.
 221             // So don't do it if that is enabled.
 222             if !self.tcx.dep_graph.is_fully_enabled() && self.hir_id < callee_hir_id {
 223                 return Ok(());
 224             }
 225
 226             // If we know for sure that the function we're calling will itself try to
 227             // call us, then we avoid inlining that function.
 228             if self
 229                 .tcx
 230                 .mir_callgraph_reachable((*callee, caller_body.source.def_id().expect_local()))
 231             {
 232                 return Err("caller might be reachable from callee (query cycle avoidance)");
 233             }
 234
 235             Ok(())
 236         } else {
 237             // This cannot result in an immediate cycle since the callee MIR is from another crate
 238             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 239             // not need to catch this here, we can wait until the inliner decides to continue
 240             // inlining a second time.
 241             trace!("functions from other crates always have MIR");
 242             Ok(())
 243         }
 244     }
 245
 246     fn resolve_callsite(
 247         &self,
 248         caller_body: &Body<'tcx>,
 249         bb: BasicBlock,
 250         bb_data: &BasicBlockData<'tcx>,
 251     ) -> Option<CallSite<'tcx>> {
 252         // Only consider direct calls to functions
 253         let terminator = bb_data.terminator();
 254         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 255             let func_ty = func.ty(caller_body, self.tcx);
 256             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 257                 // To resolve an instance its substs have to be fully normalized.
 258                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 259                 let callee =
 260                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 261
 262                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 263                     return None;
 264                 }
 265
 266                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 267
 268                 return Some(CallSite {
 269                     callee,
 270                     fn_sig,
 271                     block: bb,
 272                     target: destination.map(|(_, target)| target),
 273                     source_info: terminator.source_info,
 274                 });
 275             }
 276         }
 277
 278         None
 279     }
 280
 281     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 282     /// indicates that inlining decision should be based on other criteria.
 283     fn check_codegen_attributes(
 284         &self,
 285         callsite: &CallSite<'tcx>,
 286         callee_attrs: &CodegenFnAttrs,
 287     ) -> Result<(), &'satic str> {
 288         if let InlineAttr::Never = callee_attrs.inline {
 289             return Err("never inline hint");
 290         }
 291
 292         // Only inline local functions if they would be eligible for cross-crate
 293         // inlining. This is to ensure that the final crate doesn't have MIR that
 294         // reference unexported symbols
 295         if callsite.callee.def_id().is_local() {
 296             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 297             if !is_generic && !callee_attrs.requests_inline() {
 298                 return Err("not exported");
 299             }
 300         }
 301
 302         if callsite.fn_sig.c_variadic() {
 303             return Err("C variadic");
 304         }
 305
 306         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 307             return Err("naked");
 308         }
 309
 310         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 311             return Err("cold");
 312         }
 313
 314         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 315             return Err("incompatible sanitizer set");
 316         }
 317
 318         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 319             return Err("incompatible instruction set");
 320         }
 321
 322         for feature in &callee_attrs.target_features {
 323             if !self.codegen_fn_attrs.target_features.contains(feature) {
 324                 return Err("incompatible target feature");
 325             }
 326         }
 327
 328         Ok(())
 329     }
 330
 331     /// Returns inlining decision that is based on the examination of callee MIR body.
 332     /// Assumes that codegen attributes have been checked for compatibility already.
 333     #[instrument(level = "debug", skip(self, callee_body))]
 334     fn check_mir_body(
 335         &self,
 336         callsite: &CallSite<'tcx>,
 337         callee_body: &Body<'tcx>,
 338         callee_attrs: &CodegenFnAttrs,
 339     ) -> Result<(), &'static str> {
 340         let tcx = self.tcx;
 341
 342         let mut threshold = if callee_attrs.requests_inline() {
 343             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 344         } else {
 345             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 346         };
 347
 348         // Give a bonus functions with a small number of blocks,
 349         // We normally have two or three blocks for even
 350         // very small functions.
 351         if callee_body.basic_blocks().len() <= 3 {
 352             threshold += threshold / 4;
 353         }
 354         debug!("    final inline threshold = {}", threshold);
 355
 356         // FIXME: Give a bonus to functions with only a single caller
 357         let mut first_block = true;
 358         let mut cost = 0;
 359
 360         // Traverse the MIR manually so we can account for the effects of
 361         // inlining on the CFG.
 362         let mut work_list = vec![START_BLOCK];
 363         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 364         while let Some(bb) = work_list.pop() {
 365             if !visited.insert(bb.index()) {
 366                 continue;
 367             }
 368             let blk = &callee_body.basic_blocks()[bb];
 369
 370             for stmt in &blk.statements {
 371                 // Don't count StorageLive/StorageDead in the inlining cost.
 372                 match stmt.kind {
 373                     StatementKind::StorageLive(_)
 374                     | StatementKind::StorageDead(_)
 375                     | StatementKind::Nop => {}
 376                     _ => cost += INSTR_COST,
 377                 }
 378             }
 379             let term = blk.terminator();
 380             let mut is_drop = false;
 381             match term.kind {
 382                 TerminatorKind::Drop { ref place, target, unwind }
 383                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 384                     is_drop = true;
 385                     work_list.push(target);
 386                     // If the place doesn't actually need dropping, treat it like
 387                     // a regular goto.
 388                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 389                     if ty.needs_drop(tcx, self.param_env) {
 390                         cost += CALL_PENALTY;
 391                         if let Some(unwind) = unwind {
 392                             cost += LANDINGPAD_PENALTY;
 393                             work_list.push(unwind);
 394                         }
 395                     } else {
 396                         cost += INSTR_COST;
 397                     }
 398                 }
 399
 400                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 401                     if first_block =>
 402                 {
 403                     // If the function always diverges, don't inline
 404                     // unless the cost is zero
 405                     threshold = 0;
 406                 }
 407
 408                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 409                     if let ty::FnDef(def_id, substs) =
 410                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty()).kind()
 411                     {
 412                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 413                         if let Ok(Some(instance)) =
 414                             Instance::resolve(self.tcx, self.param_env, def_id, substs)
 415                         {
 416                             if callsite.callee.def_id() == instance.def_id() {
 417                                 return Err("self-recursion");
 418                             } else if self.history.contains(&instance) {
 419                                 return Err("already inlined");
 420                             }
 421                         }
 422                         // Don't give intrinsics the extra penalty for calls
 423                         let f = tcx.fn_sig(def_id);
 424                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 425                             cost += INSTR_COST;
 426                         } else {
 427                             cost += CALL_PENALTY;
 428                         }
 429                     } else {
 430                         cost += CALL_PENALTY;
 431                     }
 432                     if cleanup.is_some() {
 433                         cost += LANDINGPAD_PENALTY;
 434                     }
 435                 }
 436                 TerminatorKind::Assert { cleanup, .. } => {
 437                     cost += CALL_PENALTY;
 438
 439                     if cleanup.is_some() {
 440                         cost += LANDINGPAD_PENALTY;
 441                     }
 442                 }
 443                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 444                 _ => cost += INSTR_COST,
 445             }
 446
 447             if !is_drop {
 448                 for &succ in term.successors() {
 449                     work_list.push(succ);
 450                 }
 451             }
 452
 453             first_block = false;
 454         }
 455
 456         // Count up the cost of local variables and temps, if we know the size
 457         // use that, otherwise we use a moderately-large dummy cost.
 458
 459         let ptr_size = tcx.data_layout.pointer_size.bytes();
 460
 461         for v in callee_body.vars_and_temps_iter() {
 462             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 463             // Cost of the var is the size in machine-words, if we know
 464             // it.
 465             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 466                 cost += ((size + ptr_size - 1) / ptr_size) as usize;
 467             } else {
 468                 cost += UNKNOWN_SIZE_COST;
 469             }
 470         }
 471
 472         if let InlineAttr::Always = callee_attrs.inline {
 473             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 474             Ok(())
 475         } else {
 476             if cost <= threshold {
 477                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 478                 Ok(())
 479             } else {
 480                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 481                 Err("cost above threshold")
 482             }
 483         }
 484     }
 485
 486     fn inline_call(
 487         &self,
 488         caller_body: &mut Body<'tcx>,
 489         callsite: &CallSite<'tcx>,
 490         mut callee_body: Body<'tcx>,
 491     ) {
 492         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 493         match terminator.kind {
 494             TerminatorKind::Call { args, destination, cleanup, .. } => {
 495                 // If the call is something like `a[*i] = f(i)`, where
 496                 // `i : &mut usize`, then just duplicating the `a[*i]`
 497                 // Place could result in two different locations if `f`
 498                 // writes to `i`. To prevent this we need to create a temporary
 499                 // borrow of the place and pass the destination as `*temp` instead.
 500                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 501                     for elem in place.projection.iter() {
 502                         match elem {
 503                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 504                             _ => {}
 505                         }
 506                     }
 507
 508                     false
 509                 }
 510
 511                 let dest = if let Some((destination_place, _)) = destination {
 512                     if dest_needs_borrow(destination_place) {
 513                         trace!("creating temp for return destination");
 514                         let dest = Rvalue::Ref(
 515                             self.tcx.lifetimes.re_erased,
 516                             BorrowKind::Mut { allow_two_phase_borrow: false },
 517                             destination_place,
 518                         );
 519                         let dest_ty = dest.ty(caller_body, self.tcx);
 520                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 521                         caller_body[callsite.block].statements.push(Statement {
 522                             source_info: callsite.source_info,
 523                             kind: StatementKind::Assign(box (temp, dest)),
 524                         });
 525                         self.tcx.mk_place_deref(temp)
 526                     } else {
 527                         destination_place
 528                     }
 529                 } else {
 530                     trace!("creating temp for return place");
 531                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 532                 };
 533
 534                 // Copy the arguments if needed.
 535                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 536
 537                 let mut integrator = Integrator {
 538                     args: &args,
 539                     new_locals: Local::new(caller_body.local_decls.len())..,
 540                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 541                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 542                     destination: dest,
 543                     return_block: callsite.target,
 544                     cleanup_block: cleanup,
 545                     in_cleanup_block: false,
 546                     tcx: self.tcx,
 547                     callsite_span: callsite.source_info.span,
 548                     body_span: callee_body.span,
 549                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 550                 };
 551
 552                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 553                 // (or existing ones, in a few special cases) in the caller.
 554                 integrator.visit_body(&mut callee_body);
 555
 556                 for scope in &mut callee_body.source_scopes {
 557                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 558                     if scope.parent_scope.is_none() {
 559                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 560
 561                         // Attach the outermost callee scope as a child of the callsite
 562                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 563                         scope.parent_scope = Some(callsite.source_info.scope);
 564                         assert_eq!(scope.inlined_parent_scope, None);
 565                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 566                             Some(callsite.source_info.scope)
 567                         } else {
 568                             callsite_scope.inlined_parent_scope
 569                         };
 570
 571                         // Mark the outermost callee scope as an inlined one.
 572                         assert_eq!(scope.inlined, None);
 573                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 574                     } else if scope.inlined_parent_scope.is_none() {
 575                         // Make it easy to find the scope with `inlined` set above.
 576                         scope.inlined_parent_scope =
 577                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 578                     }
 579                 }
 580
 581                 // If there are any locals without storage markers, give them storage only for the
 582                 // duration of the call.
 583                 for local in callee_body.vars_and_temps_iter() {
 584                     if integrator.always_live_locals.contains(local) {
 585                         let new_local = integrator.map_local(local);
 586                         caller_body[callsite.block].statements.push(Statement {
 587                             source_info: callsite.source_info,
 588                             kind: StatementKind::StorageLive(new_local),
 589                         });
 590                     }
 591                 }
 592                 if let Some(block) = callsite.target {
 593                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 594                     // the slice once.
 595                     let mut n = 0;
 596                     for local in callee_body.vars_and_temps_iter().rev() {
 597                         if integrator.always_live_locals.contains(local) {
 598                             let new_local = integrator.map_local(local);
 599                             caller_body[block].statements.push(Statement {
 600                                 source_info: callsite.source_info,
 601                                 kind: StatementKind::StorageDead(new_local),
 602                             });
 603                             n += 1;
 604                         }
 605                     }
 606                     caller_body[block].statements.rotate_right(n);
 607                 }
 608
 609                 // Insert all of the (mapped) parts of the callee body into the caller.
 610                 caller_body.local_decls.extend(
 611                     // FIXME(eddyb) make `Range<Local>` iterable so that we can use
 612                     // `callee_body.local_decls.drain(callee_body.vars_and_temps())`
 613                     callee_body
 614                         .vars_and_temps_iter()
 615                         .map(|local| callee_body.local_decls[local].clone()),
 616                 );
 617                 caller_body.source_scopes.extend(callee_body.source_scopes.drain(..));
 618                 caller_body.var_debug_info.extend(callee_body.var_debug_info.drain(..));
 619                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 620
 621                 caller_body[callsite.block].terminator = Some(Terminator {
 622                     source_info: callsite.source_info,
 623                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 624                 });
 625
 626                 // Copy only unevaluated constants from the callee_body into the caller_body.
 627                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 628                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 629                 // because we are calling `subst_and_normalize_erasing_regions`.
 630                 caller_body.required_consts.extend(
 631                     callee_body.required_consts.iter().copied().filter(|&ct| {
 632                         match ct.literal.const_for_ty() {
 633                             Some(ct) => matches!(ct.val, ConstKind::Unevaluated(_)),
 634                             None => true,
 635                         }
 636                     }),
 637                 );
 638             }
 639             kind => bug!("unexpected terminator kind {:?}", kind),
 640         }
 641     }
 642
 643     fn make_call_args(
 644         &self,
 645         args: Vec<Operand<'tcx>>,
 646         callsite: &CallSite<'tcx>,
 647         caller_body: &mut Body<'tcx>,
 648         callee_body: &Body<'tcx>,
 649     ) -> Vec<Local> {
 650         let tcx = self.tcx;
 651
 652         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 653         // The caller provides the arguments wrapped up in a tuple:
 654         //
 655         //     tuple_tmp = (a, b, c)
 656         //     Fn::call(closure_ref, tuple_tmp)
 657         //
 658         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 659         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 660         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 661         // a vector like
 662         //
 663         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 664         //
 665         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 666         // if we "spill" that into *another* temporary, so that we can map the argument
 667         // variable in the callee MIR directly to an argument variable on our side.
 668         // So we introduce temporaries like:
 669         //
 670         //     tmp0 = tuple_tmp.0
 671         //     tmp1 = tuple_tmp.1
 672         //     tmp2 = tuple_tmp.2
 673         //
 674         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 675         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 676             let mut args = args.into_iter();
 677             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 678             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 679             assert!(args.next().is_none());
 680
 681             let tuple = Place::from(tuple);
 682             let tuple_tys = if let ty::Tuple(s) = tuple.ty(caller_body, tcx).ty.kind() {
 683                 s
 684             } else {
 685                 bug!("Closure arguments are not passed as a tuple");
 686             };
 687
 688             // The `closure_ref` in our example above.
 689             let closure_ref_arg = iter::once(self_);
 690
 691             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 692             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 693                 // This is e.g., `tuple_tmp.0` in our example above.
 694                 let tuple_field =
 695                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 696
 697                 // Spill to a local to make e.g., `tmp0`.
 698                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 699             });
 700
 701             closure_ref_arg.chain(tuple_tmp_args).collect()
 702         } else {
 703             args.into_iter()
 704                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 705                 .collect()
 706         }
 707     }
 708
 709     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 710     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 711     fn create_temp_if_necessary(
 712         &self,
 713         arg: Operand<'tcx>,
 714         callsite: &CallSite<'tcx>,
 715         caller_body: &mut Body<'tcx>,
 716     ) -> Local {
 717         // Reuse the operand if it is a moved temporary.
 718         if let Operand::Move(place) = &arg {
 719             if let Some(local) = place.as_local() {
 720                 if caller_body.local_kind(local) == LocalKind::Temp {
 721                     return local;
 722                 }
 723             }
 724         }
 725
 726         // Otherwise, create a temporary for the argument.
 727         trace!("creating temp for argument {:?}", arg);
 728         let arg_ty = arg.ty(caller_body, self.tcx);
 729         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 730         caller_body[callsite.block].statements.push(Statement {
 731             source_info: callsite.source_info,
 732             kind: StatementKind::Assign(box (Place::from(local), Rvalue::Use(arg))),
 733         });
 734         local
 735     }
 736
 737     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 738     fn new_call_temp(
 739         &self,
 740         caller_body: &mut Body<'tcx>,
 741         callsite: &CallSite<'tcx>,
 742         ty: Ty<'tcx>,
 743     ) -> Local {
 744         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 745
 746         caller_body[callsite.block].statements.push(Statement {
 747             source_info: callsite.source_info,
 748             kind: StatementKind::StorageLive(local),
 749         });
 750
 751         if let Some(block) = callsite.target {
 752             caller_body[block].statements.insert(
 753                 0,
 754                 Statement {
 755                     source_info: callsite.source_info,
 756                     kind: StatementKind::StorageDead(local),
 757                 },
 758             );
 759         }
 760
 761         local
 762     }
 763 }
 764
 765 fn type_size_of<'tcx>(
 766     tcx: TyCtxt<'tcx>,
 767     param_env: ty::ParamEnv<'tcx>,
 768     ty: Ty<'tcx>,
 769 ) -> Option<u64> {
 770     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 771 }
 772
 773 /**
 774  * Integrator.
 775  *
 776  * Integrates blocks from the callee function into the calling function.
 777  * Updates block indices, references to locals and other control flow
 778  * stuff.
 779 */
 780 struct Integrator<'a, 'tcx> {
 781     args: &'a [Local],
 782     new_locals: RangeFrom<Local>,
 783     new_scopes: RangeFrom<SourceScope>,
 784     new_blocks: RangeFrom<BasicBlock>,
 785     destination: Place<'tcx>,
 786     return_block: Option<BasicBlock>,
 787     cleanup_block: Option<BasicBlock>,
 788     in_cleanup_block: bool,
 789     tcx: TyCtxt<'tcx>,
 790     callsite_span: Span,
 791     body_span: Span,
 792     always_live_locals: BitSet<Local>,
 793 }
 794
 795 impl<'a, 'tcx> Integrator<'a, 'tcx> {
 796     fn map_local(&self, local: Local) -> Local {
 797         let new = if local == RETURN_PLACE {
 798             self.destination.local
 799         } else {
 800             let idx = local.index() - 1;
 801             if idx < self.args.len() {
 802                 self.args[idx]
 803             } else {
 804                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 805             }
 806         };
 807         trace!("mapping local `{:?}` to `{:?}`", local, new);
 808         new
 809     }
 810
 811     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 812         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 813         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 814         new
 815     }
 816
 817     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 818         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 819         trace!("mapping block `{:?}` to `{:?}`", block, new);
 820         new
 821     }
 822 }
 823
 824 impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
 825     fn tcx(&self) -> TyCtxt<'tcx> {
 826         self.tcx
 827     }
 828
 829     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 830         *local = self.map_local(*local);
 831     }
 832
 833     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 834         *scope = self.map_scope(*scope);
 835     }
 836
 837     fn visit_span(&mut self, span: &mut Span) {
 838         let mut expn_data =
 839             ExpnData::default(ExpnKind::Inlined, *span, self.tcx.sess.edition(), None);
 840         expn_data.def_site = self.body_span;
 841         // Make sure that all spans track the fact that they were inlined.
 842         *span = self.callsite_span.fresh_expansion(expn_data);
 843     }
 844
 845     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 846         for elem in place.projection {
 847             // FIXME: Make sure that return place is not used in an indexing projection, since it
 848             // won't be rebased as it is supposed to be.
 849             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 850         }
 851
 852         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 853         let dest_proj_len = self.destination.projection.len();
 854         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 855             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 856             projs.extend(self.destination.projection);
 857             projs.extend(place.projection);
 858
 859             place.projection = self.tcx.intern_place_elems(&*projs);
 860         }
 861         // Handles integrating any locals that occur in the base
 862         // or projections
 863         self.super_place(place, context, location)
 864     }
 865
 866     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 867         self.in_cleanup_block = data.is_cleanup;
 868         self.super_basic_block_data(block, data);
 869         self.in_cleanup_block = false;
 870     }
 871
 872     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 873         self.super_retag(kind, place, loc);
 874
 875         // We have to patch all inlined retags to be aware that they are no longer
 876         // happening on function entry.
 877         if *kind == RetagKind::FnEntry {
 878             *kind = RetagKind::Default;
 879         }
 880     }
 881
 882     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 883         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 884             statement.kind
 885         {
 886             self.always_live_locals.remove(local);
 887         }
 888         self.super_statement(statement, location);
 889     }
 890
 891     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 892         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 893         // replaced down below anyways).
 894         if !matches!(terminator.kind, TerminatorKind::Return) {
 895             self.super_terminator(terminator, loc);
 896         }
 897
 898         match terminator.kind {
 899             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 900             TerminatorKind::Goto { ref mut target } => {
 901                 *target = self.map_block(*target);
 902             }
 903             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 904                 for tgt in targets.all_targets_mut() {
 905                     *tgt = self.map_block(*tgt);
 906                 }
 907             }
 908             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 909             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 910                 *target = self.map_block(*target);
 911                 if let Some(tgt) = *unwind {
 912                     *unwind = Some(self.map_block(tgt));
 913                 } else if !self.in_cleanup_block {
 914                     // Unless this drop is in a cleanup block, add an unwind edge to
 915                     // the original call's cleanup block
 916                     *unwind = self.cleanup_block;
 917                 }
 918             }
 919             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 920                 if let Some((_, ref mut tgt)) = *destination {
 921                     *tgt = self.map_block(*tgt);
 922                 }
 923                 if let Some(tgt) = *cleanup {
 924                     *cleanup = Some(self.map_block(tgt));
 925                 } else if !self.in_cleanup_block {
 926                     // Unless this call is in a cleanup block, add an unwind edge to
 927                     // the original call's cleanup block
 928                     *cleanup = self.cleanup_block;
 929                 }
 930             }
 931             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 932                 *target = self.map_block(*target);
 933                 if let Some(tgt) = *cleanup {
 934                     *cleanup = Some(self.map_block(tgt));
 935                 } else if !self.in_cleanup_block {
 936                     // Unless this assert is in a cleanup block, add an unwind edge to
 937                     // the original call's cleanup block
 938                     *cleanup = self.cleanup_block;
 939                 }
 940             }
 941             TerminatorKind::Return => {
 942                 terminator.kind = if let Some(tgt) = self.return_block {
 943                     TerminatorKind::Goto { target: tgt }
 944                 } else {
 945                     TerminatorKind::Unreachable
 946                 }
 947             }
 948             TerminatorKind::Resume => {
 949                 if let Some(tgt) = self.cleanup_block {
 950                     terminator.kind = TerminatorKind::Goto { target: tgt }
 951                 }
 952             }
 953             TerminatorKind::Abort => {}
 954             TerminatorKind::Unreachable => {}
 955             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 956                 *real_target = self.map_block(*real_target);
 957                 *imaginary_target = self.map_block(*imaginary_target);
 958             }
 959             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 960             // see the ordering of passes in the optimized_mir query.
 961             {
 962                 bug!("False unwinds should have been removed before inlining")
 963             }
 964             TerminatorKind::InlineAsm { ref mut destination, .. } => {
 965                 if let Some(ref mut tgt) = *destination {
 966                     *tgt = self.map_block(*tgt);
 967                 }
 968             }
 969         }
 970     }
 971 }