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 tcx.sess.opts.debugging_opts.instrument_coverage {
  43         // Since `Inline` happens after `InstrumentCoverage`, the function-specific coverage
  44         // counters can be invalidated, such as by merging coverage counter statements from
  45         // a pre-inlined function into a different function. This kind of change is invalid,
  46         // so inlining must be skipped. Note: This check is performed here so inlining can
  47         // be disabled without preventing other optimizations (regardless of `mir_opt_level`).
  48         return false;
  49     }
  50
  51     if let Some(enabled) = tcx.sess.opts.debugging_opts.inline_mir {
  52         return enabled;
  53     }
  54
  55     tcx.sess.opts.debugging_opts.mir_opt_level >= 2
  56 }
  57
  58 impl<'tcx> MirPass<'tcx> for Inline {
  59     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  60         if !is_enabled(tcx) {
  61             return;
  62         }
  63
  64         let span = trace_span!("inline", body = %tcx.def_path_str(body.source.def_id()));
  65         let _guard = span.enter();
  66         if inline(tcx, body) {
  67             debug!("running simplify cfg on {:?}", body.source);
  68             CfgSimplifier::new(body).simplify();
  69             remove_dead_blocks(body);
  70         }
  71     }
  72 }
  73
  74 fn inline(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  75     let def_id = body.source.def_id();
  76     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  77
  78     // Only do inlining into fn bodies.
  79     if !tcx.hir().body_owner_kind(hir_id).is_fn_or_closure() {
  80         return false;
  81     }
  82     if body.source.promoted.is_some() {
  83         return false;
  84     }
  85
  86     let mut this = Inliner {
  87         tcx,
  88         param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()),
  89         codegen_fn_attrs: tcx.codegen_fn_attrs(body.source.def_id()),
  90         hir_id,
  91         history: Vec::new(),
  92         changed: false,
  93     };
  94     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  95     this.process_blocks(body, blocks);
  96     this.changed
  97 }
  98
  99 struct Inliner<'tcx> {
 100     tcx: TyCtxt<'tcx>,
 101     param_env: ParamEnv<'tcx>,
 102     /// Caller codegen attributes.
 103     codegen_fn_attrs: &'tcx CodegenFnAttrs,
 104     /// Caller HirID.
 105     hir_id: hir::HirId,
 106     /// Stack of inlined Instances.
 107     history: Vec<ty::Instance<'tcx>>,
 108     /// Indicates that the caller body has been modified.
 109     changed: bool,
 110 }
 111
 112 impl Inliner<'tcx> {
 113     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 114         for bb in blocks {
 115             let bb_data = &caller_body[bb];
 116             if bb_data.is_cleanup {
 117                 continue;
 118             }
 119
 120             let callsite = match self.resolve_callsite(caller_body, bb, bb_data) {
 121                 None => continue,
 122                 Some(it) => it,
 123             };
 124
 125             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 126             let _guard = span.enter();
 127
 128             match self.try_inlining(caller_body, &callsite) {
 129                 Err(reason) => {
 130                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 131                     continue;
 132                 }
 133                 Ok(new_blocks) => {
 134                     debug!("inlined {}", callsite.callee);
 135                     self.changed = true;
 136                     self.history.push(callsite.callee);
 137                     self.process_blocks(caller_body, new_blocks);
 138                     self.history.pop();
 139                 }
 140             }
 141         }
 142     }
 143
 144     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 145     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 146     /// place.
 147     fn try_inlining(
 148         &self,
 149         caller_body: &mut Body<'tcx>,
 150         callsite: &CallSite<'tcx>,
 151     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 152         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 153         self.check_codegen_attributes(callsite, callee_attrs)?;
 154         self.check_mir_is_available(caller_body, &callsite.callee)?;
 155         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 156         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 157
 158         if !self.tcx.consider_optimizing(|| {
 159             format!("Inline {:?} into {}", callee_body.span, callsite.callee)
 160         }) {
 161             return Err("optimization fuel exhausted");
 162         }
 163
 164         let callee_body = callsite.callee.subst_mir_and_normalize_erasing_regions(
 165             self.tcx,
 166             self.param_env,
 167             callee_body.clone(),
 168         );
 169
 170         let old_blocks = caller_body.basic_blocks().next_index();
 171         self.inline_call(caller_body, &callsite, callee_body);
 172         let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 173
 174         Ok(new_blocks)
 175     }
 176
 177     fn check_mir_is_available(
 178         &self,
 179         caller_body: &Body<'tcx>,
 180         callee: &Instance<'tcx>,
 181     ) -> Result<(), &'static str> {
 182         if callee.def_id() == caller_body.source.def_id() {
 183             return Err("self-recursion");
 184         }
 185
 186         match callee.def {
 187             InstanceDef::Item(_) => {
 188                 // If there is no MIR available (either because it was not in metadata or
 189                 // because it has no MIR because it's an extern function), then the inliner
 190                 // won't cause cycles on this.
 191                 if !self.tcx.is_mir_available(callee.def_id()) {
 192                     return Err("item MIR unavailable");
 193                 }
 194             }
 195             // These have no own callable MIR.
 196             InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
 197                 return Err("instance without MIR (intrinsic / virtual)");
 198             }
 199             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
 200             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
 201             // do not need to catch this here, we can wait until the inliner decides to continue
 202             // inlining a second time.
 203             InstanceDef::VtableShim(_)
 204             | InstanceDef::ReifyShim(_)
 205             | InstanceDef::FnPtrShim(..)
 206             | InstanceDef::ClosureOnceShim { .. }
 207             | InstanceDef::DropGlue(..)
 208             | InstanceDef::CloneShim(..) => return Ok(()),
 209         }
 210
 211         if self.tcx.is_constructor(callee.def_id()) {
 212             trace!("constructors always have MIR");
 213             // Constructor functions cannot cause a query cycle.
 214             return Ok(());
 215         }
 216
 217         if let Some(callee_def_id) = callee.def_id().as_local() {
 218             let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
 219             // Avoid inlining into generators,
 220             // since their `optimized_mir` is used for layout computation, which can
 221             // create a cycle, even when no attempt is made to inline the function
 222             // in the other direction.
 223             if caller_body.generator.is_some() {
 224                 return Err("local generator (query cycle avoidance)");
 225             }
 226
 227             // Avoid a cycle here by only using `instance_mir` only if we have
 228             // a lower `HirId` than the callee. This ensures that the callee will
 229             // not inline us. This trick only works without incremental compilation.
 230             // So don't do it if that is enabled.
 231             if !self.tcx.dep_graph.is_fully_enabled() && self.hir_id < callee_hir_id {
 232                 return Ok(());
 233             }
 234
 235             // If we know for sure that the function we're calling will itself try to
 236             // call us, then we avoid inlining that function.
 237             if self
 238                 .tcx
 239                 .mir_callgraph_reachable((*callee, caller_body.source.def_id().expect_local()))
 240             {
 241                 return Err("caller might be reachable from callee (query cycle avoidance)");
 242             }
 243
 244             Ok(())
 245         } else {
 246             // This cannot result in an immediate cycle since the callee MIR is from another crate
 247             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 248             // not need to catch this here, we can wait until the inliner decides to continue
 249             // inlining a second time.
 250             trace!("functions from other crates always have MIR");
 251             Ok(())
 252         }
 253     }
 254
 255     fn resolve_callsite(
 256         &self,
 257         caller_body: &Body<'tcx>,
 258         bb: BasicBlock,
 259         bb_data: &BasicBlockData<'tcx>,
 260     ) -> Option<CallSite<'tcx>> {
 261         // Only consider direct calls to functions
 262         let terminator = bb_data.terminator();
 263         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 264             let func_ty = func.ty(caller_body, self.tcx);
 265             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 266                 // To resolve an instance its substs have to be fully normalized.
 267                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 268                 let callee =
 269                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 270
 271                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 272                     return None;
 273                 }
 274
 275                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 276
 277                 return Some(CallSite {
 278                     callee,
 279                     fn_sig,
 280                     block: bb,
 281                     target: destination.map(|(_, target)| target),
 282                     source_info: terminator.source_info,
 283                 });
 284             }
 285         }
 286
 287         None
 288     }
 289
 290     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 291     /// indicates that inlining decision should be based on other criteria.
 292     fn check_codegen_attributes(
 293         &self,
 294         callsite: &CallSite<'tcx>,
 295         callee_attrs: &CodegenFnAttrs,
 296     ) -> Result<(), &'satic str> {
 297         if let InlineAttr::Never = callee_attrs.inline {
 298             return Err("never inline hint");
 299         }
 300
 301         // Only inline local functions if they would be eligible for cross-crate
 302         // inlining. This is to ensure that the final crate doesn't have MIR that
 303         // reference unexported symbols
 304         if callsite.callee.def_id().is_local() {
 305             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 306             if !is_generic && !callee_attrs.requests_inline() {
 307                 return Err("not exported");
 308             }
 309         }
 310
 311         if callsite.fn_sig.c_variadic() {
 312             return Err("C variadic");
 313         }
 314
 315         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 316             return Err("naked");
 317         }
 318
 319         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 320             return Err("cold");
 321         }
 322
 323         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 324             return Err("incompatible sanitizer set");
 325         }
 326
 327         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 328             return Err("incompatible instruction set");
 329         }
 330
 331         for feature in &callee_attrs.target_features {
 332             if !self.codegen_fn_attrs.target_features.contains(feature) {
 333                 return Err("incompatible target feature");
 334             }
 335         }
 336
 337         Ok(())
 338     }
 339
 340     /// Returns inlining decision that is based on the examination of callee MIR body.
 341     /// Assumes that codegen attributes have been checked for compatibility already.
 342     #[instrument(level = "debug", skip(self, callee_body))]
 343     fn check_mir_body(
 344         &self,
 345         callsite: &CallSite<'tcx>,
 346         callee_body: &Body<'tcx>,
 347         callee_attrs: &CodegenFnAttrs,
 348     ) -> Result<(), &'static str> {
 349         let tcx = self.tcx;
 350
 351         let mut threshold = if callee_attrs.requests_inline() {
 352             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 353         } else {
 354             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 355         };
 356
 357         // Give a bonus functions with a small number of blocks,
 358         // We normally have two or three blocks for even
 359         // very small functions.
 360         if callee_body.basic_blocks().len() <= 3 {
 361             threshold += threshold / 4;
 362         }
 363         debug!("    final inline threshold = {}", threshold);
 364
 365         // FIXME: Give a bonus to functions with only a single caller
 366         let mut first_block = true;
 367         let mut cost = 0;
 368
 369         // Traverse the MIR manually so we can account for the effects of
 370         // inlining on the CFG.
 371         let mut work_list = vec![START_BLOCK];
 372         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 373         while let Some(bb) = work_list.pop() {
 374             if !visited.insert(bb.index()) {
 375                 continue;
 376             }
 377             let blk = &callee_body.basic_blocks()[bb];
 378
 379             for stmt in &blk.statements {
 380                 // Don't count StorageLive/StorageDead in the inlining cost.
 381                 match stmt.kind {
 382                     StatementKind::StorageLive(_)
 383                     | StatementKind::StorageDead(_)
 384                     | StatementKind::Nop => {}
 385                     _ => cost += INSTR_COST,
 386                 }
 387             }
 388             let term = blk.terminator();
 389             let mut is_drop = false;
 390             match term.kind {
 391                 TerminatorKind::Drop { ref place, target, unwind }
 392                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 393                     is_drop = true;
 394                     work_list.push(target);
 395                     // If the place doesn't actually need dropping, treat it like
 396                     // a regular goto.
 397                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 398                     if ty.needs_drop(tcx, self.param_env) {
 399                         cost += CALL_PENALTY;
 400                         if let Some(unwind) = unwind {
 401                             cost += LANDINGPAD_PENALTY;
 402                             work_list.push(unwind);
 403                         }
 404                     } else {
 405                         cost += INSTR_COST;
 406                     }
 407                 }
 408
 409                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 410                     if first_block =>
 411                 {
 412                     // If the function always diverges, don't inline
 413                     // unless the cost is zero
 414                     threshold = 0;
 415                 }
 416
 417                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 418                     if let ty::FnDef(def_id, substs) =
 419                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty).kind()
 420                     {
 421                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 422                         if let Ok(Some(instance)) =
 423                             Instance::resolve(self.tcx, self.param_env, def_id, substs)
 424                         {
 425                             if callsite.callee.def_id() == instance.def_id() {
 426                                 return Err("self-recursion");
 427                             } else if self.history.contains(&instance) {
 428                                 return Err("already inlined");
 429                             }
 430                         }
 431                         // Don't give intrinsics the extra penalty for calls
 432                         let f = tcx.fn_sig(def_id);
 433                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 434                             cost += INSTR_COST;
 435                         } else {
 436                             cost += CALL_PENALTY;
 437                         }
 438                     } else {
 439                         cost += CALL_PENALTY;
 440                     }
 441                     if cleanup.is_some() {
 442                         cost += LANDINGPAD_PENALTY;
 443                     }
 444                 }
 445                 TerminatorKind::Assert { cleanup, .. } => {
 446                     cost += CALL_PENALTY;
 447
 448                     if cleanup.is_some() {
 449                         cost += LANDINGPAD_PENALTY;
 450                     }
 451                 }
 452                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 453                 _ => cost += INSTR_COST,
 454             }
 455
 456             if !is_drop {
 457                 for &succ in term.successors() {
 458                     work_list.push(succ);
 459                 }
 460             }
 461
 462             first_block = false;
 463         }
 464
 465         // Count up the cost of local variables and temps, if we know the size
 466         // use that, otherwise we use a moderately-large dummy cost.
 467
 468         let ptr_size = tcx.data_layout.pointer_size.bytes();
 469
 470         for v in callee_body.vars_and_temps_iter() {
 471             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 472             // Cost of the var is the size in machine-words, if we know
 473             // it.
 474             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 475                 cost += ((size + ptr_size - 1) / ptr_size) as usize;
 476             } else {
 477                 cost += UNKNOWN_SIZE_COST;
 478             }
 479         }
 480
 481         if let InlineAttr::Always = callee_attrs.inline {
 482             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 483             Ok(())
 484         } else {
 485             if cost <= threshold {
 486                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 487                 Ok(())
 488             } else {
 489                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 490                 Err("cost above threshold")
 491             }
 492         }
 493     }
 494
 495     fn inline_call(
 496         &self,
 497         caller_body: &mut Body<'tcx>,
 498         callsite: &CallSite<'tcx>,
 499         mut callee_body: Body<'tcx>,
 500     ) {
 501         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 502         match terminator.kind {
 503             TerminatorKind::Call { args, destination, cleanup, .. } => {
 504                 // If the call is something like `a[*i] = f(i)`, where
 505                 // `i : &mut usize`, then just duplicating the `a[*i]`
 506                 // Place could result in two different locations if `f`
 507                 // writes to `i`. To prevent this we need to create a temporary
 508                 // borrow of the place and pass the destination as `*temp` instead.
 509                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 510                     for elem in place.projection.iter() {
 511                         match elem {
 512                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 513                             _ => {}
 514                         }
 515                     }
 516
 517                     false
 518                 }
 519
 520                 let dest = if let Some((destination_place, _)) = destination {
 521                     if dest_needs_borrow(destination_place) {
 522                         trace!("creating temp for return destination");
 523                         let dest = Rvalue::Ref(
 524                             self.tcx.lifetimes.re_erased,
 525                             BorrowKind::Mut { allow_two_phase_borrow: false },
 526                             destination_place,
 527                         );
 528                         let dest_ty = dest.ty(caller_body, self.tcx);
 529                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 530                         caller_body[callsite.block].statements.push(Statement {
 531                             source_info: callsite.source_info,
 532                             kind: StatementKind::Assign(box (temp, dest)),
 533                         });
 534                         self.tcx.mk_place_deref(temp)
 535                     } else {
 536                         destination_place
 537                     }
 538                 } else {
 539                     trace!("creating temp for return place");
 540                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 541                 };
 542
 543                 // Copy the arguments if needed.
 544                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 545
 546                 let mut integrator = Integrator {
 547                     args: &args,
 548                     new_locals: Local::new(caller_body.local_decls.len())..,
 549                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 550                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 551                     destination: dest,
 552                     return_block: callsite.target,
 553                     cleanup_block: cleanup,
 554                     in_cleanup_block: false,
 555                     tcx: self.tcx,
 556                     callsite_span: callsite.source_info.span,
 557                     body_span: callee_body.span,
 558                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 559                 };
 560
 561                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 562                 // (or existing ones, in a few special cases) in the caller.
 563                 integrator.visit_body(&mut callee_body);
 564
 565                 for scope in &mut callee_body.source_scopes {
 566                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 567                     if scope.parent_scope.is_none() {
 568                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 569
 570                         // Attach the outermost callee scope as a child of the callsite
 571                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 572                         scope.parent_scope = Some(callsite.source_info.scope);
 573                         assert_eq!(scope.inlined_parent_scope, None);
 574                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 575                             Some(callsite.source_info.scope)
 576                         } else {
 577                             callsite_scope.inlined_parent_scope
 578                         };
 579
 580                         // Mark the outermost callee scope as an inlined one.
 581                         assert_eq!(scope.inlined, None);
 582                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 583                     } else if scope.inlined_parent_scope.is_none() {
 584                         // Make it easy to find the scope with `inlined` set above.
 585                         scope.inlined_parent_scope =
 586                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 587                     }
 588                 }
 589
 590                 // If there are any locals without storage markers, give them storage only for the
 591                 // duration of the call.
 592                 for local in callee_body.vars_and_temps_iter() {
 593                     if integrator.always_live_locals.contains(local) {
 594                         let new_local = integrator.map_local(local);
 595                         caller_body[callsite.block].statements.push(Statement {
 596                             source_info: callsite.source_info,
 597                             kind: StatementKind::StorageLive(new_local),
 598                         });
 599                     }
 600                 }
 601                 if let Some(block) = callsite.target {
 602                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 603                     // the slice once.
 604                     let mut n = 0;
 605                     for local in callee_body.vars_and_temps_iter().rev() {
 606                         if integrator.always_live_locals.contains(local) {
 607                             let new_local = integrator.map_local(local);
 608                             caller_body[block].statements.push(Statement {
 609                                 source_info: callsite.source_info,
 610                                 kind: StatementKind::StorageDead(new_local),
 611                             });
 612                             n += 1;
 613                         }
 614                     }
 615                     caller_body[block].statements.rotate_right(n);
 616                 }
 617
 618                 // Insert all of the (mapped) parts of the callee body into the caller.
 619                 caller_body.local_decls.extend(
 620                     // FIXME(eddyb) make `Range<Local>` iterable so that we can use
 621                     // `callee_body.local_decls.drain(callee_body.vars_and_temps())`
 622                     callee_body
 623                         .vars_and_temps_iter()
 624                         .map(|local| callee_body.local_decls[local].clone()),
 625                 );
 626                 caller_body.source_scopes.extend(callee_body.source_scopes.drain(..));
 627                 caller_body.var_debug_info.extend(callee_body.var_debug_info.drain(..));
 628                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 629
 630                 caller_body[callsite.block].terminator = Some(Terminator {
 631                     source_info: callsite.source_info,
 632                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 633                 });
 634
 635                 // Copy only unevaluated constants from the callee_body into the caller_body.
 636                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 637                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 638                 // because we are calling `subst_and_normalize_erasing_regions`.
 639                 caller_body.required_consts.extend(
 640                     callee_body.required_consts.iter().copied().filter(|&constant| {
 641                         matches!(constant.literal.val, ConstKind::Unevaluated(_, _, _))
 642                     }),
 643                 );
 644             }
 645             kind => bug!("unexpected terminator kind {:?}", kind),
 646         }
 647     }
 648
 649     fn make_call_args(
 650         &self,
 651         args: Vec<Operand<'tcx>>,
 652         callsite: &CallSite<'tcx>,
 653         caller_body: &mut Body<'tcx>,
 654         callee_body: &Body<'tcx>,
 655     ) -> Vec<Local> {
 656         let tcx = self.tcx;
 657
 658         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 659         // The caller provides the arguments wrapped up in a tuple:
 660         //
 661         //     tuple_tmp = (a, b, c)
 662         //     Fn::call(closure_ref, tuple_tmp)
 663         //
 664         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 665         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 666         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 667         // a vector like
 668         //
 669         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 670         //
 671         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 672         // if we "spill" that into *another* temporary, so that we can map the argument
 673         // variable in the callee MIR directly to an argument variable on our side.
 674         // So we introduce temporaries like:
 675         //
 676         //     tmp0 = tuple_tmp.0
 677         //     tmp1 = tuple_tmp.1
 678         //     tmp2 = tuple_tmp.2
 679         //
 680         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 681         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 682             let mut args = args.into_iter();
 683             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 684             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 685             assert!(args.next().is_none());
 686
 687             let tuple = Place::from(tuple);
 688             let tuple_tys = if let ty::Tuple(s) = tuple.ty(caller_body, tcx).ty.kind() {
 689                 s
 690             } else {
 691                 bug!("Closure arguments are not passed as a tuple");
 692             };
 693
 694             // The `closure_ref` in our example above.
 695             let closure_ref_arg = iter::once(self_);
 696
 697             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 698             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 699                 // This is e.g., `tuple_tmp.0` in our example above.
 700                 let tuple_field =
 701                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 702
 703                 // Spill to a local to make e.g., `tmp0`.
 704                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 705             });
 706
 707             closure_ref_arg.chain(tuple_tmp_args).collect()
 708         } else {
 709             args.into_iter()
 710                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 711                 .collect()
 712         }
 713     }
 714
 715     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 716     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 717     fn create_temp_if_necessary(
 718         &self,
 719         arg: Operand<'tcx>,
 720         callsite: &CallSite<'tcx>,
 721         caller_body: &mut Body<'tcx>,
 722     ) -> Local {
 723         // Reuse the operand if it is a moved temporary.
 724         if let Operand::Move(place) = &arg {
 725             if let Some(local) = place.as_local() {
 726                 if caller_body.local_kind(local) == LocalKind::Temp {
 727                     return local;
 728                 }
 729             }
 730         }
 731
 732         // Otherwise, create a temporary for the argument.
 733         trace!("creating temp for argument {:?}", arg);
 734         let arg_ty = arg.ty(caller_body, self.tcx);
 735         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 736         caller_body[callsite.block].statements.push(Statement {
 737             source_info: callsite.source_info,
 738             kind: StatementKind::Assign(box (Place::from(local), Rvalue::Use(arg))),
 739         });
 740         local
 741     }
 742
 743     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 744     fn new_call_temp(
 745         &self,
 746         caller_body: &mut Body<'tcx>,
 747         callsite: &CallSite<'tcx>,
 748         ty: Ty<'tcx>,
 749     ) -> Local {
 750         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 751
 752         caller_body[callsite.block].statements.push(Statement {
 753             source_info: callsite.source_info,
 754             kind: StatementKind::StorageLive(local),
 755         });
 756
 757         if let Some(block) = callsite.target {
 758             caller_body[block].statements.insert(
 759                 0,
 760                 Statement {
 761                     source_info: callsite.source_info,
 762                     kind: StatementKind::StorageDead(local),
 763                 },
 764             );
 765         }
 766
 767         local
 768     }
 769 }
 770
 771 fn type_size_of<'tcx>(
 772     tcx: TyCtxt<'tcx>,
 773     param_env: ty::ParamEnv<'tcx>,
 774     ty: Ty<'tcx>,
 775 ) -> Option<u64> {
 776     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 777 }
 778
 779 /**
 780  * Integrator.
 781  *
 782  * Integrates blocks from the callee function into the calling function.
 783  * Updates block indices, references to locals and other control flow
 784  * stuff.
 785 */
 786 struct Integrator<'a, 'tcx> {
 787     args: &'a [Local],
 788     new_locals: RangeFrom<Local>,
 789     new_scopes: RangeFrom<SourceScope>,
 790     new_blocks: RangeFrom<BasicBlock>,
 791     destination: Place<'tcx>,
 792     return_block: Option<BasicBlock>,
 793     cleanup_block: Option<BasicBlock>,
 794     in_cleanup_block: bool,
 795     tcx: TyCtxt<'tcx>,
 796     callsite_span: Span,
 797     body_span: Span,
 798     always_live_locals: BitSet<Local>,
 799 }
 800
 801 impl<'a, 'tcx> Integrator<'a, 'tcx> {
 802     fn map_local(&self, local: Local) -> Local {
 803         let new = if local == RETURN_PLACE {
 804             self.destination.local
 805         } else {
 806             let idx = local.index() - 1;
 807             if idx < self.args.len() {
 808                 self.args[idx]
 809             } else {
 810                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 811             }
 812         };
 813         trace!("mapping local `{:?}` to `{:?}`", local, new);
 814         new
 815     }
 816
 817     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 818         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 819         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 820         new
 821     }
 822
 823     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 824         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 825         trace!("mapping block `{:?}` to `{:?}`", block, new);
 826         new
 827     }
 828 }
 829
 830 impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
 831     fn tcx(&self) -> TyCtxt<'tcx> {
 832         self.tcx
 833     }
 834
 835     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 836         *local = self.map_local(*local);
 837     }
 838
 839     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 840         *scope = self.map_scope(*scope);
 841     }
 842
 843     fn visit_span(&mut self, span: &mut Span) {
 844         let mut expn_data =
 845             ExpnData::default(ExpnKind::Inlined, *span, self.tcx.sess.edition(), None);
 846         expn_data.def_site = self.body_span;
 847         // Make sure that all spans track the fact that they were inlined.
 848         *span = self.callsite_span.fresh_expansion(expn_data);
 849     }
 850
 851     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 852         for elem in place.projection {
 853             // FIXME: Make sure that return place is not used in an indexing projection, since it
 854             // won't be rebased as it is supposed to be.
 855             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 856         }
 857
 858         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 859         let dest_proj_len = self.destination.projection.len();
 860         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 861             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 862             projs.extend(self.destination.projection);
 863             projs.extend(place.projection);
 864
 865             place.projection = self.tcx.intern_place_elems(&*projs);
 866         }
 867         // Handles integrating any locals that occur in the base
 868         // or projections
 869         self.super_place(place, context, location)
 870     }
 871
 872     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 873         self.in_cleanup_block = data.is_cleanup;
 874         self.super_basic_block_data(block, data);
 875         self.in_cleanup_block = false;
 876     }
 877
 878     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 879         self.super_retag(kind, place, loc);
 880
 881         // We have to patch all inlined retags to be aware that they are no longer
 882         // happening on function entry.
 883         if *kind == RetagKind::FnEntry {
 884             *kind = RetagKind::Default;
 885         }
 886     }
 887
 888     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 889         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 890             statement.kind
 891         {
 892             self.always_live_locals.remove(local);
 893         }
 894         self.super_statement(statement, location);
 895     }
 896
 897     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 898         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 899         // replaced down below anyways).
 900         if !matches!(terminator.kind, TerminatorKind::Return) {
 901             self.super_terminator(terminator, loc);
 902         }
 903
 904         match terminator.kind {
 905             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 906             TerminatorKind::Goto { ref mut target } => {
 907                 *target = self.map_block(*target);
 908             }
 909             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 910                 for tgt in targets.all_targets_mut() {
 911                     *tgt = self.map_block(*tgt);
 912                 }
 913             }
 914             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 915             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 916                 *target = self.map_block(*target);
 917                 if let Some(tgt) = *unwind {
 918                     *unwind = Some(self.map_block(tgt));
 919                 } else if !self.in_cleanup_block {
 920                     // Unless this drop is in a cleanup block, add an unwind edge to
 921                     // the original call's cleanup block
 922                     *unwind = self.cleanup_block;
 923                 }
 924             }
 925             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 926                 if let Some((_, ref mut tgt)) = *destination {
 927                     *tgt = self.map_block(*tgt);
 928                 }
 929                 if let Some(tgt) = *cleanup {
 930                     *cleanup = Some(self.map_block(tgt));
 931                 } else if !self.in_cleanup_block {
 932                     // Unless this call is in a cleanup block, add an unwind edge to
 933                     // the original call's cleanup block
 934                     *cleanup = self.cleanup_block;
 935                 }
 936             }
 937             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 938                 *target = self.map_block(*target);
 939                 if let Some(tgt) = *cleanup {
 940                     *cleanup = Some(self.map_block(tgt));
 941                 } else if !self.in_cleanup_block {
 942                     // Unless this assert is in a cleanup block, add an unwind edge to
 943                     // the original call's cleanup block
 944                     *cleanup = self.cleanup_block;
 945                 }
 946             }
 947             TerminatorKind::Return => {
 948                 terminator.kind = if let Some(tgt) = self.return_block {
 949                     TerminatorKind::Goto { target: tgt }
 950                 } else {
 951                     TerminatorKind::Unreachable
 952                 }
 953             }
 954             TerminatorKind::Resume => {
 955                 if let Some(tgt) = self.cleanup_block {
 956                     terminator.kind = TerminatorKind::Goto { target: tgt }
 957                 }
 958             }
 959             TerminatorKind::Abort => {}
 960             TerminatorKind::Unreachable => {}
 961             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 962                 *real_target = self.map_block(*real_target);
 963                 *imaginary_target = self.map_block(*imaginary_target);
 964             }
 965             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 966             // see the ordering of passes in the optimized_mir query.
 967             {
 968                 bug!("False unwinds should have been removed before inlining")
 969             }
 970             TerminatorKind::InlineAsm { ref mut destination, .. } => {
 971                 if let Some(ref mut tgt) = *destination {
 972                     *tgt = self.map_block(*tgt);
 973                 }
 974             }
 975         }
 976     }
 977 }