compiler/rustc_mir_transform/src/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::traits::ObligationCause;
  11 use rustc_middle::ty::subst::Subst;
  12 use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
  13 use rustc_span::{hygiene::ExpnKind, ExpnData, LocalExpnId, Span};
  14 use rustc_target::spec::abi::Abi;
  15
  16 use super::simplify::{remove_dead_blocks, CfgSimplifier};
  17 use crate::MirPass;
  18 use std::iter;
  19 use std::ops::{Range, RangeFrom};
  20
  21 crate mod cycle;
  22
  23 const INSTR_COST: usize = 5;
  24 const CALL_PENALTY: usize = 25;
  25 const LANDINGPAD_PENALTY: usize = 50;
  26 const RESUME_PENALTY: usize = 45;
  27
  28 const UNKNOWN_SIZE_COST: usize = 10;
  29
  30 pub struct Inline;
  31
  32 #[derive(Copy, Clone, Debug)]
  33 struct CallSite<'tcx> {
  34     callee: Instance<'tcx>,
  35     fn_sig: ty::PolyFnSig<'tcx>,
  36     block: BasicBlock,
  37     target: Option<BasicBlock>,
  38     source_info: SourceInfo,
  39 }
  40
  41 impl<'tcx> MirPass<'tcx> for Inline {
  42     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
  43         if let Some(enabled) = sess.opts.debugging_opts.inline_mir {
  44             return enabled;
  45         }
  46
  47         sess.opts.mir_opt_level() >= 3
  48     }
  49
  50     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  51         let span = trace_span!("inline", body = %tcx.def_path_str(body.source.def_id()));
  52         let _guard = span.enter();
  53         if inline(tcx, body) {
  54             debug!("running simplify cfg on {:?}", body.source);
  55             CfgSimplifier::new(body).simplify();
  56             remove_dead_blocks(tcx, body);
  57         }
  58     }
  59 }
  60
  61 fn inline<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  62     let def_id = body.source.def_id();
  63     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  64
  65     // Only do inlining into fn bodies.
  66     if !tcx.hir().body_owner_kind(hir_id).is_fn_or_closure() {
  67         return false;
  68     }
  69     if body.source.promoted.is_some() {
  70         return false;
  71     }
  72     // Avoid inlining into generators, since their `optimized_mir` is used for layout computation,
  73     // which can create a cycle, even when no attempt is made to inline the function in the other
  74     // direction.
  75     if body.generator.is_some() {
  76         return false;
  77     }
  78
  79     let param_env = tcx.param_env_reveal_all_normalized(def_id);
  80     let param_env = rustc_trait_selection::traits::normalize_param_env_or_error(
  81         tcx,
  82         def_id,
  83         param_env,
  84         ObligationCause::misc(body.span, hir_id),
  85     );
  86
  87     let mut this = Inliner {
  88         tcx,
  89         param_env,
  90         codegen_fn_attrs: tcx.codegen_fn_attrs(def_id),
  91         hir_id,
  92         history: Vec::new(),
  93         changed: false,
  94     };
  95     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  96     this.process_blocks(body, blocks);
  97     this.changed
  98 }
  99
 100 struct Inliner<'tcx> {
 101     tcx: TyCtxt<'tcx>,
 102     param_env: ParamEnv<'tcx>,
 103     /// Caller codegen attributes.
 104     codegen_fn_attrs: &'tcx CodegenFnAttrs,
 105     /// Caller HirID.
 106     hir_id: hir::HirId,
 107     /// Stack of inlined Instances.
 108     history: Vec<ty::Instance<'tcx>>,
 109     /// Indicates that the caller body has been modified.
 110     changed: bool,
 111 }
 112
 113 impl<'tcx> Inliner<'tcx> {
 114     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 115         for bb in blocks {
 116             let bb_data = &caller_body[bb];
 117             if bb_data.is_cleanup {
 118                 continue;
 119             }
 120
 121             let Some(callsite) = self.resolve_callsite(caller_body, bb, bb_data) else {
 122                 continue;
 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 {:?}", callsite.callee, caller_body.source)
 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 a cycle here by only using `instance_mir` only if we have
 220             // a lower `HirId` than the callee. This ensures that the callee will
 221             // not inline us. This trick only works without incremental compilation.
 222             // So don't do it if that is enabled.
 223             if !self.tcx.dep_graph.is_fully_enabled() && self.hir_id.index() < callee_hir_id.index()
 224             {
 225                 return Ok(());
 226             }
 227
 228             // If we know for sure that the function we're calling will itself try to
 229             // call us, then we avoid inlining that function.
 230             if self
 231                 .tcx
 232                 .mir_callgraph_reachable((*callee, caller_body.source.def_id().expect_local()))
 233             {
 234                 return Err("caller might be reachable from callee (query cycle avoidance)");
 235             }
 236
 237             Ok(())
 238         } else {
 239             // This cannot result in an immediate cycle since the callee MIR is from another crate
 240             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 241             // not need to catch this here, we can wait until the inliner decides to continue
 242             // inlining a second time.
 243             trace!("functions from other crates always have MIR");
 244             Ok(())
 245         }
 246     }
 247
 248     fn resolve_callsite(
 249         &self,
 250         caller_body: &Body<'tcx>,
 251         bb: BasicBlock,
 252         bb_data: &BasicBlockData<'tcx>,
 253     ) -> Option<CallSite<'tcx>> {
 254         // Only consider direct calls to functions
 255         let terminator = bb_data.terminator();
 256         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 257             let func_ty = func.ty(caller_body, self.tcx);
 258             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 259                 // To resolve an instance its substs have to be fully normalized.
 260                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 261                 let callee =
 262                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 263
 264                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 265                     return None;
 266                 }
 267
 268                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 269
 270                 return Some(CallSite {
 271                     callee,
 272                     fn_sig,
 273                     block: bb,
 274                     target: destination.map(|(_, target)| target),
 275                     source_info: terminator.source_info,
 276                 });
 277             }
 278         }
 279
 280         None
 281     }
 282
 283     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 284     /// indicates that inlining decision should be based on other criteria.
 285     fn check_codegen_attributes(
 286         &self,
 287         callsite: &CallSite<'tcx>,
 288         callee_attrs: &CodegenFnAttrs,
 289     ) -> Result<(), &'static str> {
 290         if let InlineAttr::Never = callee_attrs.inline {
 291             return Err("never inline hint");
 292         }
 293
 294         // Only inline local functions if they would be eligible for cross-crate
 295         // inlining. This is to ensure that the final crate doesn't have MIR that
 296         // reference unexported symbols
 297         if callsite.callee.def_id().is_local() {
 298             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 299             if !is_generic && !callee_attrs.requests_inline() {
 300                 return Err("not exported");
 301             }
 302         }
 303
 304         if callsite.fn_sig.c_variadic() {
 305             return Err("C variadic");
 306         }
 307
 308         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 309             return Err("naked");
 310         }
 311
 312         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 313             return Err("cold");
 314         }
 315
 316         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 317             return Err("incompatible sanitizer set");
 318         }
 319
 320         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 321             return Err("incompatible instruction set");
 322         }
 323
 324         for feature in &callee_attrs.target_features {
 325             if !self.codegen_fn_attrs.target_features.contains(feature) {
 326                 return Err("incompatible target feature");
 327             }
 328         }
 329
 330         Ok(())
 331     }
 332
 333     /// Returns inlining decision that is based on the examination of callee MIR body.
 334     /// Assumes that codegen attributes have been checked for compatibility already.
 335     #[instrument(level = "debug", skip(self, callee_body))]
 336     fn check_mir_body(
 337         &self,
 338         callsite: &CallSite<'tcx>,
 339         callee_body: &Body<'tcx>,
 340         callee_attrs: &CodegenFnAttrs,
 341     ) -> Result<(), &'static str> {
 342         let tcx = self.tcx;
 343
 344         let mut threshold = if callee_attrs.requests_inline() {
 345             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 346         } else {
 347             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 348         };
 349
 350         // Give a bonus functions with a small number of blocks,
 351         // We normally have two or three blocks for even
 352         // very small functions.
 353         if callee_body.basic_blocks().len() <= 3 {
 354             threshold += threshold / 4;
 355         }
 356         debug!("    final inline threshold = {}", threshold);
 357
 358         // FIXME: Give a bonus to functions with only a single caller
 359         let mut first_block = true;
 360         let mut cost = 0;
 361
 362         // Traverse the MIR manually so we can account for the effects of
 363         // inlining on the CFG.
 364         let mut work_list = vec![START_BLOCK];
 365         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 366         while let Some(bb) = work_list.pop() {
 367             if !visited.insert(bb.index()) {
 368                 continue;
 369             }
 370             let blk = &callee_body.basic_blocks()[bb];
 371
 372             for stmt in &blk.statements {
 373                 // Don't count StorageLive/StorageDead in the inlining cost.
 374                 match stmt.kind {
 375                     StatementKind::StorageLive(_)
 376                     | StatementKind::StorageDead(_)
 377                     | StatementKind::Nop => {}
 378                     _ => cost += INSTR_COST,
 379                 }
 380             }
 381             let term = blk.terminator();
 382             let mut is_drop = false;
 383             match term.kind {
 384                 TerminatorKind::Drop { ref place, target, unwind }
 385                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 386                     is_drop = true;
 387                     work_list.push(target);
 388                     // If the place doesn't actually need dropping, treat it like
 389                     // a regular goto.
 390                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 391                     if ty.needs_drop(tcx, self.param_env) {
 392                         cost += CALL_PENALTY;
 393                         if let Some(unwind) = unwind {
 394                             cost += LANDINGPAD_PENALTY;
 395                             work_list.push(unwind);
 396                         }
 397                     } else {
 398                         cost += INSTR_COST;
 399                     }
 400                 }
 401
 402                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 403                     if first_block =>
 404                 {
 405                     // If the function always diverges, don't inline
 406                     // unless the cost is zero
 407                     threshold = 0;
 408                 }
 409
 410                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 411                     if let ty::FnDef(def_id, substs) =
 412                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty()).kind()
 413                     {
 414                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 415                         if let Ok(Some(instance)) =
 416                             Instance::resolve(self.tcx, self.param_env, def_id, substs)
 417                         {
 418                             if callsite.callee.def_id() == instance.def_id() {
 419                                 return Err("self-recursion");
 420                             } else if self.history.contains(&instance) {
 421                                 return Err("already inlined");
 422                             }
 423                         }
 424                         // Don't give intrinsics the extra penalty for calls
 425                         let f = tcx.fn_sig(def_id);
 426                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 427                             cost += INSTR_COST;
 428                         } else {
 429                             cost += CALL_PENALTY;
 430                         }
 431                     } else {
 432                         cost += CALL_PENALTY;
 433                     }
 434                     if cleanup.is_some() {
 435                         cost += LANDINGPAD_PENALTY;
 436                     }
 437                 }
 438                 TerminatorKind::Assert { cleanup, .. } => {
 439                     cost += CALL_PENALTY;
 440
 441                     if cleanup.is_some() {
 442                         cost += LANDINGPAD_PENALTY;
 443                     }
 444                 }
 445                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 446                 TerminatorKind::InlineAsm { cleanup, .. } => {
 447                     cost += INSTR_COST;
 448
 449                     if cleanup.is_some() {
 450                         cost += LANDINGPAD_PENALTY;
 451                     }
 452                 }
 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::new((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 expn_data = ExpnData::default(
 547                     ExpnKind::Inlined,
 548                     callsite.source_info.span,
 549                     self.tcx.sess.edition(),
 550                     None,
 551                     None,
 552                 );
 553                 expn_data.def_site = callee_body.span;
 554                 let expn_data =
 555                     LocalExpnId::fresh(expn_data, self.tcx.create_stable_hashing_context());
 556                 let mut integrator = Integrator {
 557                     args: &args,
 558                     new_locals: Local::new(caller_body.local_decls.len())..,
 559                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 560                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 561                     destination: dest,
 562                     return_block: callsite.target,
 563                     cleanup_block: cleanup,
 564                     in_cleanup_block: false,
 565                     tcx: self.tcx,
 566                     expn_data,
 567                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 568                 };
 569
 570                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 571                 // (or existing ones, in a few special cases) in the caller.
 572                 integrator.visit_body(&mut callee_body);
 573
 574                 for scope in &mut callee_body.source_scopes {
 575                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 576                     if scope.parent_scope.is_none() {
 577                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 578
 579                         // Attach the outermost callee scope as a child of the callsite
 580                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 581                         scope.parent_scope = Some(callsite.source_info.scope);
 582                         assert_eq!(scope.inlined_parent_scope, None);
 583                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 584                             Some(callsite.source_info.scope)
 585                         } else {
 586                             callsite_scope.inlined_parent_scope
 587                         };
 588
 589                         // Mark the outermost callee scope as an inlined one.
 590                         assert_eq!(scope.inlined, None);
 591                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 592                     } else if scope.inlined_parent_scope.is_none() {
 593                         // Make it easy to find the scope with `inlined` set above.
 594                         scope.inlined_parent_scope =
 595                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 596                     }
 597                 }
 598
 599                 // If there are any locals without storage markers, give them storage only for the
 600                 // duration of the call.
 601                 for local in callee_body.vars_and_temps_iter() {
 602                     if integrator.always_live_locals.contains(local) {
 603                         let new_local = integrator.map_local(local);
 604                         caller_body[callsite.block].statements.push(Statement {
 605                             source_info: callsite.source_info,
 606                             kind: StatementKind::StorageLive(new_local),
 607                         });
 608                     }
 609                 }
 610                 if let Some(block) = callsite.target {
 611                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 612                     // the slice once.
 613                     let mut n = 0;
 614                     for local in callee_body.vars_and_temps_iter().rev() {
 615                         if integrator.always_live_locals.contains(local) {
 616                             let new_local = integrator.map_local(local);
 617                             caller_body[block].statements.push(Statement {
 618                                 source_info: callsite.source_info,
 619                                 kind: StatementKind::StorageDead(new_local),
 620                             });
 621                             n += 1;
 622                         }
 623                     }
 624                     caller_body[block].statements.rotate_right(n);
 625                 }
 626
 627                 // Insert all of the (mapped) parts of the callee body into the caller.
 628                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 629                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 630                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 631                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 632
 633                 caller_body[callsite.block].terminator = Some(Terminator {
 634                     source_info: callsite.source_info,
 635                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 636                 });
 637
 638                 // Copy only unevaluated constants from the callee_body into the caller_body.
 639                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 640                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 641                 // because we are calling `subst_and_normalize_erasing_regions`.
 642                 caller_body.required_consts.extend(
 643                     callee_body.required_consts.iter().copied().filter(|&ct| {
 644                         match ct.literal.const_for_ty() {
 645                             Some(ct) => matches!(ct.val(), ConstKind::Unevaluated(_)),
 646                             None => true,
 647                         }
 648                     }),
 649                 );
 650             }
 651             kind => bug!("unexpected terminator kind {:?}", kind),
 652         }
 653     }
 654
 655     fn make_call_args(
 656         &self,
 657         args: Vec<Operand<'tcx>>,
 658         callsite: &CallSite<'tcx>,
 659         caller_body: &mut Body<'tcx>,
 660         callee_body: &Body<'tcx>,
 661     ) -> Vec<Local> {
 662         let tcx = self.tcx;
 663
 664         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 665         // The caller provides the arguments wrapped up in a tuple:
 666         //
 667         //     tuple_tmp = (a, b, c)
 668         //     Fn::call(closure_ref, tuple_tmp)
 669         //
 670         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 671         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 672         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 673         // a vector like
 674         //
 675         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 676         //
 677         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 678         // if we "spill" that into *another* temporary, so that we can map the argument
 679         // variable in the callee MIR directly to an argument variable on our side.
 680         // So we introduce temporaries like:
 681         //
 682         //     tmp0 = tuple_tmp.0
 683         //     tmp1 = tuple_tmp.1
 684         //     tmp2 = tuple_tmp.2
 685         //
 686         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 687         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 688             let mut args = args.into_iter();
 689             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 690             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 691             assert!(args.next().is_none());
 692
 693             let tuple = Place::from(tuple);
 694             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() else {
 695                 bug!("Closure arguments are not passed as a tuple");
 696             };
 697
 698             // The `closure_ref` in our example above.
 699             let closure_ref_arg = iter::once(self_);
 700
 701             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 702             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 703                 // This is e.g., `tuple_tmp.0` in our example above.
 704                 let tuple_field = Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty));
 705
 706                 // Spill to a local to make e.g., `tmp0`.
 707                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 708             });
 709
 710             closure_ref_arg.chain(tuple_tmp_args).collect()
 711         } else {
 712             args.into_iter()
 713                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 714                 .collect()
 715         }
 716     }
 717
 718     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 719     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 720     fn create_temp_if_necessary(
 721         &self,
 722         arg: Operand<'tcx>,
 723         callsite: &CallSite<'tcx>,
 724         caller_body: &mut Body<'tcx>,
 725     ) -> Local {
 726         // Reuse the operand if it is a moved temporary.
 727         if let Operand::Move(place) = &arg
 728             && let Some(local) = place.as_local()
 729             && caller_body.local_kind(local) == LocalKind::Temp
 730         {
 731             return local;
 732         }
 733
 734         // Otherwise, create a temporary for the argument.
 735         trace!("creating temp for argument {:?}", arg);
 736         let arg_ty = arg.ty(caller_body, self.tcx);
 737         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 738         caller_body[callsite.block].statements.push(Statement {
 739             source_info: callsite.source_info,
 740             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 741         });
 742         local
 743     }
 744
 745     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 746     fn new_call_temp(
 747         &self,
 748         caller_body: &mut Body<'tcx>,
 749         callsite: &CallSite<'tcx>,
 750         ty: Ty<'tcx>,
 751     ) -> Local {
 752         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 753
 754         caller_body[callsite.block].statements.push(Statement {
 755             source_info: callsite.source_info,
 756             kind: StatementKind::StorageLive(local),
 757         });
 758
 759         if let Some(block) = callsite.target {
 760             caller_body[block].statements.insert(
 761                 0,
 762                 Statement {
 763                     source_info: callsite.source_info,
 764                     kind: StatementKind::StorageDead(local),
 765                 },
 766             );
 767         }
 768
 769         local
 770     }
 771 }
 772
 773 fn type_size_of<'tcx>(
 774     tcx: TyCtxt<'tcx>,
 775     param_env: ty::ParamEnv<'tcx>,
 776     ty: Ty<'tcx>,
 777 ) -> Option<u64> {
 778     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 779 }
 780
 781 /**
 782  * Integrator.
 783  *
 784  * Integrates blocks from the callee function into the calling function.
 785  * Updates block indices, references to locals and other control flow
 786  * stuff.
 787 */
 788 struct Integrator<'a, 'tcx> {
 789     args: &'a [Local],
 790     new_locals: RangeFrom<Local>,
 791     new_scopes: RangeFrom<SourceScope>,
 792     new_blocks: RangeFrom<BasicBlock>,
 793     destination: Place<'tcx>,
 794     return_block: Option<BasicBlock>,
 795     cleanup_block: Option<BasicBlock>,
 796     in_cleanup_block: bool,
 797     tcx: TyCtxt<'tcx>,
 798     expn_data: LocalExpnId,
 799     always_live_locals: BitSet<Local>,
 800 }
 801
 802 impl Integrator<'_, '_> {
 803     fn map_local(&self, local: Local) -> Local {
 804         let new = if local == RETURN_PLACE {
 805             self.destination.local
 806         } else {
 807             let idx = local.index() - 1;
 808             if idx < self.args.len() {
 809                 self.args[idx]
 810             } else {
 811                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 812             }
 813         };
 814         trace!("mapping local `{:?}` to `{:?}`", local, new);
 815         new
 816     }
 817
 818     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 819         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 820         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 821         new
 822     }
 823
 824     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 825         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 826         trace!("mapping block `{:?}` to `{:?}`", block, new);
 827         new
 828     }
 829 }
 830
 831 impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
 832     fn tcx(&self) -> TyCtxt<'tcx> {
 833         self.tcx
 834     }
 835
 836     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 837         *local = self.map_local(*local);
 838     }
 839
 840     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 841         *scope = self.map_scope(*scope);
 842     }
 843
 844     fn visit_span(&mut self, span: &mut Span) {
 845         // Make sure that all spans track the fact that they were inlined.
 846         *span = span.fresh_expansion(self.expn_data);
 847     }
 848
 849     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 850         for elem in place.projection {
 851             // FIXME: Make sure that return place is not used in an indexing projection, since it
 852             // won't be rebased as it is supposed to be.
 853             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 854         }
 855
 856         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 857         let dest_proj_len = self.destination.projection.len();
 858         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 859             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 860             projs.extend(self.destination.projection);
 861             projs.extend(place.projection);
 862
 863             place.projection = self.tcx.intern_place_elems(&*projs);
 864         }
 865         // Handles integrating any locals that occur in the base
 866         // or projections
 867         self.super_place(place, context, location)
 868     }
 869
 870     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 871         self.in_cleanup_block = data.is_cleanup;
 872         self.super_basic_block_data(block, data);
 873         self.in_cleanup_block = false;
 874     }
 875
 876     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 877         self.super_retag(kind, place, loc);
 878
 879         // We have to patch all inlined retags to be aware that they are no longer
 880         // happening on function entry.
 881         if *kind == RetagKind::FnEntry {
 882             *kind = RetagKind::Default;
 883         }
 884     }
 885
 886     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 887         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 888             statement.kind
 889         {
 890             self.always_live_locals.remove(local);
 891         }
 892         self.super_statement(statement, location);
 893     }
 894
 895     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 896         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 897         // replaced down below anyways).
 898         if !matches!(terminator.kind, TerminatorKind::Return) {
 899             self.super_terminator(terminator, loc);
 900         }
 901
 902         match terminator.kind {
 903             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 904             TerminatorKind::Goto { ref mut target } => {
 905                 *target = self.map_block(*target);
 906             }
 907             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 908                 for tgt in targets.all_targets_mut() {
 909                     *tgt = self.map_block(*tgt);
 910                 }
 911             }
 912             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 913             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 914                 *target = self.map_block(*target);
 915                 if let Some(tgt) = *unwind {
 916                     *unwind = Some(self.map_block(tgt));
 917                 } else if !self.in_cleanup_block {
 918                     // Unless this drop is in a cleanup block, add an unwind edge to
 919                     // the original call's cleanup block
 920                     *unwind = self.cleanup_block;
 921                 }
 922             }
 923             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 924                 if let Some((_, ref mut tgt)) = *destination {
 925                     *tgt = self.map_block(*tgt);
 926                 }
 927                 if let Some(tgt) = *cleanup {
 928                     *cleanup = Some(self.map_block(tgt));
 929                 } else if !self.in_cleanup_block {
 930                     // Unless this call is in a cleanup block, add an unwind edge to
 931                     // the original call's cleanup block
 932                     *cleanup = self.cleanup_block;
 933                 }
 934             }
 935             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 936                 *target = self.map_block(*target);
 937                 if let Some(tgt) = *cleanup {
 938                     *cleanup = Some(self.map_block(tgt));
 939                 } else if !self.in_cleanup_block {
 940                     // Unless this assert is in a cleanup block, add an unwind edge to
 941                     // the original call's cleanup block
 942                     *cleanup = self.cleanup_block;
 943                 }
 944             }
 945             TerminatorKind::Return => {
 946                 terminator.kind = if let Some(tgt) = self.return_block {
 947                     TerminatorKind::Goto { target: tgt }
 948                 } else {
 949                     TerminatorKind::Unreachable
 950                 }
 951             }
 952             TerminatorKind::Resume => {
 953                 if let Some(tgt) = self.cleanup_block {
 954                     terminator.kind = TerminatorKind::Goto { target: tgt }
 955                 }
 956             }
 957             TerminatorKind::Abort => {}
 958             TerminatorKind::Unreachable => {}
 959             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 960                 *real_target = self.map_block(*real_target);
 961                 *imaginary_target = self.map_block(*imaginary_target);
 962             }
 963             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 964             // see the ordering of passes in the optimized_mir query.
 965             {
 966                 bug!("False unwinds should have been removed before inlining")
 967             }
 968             TerminatorKind::InlineAsm { ref mut destination, ref mut cleanup, .. } => {
 969                 if let Some(ref mut tgt) = *destination {
 970                     *tgt = self.map_block(*tgt);
 971                 } else if !self.in_cleanup_block {
 972                     // Unless this inline asm is in a cleanup block, add an unwind edge to
 973                     // the original call's cleanup block
 974                     *cleanup = self.cleanup_block;
 975                 }
 976             }
 977         }
 978     }
 979 }