compiler/rustc_mir_transform/src/inline.rs

   1 //! Inlining pass for MIR functions
   2
   3 use rustc_attr::InlineAttr;
   4 use rustc_index::bit_set::BitSet;
   5 use rustc_index::vec::Idx;
   6 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
   7 use rustc_middle::mir::visit::*;
   8 use rustc_middle::mir::*;
   9 use rustc_middle::traits::ObligationCause;
  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, LocalExpnId, Span};
  13 use rustc_target::spec::abi::Abi;
  14
  15 use super::simplify::{remove_dead_blocks, CfgSimplifier};
  16 use crate::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 impl<'tcx> MirPass<'tcx> for Inline {
  41     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
  42         if let Some(enabled) = sess.opts.debugging_opts.inline_mir {
  43             return enabled;
  44         }
  45
  46         sess.opts.mir_opt_level() >= 3
  47     }
  48
  49     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  50         let span = trace_span!("inline", body = %tcx.def_path_str(body.source.def_id()));
  51         let _guard = span.enter();
  52         if inline(tcx, body) {
  53             debug!("running simplify cfg on {:?}", body.source);
  54             CfgSimplifier::new(body).simplify();
  55             remove_dead_blocks(tcx, body);
  56         }
  57     }
  58 }
  59
  60 fn inline<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  61     let def_id = body.source.def_id().expect_local();
  62
  63     // Only do inlining into fn bodies.
  64     if !tcx.hir().body_owner_kind(def_id).is_fn_or_closure() {
  65         return false;
  66     }
  67     if body.source.promoted.is_some() {
  68         return false;
  69     }
  70     // Avoid inlining into generators, since their `optimized_mir` is used for layout computation,
  71     // which can create a cycle, even when no attempt is made to inline the function in the other
  72     // direction.
  73     if body.generator.is_some() {
  74         return false;
  75     }
  76
  77     let param_env = tcx.param_env_reveal_all_normalized(def_id);
  78     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
  79     let param_env = rustc_trait_selection::traits::normalize_param_env_or_error(
  80         tcx,
  81         def_id.to_def_id(),
  82         param_env,
  83         ObligationCause::misc(body.span, hir_id),
  84     );
  85
  86     let mut this = Inliner {
  87         tcx,
  88         param_env,
  89         codegen_fn_attrs: tcx.codegen_fn_attrs(def_id),
  90         history: Vec::new(),
  91         changed: false,
  92     };
  93     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  94     this.process_blocks(body, blocks);
  95     this.changed
  96 }
  97
  98 struct Inliner<'tcx> {
  99     tcx: TyCtxt<'tcx>,
 100     param_env: ParamEnv<'tcx>,
 101     /// Caller codegen attributes.
 102     codegen_fn_attrs: &'tcx CodegenFnAttrs,
 103     /// Stack of inlined Instances.
 104     history: Vec<ty::Instance<'tcx>>,
 105     /// Indicates that the caller body has been modified.
 106     changed: bool,
 107 }
 108
 109 impl<'tcx> Inliner<'tcx> {
 110     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 111         for bb in blocks {
 112             let bb_data = &caller_body[bb];
 113             if bb_data.is_cleanup {
 114                 continue;
 115             }
 116
 117             let Some(callsite) = self.resolve_callsite(caller_body, bb, bb_data) else {
 118                 continue;
 119             };
 120
 121             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 122             let _guard = span.enter();
 123
 124             match self.try_inlining(caller_body, &callsite) {
 125                 Err(reason) => {
 126                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 127                     continue;
 128                 }
 129                 Ok(new_blocks) => {
 130                     debug!("inlined {}", callsite.callee);
 131                     self.changed = true;
 132                     self.history.push(callsite.callee);
 133                     self.process_blocks(caller_body, new_blocks);
 134                     self.history.pop();
 135                 }
 136             }
 137         }
 138     }
 139
 140     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 141     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 142     /// place.
 143     fn try_inlining(
 144         &self,
 145         caller_body: &mut Body<'tcx>,
 146         callsite: &CallSite<'tcx>,
 147     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 148         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 149         self.check_codegen_attributes(callsite, callee_attrs)?;
 150         self.check_mir_is_available(caller_body, &callsite.callee)?;
 151         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 152         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 153
 154         if !self.tcx.consider_optimizing(|| {
 155             format!("Inline {:?} into {:?}", callsite.callee, caller_body.source)
 156         }) {
 157             return Err("optimization fuel exhausted");
 158         }
 159
 160         let callee_body = callsite.callee.subst_mir_and_normalize_erasing_regions(
 161             self.tcx,
 162             self.param_env,
 163             callee_body.clone(),
 164         );
 165
 166         let old_blocks = caller_body.basic_blocks().next_index();
 167         self.inline_call(caller_body, &callsite, callee_body);
 168         let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 169
 170         Ok(new_blocks)
 171     }
 172
 173     fn check_mir_is_available(
 174         &self,
 175         caller_body: &Body<'tcx>,
 176         callee: &Instance<'tcx>,
 177     ) -> Result<(), &'static str> {
 178         let caller_def_id = caller_body.source.def_id();
 179         let callee_def_id = callee.def_id();
 180         if callee_def_id == caller_def_id {
 181             return Err("self-recursion");
 182         }
 183
 184         match callee.def {
 185             InstanceDef::Item(_) => {
 186                 // If there is no MIR available (either because it was not in metadata or
 187                 // because it has no MIR because it's an extern function), then the inliner
 188                 // won't cause cycles on this.
 189                 if !self.tcx.is_mir_available(callee_def_id) {
 190                     return Err("item MIR unavailable");
 191                 }
 192             }
 193             // These have no own callable MIR.
 194             InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
 195                 return Err("instance without MIR (intrinsic / virtual)");
 196             }
 197             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
 198             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
 199             // do not need to catch this here, we can wait until the inliner decides to continue
 200             // inlining a second time.
 201             InstanceDef::VtableShim(_)
 202             | InstanceDef::ReifyShim(_)
 203             | InstanceDef::FnPtrShim(..)
 204             | InstanceDef::ClosureOnceShim { .. }
 205             | InstanceDef::DropGlue(..)
 206             | InstanceDef::CloneShim(..) => return Ok(()),
 207         }
 208
 209         if self.tcx.is_constructor(callee_def_id) {
 210             trace!("constructors always have MIR");
 211             // Constructor functions cannot cause a query cycle.
 212             return Ok(());
 213         }
 214
 215         if callee_def_id.is_local() {
 216             // Avoid a cycle here by only using `instance_mir` only if we have
 217             // a lower `DefPathHash` than the callee. This ensures that the callee will
 218             // not inline us. This trick even works with incremental compilation,
 219             // since `DefPathHash` is stable.
 220             if self.tcx.def_path_hash(caller_def_id).local_hash()
 221                 < self.tcx.def_path_hash(callee_def_id).local_hash()
 222             {
 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.tcx.mir_callgraph_reachable((*callee, caller_def_id.expect_local())) {
 229                 return Err("caller might be reachable from callee (query cycle avoidance)");
 230             }
 231
 232             Ok(())
 233         } else {
 234             // This cannot result in an immediate cycle since the callee MIR is from another crate
 235             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 236             // not need to catch this here, we can wait until the inliner decides to continue
 237             // inlining a second time.
 238             trace!("functions from other crates always have MIR");
 239             Ok(())
 240         }
 241     }
 242
 243     fn resolve_callsite(
 244         &self,
 245         caller_body: &Body<'tcx>,
 246         bb: BasicBlock,
 247         bb_data: &BasicBlockData<'tcx>,
 248     ) -> Option<CallSite<'tcx>> {
 249         // Only consider direct calls to functions
 250         let terminator = bb_data.terminator();
 251         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 252             let func_ty = func.ty(caller_body, self.tcx);
 253             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 254                 // To resolve an instance its substs have to be fully normalized.
 255                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 256                 let callee =
 257                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 258
 259                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 260                     return None;
 261                 }
 262
 263                 let fn_sig = self.tcx.bound_fn_sig(def_id).subst(self.tcx, substs);
 264
 265                 return Some(CallSite {
 266                     callee,
 267                     fn_sig,
 268                     block: bb,
 269                     target: destination.map(|(_, target)| target),
 270                     source_info: terminator.source_info,
 271                 });
 272             }
 273         }
 274
 275         None
 276     }
 277
 278     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 279     /// indicates that inlining decision should be based on other criteria.
 280     fn check_codegen_attributes(
 281         &self,
 282         callsite: &CallSite<'tcx>,
 283         callee_attrs: &CodegenFnAttrs,
 284     ) -> Result<(), &'static str> {
 285         if let InlineAttr::Never = callee_attrs.inline {
 286             return Err("never inline hint");
 287         }
 288
 289         // Only inline local functions if they would be eligible for cross-crate
 290         // inlining. This is to ensure that the final crate doesn't have MIR that
 291         // reference unexported symbols
 292         if callsite.callee.def_id().is_local() {
 293             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 294             if !is_generic && !callee_attrs.requests_inline() {
 295                 return Err("not exported");
 296             }
 297         }
 298
 299         if callsite.fn_sig.c_variadic() {
 300             return Err("C variadic");
 301         }
 302
 303         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 304             return Err("naked");
 305         }
 306
 307         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 308             return Err("cold");
 309         }
 310
 311         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 312             return Err("incompatible sanitizer set");
 313         }
 314
 315         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 316             return Err("incompatible instruction set");
 317         }
 318
 319         for feature in &callee_attrs.target_features {
 320             if !self.codegen_fn_attrs.target_features.contains(feature) {
 321                 return Err("incompatible target feature");
 322             }
 323         }
 324
 325         Ok(())
 326     }
 327
 328     /// Returns inlining decision that is based on the examination of callee MIR body.
 329     /// Assumes that codegen attributes have been checked for compatibility already.
 330     #[instrument(level = "debug", skip(self, callee_body))]
 331     fn check_mir_body(
 332         &self,
 333         callsite: &CallSite<'tcx>,
 334         callee_body: &Body<'tcx>,
 335         callee_attrs: &CodegenFnAttrs,
 336     ) -> Result<(), &'static str> {
 337         let tcx = self.tcx;
 338
 339         let mut threshold = if callee_attrs.requests_inline() {
 340             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 341         } else {
 342             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 343         };
 344
 345         // Give a bonus functions with a small number of blocks,
 346         // We normally have two or three blocks for even
 347         // very small functions.
 348         if callee_body.basic_blocks().len() <= 3 {
 349             threshold += threshold / 4;
 350         }
 351         debug!("    final inline threshold = {}", threshold);
 352
 353         // FIXME: Give a bonus to functions with only a single caller
 354         let mut first_block = true;
 355         let mut cost = 0;
 356
 357         // Traverse the MIR manually so we can account for the effects of
 358         // inlining on the CFG.
 359         let mut work_list = vec![START_BLOCK];
 360         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 361         while let Some(bb) = work_list.pop() {
 362             if !visited.insert(bb.index()) {
 363                 continue;
 364             }
 365             let blk = &callee_body.basic_blocks()[bb];
 366
 367             for stmt in &blk.statements {
 368                 // Don't count StorageLive/StorageDead in the inlining cost.
 369                 match stmt.kind {
 370                     StatementKind::StorageLive(_)
 371                     | StatementKind::StorageDead(_)
 372                     | StatementKind::Deinit(_)
 373                     | StatementKind::Nop => {}
 374                     _ => cost += INSTR_COST,
 375                 }
 376             }
 377             let term = blk.terminator();
 378             let mut is_drop = false;
 379             match term.kind {
 380                 TerminatorKind::Drop { ref place, target, unwind }
 381                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 382                     is_drop = true;
 383                     work_list.push(target);
 384                     // If the place doesn't actually need dropping, treat it like
 385                     // a regular goto.
 386                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 387                     if ty.needs_drop(tcx, self.param_env) {
 388                         cost += CALL_PENALTY;
 389                         if let Some(unwind) = unwind {
 390                             cost += LANDINGPAD_PENALTY;
 391                             work_list.push(unwind);
 392                         }
 393                     } else {
 394                         cost += INSTR_COST;
 395                     }
 396                 }
 397
 398                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 399                     if first_block =>
 400                 {
 401                     // If the function always diverges, don't inline
 402                     // unless the cost is zero
 403                     threshold = 0;
 404                 }
 405
 406                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 407                     if let ty::FnDef(def_id, substs) =
 408                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty()).kind()
 409                     {
 410                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 411                         if let Ok(Some(instance)) =
 412                             Instance::resolve(self.tcx, self.param_env, def_id, substs)
 413                         {
 414                             if callsite.callee.def_id() == instance.def_id() {
 415                                 return Err("self-recursion");
 416                             } else if self.history.contains(&instance) {
 417                                 return Err("already inlined");
 418                             }
 419                         }
 420                         // Don't give intrinsics the extra penalty for calls
 421                         if tcx.is_intrinsic(def_id) {
 422                             cost += INSTR_COST;
 423                         } else {
 424                             cost += CALL_PENALTY;
 425                         }
 426                     } else {
 427                         cost += CALL_PENALTY;
 428                     }
 429                     if cleanup.is_some() {
 430                         cost += LANDINGPAD_PENALTY;
 431                     }
 432                 }
 433                 TerminatorKind::Assert { cleanup, .. } => {
 434                     cost += CALL_PENALTY;
 435
 436                     if cleanup.is_some() {
 437                         cost += LANDINGPAD_PENALTY;
 438                     }
 439                 }
 440                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 441                 TerminatorKind::InlineAsm { cleanup, .. } => {
 442                     cost += INSTR_COST;
 443
 444                     if cleanup.is_some() {
 445                         cost += LANDINGPAD_PENALTY;
 446                     }
 447                 }
 448                 _ => cost += INSTR_COST,
 449             }
 450
 451             if !is_drop {
 452                 for &succ in term.successors() {
 453                     work_list.push(succ);
 454                 }
 455             }
 456
 457             first_block = false;
 458         }
 459
 460         // Count up the cost of local variables and temps, if we know the size
 461         // use that, otherwise we use a moderately-large dummy cost.
 462
 463         let ptr_size = tcx.data_layout.pointer_size.bytes();
 464
 465         for v in callee_body.vars_and_temps_iter() {
 466             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 467             // Cost of the var is the size in machine-words, if we know
 468             // it.
 469             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 470                 cost += ((size + ptr_size - 1) / ptr_size) as usize;
 471             } else {
 472                 cost += UNKNOWN_SIZE_COST;
 473             }
 474         }
 475
 476         if let InlineAttr::Always = callee_attrs.inline {
 477             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 478             Ok(())
 479         } else {
 480             if cost <= threshold {
 481                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 482                 Ok(())
 483             } else {
 484                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 485                 Err("cost above threshold")
 486             }
 487         }
 488     }
 489
 490     fn inline_call(
 491         &self,
 492         caller_body: &mut Body<'tcx>,
 493         callsite: &CallSite<'tcx>,
 494         mut callee_body: Body<'tcx>,
 495     ) {
 496         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 497         match terminator.kind {
 498             TerminatorKind::Call { args, destination, cleanup, .. } => {
 499                 // If the call is something like `a[*i] = f(i)`, where
 500                 // `i : &mut usize`, then just duplicating the `a[*i]`
 501                 // Place could result in two different locations if `f`
 502                 // writes to `i`. To prevent this we need to create a temporary
 503                 // borrow of the place and pass the destination as `*temp` instead.
 504                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 505                     for elem in place.projection.iter() {
 506                         match elem {
 507                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 508                             _ => {}
 509                         }
 510                     }
 511
 512                     false
 513                 }
 514
 515                 let dest = if let Some((destination_place, _)) = destination {
 516                     if dest_needs_borrow(destination_place) {
 517                         trace!("creating temp for return destination");
 518                         let dest = Rvalue::Ref(
 519                             self.tcx.lifetimes.re_erased,
 520                             BorrowKind::Mut { allow_two_phase_borrow: false },
 521                             destination_place,
 522                         );
 523                         let dest_ty = dest.ty(caller_body, self.tcx);
 524                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 525                         caller_body[callsite.block].statements.push(Statement {
 526                             source_info: callsite.source_info,
 527                             kind: StatementKind::Assign(Box::new((temp, dest))),
 528                         });
 529                         self.tcx.mk_place_deref(temp)
 530                     } else {
 531                         destination_place
 532                     }
 533                 } else {
 534                     trace!("creating temp for return place");
 535                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 536                 };
 537
 538                 // Copy the arguments if needed.
 539                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 540
 541                 let mut expn_data = ExpnData::default(
 542                     ExpnKind::Inlined,
 543                     callsite.source_info.span,
 544                     self.tcx.sess.edition(),
 545                     None,
 546                     None,
 547                 );
 548                 expn_data.def_site = callee_body.span;
 549                 let expn_data =
 550                     LocalExpnId::fresh(expn_data, self.tcx.create_stable_hashing_context());
 551                 let mut integrator = Integrator {
 552                     args: &args,
 553                     new_locals: Local::new(caller_body.local_decls.len())..,
 554                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 555                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 556                     destination: dest,
 557                     return_block: callsite.target,
 558                     cleanup_block: cleanup,
 559                     in_cleanup_block: false,
 560                     tcx: self.tcx,
 561                     expn_data,
 562                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 563                 };
 564
 565                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 566                 // (or existing ones, in a few special cases) in the caller.
 567                 integrator.visit_body(&mut callee_body);
 568
 569                 for scope in &mut callee_body.source_scopes {
 570                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 571                     if scope.parent_scope.is_none() {
 572                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 573
 574                         // Attach the outermost callee scope as a child of the callsite
 575                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 576                         scope.parent_scope = Some(callsite.source_info.scope);
 577                         assert_eq!(scope.inlined_parent_scope, None);
 578                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 579                             Some(callsite.source_info.scope)
 580                         } else {
 581                             callsite_scope.inlined_parent_scope
 582                         };
 583
 584                         // Mark the outermost callee scope as an inlined one.
 585                         assert_eq!(scope.inlined, None);
 586                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 587                     } else if scope.inlined_parent_scope.is_none() {
 588                         // Make it easy to find the scope with `inlined` set above.
 589                         scope.inlined_parent_scope =
 590                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 591                     }
 592                 }
 593
 594                 // If there are any locals without storage markers, give them storage only for the
 595                 // duration of the call.
 596                 for local in callee_body.vars_and_temps_iter() {
 597                     if integrator.always_live_locals.contains(local) {
 598                         let new_local = integrator.map_local(local);
 599                         caller_body[callsite.block].statements.push(Statement {
 600                             source_info: callsite.source_info,
 601                             kind: StatementKind::StorageLive(new_local),
 602                         });
 603                     }
 604                 }
 605                 if let Some(block) = callsite.target {
 606                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 607                     // the slice once.
 608                     let mut n = 0;
 609                     for local in callee_body.vars_and_temps_iter().rev() {
 610                         if integrator.always_live_locals.contains(local) {
 611                             let new_local = integrator.map_local(local);
 612                             caller_body[block].statements.push(Statement {
 613                                 source_info: callsite.source_info,
 614                                 kind: StatementKind::StorageDead(new_local),
 615                             });
 616                             n += 1;
 617                         }
 618                     }
 619                     caller_body[block].statements.rotate_right(n);
 620                 }
 621
 622                 // Insert all of the (mapped) parts of the callee body into the caller.
 623                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 624                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 625                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 626                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 627
 628                 caller_body[callsite.block].terminator = Some(Terminator {
 629                     source_info: callsite.source_info,
 630                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 631                 });
 632
 633                 // Copy only unevaluated constants from the callee_body into the caller_body.
 634                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 635                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 636                 // because we are calling `subst_and_normalize_erasing_regions`.
 637                 caller_body.required_consts.extend(
 638                     callee_body.required_consts.iter().copied().filter(|&ct| {
 639                         match ct.literal.const_for_ty() {
 640                             Some(ct) => matches!(ct.val(), ConstKind::Unevaluated(_)),
 641                             None => true,
 642                         }
 643                     }),
 644                 );
 645             }
 646             kind => bug!("unexpected terminator kind {:?}", kind),
 647         }
 648     }
 649
 650     fn make_call_args(
 651         &self,
 652         args: Vec<Operand<'tcx>>,
 653         callsite: &CallSite<'tcx>,
 654         caller_body: &mut Body<'tcx>,
 655         callee_body: &Body<'tcx>,
 656     ) -> Vec<Local> {
 657         let tcx = self.tcx;
 658
 659         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 660         // The caller provides the arguments wrapped up in a tuple:
 661         //
 662         //     tuple_tmp = (a, b, c)
 663         //     Fn::call(closure_ref, tuple_tmp)
 664         //
 665         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 666         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 667         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 668         // a vector like
 669         //
 670         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 671         //
 672         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 673         // if we "spill" that into *another* temporary, so that we can map the argument
 674         // variable in the callee MIR directly to an argument variable on our side.
 675         // So we introduce temporaries like:
 676         //
 677         //     tmp0 = tuple_tmp.0
 678         //     tmp1 = tuple_tmp.1
 679         //     tmp2 = tuple_tmp.2
 680         //
 681         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 682         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 683             let mut args = args.into_iter();
 684             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 685             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 686             assert!(args.next().is_none());
 687
 688             let tuple = Place::from(tuple);
 689             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() else {
 690                 bug!("Closure arguments are not passed as a tuple");
 691             };
 692
 693             // The `closure_ref` in our example above.
 694             let closure_ref_arg = iter::once(self_);
 695
 696             // The `tmp0`, `tmp1`, and `tmp2` in our example above.
 697             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 698                 // This is e.g., `tuple_tmp.0` in our example above.
 699                 let tuple_field = Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty));
 700
 701                 // Spill to a local to make e.g., `tmp0`.
 702                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 703             });
 704
 705             closure_ref_arg.chain(tuple_tmp_args).collect()
 706         } else {
 707             args.into_iter()
 708                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 709                 .collect()
 710         }
 711     }
 712
 713     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 714     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 715     fn create_temp_if_necessary(
 716         &self,
 717         arg: Operand<'tcx>,
 718         callsite: &CallSite<'tcx>,
 719         caller_body: &mut Body<'tcx>,
 720     ) -> Local {
 721         // Reuse the operand if it is a moved temporary.
 722         if let Operand::Move(place) = &arg
 723             && let Some(local) = place.as_local()
 724             && caller_body.local_kind(local) == LocalKind::Temp
 725         {
 726             return local;
 727         }
 728
 729         // Otherwise, create a temporary for the argument.
 730         trace!("creating temp for argument {:?}", arg);
 731         let arg_ty = arg.ty(caller_body, self.tcx);
 732         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 733         caller_body[callsite.block].statements.push(Statement {
 734             source_info: callsite.source_info,
 735             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 736         });
 737         local
 738     }
 739
 740     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 741     fn new_call_temp(
 742         &self,
 743         caller_body: &mut Body<'tcx>,
 744         callsite: &CallSite<'tcx>,
 745         ty: Ty<'tcx>,
 746     ) -> Local {
 747         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 748
 749         caller_body[callsite.block].statements.push(Statement {
 750             source_info: callsite.source_info,
 751             kind: StatementKind::StorageLive(local),
 752         });
 753
 754         if let Some(block) = callsite.target {
 755             caller_body[block].statements.insert(
 756                 0,
 757                 Statement {
 758                     source_info: callsite.source_info,
 759                     kind: StatementKind::StorageDead(local),
 760                 },
 761             );
 762         }
 763
 764         local
 765     }
 766 }
 767
 768 fn type_size_of<'tcx>(
 769     tcx: TyCtxt<'tcx>,
 770     param_env: ty::ParamEnv<'tcx>,
 771     ty: Ty<'tcx>,
 772 ) -> Option<u64> {
 773     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 774 }
 775
 776 /**
 777  * Integrator.
 778  *
 779  * Integrates blocks from the callee function into the calling function.
 780  * Updates block indices, references to locals and other control flow
 781  * stuff.
 782 */
 783 struct Integrator<'a, 'tcx> {
 784     args: &'a [Local],
 785     new_locals: RangeFrom<Local>,
 786     new_scopes: RangeFrom<SourceScope>,
 787     new_blocks: RangeFrom<BasicBlock>,
 788     destination: Place<'tcx>,
 789     return_block: Option<BasicBlock>,
 790     cleanup_block: Option<BasicBlock>,
 791     in_cleanup_block: bool,
 792     tcx: TyCtxt<'tcx>,
 793     expn_data: LocalExpnId,
 794     always_live_locals: BitSet<Local>,
 795 }
 796
 797 impl Integrator<'_, '_> {
 798     fn map_local(&self, local: Local) -> Local {
 799         let new = if local == RETURN_PLACE {
 800             self.destination.local
 801         } else {
 802             let idx = local.index() - 1;
 803             if idx < self.args.len() {
 804                 self.args[idx]
 805             } else {
 806                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 807             }
 808         };
 809         trace!("mapping local `{:?}` to `{:?}`", local, new);
 810         new
 811     }
 812
 813     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 814         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 815         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 816         new
 817     }
 818
 819     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 820         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 821         trace!("mapping block `{:?}` to `{:?}`", block, new);
 822         new
 823     }
 824 }
 825
 826 impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
 827     fn tcx(&self) -> TyCtxt<'tcx> {
 828         self.tcx
 829     }
 830
 831     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 832         *local = self.map_local(*local);
 833     }
 834
 835     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 836         *scope = self.map_scope(*scope);
 837     }
 838
 839     fn visit_span(&mut self, span: &mut Span) {
 840         // Make sure that all spans track the fact that they were inlined.
 841         *span = span.fresh_expansion(self.expn_data);
 842     }
 843
 844     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 845         for elem in place.projection {
 846             // FIXME: Make sure that return place is not used in an indexing projection, since it
 847             // won't be rebased as it is supposed to be.
 848             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 849         }
 850
 851         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 852         let dest_proj_len = self.destination.projection.len();
 853         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 854             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 855             projs.extend(self.destination.projection);
 856             projs.extend(place.projection);
 857
 858             place.projection = self.tcx.intern_place_elems(&*projs);
 859         }
 860         // Handles integrating any locals that occur in the base
 861         // or projections
 862         self.super_place(place, context, location)
 863     }
 864
 865     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 866         self.in_cleanup_block = data.is_cleanup;
 867         self.super_basic_block_data(block, data);
 868         self.in_cleanup_block = false;
 869     }
 870
 871     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 872         self.super_retag(kind, place, loc);
 873
 874         // We have to patch all inlined retags to be aware that they are no longer
 875         // happening on function entry.
 876         if *kind == RetagKind::FnEntry {
 877             *kind = RetagKind::Default;
 878         }
 879     }
 880
 881     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 882         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 883             statement.kind
 884         {
 885             self.always_live_locals.remove(local);
 886         }
 887         self.super_statement(statement, location);
 888     }
 889
 890     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 891         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 892         // replaced down below anyways).
 893         if !matches!(terminator.kind, TerminatorKind::Return) {
 894             self.super_terminator(terminator, loc);
 895         }
 896
 897         match terminator.kind {
 898             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 899             TerminatorKind::Goto { ref mut target } => {
 900                 *target = self.map_block(*target);
 901             }
 902             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 903                 for tgt in targets.all_targets_mut() {
 904                     *tgt = self.map_block(*tgt);
 905                 }
 906             }
 907             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 908             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 909                 *target = self.map_block(*target);
 910                 if let Some(tgt) = *unwind {
 911                     *unwind = Some(self.map_block(tgt));
 912                 } else if !self.in_cleanup_block {
 913                     // Unless this drop is in a cleanup block, add an unwind edge to
 914                     // the original call's cleanup block
 915                     *unwind = self.cleanup_block;
 916                 }
 917             }
 918             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 919                 if let Some((_, ref mut tgt)) = *destination {
 920                     *tgt = self.map_block(*tgt);
 921                 }
 922                 if let Some(tgt) = *cleanup {
 923                     *cleanup = Some(self.map_block(tgt));
 924                 } else if !self.in_cleanup_block {
 925                     // Unless this call is in a cleanup block, add an unwind edge to
 926                     // the original call's cleanup block
 927                     *cleanup = self.cleanup_block;
 928                 }
 929             }
 930             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 931                 *target = self.map_block(*target);
 932                 if let Some(tgt) = *cleanup {
 933                     *cleanup = Some(self.map_block(tgt));
 934                 } else if !self.in_cleanup_block {
 935                     // Unless this assert is in a cleanup block, add an unwind edge to
 936                     // the original call's cleanup block
 937                     *cleanup = self.cleanup_block;
 938                 }
 939             }
 940             TerminatorKind::Return => {
 941                 terminator.kind = if let Some(tgt) = self.return_block {
 942                     TerminatorKind::Goto { target: tgt }
 943                 } else {
 944                     TerminatorKind::Unreachable
 945                 }
 946             }
 947             TerminatorKind::Resume => {
 948                 if let Some(tgt) = self.cleanup_block {
 949                     terminator.kind = TerminatorKind::Goto { target: tgt }
 950                 }
 951             }
 952             TerminatorKind::Abort => {}
 953             TerminatorKind::Unreachable => {}
 954             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 955                 *real_target = self.map_block(*real_target);
 956                 *imaginary_target = self.map_block(*imaginary_target);
 957             }
 958             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 959             // see the ordering of passes in the optimized_mir query.
 960             {
 961                 bug!("False unwinds should have been removed before inlining")
 962             }
 963             TerminatorKind::InlineAsm { ref mut destination, ref mut cleanup, .. } => {
 964                 if let Some(ref mut tgt) = *destination {
 965                     *tgt = self.map_block(*tgt);
 966                 } else if !self.in_cleanup_block {
 967                     // Unless this inline asm is in a cleanup block, add an unwind edge to
 968                     // the original call's cleanup block
 969                     *cleanup = self.cleanup_block;
 970                 }
 971             }
 972         }
 973     }
 974 }