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.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                         let f = tcx.fn_sig(def_id);
 422                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 423                             cost += INSTR_COST;
 424                         } else {
 425                             cost += CALL_PENALTY;
 426                         }
 427                     } else {
 428                         cost += CALL_PENALTY;
 429                     }
 430                     if cleanup.is_some() {
 431                         cost += LANDINGPAD_PENALTY;
 432                     }
 433                 }
 434                 TerminatorKind::Assert { cleanup, .. } => {
 435                     cost += CALL_PENALTY;
 436
 437                     if cleanup.is_some() {
 438                         cost += LANDINGPAD_PENALTY;
 439                     }
 440                 }
 441                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 442                 TerminatorKind::InlineAsm { cleanup, .. } => {
 443                     cost += INSTR_COST;
 444
 445                     if cleanup.is_some() {
 446                         cost += LANDINGPAD_PENALTY;
 447                     }
 448                 }
 449                 _ => cost += INSTR_COST,
 450             }
 451
 452             if !is_drop {
 453                 for &succ in term.successors() {
 454                     work_list.push(succ);
 455                 }
 456             }
 457
 458             first_block = false;
 459         }
 460
 461         // Count up the cost of local variables and temps, if we know the size
 462         // use that, otherwise we use a moderately-large dummy cost.
 463
 464         let ptr_size = tcx.data_layout.pointer_size.bytes();
 465
 466         for v in callee_body.vars_and_temps_iter() {
 467             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 468             // Cost of the var is the size in machine-words, if we know
 469             // it.
 470             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 471                 cost += ((size + ptr_size - 1) / ptr_size) as usize;
 472             } else {
 473                 cost += UNKNOWN_SIZE_COST;
 474             }
 475         }
 476
 477         if let InlineAttr::Always = callee_attrs.inline {
 478             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 479             Ok(())
 480         } else {
 481             if cost <= threshold {
 482                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 483                 Ok(())
 484             } else {
 485                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 486                 Err("cost above threshold")
 487             }
 488         }
 489     }
 490
 491     fn inline_call(
 492         &self,
 493         caller_body: &mut Body<'tcx>,
 494         callsite: &CallSite<'tcx>,
 495         mut callee_body: Body<'tcx>,
 496     ) {
 497         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 498         match terminator.kind {
 499             TerminatorKind::Call { args, destination, cleanup, .. } => {
 500                 // If the call is something like `a[*i] = f(i)`, where
 501                 // `i : &mut usize`, then just duplicating the `a[*i]`
 502                 // Place could result in two different locations if `f`
 503                 // writes to `i`. To prevent this we need to create a temporary
 504                 // borrow of the place and pass the destination as `*temp` instead.
 505                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 506                     for elem in place.projection.iter() {
 507                         match elem {
 508                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 509                             _ => {}
 510                         }
 511                     }
 512
 513                     false
 514                 }
 515
 516                 let dest = if let Some((destination_place, _)) = destination {
 517                     if dest_needs_borrow(destination_place) {
 518                         trace!("creating temp for return destination");
 519                         let dest = Rvalue::Ref(
 520                             self.tcx.lifetimes.re_erased,
 521                             BorrowKind::Mut { allow_two_phase_borrow: false },
 522                             destination_place,
 523                         );
 524                         let dest_ty = dest.ty(caller_body, self.tcx);
 525                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 526                         caller_body[callsite.block].statements.push(Statement {
 527                             source_info: callsite.source_info,
 528                             kind: StatementKind::Assign(Box::new((temp, dest))),
 529                         });
 530                         self.tcx.mk_place_deref(temp)
 531                     } else {
 532                         destination_place
 533                     }
 534                 } else {
 535                     trace!("creating temp for return place");
 536                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 537                 };
 538
 539                 // Copy the arguments if needed.
 540                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 541
 542                 let mut expn_data = ExpnData::default(
 543                     ExpnKind::Inlined,
 544                     callsite.source_info.span,
 545                     self.tcx.sess.edition(),
 546                     None,
 547                     None,
 548                 );
 549                 expn_data.def_site = callee_body.span;
 550                 let expn_data =
 551                     LocalExpnId::fresh(expn_data, self.tcx.create_stable_hashing_context());
 552                 let mut integrator = Integrator {
 553                     args: &args,
 554                     new_locals: Local::new(caller_body.local_decls.len())..,
 555                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 556                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 557                     destination: dest,
 558                     return_block: callsite.target,
 559                     cleanup_block: cleanup,
 560                     in_cleanup_block: false,
 561                     tcx: self.tcx,
 562                     expn_data,
 563                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 564                 };
 565
 566                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 567                 // (or existing ones, in a few special cases) in the caller.
 568                 integrator.visit_body(&mut callee_body);
 569
 570                 for scope in &mut callee_body.source_scopes {
 571                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 572                     if scope.parent_scope.is_none() {
 573                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 574
 575                         // Attach the outermost callee scope as a child of the callsite
 576                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 577                         scope.parent_scope = Some(callsite.source_info.scope);
 578                         assert_eq!(scope.inlined_parent_scope, None);
 579                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 580                             Some(callsite.source_info.scope)
 581                         } else {
 582                             callsite_scope.inlined_parent_scope
 583                         };
 584
 585                         // Mark the outermost callee scope as an inlined one.
 586                         assert_eq!(scope.inlined, None);
 587                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 588                     } else if scope.inlined_parent_scope.is_none() {
 589                         // Make it easy to find the scope with `inlined` set above.
 590                         scope.inlined_parent_scope =
 591                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 592                     }
 593                 }
 594
 595                 // If there are any locals without storage markers, give them storage only for the
 596                 // duration of the call.
 597                 for local in callee_body.vars_and_temps_iter() {
 598                     if integrator.always_live_locals.contains(local) {
 599                         let new_local = integrator.map_local(local);
 600                         caller_body[callsite.block].statements.push(Statement {
 601                             source_info: callsite.source_info,
 602                             kind: StatementKind::StorageLive(new_local),
 603                         });
 604                     }
 605                 }
 606                 if let Some(block) = callsite.target {
 607                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 608                     // the slice once.
 609                     let mut n = 0;
 610                     for local in callee_body.vars_and_temps_iter().rev() {
 611                         if integrator.always_live_locals.contains(local) {
 612                             let new_local = integrator.map_local(local);
 613                             caller_body[block].statements.push(Statement {
 614                                 source_info: callsite.source_info,
 615                                 kind: StatementKind::StorageDead(new_local),
 616                             });
 617                             n += 1;
 618                         }
 619                     }
 620                     caller_body[block].statements.rotate_right(n);
 621                 }
 622
 623                 // Insert all of the (mapped) parts of the callee body into the caller.
 624                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 625                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 626                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 627                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 628
 629                 caller_body[callsite.block].terminator = Some(Terminator {
 630                     source_info: callsite.source_info,
 631                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 632                 });
 633
 634                 // Copy only unevaluated constants from the callee_body into the caller_body.
 635                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 636                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 637                 // because we are calling `subst_and_normalize_erasing_regions`.
 638                 caller_body.required_consts.extend(
 639                     callee_body.required_consts.iter().copied().filter(|&ct| {
 640                         match ct.literal.const_for_ty() {
 641                             Some(ct) => matches!(ct.val(), ConstKind::Unevaluated(_)),
 642                             None => true,
 643                         }
 644                     }),
 645                 );
 646             }
 647             kind => bug!("unexpected terminator kind {:?}", kind),
 648         }
 649     }
 650
 651     fn make_call_args(
 652         &self,
 653         args: Vec<Operand<'tcx>>,
 654         callsite: &CallSite<'tcx>,
 655         caller_body: &mut Body<'tcx>,
 656         callee_body: &Body<'tcx>,
 657     ) -> Vec<Local> {
 658         let tcx = self.tcx;
 659
 660         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 661         // The caller provides the arguments wrapped up in a tuple:
 662         //
 663         //     tuple_tmp = (a, b, c)
 664         //     Fn::call(closure_ref, tuple_tmp)
 665         //
 666         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 667         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 668         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 669         // a vector like
 670         //
 671         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 672         //
 673         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 674         // if we "spill" that into *another* temporary, so that we can map the argument
 675         // variable in the callee MIR directly to an argument variable on our side.
 676         // So we introduce temporaries like:
 677         //
 678         //     tmp0 = tuple_tmp.0
 679         //     tmp1 = tuple_tmp.1
 680         //     tmp2 = tuple_tmp.2
 681         //
 682         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 683         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 684             let mut args = args.into_iter();
 685             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 686             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 687             assert!(args.next().is_none());
 688
 689             let tuple = Place::from(tuple);
 690             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() 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 above.
 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 = Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty));
 701
 702                 // Spill to a local to make e.g., `tmp0`.
 703                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 704             });
 705
 706             closure_ref_arg.chain(tuple_tmp_args).collect()
 707         } else {
 708             args.into_iter()
 709                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 710                 .collect()
 711         }
 712     }
 713
 714     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 715     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 716     fn create_temp_if_necessary(
 717         &self,
 718         arg: Operand<'tcx>,
 719         callsite: &CallSite<'tcx>,
 720         caller_body: &mut Body<'tcx>,
 721     ) -> Local {
 722         // Reuse the operand if it is a moved temporary.
 723         if let Operand::Move(place) = &arg
 724             && let Some(local) = place.as_local()
 725             && caller_body.local_kind(local) == LocalKind::Temp
 726         {
 727             return local;
 728         }
 729
 730         // Otherwise, create a temporary for the argument.
 731         trace!("creating temp for argument {:?}", arg);
 732         let arg_ty = arg.ty(caller_body, self.tcx);
 733         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 734         caller_body[callsite.block].statements.push(Statement {
 735             source_info: callsite.source_info,
 736             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 737         });
 738         local
 739     }
 740
 741     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 742     fn new_call_temp(
 743         &self,
 744         caller_body: &mut Body<'tcx>,
 745         callsite: &CallSite<'tcx>,
 746         ty: Ty<'tcx>,
 747     ) -> Local {
 748         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 749
 750         caller_body[callsite.block].statements.push(Statement {
 751             source_info: callsite.source_info,
 752             kind: StatementKind::StorageLive(local),
 753         });
 754
 755         if let Some(block) = callsite.target {
 756             caller_body[block].statements.insert(
 757                 0,
 758                 Statement {
 759                     source_info: callsite.source_info,
 760                     kind: StatementKind::StorageDead(local),
 761                 },
 762             );
 763         }
 764
 765         local
 766     }
 767 }
 768
 769 fn type_size_of<'tcx>(
 770     tcx: TyCtxt<'tcx>,
 771     param_env: ty::ParamEnv<'tcx>,
 772     ty: Ty<'tcx>,
 773 ) -> Option<u64> {
 774     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 775 }
 776
 777 /**
 778  * Integrator.
 779  *
 780  * Integrates blocks from the callee function into the calling function.
 781  * Updates block indices, references to locals and other control flow
 782  * stuff.
 783 */
 784 struct Integrator<'a, 'tcx> {
 785     args: &'a [Local],
 786     new_locals: RangeFrom<Local>,
 787     new_scopes: RangeFrom<SourceScope>,
 788     new_blocks: RangeFrom<BasicBlock>,
 789     destination: Place<'tcx>,
 790     return_block: Option<BasicBlock>,
 791     cleanup_block: Option<BasicBlock>,
 792     in_cleanup_block: bool,
 793     tcx: TyCtxt<'tcx>,
 794     expn_data: LocalExpnId,
 795     always_live_locals: BitSet<Local>,
 796 }
 797
 798 impl Integrator<'_, '_> {
 799     fn map_local(&self, local: Local) -> Local {
 800         let new = if local == RETURN_PLACE {
 801             self.destination.local
 802         } else {
 803             let idx = local.index() - 1;
 804             if idx < self.args.len() {
 805                 self.args[idx]
 806             } else {
 807                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 808             }
 809         };
 810         trace!("mapping local `{:?}` to `{:?}`", local, new);
 811         new
 812     }
 813
 814     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 815         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 816         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 817         new
 818     }
 819
 820     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 821         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 822         trace!("mapping block `{:?}` to `{:?}`", block, new);
 823         new
 824     }
 825 }
 826
 827 impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
 828     fn tcx(&self) -> TyCtxt<'tcx> {
 829         self.tcx
 830     }
 831
 832     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 833         *local = self.map_local(*local);
 834     }
 835
 836     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 837         *scope = self.map_scope(*scope);
 838     }
 839
 840     fn visit_span(&mut self, span: &mut Span) {
 841         // Make sure that all spans track the fact that they were inlined.
 842         *span = span.fresh_expansion(self.expn_data);
 843     }
 844
 845     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 846         for elem in place.projection {
 847             // FIXME: Make sure that return place is not used in an indexing projection, since it
 848             // won't be rebased as it is supposed to be.
 849             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 850         }
 851
 852         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 853         let dest_proj_len = self.destination.projection.len();
 854         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 855             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 856             projs.extend(self.destination.projection);
 857             projs.extend(place.projection);
 858
 859             place.projection = self.tcx.intern_place_elems(&*projs);
 860         }
 861         // Handles integrating any locals that occur in the base
 862         // or projections
 863         self.super_place(place, context, location)
 864     }
 865
 866     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 867         self.in_cleanup_block = data.is_cleanup;
 868         self.super_basic_block_data(block, data);
 869         self.in_cleanup_block = false;
 870     }
 871
 872     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 873         self.super_retag(kind, place, loc);
 874
 875         // We have to patch all inlined retags to be aware that they are no longer
 876         // happening on function entry.
 877         if *kind == RetagKind::FnEntry {
 878             *kind = RetagKind::Default;
 879         }
 880     }
 881
 882     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 883         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 884             statement.kind
 885         {
 886             self.always_live_locals.remove(local);
 887         }
 888         self.super_statement(statement, location);
 889     }
 890
 891     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 892         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 893         // replaced down below anyways).
 894         if !matches!(terminator.kind, TerminatorKind::Return) {
 895             self.super_terminator(terminator, loc);
 896         }
 897
 898         match terminator.kind {
 899             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 900             TerminatorKind::Goto { ref mut target } => {
 901                 *target = self.map_block(*target);
 902             }
 903             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 904                 for tgt in targets.all_targets_mut() {
 905                     *tgt = self.map_block(*tgt);
 906                 }
 907             }
 908             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 909             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 910                 *target = self.map_block(*target);
 911                 if let Some(tgt) = *unwind {
 912                     *unwind = Some(self.map_block(tgt));
 913                 } else if !self.in_cleanup_block {
 914                     // Unless this drop is in a cleanup block, add an unwind edge to
 915                     // the original call's cleanup block
 916                     *unwind = self.cleanup_block;
 917                 }
 918             }
 919             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 920                 if let Some((_, ref mut tgt)) = *destination {
 921                     *tgt = self.map_block(*tgt);
 922                 }
 923                 if let Some(tgt) = *cleanup {
 924                     *cleanup = Some(self.map_block(tgt));
 925                 } else if !self.in_cleanup_block {
 926                     // Unless this call is in a cleanup block, add an unwind edge to
 927                     // the original call's cleanup block
 928                     *cleanup = self.cleanup_block;
 929                 }
 930             }
 931             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 932                 *target = self.map_block(*target);
 933                 if let Some(tgt) = *cleanup {
 934                     *cleanup = Some(self.map_block(tgt));
 935                 } else if !self.in_cleanup_block {
 936                     // Unless this assert is in a cleanup block, add an unwind edge to
 937                     // the original call's cleanup block
 938                     *cleanup = self.cleanup_block;
 939                 }
 940             }
 941             TerminatorKind::Return => {
 942                 terminator.kind = if let Some(tgt) = self.return_block {
 943                     TerminatorKind::Goto { target: tgt }
 944                 } else {
 945                     TerminatorKind::Unreachable
 946                 }
 947             }
 948             TerminatorKind::Resume => {
 949                 if let Some(tgt) = self.cleanup_block {
 950                     terminator.kind = TerminatorKind::Goto { target: tgt }
 951                 }
 952             }
 953             TerminatorKind::Abort => {}
 954             TerminatorKind::Unreachable => {}
 955             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 956                 *real_target = self.map_block(*real_target);
 957                 *imaginary_target = self.map_block(*imaginary_target);
 958             }
 959             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 960             // see the ordering of passes in the optimized_mir query.
 961             {
 962                 bug!("False unwinds should have been removed before inlining")
 963             }
 964             TerminatorKind::InlineAsm { ref mut destination, ref mut cleanup, .. } => {
 965                 if let Some(ref mut tgt) = *destination {
 966                     *tgt = self.map_block(*tgt);
 967                 } else if !self.in_cleanup_block {
 968                     // Unless this inline asm is in a cleanup block, add an unwind edge to
 969                     // the original call's cleanup block
 970                     *cleanup = self.cleanup_block;
 971                 }
 972             }
 973         }
 974     }
 975 }