compiler/rustc_mir_transform/src/inline.rs

   1 //! Inlining pass for MIR functions
   2 use crate::deref_separator::deref_finder;
   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 pub(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             deref_finder(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().expect_local();
  63
  64     // Only do inlining into fn bodies.
  65     if !tcx.hir().body_owner_kind(def_id).is_fn_or_closure() {
  66         return false;
  67     }
  68     if body.source.promoted.is_some() {
  69         return false;
  70     }
  71     // Avoid inlining into generators, since their `optimized_mir` is used for layout computation,
  72     // which can create a cycle, even when no attempt is made to inline the function in the other
  73     // direction.
  74     if body.generator.is_some() {
  75         return false;
  76     }
  77
  78     let param_env = tcx.param_env_reveal_all_normalized(def_id);
  79     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
  80     let param_env = rustc_trait_selection::traits::normalize_param_env_or_error(
  81         tcx,
  82         def_id.to_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         history: Vec::new(),
  92         changed: false,
  93     };
  94     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  95     this.process_blocks(body, blocks);
  96     this.changed
  97 }
  98
  99 struct Inliner<'tcx> {
 100     tcx: TyCtxt<'tcx>,
 101     param_env: ParamEnv<'tcx>,
 102     /// Caller codegen attributes.
 103     codegen_fn_attrs: &'tcx CodegenFnAttrs,
 104     /// Stack of inlined Instances.
 105     history: Vec<ty::Instance<'tcx>>,
 106     /// Indicates that the caller body has been modified.
 107     changed: bool,
 108 }
 109
 110 impl<'tcx> Inliner<'tcx> {
 111     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 112         for bb in blocks {
 113             let bb_data = &caller_body[bb];
 114             if bb_data.is_cleanup {
 115                 continue;
 116             }
 117
 118             let Some(callsite) = self.resolve_callsite(caller_body, bb, bb_data) else {
 119                 continue;
 120             };
 121
 122             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 123             let _guard = span.enter();
 124
 125             match self.try_inlining(caller_body, &callsite) {
 126                 Err(reason) => {
 127                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 128                     continue;
 129                 }
 130                 Ok(new_blocks) => {
 131                     debug!("inlined {}", callsite.callee);
 132                     self.changed = true;
 133                     self.history.push(callsite.callee);
 134                     self.process_blocks(caller_body, new_blocks);
 135                     self.history.pop();
 136                 }
 137             }
 138         }
 139     }
 140
 141     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 142     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 143     /// place.
 144     fn try_inlining(
 145         &self,
 146         caller_body: &mut Body<'tcx>,
 147         callsite: &CallSite<'tcx>,
 148     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 149         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 150         self.check_codegen_attributes(callsite, callee_attrs)?;
 151         self.check_mir_is_available(caller_body, &callsite.callee)?;
 152         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 153         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 154
 155         if !self.tcx.consider_optimizing(|| {
 156             format!("Inline {:?} into {:?}", callsite.callee, caller_body.source)
 157         }) {
 158             return Err("optimization fuel exhausted");
 159         }
 160
 161         let Ok(callee_body) = callsite.callee.try_subst_mir_and_normalize_erasing_regions(
 162             self.tcx,
 163             self.param_env,
 164             callee_body.clone(),
 165         ) else {
 166             return Err("failed to normalize callee body");
 167         };
 168
 169         let old_blocks = caller_body.basic_blocks().next_index();
 170         self.inline_call(caller_body, &callsite, callee_body);
 171         let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 172
 173         Ok(new_blocks)
 174     }
 175
 176     fn check_mir_is_available(
 177         &self,
 178         caller_body: &Body<'tcx>,
 179         callee: &Instance<'tcx>,
 180     ) -> Result<(), &'static str> {
 181         let caller_def_id = caller_body.source.def_id();
 182         let callee_def_id = callee.def_id();
 183         if callee_def_id == caller_def_id {
 184             return Err("self-recursion");
 185         }
 186
 187         match callee.def {
 188             InstanceDef::Item(_) => {
 189                 // If there is no MIR available (either because it was not in metadata or
 190                 // because it has no MIR because it's an extern function), then the inliner
 191                 // won't cause cycles on this.
 192                 if !self.tcx.is_mir_available(callee_def_id) {
 193                     return Err("item MIR unavailable");
 194                 }
 195             }
 196             // These have no own callable MIR.
 197             InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
 198                 return Err("instance without MIR (intrinsic / virtual)");
 199             }
 200             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
 201             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
 202             // do not need to catch this here, we can wait until the inliner decides to continue
 203             // inlining a second time.
 204             InstanceDef::VtableShim(_)
 205             | InstanceDef::ReifyShim(_)
 206             | InstanceDef::FnPtrShim(..)
 207             | InstanceDef::ClosureOnceShim { .. }
 208             | InstanceDef::DropGlue(..)
 209             | InstanceDef::CloneShim(..) => return Ok(()),
 210         }
 211
 212         if self.tcx.is_constructor(callee_def_id) {
 213             trace!("constructors always have MIR");
 214             // Constructor functions cannot cause a query cycle.
 215             return Ok(());
 216         }
 217
 218         if callee_def_id.is_local() {
 219             // Avoid a cycle here by only using `instance_mir` only if we have
 220             // a lower `DefPathHash` than the callee. This ensures that the callee will
 221             // not inline us. This trick even works with incremental compilation,
 222             // since `DefPathHash` is stable.
 223             if self.tcx.def_path_hash(caller_def_id).local_hash()
 224                 < self.tcx.def_path_hash(callee_def_id).local_hash()
 225             {
 226                 return Ok(());
 227             }
 228
 229             // If we know for sure that the function we're calling will itself try to
 230             // call us, then we avoid inlining that function.
 231             if self.tcx.mir_callgraph_reachable((*callee, caller_def_id.expect_local())) {
 232                 return Err("caller might be reachable from callee (query cycle avoidance)");
 233             }
 234
 235             Ok(())
 236         } else {
 237             // This cannot result in an immediate cycle since the callee MIR is from another crate
 238             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 239             // not need to catch this here, we can wait until the inliner decides to continue
 240             // inlining a second time.
 241             trace!("functions from other crates always have MIR");
 242             Ok(())
 243         }
 244     }
 245
 246     fn resolve_callsite(
 247         &self,
 248         caller_body: &Body<'tcx>,
 249         bb: BasicBlock,
 250         bb_data: &BasicBlockData<'tcx>,
 251     ) -> Option<CallSite<'tcx>> {
 252         // Only consider direct calls to functions
 253         let terminator = bb_data.terminator();
 254         if let TerminatorKind::Call { ref func, target, .. } = terminator.kind {
 255             let func_ty = func.ty(caller_body, self.tcx);
 256             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 257                 // To resolve an instance its substs have to be fully normalized.
 258                 let substs = self.tcx.try_normalize_erasing_regions(self.param_env, substs).ok()?;
 259                 let callee =
 260                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 261
 262                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 263                     return None;
 264                 }
 265
 266                 let fn_sig = self.tcx.bound_fn_sig(def_id).subst(self.tcx, substs);
 267
 268                 return Some(CallSite {
 269                     callee,
 270                     fn_sig,
 271                     block: bb,
 272                     target,
 273                     source_info: terminator.source_info,
 274                 });
 275             }
 276         }
 277
 278         None
 279     }
 280
 281     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 282     /// indicates that inlining decision should be based on other criteria.
 283     fn check_codegen_attributes(
 284         &self,
 285         callsite: &CallSite<'tcx>,
 286         callee_attrs: &CodegenFnAttrs,
 287     ) -> Result<(), &'static str> {
 288         if let InlineAttr::Never = callee_attrs.inline {
 289             return Err("never inline hint");
 290         }
 291
 292         // Only inline local functions if they would be eligible for cross-crate
 293         // inlining. This is to ensure that the final crate doesn't have MIR that
 294         // reference unexported symbols
 295         if callsite.callee.def_id().is_local() {
 296             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 297             if !is_generic && !callee_attrs.requests_inline() {
 298                 return Err("not exported");
 299             }
 300         }
 301
 302         if callsite.fn_sig.c_variadic() {
 303             return Err("C variadic");
 304         }
 305
 306         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 307             return Err("naked");
 308         }
 309
 310         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 311             return Err("cold");
 312         }
 313
 314         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 315             return Err("incompatible sanitizer set");
 316         }
 317
 318         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 319             return Err("incompatible instruction set");
 320         }
 321
 322         for feature in &callee_attrs.target_features {
 323             if !self.codegen_fn_attrs.target_features.contains(feature) {
 324                 return Err("incompatible target feature");
 325             }
 326         }
 327
 328         Ok(())
 329     }
 330
 331     /// Returns inlining decision that is based on the examination of callee MIR body.
 332     /// Assumes that codegen attributes have been checked for compatibility already.
 333     #[instrument(level = "debug", skip(self, callee_body))]
 334     fn check_mir_body(
 335         &self,
 336         callsite: &CallSite<'tcx>,
 337         callee_body: &Body<'tcx>,
 338         callee_attrs: &CodegenFnAttrs,
 339     ) -> Result<(), &'static str> {
 340         let tcx = self.tcx;
 341
 342         let mut threshold = if callee_attrs.requests_inline() {
 343             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 344         } else {
 345             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 346         };
 347
 348         // Give a bonus functions with a small number of blocks,
 349         // We normally have two or three blocks for even
 350         // very small functions.
 351         if callee_body.basic_blocks().len() <= 3 {
 352             threshold += threshold / 4;
 353         }
 354         debug!("    final inline threshold = {}", threshold);
 355
 356         // FIXME: Give a bonus to functions with only a single caller
 357         let mut first_block = true;
 358         let mut cost = 0;
 359
 360         // Traverse the MIR manually so we can account for the effects of
 361         // inlining on the CFG.
 362         let mut work_list = vec![START_BLOCK];
 363         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 364         while let Some(bb) = work_list.pop() {
 365             if !visited.insert(bb.index()) {
 366                 continue;
 367             }
 368             let blk = &callee_body.basic_blocks()[bb];
 369
 370             for stmt in &blk.statements {
 371                 // Don't count StorageLive/StorageDead in the inlining cost.
 372                 match stmt.kind {
 373                     StatementKind::StorageLive(_)
 374                     | StatementKind::StorageDead(_)
 375                     | StatementKind::Deinit(_)
 376                     | StatementKind::Nop => {}
 377                     _ => cost += INSTR_COST,
 378                 }
 379             }
 380             let term = blk.terminator();
 381             let mut is_drop = false;
 382             match term.kind {
 383                 TerminatorKind::Drop { ref place, target, unwind }
 384                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 385                     is_drop = true;
 386                     work_list.push(target);
 387                     // If the place doesn't actually need dropping, treat it like
 388                     // a regular goto.
 389                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 390                     if ty.needs_drop(tcx, self.param_env) {
 391                         cost += CALL_PENALTY;
 392                         if let Some(unwind) = unwind {
 393                             cost += LANDINGPAD_PENALTY;
 394                             work_list.push(unwind);
 395                         }
 396                     } else {
 397                         cost += INSTR_COST;
 398                     }
 399                 }
 400
 401                 TerminatorKind::Unreachable | TerminatorKind::Call { target: None, .. }
 402                     if first_block =>
 403                 {
 404                     // If the function always diverges, don't inline
 405                     // unless the cost is zero
 406                     threshold = 0;
 407                 }
 408
 409                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 410                     if let ty::FnDef(def_id, substs) =
 411                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty()).kind()
 412                     {
 413                         if let Ok(substs) =
 414                             self.tcx.try_normalize_erasing_regions(self.param_env, substs)
 415                         {
 416                             if let Ok(Some(instance)) =
 417                                 Instance::resolve(self.tcx, self.param_env, def_id, substs)
 418                             {
 419                                 if callsite.callee.def_id() == instance.def_id() {
 420                                     return Err("self-recursion");
 421                                 } else if self.history.contains(&instance) {
 422                                     return Err("already inlined");
 423                                 }
 424                             }
 425                         }
 426                         // Don't give intrinsics the extra penalty for calls
 427                         if tcx.is_intrinsic(def_id) {
 428                             cost += INSTR_COST;
 429                         } else {
 430                             cost += CALL_PENALTY;
 431                         }
 432                     } else {
 433                         cost += CALL_PENALTY;
 434                     }
 435                     if cleanup.is_some() {
 436                         cost += LANDINGPAD_PENALTY;
 437                     }
 438                 }
 439                 TerminatorKind::Assert { cleanup, .. } => {
 440                     cost += CALL_PENALTY;
 441
 442                     if cleanup.is_some() {
 443                         cost += LANDINGPAD_PENALTY;
 444                     }
 445                 }
 446                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 447                 TerminatorKind::InlineAsm { cleanup, .. } => {
 448                     cost += INSTR_COST;
 449
 450                     if cleanup.is_some() {
 451                         cost += LANDINGPAD_PENALTY;
 452                     }
 453                 }
 454                 _ => cost += INSTR_COST,
 455             }
 456
 457             if !is_drop {
 458                 for succ in term.successors() {
 459                     work_list.push(succ);
 460                 }
 461             }
 462
 463             first_block = false;
 464         }
 465
 466         // Count up the cost of local variables and temps, if we know the size
 467         // use that, otherwise we use a moderately-large dummy cost.
 468
 469         let ptr_size = tcx.data_layout.pointer_size.bytes();
 470
 471         for v in callee_body.vars_and_temps_iter() {
 472             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 473             // Cost of the var is the size in machine-words, if we know
 474             // it.
 475             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 476                 cost += ((size + ptr_size - 1) / ptr_size) as usize;
 477             } else {
 478                 cost += UNKNOWN_SIZE_COST;
 479             }
 480         }
 481
 482         if let InlineAttr::Always = callee_attrs.inline {
 483             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 484             Ok(())
 485         } else {
 486             if cost <= threshold {
 487                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 488                 Ok(())
 489             } else {
 490                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 491                 Err("cost above threshold")
 492             }
 493         }
 494     }
 495
 496     fn inline_call(
 497         &self,
 498         caller_body: &mut Body<'tcx>,
 499         callsite: &CallSite<'tcx>,
 500         mut callee_body: Body<'tcx>,
 501     ) {
 502         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 503         match terminator.kind {
 504             TerminatorKind::Call { args, destination, cleanup, .. } => {
 505                 // If the call is something like `a[*i] = f(i)`, where
 506                 // `i : &mut usize`, then just duplicating the `a[*i]`
 507                 // Place could result in two different locations if `f`
 508                 // writes to `i`. To prevent this we need to create a temporary
 509                 // borrow of the place and pass the destination as `*temp` instead.
 510                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 511                     for elem in place.projection.iter() {
 512                         match elem {
 513                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 514                             _ => {}
 515                         }
 516                     }
 517
 518                     false
 519                 }
 520
 521                 let dest = if dest_needs_borrow(destination) {
 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,
 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
 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                     callsite_scope: caller_body.source_scopes[callsite.source_info.scope].clone(),
 559                     callsite,
 560                     cleanup_block: cleanup,
 561                     in_cleanup_block: false,
 562                     tcx: self.tcx,
 563                     expn_data,
 564                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 565                 };
 566
 567                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 568                 // (or existing ones, in a few special cases) in the caller.
 569                 integrator.visit_body(&mut callee_body);
 570
 571                 // If there are any locals without storage markers, give them storage only for the
 572                 // duration of the call.
 573                 for local in callee_body.vars_and_temps_iter() {
 574                     if integrator.always_live_locals.contains(local) {
 575                         let new_local = integrator.map_local(local);
 576                         caller_body[callsite.block].statements.push(Statement {
 577                             source_info: callsite.source_info,
 578                             kind: StatementKind::StorageLive(new_local),
 579                         });
 580                     }
 581                 }
 582                 if let Some(block) = callsite.target {
 583                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 584                     // the slice once.
 585                     let mut n = 0;
 586                     for local in callee_body.vars_and_temps_iter().rev() {
 587                         if integrator.always_live_locals.contains(local) {
 588                             let new_local = integrator.map_local(local);
 589                             caller_body[block].statements.push(Statement {
 590                                 source_info: callsite.source_info,
 591                                 kind: StatementKind::StorageDead(new_local),
 592                             });
 593                             n += 1;
 594                         }
 595                     }
 596                     caller_body[block].statements.rotate_right(n);
 597                 }
 598
 599                 // Insert all of the (mapped) parts of the callee body into the caller.
 600                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 601                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 602                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 603                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 604
 605                 caller_body[callsite.block].terminator = Some(Terminator {
 606                     source_info: callsite.source_info,
 607                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 608                 });
 609
 610                 // Copy only unevaluated constants from the callee_body into the caller_body.
 611                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 612                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 613                 // because we are calling `subst_and_normalize_erasing_regions`.
 614                 caller_body.required_consts.extend(
 615                     callee_body.required_consts.iter().copied().filter(|&ct| {
 616                         match ct.literal.const_for_ty() {
 617                             Some(ct) => matches!(ct.kind(), ConstKind::Unevaluated(_)),
 618                             None => true,
 619                         }
 620                     }),
 621                 );
 622             }
 623             kind => bug!("unexpected terminator kind {:?}", kind),
 624         }
 625     }
 626
 627     fn make_call_args(
 628         &self,
 629         args: Vec<Operand<'tcx>>,
 630         callsite: &CallSite<'tcx>,
 631         caller_body: &mut Body<'tcx>,
 632         callee_body: &Body<'tcx>,
 633     ) -> Vec<Local> {
 634         let tcx = self.tcx;
 635
 636         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 637         // The caller provides the arguments wrapped up in a tuple:
 638         //
 639         //     tuple_tmp = (a, b, c)
 640         //     Fn::call(closure_ref, tuple_tmp)
 641         //
 642         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 643         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 644         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 645         // a vector like
 646         //
 647         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 648         //
 649         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 650         // if we "spill" that into *another* temporary, so that we can map the argument
 651         // variable in the callee MIR directly to an argument variable on our side.
 652         // So we introduce temporaries like:
 653         //
 654         //     tmp0 = tuple_tmp.0
 655         //     tmp1 = tuple_tmp.1
 656         //     tmp2 = tuple_tmp.2
 657         //
 658         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 659         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 660             let mut args = args.into_iter();
 661             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 662             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 663             assert!(args.next().is_none());
 664
 665             let tuple = Place::from(tuple);
 666             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() else {
 667                 bug!("Closure arguments are not passed as a tuple");
 668             };
 669
 670             // The `closure_ref` in our example above.
 671             let closure_ref_arg = iter::once(self_);
 672
 673             // The `tmp0`, `tmp1`, and `tmp2` in our example above.
 674             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 675                 // This is e.g., `tuple_tmp.0` in our example above.
 676                 let tuple_field = Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty));
 677
 678                 // Spill to a local to make e.g., `tmp0`.
 679                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 680             });
 681
 682             closure_ref_arg.chain(tuple_tmp_args).collect()
 683         } else {
 684             args.into_iter()
 685                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 686                 .collect()
 687         }
 688     }
 689
 690     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 691     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 692     fn create_temp_if_necessary(
 693         &self,
 694         arg: Operand<'tcx>,
 695         callsite: &CallSite<'tcx>,
 696         caller_body: &mut Body<'tcx>,
 697     ) -> Local {
 698         // Reuse the operand if it is a moved temporary.
 699         if let Operand::Move(place) = &arg
 700             && let Some(local) = place.as_local()
 701             && caller_body.local_kind(local) == LocalKind::Temp
 702         {
 703             return local;
 704         }
 705
 706         // Otherwise, create a temporary for the argument.
 707         trace!("creating temp for argument {:?}", arg);
 708         let arg_ty = arg.ty(caller_body, self.tcx);
 709         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 710         caller_body[callsite.block].statements.push(Statement {
 711             source_info: callsite.source_info,
 712             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 713         });
 714         local
 715     }
 716
 717     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 718     fn new_call_temp(
 719         &self,
 720         caller_body: &mut Body<'tcx>,
 721         callsite: &CallSite<'tcx>,
 722         ty: Ty<'tcx>,
 723     ) -> Local {
 724         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 725
 726         caller_body[callsite.block].statements.push(Statement {
 727             source_info: callsite.source_info,
 728             kind: StatementKind::StorageLive(local),
 729         });
 730
 731         if let Some(block) = callsite.target {
 732             caller_body[block].statements.insert(
 733                 0,
 734                 Statement {
 735                     source_info: callsite.source_info,
 736                     kind: StatementKind::StorageDead(local),
 737                 },
 738             );
 739         }
 740
 741         local
 742     }
 743 }
 744
 745 fn type_size_of<'tcx>(
 746     tcx: TyCtxt<'tcx>,
 747     param_env: ty::ParamEnv<'tcx>,
 748     ty: Ty<'tcx>,
 749 ) -> Option<u64> {
 750     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 751 }
 752
 753 /**
 754  * Integrator.
 755  *
 756  * Integrates blocks from the callee function into the calling function.
 757  * Updates block indices, references to locals and other control flow
 758  * stuff.
 759 */
 760 struct Integrator<'a, 'tcx> {
 761     args: &'a [Local],
 762     new_locals: RangeFrom<Local>,
 763     new_scopes: RangeFrom<SourceScope>,
 764     new_blocks: RangeFrom<BasicBlock>,
 765     destination: Place<'tcx>,
 766     callsite_scope: SourceScopeData<'tcx>,
 767     callsite: &'a CallSite<'tcx>,
 768     cleanup_block: Option<BasicBlock>,
 769     in_cleanup_block: bool,
 770     tcx: TyCtxt<'tcx>,
 771     expn_data: LocalExpnId,
 772     always_live_locals: BitSet<Local>,
 773 }
 774
 775 impl Integrator<'_, '_> {
 776     fn map_local(&self, local: Local) -> Local {
 777         let new = if local == RETURN_PLACE {
 778             self.destination.local
 779         } else {
 780             let idx = local.index() - 1;
 781             if idx < self.args.len() {
 782                 self.args[idx]
 783             } else {
 784                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 785             }
 786         };
 787         trace!("mapping local `{:?}` to `{:?}`", local, new);
 788         new
 789     }
 790
 791     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 792         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 793         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 794         new
 795     }
 796
 797     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 798         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 799         trace!("mapping block `{:?}` to `{:?}`", block, new);
 800         new
 801     }
 802 }
 803
 804 impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
 805     fn tcx(&self) -> TyCtxt<'tcx> {
 806         self.tcx
 807     }
 808
 809     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 810         *local = self.map_local(*local);
 811     }
 812
 813     fn visit_source_scope_data(&mut self, scope_data: &mut SourceScopeData<'tcx>) {
 814         self.super_source_scope_data(scope_data);
 815         if scope_data.parent_scope.is_none() {
 816             // Attach the outermost callee scope as a child of the callsite
 817             // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 818             scope_data.parent_scope = Some(self.callsite.source_info.scope);
 819             assert_eq!(scope_data.inlined_parent_scope, None);
 820             scope_data.inlined_parent_scope = if self.callsite_scope.inlined.is_some() {
 821                 Some(self.callsite.source_info.scope)
 822             } else {
 823                 self.callsite_scope.inlined_parent_scope
 824             };
 825
 826             // Mark the outermost callee scope as an inlined one.
 827             assert_eq!(scope_data.inlined, None);
 828             scope_data.inlined = Some((self.callsite.callee, self.callsite.source_info.span));
 829         } else if scope_data.inlined_parent_scope.is_none() {
 830             // Make it easy to find the scope with `inlined` set above.
 831             scope_data.inlined_parent_scope = Some(self.map_scope(OUTERMOST_SOURCE_SCOPE));
 832         }
 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 target, ref mut cleanup, .. } => {
 919                 if let Some(ref mut tgt) = *target {
 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.callsite.target {
 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 }