compiler/rustc_mir_transform/src/inline.rs

   1 //! Inlining pass for MIR functions
   2
   3 use rustc_attr::InlineAttr;
   4 use rustc_hir as hir;
   5 use rustc_index::bit_set::BitSet;
   6 use rustc_index::vec::Idx;
   7 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
   8 use rustc_middle::mir::visit::*;
   9 use rustc_middle::mir::*;
  10 use rustc_middle::traits::ObligationCause;
  11 use rustc_middle::ty::subst::Subst;
  12 use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
  13 use rustc_span::{hygiene::ExpnKind, ExpnData, Span};
  14 use rustc_target::spec::abi::Abi;
  15
  16 use super::simplify::{remove_dead_blocks, CfgSimplifier};
  17 use crate::MirPass;
  18 use std::iter;
  19 use std::ops::{Range, RangeFrom};
  20
  21 crate mod cycle;
  22
  23 const INSTR_COST: usize = 5;
  24 const CALL_PENALTY: usize = 25;
  25 const LANDINGPAD_PENALTY: usize = 50;
  26 const RESUME_PENALTY: usize = 45;
  27
  28 const UNKNOWN_SIZE_COST: usize = 10;
  29
  30 pub struct Inline;
  31
  32 #[derive(Copy, Clone, Debug)]
  33 struct CallSite<'tcx> {
  34     callee: Instance<'tcx>,
  35     fn_sig: ty::PolyFnSig<'tcx>,
  36     block: BasicBlock,
  37     target: Option<BasicBlock>,
  38     source_info: SourceInfo,
  39 }
  40
  41 impl<'tcx> MirPass<'tcx> for Inline {
  42     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
  43         if let Some(enabled) = sess.opts.debugging_opts.inline_mir {
  44             return enabled;
  45         }
  46
  47         sess.opts.mir_opt_level() >= 3
  48     }
  49
  50     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  51         let span = trace_span!("inline", body = %tcx.def_path_str(body.source.def_id()));
  52         let _guard = span.enter();
  53         if inline(tcx, body) {
  54             debug!("running simplify cfg on {:?}", body.source);
  55             CfgSimplifier::new(body).simplify();
  56             remove_dead_blocks(tcx, body);
  57         }
  58     }
  59 }
  60
  61 fn inline<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  62     let def_id = body.source.def_id();
  63     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  64
  65     // Only do inlining into fn bodies.
  66     if !tcx.hir().body_owner_kind(hir_id).is_fn_or_closure() {
  67         return false;
  68     }
  69     if body.source.promoted.is_some() {
  70         return false;
  71     }
  72     // Avoid inlining into generators, since their `optimized_mir` is used for layout computation,
  73     // which can create a cycle, even when no attempt is made to inline the function in the other
  74     // direction.
  75     if body.generator.is_some() {
  76         return false;
  77     }
  78
  79     let param_env = tcx.param_env_reveal_all_normalized(def_id);
  80     let param_env = rustc_trait_selection::traits::normalize_param_env_or_error(
  81         tcx,
  82         def_id,
  83         param_env,
  84         ObligationCause::misc(body.span, hir_id),
  85     );
  86
  87     let mut this = Inliner {
  88         tcx,
  89         param_env,
  90         codegen_fn_attrs: tcx.codegen_fn_attrs(def_id),
  91         hir_id,
  92         history: Vec::new(),
  93         changed: false,
  94     };
  95     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  96     this.process_blocks(body, blocks);
  97     this.changed
  98 }
  99
 100 struct Inliner<'tcx> {
 101     tcx: TyCtxt<'tcx>,
 102     param_env: ParamEnv<'tcx>,
 103     /// Caller codegen attributes.
 104     codegen_fn_attrs: &'tcx CodegenFnAttrs,
 105     /// Caller HirID.
 106     hir_id: hir::HirId,
 107     /// Stack of inlined Instances.
 108     history: Vec<ty::Instance<'tcx>>,
 109     /// Indicates that the caller body has been modified.
 110     changed: bool,
 111 }
 112
 113 impl<'tcx> Inliner<'tcx> {
 114     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 115         for bb in blocks {
 116             let bb_data = &caller_body[bb];
 117             if bb_data.is_cleanup {
 118                 continue;
 119             }
 120
 121             let callsite = match self.resolve_callsite(caller_body, bb, bb_data) {
 122                 None => continue,
 123                 Some(it) => it,
 124             };
 125
 126             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 127             let _guard = span.enter();
 128
 129             match self.try_inlining(caller_body, &callsite) {
 130                 Err(reason) => {
 131                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 132                     continue;
 133                 }
 134                 Ok(new_blocks) => {
 135                     debug!("inlined {}", callsite.callee);
 136                     self.changed = true;
 137                     self.history.push(callsite.callee);
 138                     self.process_blocks(caller_body, new_blocks);
 139                     self.history.pop();
 140                 }
 141             }
 142         }
 143     }
 144
 145     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 146     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 147     /// place.
 148     fn try_inlining(
 149         &self,
 150         caller_body: &mut Body<'tcx>,
 151         callsite: &CallSite<'tcx>,
 152     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 153         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 154         self.check_codegen_attributes(callsite, callee_attrs)?;
 155         self.check_mir_is_available(caller_body, &callsite.callee)?;
 156         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 157         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 158
 159         if !self.tcx.consider_optimizing(|| {
 160             format!("Inline {:?} into {:?}", callsite.callee, caller_body.source)
 161         }) {
 162             return Err("optimization fuel exhausted");
 163         }
 164
 165         let callee_body = callsite.callee.subst_mir_and_normalize_erasing_regions(
 166             self.tcx,
 167             self.param_env,
 168             callee_body.clone(),
 169         );
 170
 171         let old_blocks = caller_body.basic_blocks().next_index();
 172         self.inline_call(caller_body, &callsite, callee_body);
 173         let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 174
 175         Ok(new_blocks)
 176     }
 177
 178     fn check_mir_is_available(
 179         &self,
 180         caller_body: &Body<'tcx>,
 181         callee: &Instance<'tcx>,
 182     ) -> Result<(), &'static str> {
 183         if callee.def_id() == caller_body.source.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 let Some(callee_def_id) = callee.def_id().as_local() {
 219             let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
 220             // Avoid a cycle here by only using `instance_mir` only if we have
 221             // a lower `HirId` than the callee. This ensures that the callee will
 222             // not inline us. This trick only works without incremental compilation.
 223             // So don't do it if that is enabled.
 224             if !self.tcx.dep_graph.is_fully_enabled() && self.hir_id.index() < callee_hir_id.index()
 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
 232                 .tcx
 233                 .mir_callgraph_reachable((*callee, caller_body.source.def_id().expect_local()))
 234             {
 235                 return Err("caller might be reachable from callee (query cycle avoidance)");
 236             }
 237
 238             Ok(())
 239         } else {
 240             // This cannot result in an immediate cycle since the callee MIR is from another crate
 241             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 242             // not need to catch this here, we can wait until the inliner decides to continue
 243             // inlining a second time.
 244             trace!("functions from other crates always have MIR");
 245             Ok(())
 246         }
 247     }
 248
 249     fn resolve_callsite(
 250         &self,
 251         caller_body: &Body<'tcx>,
 252         bb: BasicBlock,
 253         bb_data: &BasicBlockData<'tcx>,
 254     ) -> Option<CallSite<'tcx>> {
 255         // Only consider direct calls to functions
 256         let terminator = bb_data.terminator();
 257         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 258             let func_ty = func.ty(caller_body, self.tcx);
 259             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 260                 // To resolve an instance its substs have to be fully normalized.
 261                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 262                 let callee =
 263                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 264
 265                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 266                     return None;
 267                 }
 268
 269                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 270
 271                 return Some(CallSite {
 272                     callee,
 273                     fn_sig,
 274                     block: bb,
 275                     target: destination.map(|(_, target)| target),
 276                     source_info: terminator.source_info,
 277                 });
 278             }
 279         }
 280
 281         None
 282     }
 283
 284     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 285     /// indicates that inlining decision should be based on other criteria.
 286     fn check_codegen_attributes(
 287         &self,
 288         callsite: &CallSite<'tcx>,
 289         callee_attrs: &CodegenFnAttrs,
 290     ) -> Result<(), &'static str> {
 291         if let InlineAttr::Never = callee_attrs.inline {
 292             return Err("never inline hint");
 293         }
 294
 295         // Only inline local functions if they would be eligible for cross-crate
 296         // inlining. This is to ensure that the final crate doesn't have MIR that
 297         // reference unexported symbols
 298         if callsite.callee.def_id().is_local() {
 299             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 300             if !is_generic && !callee_attrs.requests_inline() {
 301                 return Err("not exported");
 302             }
 303         }
 304
 305         if callsite.fn_sig.c_variadic() {
 306             return Err("C variadic");
 307         }
 308
 309         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 310             return Err("naked");
 311         }
 312
 313         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 314             return Err("cold");
 315         }
 316
 317         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 318             return Err("incompatible sanitizer set");
 319         }
 320
 321         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 322             return Err("incompatible instruction set");
 323         }
 324
 325         for feature in &callee_attrs.target_features {
 326             if !self.codegen_fn_attrs.target_features.contains(feature) {
 327                 return Err("incompatible target feature");
 328             }
 329         }
 330
 331         Ok(())
 332     }
 333
 334     /// Returns inlining decision that is based on the examination of callee MIR body.
 335     /// Assumes that codegen attributes have been checked for compatibility already.
 336     #[instrument(level = "debug", skip(self, callee_body))]
 337     fn check_mir_body(
 338         &self,
 339         callsite: &CallSite<'tcx>,
 340         callee_body: &Body<'tcx>,
 341         callee_attrs: &CodegenFnAttrs,
 342     ) -> Result<(), &'static str> {
 343         let tcx = self.tcx;
 344
 345         let mut threshold = if callee_attrs.requests_inline() {
 346             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 347         } else {
 348             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 349         };
 350
 351         // Give a bonus functions with a small number of blocks,
 352         // We normally have two or three blocks for even
 353         // very small functions.
 354         if callee_body.basic_blocks().len() <= 3 {
 355             threshold += threshold / 4;
 356         }
 357         debug!("    final inline threshold = {}", threshold);
 358
 359         // FIXME: Give a bonus to functions with only a single caller
 360         let mut first_block = true;
 361         let mut cost = 0;
 362
 363         // Traverse the MIR manually so we can account for the effects of
 364         // inlining on the CFG.
 365         let mut work_list = vec![START_BLOCK];
 366         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 367         while let Some(bb) = work_list.pop() {
 368             if !visited.insert(bb.index()) {
 369                 continue;
 370             }
 371             let blk = &callee_body.basic_blocks()[bb];
 372
 373             for stmt in &blk.statements {
 374                 // Don't count StorageLive/StorageDead in the inlining cost.
 375                 match stmt.kind {
 376                     StatementKind::StorageLive(_)
 377                     | StatementKind::StorageDead(_)
 378                     | StatementKind::Nop => {}
 379                     _ => cost += INSTR_COST,
 380                 }
 381             }
 382             let term = blk.terminator();
 383             let mut is_drop = false;
 384             match term.kind {
 385                 TerminatorKind::Drop { ref place, target, unwind }
 386                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 387                     is_drop = true;
 388                     work_list.push(target);
 389                     // If the place doesn't actually need dropping, treat it like
 390                     // a regular goto.
 391                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 392                     if ty.needs_drop(tcx, self.param_env) {
 393                         cost += CALL_PENALTY;
 394                         if let Some(unwind) = unwind {
 395                             cost += LANDINGPAD_PENALTY;
 396                             work_list.push(unwind);
 397                         }
 398                     } else {
 399                         cost += INSTR_COST;
 400                     }
 401                 }
 402
 403                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 404                     if first_block =>
 405                 {
 406                     // If the function always diverges, don't inline
 407                     // unless the cost is zero
 408                     threshold = 0;
 409                 }
 410
 411                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 412                     if let ty::FnDef(def_id, substs) =
 413                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty()).kind()
 414                     {
 415                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 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                         // Don't give intrinsics the extra penalty for calls
 426                         let f = tcx.fn_sig(def_id);
 427                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 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 let Some((destination_place, _)) = destination {
 522                     if dest_needs_borrow(destination_place) {
 523                         trace!("creating temp for return destination");
 524                         let dest = Rvalue::Ref(
 525                             self.tcx.lifetimes.re_erased,
 526                             BorrowKind::Mut { allow_two_phase_borrow: false },
 527                             destination_place,
 528                         );
 529                         let dest_ty = dest.ty(caller_body, self.tcx);
 530                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 531                         caller_body[callsite.block].statements.push(Statement {
 532                             source_info: callsite.source_info,
 533                             kind: StatementKind::Assign(Box::new((temp, dest))),
 534                         });
 535                         self.tcx.mk_place_deref(temp)
 536                     } else {
 537                         destination_place
 538                     }
 539                 } else {
 540                     trace!("creating temp for return place");
 541                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 542                 };
 543
 544                 // Copy the arguments if needed.
 545                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 546
 547                 let mut integrator = Integrator {
 548                     args: &args,
 549                     new_locals: Local::new(caller_body.local_decls.len())..,
 550                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 551                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 552                     destination: dest,
 553                     return_block: callsite.target,
 554                     cleanup_block: cleanup,
 555                     in_cleanup_block: false,
 556                     tcx: self.tcx,
 557                     callsite_span: callsite.source_info.span,
 558                     body_span: callee_body.span,
 559                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 560                 };
 561
 562                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 563                 // (or existing ones, in a few special cases) in the caller.
 564                 integrator.visit_body(&mut callee_body);
 565
 566                 for scope in &mut callee_body.source_scopes {
 567                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 568                     if scope.parent_scope.is_none() {
 569                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 570
 571                         // Attach the outermost callee scope as a child of the callsite
 572                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 573                         scope.parent_scope = Some(callsite.source_info.scope);
 574                         assert_eq!(scope.inlined_parent_scope, None);
 575                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 576                             Some(callsite.source_info.scope)
 577                         } else {
 578                             callsite_scope.inlined_parent_scope
 579                         };
 580
 581                         // Mark the outermost callee scope as an inlined one.
 582                         assert_eq!(scope.inlined, None);
 583                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 584                     } else if scope.inlined_parent_scope.is_none() {
 585                         // Make it easy to find the scope with `inlined` set above.
 586                         scope.inlined_parent_scope =
 587                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 588                     }
 589                 }
 590
 591                 // If there are any locals without storage markers, give them storage only for the
 592                 // duration of the call.
 593                 for local in callee_body.vars_and_temps_iter() {
 594                     if integrator.always_live_locals.contains(local) {
 595                         let new_local = integrator.map_local(local);
 596                         caller_body[callsite.block].statements.push(Statement {
 597                             source_info: callsite.source_info,
 598                             kind: StatementKind::StorageLive(new_local),
 599                         });
 600                     }
 601                 }
 602                 if let Some(block) = callsite.target {
 603                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 604                     // the slice once.
 605                     let mut n = 0;
 606                     for local in callee_body.vars_and_temps_iter().rev() {
 607                         if integrator.always_live_locals.contains(local) {
 608                             let new_local = integrator.map_local(local);
 609                             caller_body[block].statements.push(Statement {
 610                                 source_info: callsite.source_info,
 611                                 kind: StatementKind::StorageDead(new_local),
 612                             });
 613                             n += 1;
 614                         }
 615                     }
 616                     caller_body[block].statements.rotate_right(n);
 617                 }
 618
 619                 // Insert all of the (mapped) parts of the callee body into the caller.
 620                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 621                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 622                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 623                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 624
 625                 caller_body[callsite.block].terminator = Some(Terminator {
 626                     source_info: callsite.source_info,
 627                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 628                 });
 629
 630                 // Copy only unevaluated constants from the callee_body into the caller_body.
 631                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 632                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 633                 // because we are calling `subst_and_normalize_erasing_regions`.
 634                 caller_body.required_consts.extend(
 635                     callee_body.required_consts.iter().copied().filter(|&ct| {
 636                         match ct.literal.const_for_ty() {
 637                             Some(ct) => matches!(ct.val(), ConstKind::Unevaluated(_)),
 638                             None => true,
 639                         }
 640                     }),
 641                 );
 642             }
 643             kind => bug!("unexpected terminator kind {:?}", kind),
 644         }
 645     }
 646
 647     fn make_call_args(
 648         &self,
 649         args: Vec<Operand<'tcx>>,
 650         callsite: &CallSite<'tcx>,
 651         caller_body: &mut Body<'tcx>,
 652         callee_body: &Body<'tcx>,
 653     ) -> Vec<Local> {
 654         let tcx = self.tcx;
 655
 656         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 657         // The caller provides the arguments wrapped up in a tuple:
 658         //
 659         //     tuple_tmp = (a, b, c)
 660         //     Fn::call(closure_ref, tuple_tmp)
 661         //
 662         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 663         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 664         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 665         // a vector like
 666         //
 667         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 668         //
 669         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 670         // if we "spill" that into *another* temporary, so that we can map the argument
 671         // variable in the callee MIR directly to an argument variable on our side.
 672         // So we introduce temporaries like:
 673         //
 674         //     tmp0 = tuple_tmp.0
 675         //     tmp1 = tuple_tmp.1
 676         //     tmp2 = tuple_tmp.2
 677         //
 678         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 679         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 680             let mut args = args.into_iter();
 681             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 682             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 683             assert!(args.next().is_none());
 684
 685             let tuple = Place::from(tuple);
 686             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() else {
 687                 bug!("Closure arguments are not passed as a tuple");
 688             };
 689
 690             // The `closure_ref` in our example above.
 691             let closure_ref_arg = iter::once(self_);
 692
 693             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 694             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 695                 // This is e.g., `tuple_tmp.0` in our example above.
 696                 let tuple_field =
 697                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 698
 699                 // Spill to a local to make e.g., `tmp0`.
 700                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 701             });
 702
 703             closure_ref_arg.chain(tuple_tmp_args).collect()
 704         } else {
 705             args.into_iter()
 706                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 707                 .collect()
 708         }
 709     }
 710
 711     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 712     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 713     fn create_temp_if_necessary(
 714         &self,
 715         arg: Operand<'tcx>,
 716         callsite: &CallSite<'tcx>,
 717         caller_body: &mut Body<'tcx>,
 718     ) -> Local {
 719         // Reuse the operand if it is a moved temporary.
 720         if let Operand::Move(place) = &arg {
 721             if let Some(local) = place.as_local() {
 722                 if caller_body.local_kind(local) == LocalKind::Temp {
 723                     return local;
 724                 }
 725             }
 726         }
 727
 728         // Otherwise, create a temporary for the argument.
 729         trace!("creating temp for argument {:?}", arg);
 730         let arg_ty = arg.ty(caller_body, self.tcx);
 731         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 732         caller_body[callsite.block].statements.push(Statement {
 733             source_info: callsite.source_info,
 734             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 735         });
 736         local
 737     }
 738
 739     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 740     fn new_call_temp(
 741         &self,
 742         caller_body: &mut Body<'tcx>,
 743         callsite: &CallSite<'tcx>,
 744         ty: Ty<'tcx>,
 745     ) -> Local {
 746         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 747
 748         caller_body[callsite.block].statements.push(Statement {
 749             source_info: callsite.source_info,
 750             kind: StatementKind::StorageLive(local),
 751         });
 752
 753         if let Some(block) = callsite.target {
 754             caller_body[block].statements.insert(
 755                 0,
 756                 Statement {
 757                     source_info: callsite.source_info,
 758                     kind: StatementKind::StorageDead(local),
 759                 },
 760             );
 761         }
 762
 763         local
 764     }
 765 }
 766
 767 fn type_size_of<'tcx>(
 768     tcx: TyCtxt<'tcx>,
 769     param_env: ty::ParamEnv<'tcx>,
 770     ty: Ty<'tcx>,
 771 ) -> Option<u64> {
 772     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 773 }
 774
 775 /**
 776  * Integrator.
 777  *
 778  * Integrates blocks from the callee function into the calling function.
 779  * Updates block indices, references to locals and other control flow
 780  * stuff.
 781 */
 782 struct Integrator<'a, 'tcx> {
 783     args: &'a [Local],
 784     new_locals: RangeFrom<Local>,
 785     new_scopes: RangeFrom<SourceScope>,
 786     new_blocks: RangeFrom<BasicBlock>,
 787     destination: Place<'tcx>,
 788     return_block: Option<BasicBlock>,
 789     cleanup_block: Option<BasicBlock>,
 790     in_cleanup_block: bool,
 791     tcx: TyCtxt<'tcx>,
 792     callsite_span: Span,
 793     body_span: Span,
 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         let mut expn_data =
 841             ExpnData::default(ExpnKind::Inlined, *span, self.tcx.sess.edition(), None, None);
 842         expn_data.def_site = self.body_span;
 843         // Make sure that all spans track the fact that they were inlined.
 844         *span =
 845             self.callsite_span.fresh_expansion(expn_data, self.tcx.create_stable_hashing_context());
 846     }
 847
 848     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 849         for elem in place.projection {
 850             // FIXME: Make sure that return place is not used in an indexing projection, since it
 851             // won't be rebased as it is supposed to be.
 852             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 853         }
 854
 855         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 856         let dest_proj_len = self.destination.projection.len();
 857         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 858             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 859             projs.extend(self.destination.projection);
 860             projs.extend(place.projection);
 861
 862             place.projection = self.tcx.intern_place_elems(&*projs);
 863         }
 864         // Handles integrating any locals that occur in the base
 865         // or projections
 866         self.super_place(place, context, location)
 867     }
 868
 869     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 870         self.in_cleanup_block = data.is_cleanup;
 871         self.super_basic_block_data(block, data);
 872         self.in_cleanup_block = false;
 873     }
 874
 875     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 876         self.super_retag(kind, place, loc);
 877
 878         // We have to patch all inlined retags to be aware that they are no longer
 879         // happening on function entry.
 880         if *kind == RetagKind::FnEntry {
 881             *kind = RetagKind::Default;
 882         }
 883     }
 884
 885     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 886         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 887             statement.kind
 888         {
 889             self.always_live_locals.remove(local);
 890         }
 891         self.super_statement(statement, location);
 892     }
 893
 894     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 895         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 896         // replaced down below anyways).
 897         if !matches!(terminator.kind, TerminatorKind::Return) {
 898             self.super_terminator(terminator, loc);
 899         }
 900
 901         match terminator.kind {
 902             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 903             TerminatorKind::Goto { ref mut target } => {
 904                 *target = self.map_block(*target);
 905             }
 906             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 907                 for tgt in targets.all_targets_mut() {
 908                     *tgt = self.map_block(*tgt);
 909                 }
 910             }
 911             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 912             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 913                 *target = self.map_block(*target);
 914                 if let Some(tgt) = *unwind {
 915                     *unwind = Some(self.map_block(tgt));
 916                 } else if !self.in_cleanup_block {
 917                     // Unless this drop is in a cleanup block, add an unwind edge to
 918                     // the original call's cleanup block
 919                     *unwind = self.cleanup_block;
 920                 }
 921             }
 922             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 923                 if let Some((_, ref mut tgt)) = *destination {
 924                     *tgt = self.map_block(*tgt);
 925                 }
 926                 if let Some(tgt) = *cleanup {
 927                     *cleanup = Some(self.map_block(tgt));
 928                 } else if !self.in_cleanup_block {
 929                     // Unless this call is in a cleanup block, add an unwind edge to
 930                     // the original call's cleanup block
 931                     *cleanup = self.cleanup_block;
 932                 }
 933             }
 934             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 935                 *target = self.map_block(*target);
 936                 if let Some(tgt) = *cleanup {
 937                     *cleanup = Some(self.map_block(tgt));
 938                 } else if !self.in_cleanup_block {
 939                     // Unless this assert is in a cleanup block, add an unwind edge to
 940                     // the original call's cleanup block
 941                     *cleanup = self.cleanup_block;
 942                 }
 943             }
 944             TerminatorKind::Return => {
 945                 terminator.kind = if let Some(tgt) = self.return_block {
 946                     TerminatorKind::Goto { target: tgt }
 947                 } else {
 948                     TerminatorKind::Unreachable
 949                 }
 950             }
 951             TerminatorKind::Resume => {
 952                 if let Some(tgt) = self.cleanup_block {
 953                     terminator.kind = TerminatorKind::Goto { target: tgt }
 954                 }
 955             }
 956             TerminatorKind::Abort => {}
 957             TerminatorKind::Unreachable => {}
 958             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 959                 *real_target = self.map_block(*real_target);
 960                 *imaginary_target = self.map_block(*imaginary_target);
 961             }
 962             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 963             // see the ordering of passes in the optimized_mir query.
 964             {
 965                 bug!("False unwinds should have been removed before inlining")
 966             }
 967             TerminatorKind::InlineAsm { ref mut destination, ref mut cleanup, .. } => {
 968                 if let Some(ref mut tgt) = *destination {
 969                     *tgt = self.map_block(*tgt);
 970                 } else if !self.in_cleanup_block {
 971                     // Unless this inline asm is in a cleanup block, add an unwind edge to
 972                     // the original call's cleanup block
 973                     *cleanup = self.cleanup_block;
 974                 }
 975             }
 976         }
 977     }
 978 }