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::ty::subst::Subst;
  11 use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
  12 use rustc_span::{hygiene::ExpnKind, ExpnData, 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();
  62     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  63
  64     // Only do inlining into fn bodies.
  65     if !tcx.hir().body_owner_kind(hir_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 mut this = Inliner {
  79         tcx,
  80         param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()),
  81         codegen_fn_attrs: tcx.codegen_fn_attrs(body.source.def_id()),
  82         hir_id,
  83         history: Vec::new(),
  84         changed: false,
  85     };
  86     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  87     this.process_blocks(body, blocks);
  88     this.changed
  89 }
  90
  91 struct Inliner<'tcx> {
  92     tcx: TyCtxt<'tcx>,
  93     param_env: ParamEnv<'tcx>,
  94     /// Caller codegen attributes.
  95     codegen_fn_attrs: &'tcx CodegenFnAttrs,
  96     /// Caller HirID.
  97     hir_id: hir::HirId,
  98     /// Stack of inlined Instances.
  99     history: Vec<ty::Instance<'tcx>>,
 100     /// Indicates that the caller body has been modified.
 101     changed: bool,
 102 }
 103
 104 impl<'tcx> Inliner<'tcx> {
 105     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 106         for bb in blocks {
 107             let bb_data = &caller_body[bb];
 108             if bb_data.is_cleanup {
 109                 continue;
 110             }
 111
 112             let callsite = match self.resolve_callsite(caller_body, bb, bb_data) {
 113                 None => continue,
 114                 Some(it) => it,
 115             };
 116
 117             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 118             let _guard = span.enter();
 119
 120             match self.try_inlining(caller_body, &callsite) {
 121                 Err(reason) => {
 122                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 123                     continue;
 124                 }
 125                 Ok(new_blocks) => {
 126                     debug!("inlined {}", callsite.callee);
 127                     self.changed = true;
 128                     self.history.push(callsite.callee);
 129                     self.process_blocks(caller_body, new_blocks);
 130                     self.history.pop();
 131                 }
 132             }
 133         }
 134     }
 135
 136     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 137     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 138     /// place.
 139     fn try_inlining(
 140         &self,
 141         caller_body: &mut Body<'tcx>,
 142         callsite: &CallSite<'tcx>,
 143     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 144         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 145         self.check_codegen_attributes(callsite, callee_attrs)?;
 146         self.check_mir_is_available(caller_body, &callsite.callee)?;
 147         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 148         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 149
 150         if !self.tcx.consider_optimizing(|| {
 151             format!("Inline {:?} into {:?}", callsite.callee, caller_body.source)
 152         }) {
 153             return Err("optimization fuel exhausted");
 154         }
 155
 156         let callee_body = callsite.callee.subst_mir_and_normalize_erasing_regions(
 157             self.tcx,
 158             self.param_env,
 159             callee_body.clone(),
 160         );
 161
 162         let old_blocks = caller_body.basic_blocks().next_index();
 163         self.inline_call(caller_body, &callsite, callee_body);
 164         let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 165
 166         Ok(new_blocks)
 167     }
 168
 169     fn check_mir_is_available(
 170         &self,
 171         caller_body: &Body<'tcx>,
 172         callee: &Instance<'tcx>,
 173     ) -> Result<(), &'static str> {
 174         if callee.def_id() == caller_body.source.def_id() {
 175             return Err("self-recursion");
 176         }
 177
 178         match callee.def {
 179             InstanceDef::Item(_) => {
 180                 // If there is no MIR available (either because it was not in metadata or
 181                 // because it has no MIR because it's an extern function), then the inliner
 182                 // won't cause cycles on this.
 183                 if !self.tcx.is_mir_available(callee.def_id()) {
 184                     return Err("item MIR unavailable");
 185                 }
 186             }
 187             // These have no own callable MIR.
 188             InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
 189                 return Err("instance without MIR (intrinsic / virtual)");
 190             }
 191             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
 192             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
 193             // do not need to catch this here, we can wait until the inliner decides to continue
 194             // inlining a second time.
 195             InstanceDef::VtableShim(_)
 196             | InstanceDef::ReifyShim(_)
 197             | InstanceDef::FnPtrShim(..)
 198             | InstanceDef::ClosureOnceShim { .. }
 199             | InstanceDef::DropGlue(..)
 200             | InstanceDef::CloneShim(..) => return Ok(()),
 201         }
 202
 203         if self.tcx.is_constructor(callee.def_id()) {
 204             trace!("constructors always have MIR");
 205             // Constructor functions cannot cause a query cycle.
 206             return Ok(());
 207         }
 208
 209         if let Some(callee_def_id) = callee.def_id().as_local() {
 210             let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
 211             // Avoid a cycle here by only using `instance_mir` only if we have
 212             // a lower `HirId` than the callee. This ensures that the callee will
 213             // not inline us. This trick only works without incremental compilation.
 214             // So don't do it if that is enabled.
 215             if !self.tcx.dep_graph.is_fully_enabled() && self.hir_id.index() < callee_hir_id.index()
 216             {
 217                 return Ok(());
 218             }
 219
 220             // If we know for sure that the function we're calling will itself try to
 221             // call us, then we avoid inlining that function.
 222             if self
 223                 .tcx
 224                 .mir_callgraph_reachable((*callee, caller_body.source.def_id().expect_local()))
 225             {
 226                 return Err("caller might be reachable from callee (query cycle avoidance)");
 227             }
 228
 229             Ok(())
 230         } else {
 231             // This cannot result in an immediate cycle since the callee MIR is from another crate
 232             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 233             // not need to catch this here, we can wait until the inliner decides to continue
 234             // inlining a second time.
 235             trace!("functions from other crates always have MIR");
 236             Ok(())
 237         }
 238     }
 239
 240     fn resolve_callsite(
 241         &self,
 242         caller_body: &Body<'tcx>,
 243         bb: BasicBlock,
 244         bb_data: &BasicBlockData<'tcx>,
 245     ) -> Option<CallSite<'tcx>> {
 246         // Only consider direct calls to functions
 247         let terminator = bb_data.terminator();
 248         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 249             let func_ty = func.ty(caller_body, self.tcx);
 250             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 251                 // To resolve an instance its substs have to be fully normalized.
 252                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 253                 let callee =
 254                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 255
 256                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 257                     return None;
 258                 }
 259
 260                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 261
 262                 return Some(CallSite {
 263                     callee,
 264                     fn_sig,
 265                     block: bb,
 266                     target: destination.map(|(_, target)| target),
 267                     source_info: terminator.source_info,
 268                 });
 269             }
 270         }
 271
 272         None
 273     }
 274
 275     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 276     /// indicates that inlining decision should be based on other criteria.
 277     fn check_codegen_attributes(
 278         &self,
 279         callsite: &CallSite<'tcx>,
 280         callee_attrs: &CodegenFnAttrs,
 281     ) -> Result<(), &'static str> {
 282         if let InlineAttr::Never = callee_attrs.inline {
 283             return Err("never inline hint");
 284         }
 285
 286         // Only inline local functions if they would be eligible for cross-crate
 287         // inlining. This is to ensure that the final crate doesn't have MIR that
 288         // reference unexported symbols
 289         if callsite.callee.def_id().is_local() {
 290             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 291             if !is_generic && !callee_attrs.requests_inline() {
 292                 return Err("not exported");
 293             }
 294         }
 295
 296         if callsite.fn_sig.c_variadic() {
 297             return Err("C variadic");
 298         }
 299
 300         if callee_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 301             return Err("naked");
 302         }
 303
 304         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 305             return Err("cold");
 306         }
 307
 308         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 309             return Err("incompatible sanitizer set");
 310         }
 311
 312         if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set {
 313             return Err("incompatible instruction set");
 314         }
 315
 316         for feature in &callee_attrs.target_features {
 317             if !self.codegen_fn_attrs.target_features.contains(feature) {
 318                 return Err("incompatible target feature");
 319             }
 320         }
 321
 322         Ok(())
 323     }
 324
 325     /// Returns inlining decision that is based on the examination of callee MIR body.
 326     /// Assumes that codegen attributes have been checked for compatibility already.
 327     #[instrument(level = "debug", skip(self, callee_body))]
 328     fn check_mir_body(
 329         &self,
 330         callsite: &CallSite<'tcx>,
 331         callee_body: &Body<'tcx>,
 332         callee_attrs: &CodegenFnAttrs,
 333     ) -> Result<(), &'static str> {
 334         let tcx = self.tcx;
 335
 336         let mut threshold = if callee_attrs.requests_inline() {
 337             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
 338         } else {
 339             self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
 340         };
 341
 342         // Give a bonus functions with a small number of blocks,
 343         // We normally have two or three blocks for even
 344         // very small functions.
 345         if callee_body.basic_blocks().len() <= 3 {
 346             threshold += threshold / 4;
 347         }
 348         debug!("    final inline threshold = {}", threshold);
 349
 350         // FIXME: Give a bonus to functions with only a single caller
 351         let mut first_block = true;
 352         let mut cost = 0;
 353
 354         // Traverse the MIR manually so we can account for the effects of
 355         // inlining on the CFG.
 356         let mut work_list = vec![START_BLOCK];
 357         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 358         while let Some(bb) = work_list.pop() {
 359             if !visited.insert(bb.index()) {
 360                 continue;
 361             }
 362             let blk = &callee_body.basic_blocks()[bb];
 363
 364             for stmt in &blk.statements {
 365                 // Don't count StorageLive/StorageDead in the inlining cost.
 366                 match stmt.kind {
 367                     StatementKind::StorageLive(_)
 368                     | StatementKind::StorageDead(_)
 369                     | StatementKind::Nop => {}
 370                     _ => cost += INSTR_COST,
 371                 }
 372             }
 373             let term = blk.terminator();
 374             let mut is_drop = false;
 375             match term.kind {
 376                 TerminatorKind::Drop { ref place, target, unwind }
 377                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 378                     is_drop = true;
 379                     work_list.push(target);
 380                     // If the place doesn't actually need dropping, treat it like
 381                     // a regular goto.
 382                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 383                     if ty.needs_drop(tcx, self.param_env) {
 384                         cost += CALL_PENALTY;
 385                         if let Some(unwind) = unwind {
 386                             cost += LANDINGPAD_PENALTY;
 387                             work_list.push(unwind);
 388                         }
 389                     } else {
 390                         cost += INSTR_COST;
 391                     }
 392                 }
 393
 394                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 395                     if first_block =>
 396                 {
 397                     // If the function always diverges, don't inline
 398                     // unless the cost is zero
 399                     threshold = 0;
 400                 }
 401
 402                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 403                     if let ty::FnDef(def_id, substs) =
 404                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty()).kind()
 405                     {
 406                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 407                         if let Ok(Some(instance)) =
 408                             Instance::resolve(self.tcx, self.param_env, def_id, substs)
 409                         {
 410                             if callsite.callee.def_id() == instance.def_id() {
 411                                 return Err("self-recursion");
 412                             } else if self.history.contains(&instance) {
 413                                 return Err("already inlined");
 414                             }
 415                         }
 416                         // Don't give intrinsics the extra penalty for calls
 417                         let f = tcx.fn_sig(def_id);
 418                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 419                             cost += INSTR_COST;
 420                         } else {
 421                             cost += CALL_PENALTY;
 422                         }
 423                     } else {
 424                         cost += CALL_PENALTY;
 425                     }
 426                     if cleanup.is_some() {
 427                         cost += LANDINGPAD_PENALTY;
 428                     }
 429                 }
 430                 TerminatorKind::Assert { cleanup, .. } => {
 431                     cost += CALL_PENALTY;
 432
 433                     if cleanup.is_some() {
 434                         cost += LANDINGPAD_PENALTY;
 435                     }
 436                 }
 437                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 438                 TerminatorKind::InlineAsm { cleanup, .. } => {
 439                     cost += INSTR_COST;
 440
 441                     if cleanup.is_some() {
 442                         cost += LANDINGPAD_PENALTY;
 443                     }
 444                 }
 445                 _ => cost += INSTR_COST,
 446             }
 447
 448             if !is_drop {
 449                 for &succ in term.successors() {
 450                     work_list.push(succ);
 451                 }
 452             }
 453
 454             first_block = false;
 455         }
 456
 457         // Count up the cost of local variables and temps, if we know the size
 458         // use that, otherwise we use a moderately-large dummy cost.
 459
 460         let ptr_size = tcx.data_layout.pointer_size.bytes();
 461
 462         for v in callee_body.vars_and_temps_iter() {
 463             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 464             // Cost of the var is the size in machine-words, if we know
 465             // it.
 466             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 467                 cost += ((size + ptr_size - 1) / ptr_size) as usize;
 468             } else {
 469                 cost += UNKNOWN_SIZE_COST;
 470             }
 471         }
 472
 473         if let InlineAttr::Always = callee_attrs.inline {
 474             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 475             Ok(())
 476         } else {
 477             if cost <= threshold {
 478                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 479                 Ok(())
 480             } else {
 481                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 482                 Err("cost above threshold")
 483             }
 484         }
 485     }
 486
 487     fn inline_call(
 488         &self,
 489         caller_body: &mut Body<'tcx>,
 490         callsite: &CallSite<'tcx>,
 491         mut callee_body: Body<'tcx>,
 492     ) {
 493         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 494         match terminator.kind {
 495             TerminatorKind::Call { args, destination, cleanup, .. } => {
 496                 // If the call is something like `a[*i] = f(i)`, where
 497                 // `i : &mut usize`, then just duplicating the `a[*i]`
 498                 // Place could result in two different locations if `f`
 499                 // writes to `i`. To prevent this we need to create a temporary
 500                 // borrow of the place and pass the destination as `*temp` instead.
 501                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 502                     for elem in place.projection.iter() {
 503                         match elem {
 504                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 505                             _ => {}
 506                         }
 507                     }
 508
 509                     false
 510                 }
 511
 512                 let dest = if let Some((destination_place, _)) = destination {
 513                     if dest_needs_borrow(destination_place) {
 514                         trace!("creating temp for return destination");
 515                         let dest = Rvalue::Ref(
 516                             self.tcx.lifetimes.re_erased,
 517                             BorrowKind::Mut { allow_two_phase_borrow: false },
 518                             destination_place,
 519                         );
 520                         let dest_ty = dest.ty(caller_body, self.tcx);
 521                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 522                         caller_body[callsite.block].statements.push(Statement {
 523                             source_info: callsite.source_info,
 524                             kind: StatementKind::Assign(Box::new((temp, dest))),
 525                         });
 526                         self.tcx.mk_place_deref(temp)
 527                     } else {
 528                         destination_place
 529                     }
 530                 } else {
 531                     trace!("creating temp for return place");
 532                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 533                 };
 534
 535                 // Copy the arguments if needed.
 536                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 537
 538                 let mut integrator = Integrator {
 539                     args: &args,
 540                     new_locals: Local::new(caller_body.local_decls.len())..,
 541                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 542                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 543                     destination: dest,
 544                     return_block: callsite.target,
 545                     cleanup_block: cleanup,
 546                     in_cleanup_block: false,
 547                     tcx: self.tcx,
 548                     callsite_span: callsite.source_info.span,
 549                     body_span: callee_body.span,
 550                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 551                 };
 552
 553                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 554                 // (or existing ones, in a few special cases) in the caller.
 555                 integrator.visit_body(&mut callee_body);
 556
 557                 for scope in &mut callee_body.source_scopes {
 558                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 559                     if scope.parent_scope.is_none() {
 560                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 561
 562                         // Attach the outermost callee scope as a child of the callsite
 563                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 564                         scope.parent_scope = Some(callsite.source_info.scope);
 565                         assert_eq!(scope.inlined_parent_scope, None);
 566                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 567                             Some(callsite.source_info.scope)
 568                         } else {
 569                             callsite_scope.inlined_parent_scope
 570                         };
 571
 572                         // Mark the outermost callee scope as an inlined one.
 573                         assert_eq!(scope.inlined, None);
 574                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 575                     } else if scope.inlined_parent_scope.is_none() {
 576                         // Make it easy to find the scope with `inlined` set above.
 577                         scope.inlined_parent_scope =
 578                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 579                     }
 580                 }
 581
 582                 // If there are any locals without storage markers, give them storage only for the
 583                 // duration of the call.
 584                 for local in callee_body.vars_and_temps_iter() {
 585                     if integrator.always_live_locals.contains(local) {
 586                         let new_local = integrator.map_local(local);
 587                         caller_body[callsite.block].statements.push(Statement {
 588                             source_info: callsite.source_info,
 589                             kind: StatementKind::StorageLive(new_local),
 590                         });
 591                     }
 592                 }
 593                 if let Some(block) = callsite.target {
 594                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 595                     // the slice once.
 596                     let mut n = 0;
 597                     for local in callee_body.vars_and_temps_iter().rev() {
 598                         if integrator.always_live_locals.contains(local) {
 599                             let new_local = integrator.map_local(local);
 600                             caller_body[block].statements.push(Statement {
 601                                 source_info: callsite.source_info,
 602                                 kind: StatementKind::StorageDead(new_local),
 603                             });
 604                             n += 1;
 605                         }
 606                     }
 607                     caller_body[block].statements.rotate_right(n);
 608                 }
 609
 610                 // Insert all of the (mapped) parts of the callee body into the caller.
 611                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 612                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 613                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 614                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 615
 616                 caller_body[callsite.block].terminator = Some(Terminator {
 617                     source_info: callsite.source_info,
 618                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 619                 });
 620
 621                 // Copy only unevaluated constants from the callee_body into the caller_body.
 622                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 623                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 624                 // because we are calling `subst_and_normalize_erasing_regions`.
 625                 caller_body.required_consts.extend(
 626                     callee_body.required_consts.iter().copied().filter(|&ct| {
 627                         match ct.literal.const_for_ty() {
 628                             Some(ct) => matches!(ct.val, ConstKind::Unevaluated(_)),
 629                             None => true,
 630                         }
 631                     }),
 632                 );
 633             }
 634             kind => bug!("unexpected terminator kind {:?}", kind),
 635         }
 636     }
 637
 638     fn make_call_args(
 639         &self,
 640         args: Vec<Operand<'tcx>>,
 641         callsite: &CallSite<'tcx>,
 642         caller_body: &mut Body<'tcx>,
 643         callee_body: &Body<'tcx>,
 644     ) -> Vec<Local> {
 645         let tcx = self.tcx;
 646
 647         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 648         // The caller provides the arguments wrapped up in a tuple:
 649         //
 650         //     tuple_tmp = (a, b, c)
 651         //     Fn::call(closure_ref, tuple_tmp)
 652         //
 653         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 654         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 655         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 656         // a vector like
 657         //
 658         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 659         //
 660         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 661         // if we "spill" that into *another* temporary, so that we can map the argument
 662         // variable in the callee MIR directly to an argument variable on our side.
 663         // So we introduce temporaries like:
 664         //
 665         //     tmp0 = tuple_tmp.0
 666         //     tmp1 = tuple_tmp.1
 667         //     tmp2 = tuple_tmp.2
 668         //
 669         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 670         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 671             let mut args = args.into_iter();
 672             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 673             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 674             assert!(args.next().is_none());
 675
 676             let tuple = Place::from(tuple);
 677             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() else {
 678                 bug!("Closure arguments are not passed as a tuple");
 679             };
 680
 681             // The `closure_ref` in our example above.
 682             let closure_ref_arg = iter::once(self_);
 683
 684             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 685             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 686                 // This is e.g., `tuple_tmp.0` in our example above.
 687                 let tuple_field =
 688                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 689
 690                 // Spill to a local to make e.g., `tmp0`.
 691                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 692             });
 693
 694             closure_ref_arg.chain(tuple_tmp_args).collect()
 695         } else {
 696             args.into_iter()
 697                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 698                 .collect()
 699         }
 700     }
 701
 702     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 703     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 704     fn create_temp_if_necessary(
 705         &self,
 706         arg: Operand<'tcx>,
 707         callsite: &CallSite<'tcx>,
 708         caller_body: &mut Body<'tcx>,
 709     ) -> Local {
 710         // Reuse the operand if it is a moved temporary.
 711         if let Operand::Move(place) = &arg {
 712             if let Some(local) = place.as_local() {
 713                 if caller_body.local_kind(local) == LocalKind::Temp {
 714                     return local;
 715                 }
 716             }
 717         }
 718
 719         // Otherwise, create a temporary for the argument.
 720         trace!("creating temp for argument {:?}", arg);
 721         let arg_ty = arg.ty(caller_body, self.tcx);
 722         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 723         caller_body[callsite.block].statements.push(Statement {
 724             source_info: callsite.source_info,
 725             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 726         });
 727         local
 728     }
 729
 730     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 731     fn new_call_temp(
 732         &self,
 733         caller_body: &mut Body<'tcx>,
 734         callsite: &CallSite<'tcx>,
 735         ty: Ty<'tcx>,
 736     ) -> Local {
 737         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 738
 739         caller_body[callsite.block].statements.push(Statement {
 740             source_info: callsite.source_info,
 741             kind: StatementKind::StorageLive(local),
 742         });
 743
 744         if let Some(block) = callsite.target {
 745             caller_body[block].statements.insert(
 746                 0,
 747                 Statement {
 748                     source_info: callsite.source_info,
 749                     kind: StatementKind::StorageDead(local),
 750                 },
 751             );
 752         }
 753
 754         local
 755     }
 756 }
 757
 758 fn type_size_of<'tcx>(
 759     tcx: TyCtxt<'tcx>,
 760     param_env: ty::ParamEnv<'tcx>,
 761     ty: Ty<'tcx>,
 762 ) -> Option<u64> {
 763     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 764 }
 765
 766 /**
 767  * Integrator.
 768  *
 769  * Integrates blocks from the callee function into the calling function.
 770  * Updates block indices, references to locals and other control flow
 771  * stuff.
 772 */
 773 struct Integrator<'a, 'tcx> {
 774     args: &'a [Local],
 775     new_locals: RangeFrom<Local>,
 776     new_scopes: RangeFrom<SourceScope>,
 777     new_blocks: RangeFrom<BasicBlock>,
 778     destination: Place<'tcx>,
 779     return_block: Option<BasicBlock>,
 780     cleanup_block: Option<BasicBlock>,
 781     in_cleanup_block: bool,
 782     tcx: TyCtxt<'tcx>,
 783     callsite_span: Span,
 784     body_span: Span,
 785     always_live_locals: BitSet<Local>,
 786 }
 787
 788 impl Integrator<'_, '_> {
 789     fn map_local(&self, local: Local) -> Local {
 790         let new = if local == RETURN_PLACE {
 791             self.destination.local
 792         } else {
 793             let idx = local.index() - 1;
 794             if idx < self.args.len() {
 795                 self.args[idx]
 796             } else {
 797                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 798             }
 799         };
 800         trace!("mapping local `{:?}` to `{:?}`", local, new);
 801         new
 802     }
 803
 804     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 805         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 806         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 807         new
 808     }
 809
 810     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 811         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 812         trace!("mapping block `{:?}` to `{:?}`", block, new);
 813         new
 814     }
 815 }
 816
 817 impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
 818     fn tcx(&self) -> TyCtxt<'tcx> {
 819         self.tcx
 820     }
 821
 822     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 823         *local = self.map_local(*local);
 824     }
 825
 826     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 827         *scope = self.map_scope(*scope);
 828     }
 829
 830     fn visit_span(&mut self, span: &mut Span) {
 831         let mut expn_data =
 832             ExpnData::default(ExpnKind::Inlined, *span, self.tcx.sess.edition(), None, None);
 833         expn_data.def_site = self.body_span;
 834         // Make sure that all spans track the fact that they were inlined.
 835         *span =
 836             self.callsite_span.fresh_expansion(expn_data, self.tcx.create_stable_hashing_context());
 837     }
 838
 839     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 840         for elem in place.projection {
 841             // FIXME: Make sure that return place is not used in an indexing projection, since it
 842             // won't be rebased as it is supposed to be.
 843             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 844         }
 845
 846         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 847         let dest_proj_len = self.destination.projection.len();
 848         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 849             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 850             projs.extend(self.destination.projection);
 851             projs.extend(place.projection);
 852
 853             place.projection = self.tcx.intern_place_elems(&*projs);
 854         }
 855         // Handles integrating any locals that occur in the base
 856         // or projections
 857         self.super_place(place, context, location)
 858     }
 859
 860     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 861         self.in_cleanup_block = data.is_cleanup;
 862         self.super_basic_block_data(block, data);
 863         self.in_cleanup_block = false;
 864     }
 865
 866     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 867         self.super_retag(kind, place, loc);
 868
 869         // We have to patch all inlined retags to be aware that they are no longer
 870         // happening on function entry.
 871         if *kind == RetagKind::FnEntry {
 872             *kind = RetagKind::Default;
 873         }
 874     }
 875
 876     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 877         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 878             statement.kind
 879         {
 880             self.always_live_locals.remove(local);
 881         }
 882         self.super_statement(statement, location);
 883     }
 884
 885     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 886         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 887         // replaced down below anyways).
 888         if !matches!(terminator.kind, TerminatorKind::Return) {
 889             self.super_terminator(terminator, loc);
 890         }
 891
 892         match terminator.kind {
 893             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 894             TerminatorKind::Goto { ref mut target } => {
 895                 *target = self.map_block(*target);
 896             }
 897             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 898                 for tgt in targets.all_targets_mut() {
 899                     *tgt = self.map_block(*tgt);
 900                 }
 901             }
 902             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 903             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 904                 *target = self.map_block(*target);
 905                 if let Some(tgt) = *unwind {
 906                     *unwind = Some(self.map_block(tgt));
 907                 } else if !self.in_cleanup_block {
 908                     // Unless this drop is in a cleanup block, add an unwind edge to
 909                     // the original call's cleanup block
 910                     *unwind = self.cleanup_block;
 911                 }
 912             }
 913             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 914                 if let Some((_, ref mut tgt)) = *destination {
 915                     *tgt = self.map_block(*tgt);
 916                 }
 917                 if let Some(tgt) = *cleanup {
 918                     *cleanup = Some(self.map_block(tgt));
 919                 } else if !self.in_cleanup_block {
 920                     // Unless this call is in a cleanup block, add an unwind edge to
 921                     // the original call's cleanup block
 922                     *cleanup = self.cleanup_block;
 923                 }
 924             }
 925             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 926                 *target = self.map_block(*target);
 927                 if let Some(tgt) = *cleanup {
 928                     *cleanup = Some(self.map_block(tgt));
 929                 } else if !self.in_cleanup_block {
 930                     // Unless this assert is in a cleanup block, add an unwind edge to
 931                     // the original call's cleanup block
 932                     *cleanup = self.cleanup_block;
 933                 }
 934             }
 935             TerminatorKind::Return => {
 936                 terminator.kind = if let Some(tgt) = self.return_block {
 937                     TerminatorKind::Goto { target: tgt }
 938                 } else {
 939                     TerminatorKind::Unreachable
 940                 }
 941             }
 942             TerminatorKind::Resume => {
 943                 if let Some(tgt) = self.cleanup_block {
 944                     terminator.kind = TerminatorKind::Goto { target: tgt }
 945                 }
 946             }
 947             TerminatorKind::Abort => {}
 948             TerminatorKind::Unreachable => {}
 949             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 950                 *real_target = self.map_block(*real_target);
 951                 *imaginary_target = self.map_block(*imaginary_target);
 952             }
 953             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 954             // see the ordering of passes in the optimized_mir query.
 955             {
 956                 bug!("False unwinds should have been removed before inlining")
 957             }
 958             TerminatorKind::InlineAsm { ref mut destination, ref mut cleanup, .. } => {
 959                 if let Some(ref mut tgt) = *destination {
 960                     *tgt = self.map_block(*tgt);
 961                 } else if !self.in_cleanup_block {
 962                     // Unless this inline asm is in a cleanup block, add an unwind edge to
 963                     // the original call's cleanup block
 964                     *cleanup = self.cleanup_block;
 965                 }
 966             }
 967         }
 968     }
 969 }