compiler/rustc_mir/src/transform/inline.rs

   1 //! Inlining pass for MIR functions
   2
   3 use rustc_attr as attr;
   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::transform::MirPass;
  17 use std::iter;
  18 use std::ops::{Range, RangeFrom};
  19
  20 const INSTR_COST: usize = 5;
  21 const CALL_PENALTY: usize = 25;
  22 const LANDINGPAD_PENALTY: usize = 50;
  23 const RESUME_PENALTY: usize = 45;
  24
  25 const UNKNOWN_SIZE_COST: usize = 10;
  26
  27 pub struct Inline;
  28
  29 #[derive(Copy, Clone, Debug)]
  30 struct CallSite<'tcx> {
  31     callee: Instance<'tcx>,
  32     fn_sig: ty::PolyFnSig<'tcx>,
  33     block: BasicBlock,
  34     target: Option<BasicBlock>,
  35     source_info: SourceInfo,
  36 }
  37
  38 impl<'tcx> MirPass<'tcx> for Inline {
  39     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  40         if tcx.sess.opts.debugging_opts.mir_opt_level < 2 {
  41             return;
  42         }
  43
  44         if inline(tcx, body) {
  45             debug!("running simplify cfg on {:?}", body.source);
  46             CfgSimplifier::new(body).simplify();
  47             remove_dead_blocks(body);
  48         }
  49     }
  50 }
  51
  52 fn inline(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  53     let def_id = body.source.def_id();
  54     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  55
  56     // Only do inlining into fn bodies.
  57     if !tcx.hir().body_owner_kind(hir_id).is_fn_or_closure() {
  58         return false;
  59     }
  60     if body.source.promoted.is_some() {
  61         return false;
  62     }
  63
  64     let mut this = Inliner {
  65         tcx,
  66         param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()),
  67         codegen_fn_attrs: tcx.codegen_fn_attrs(body.source.def_id()),
  68         hir_id,
  69         history: Vec::new(),
  70         changed: false,
  71     };
  72     let blocks = BasicBlock::new(0)..body.basic_blocks().next_index();
  73     this.process_blocks(body, blocks);
  74     this.changed
  75 }
  76
  77 struct Inliner<'tcx> {
  78     tcx: TyCtxt<'tcx>,
  79     param_env: ParamEnv<'tcx>,
  80     /// Caller codegen attributes.
  81     codegen_fn_attrs: &'tcx CodegenFnAttrs,
  82     /// Caller HirID.
  83     hir_id: hir::HirId,
  84     /// Stack of inlined instances.
  85     history: Vec<Instance<'tcx>>,
  86     /// Indicates that the caller body has been modified.
  87     changed: bool,
  88 }
  89
  90 impl Inliner<'tcx> {
  91     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
  92         for bb in blocks {
  93             let callsite = match self.get_valid_function_call(bb, &caller_body[bb], caller_body) {
  94                 None => continue,
  95                 Some(it) => it,
  96             };
  97
  98             if !self.is_mir_available(&callsite.callee, caller_body) {
  99                 debug!("MIR unavailable {}", callsite.callee);
 100                 continue;
 101             }
 102
 103             let callee_body = self.tcx.instance_mir(callsite.callee.def);
 104             if !self.should_inline(callsite, callee_body) {
 105                 continue;
 106             }
 107
 108             if !self.tcx.consider_optimizing(|| {
 109                 format!("Inline {:?} into {}", callee_body.span, callsite.callee)
 110             }) {
 111                 return;
 112             }
 113
 114             let callee_body = callsite.callee.subst_mir_and_normalize_erasing_regions(
 115                 self.tcx,
 116                 self.param_env,
 117                 callee_body.clone(),
 118             );
 119
 120             let old_blocks = caller_body.basic_blocks().next_index();
 121             self.inline_call(callsite, caller_body, callee_body);
 122             let new_blocks = old_blocks..caller_body.basic_blocks().next_index();
 123             self.changed = true;
 124
 125             self.history.push(callsite.callee);
 126             self.process_blocks(caller_body, new_blocks);
 127             self.history.pop();
 128         }
 129     }
 130
 131     fn is_mir_available(&self, callee: &Instance<'tcx>, caller_body: &Body<'tcx>) -> bool {
 132         if let InstanceDef::Item(_) = callee.def {
 133             if !self.tcx.is_mir_available(callee.def_id()) {
 134                 return false;
 135             }
 136         }
 137
 138         if let Some(callee_def_id) = callee.def_id().as_local() {
 139             let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
 140             // Avoid a cycle here by only using `instance_mir` only if we have
 141             // a lower `HirId` than the callee. This ensures that the callee will
 142             // not inline us. This trick only works without incremental compilation.
 143             // So don't do it if that is enabled. Also avoid inlining into generators,
 144             // since their `optimized_mir` is used for layout computation, which can
 145             // create a cycle, even when no attempt is made to inline the function
 146             // in the other direction.
 147             !self.tcx.dep_graph.is_fully_enabled()
 148                 && self.hir_id < callee_hir_id
 149                 && caller_body.generator_kind.is_none()
 150         } else {
 151             // This cannot result in a cycle since the callee MIR is from another crate
 152             // and is already optimized.
 153             true
 154         }
 155     }
 156
 157     fn get_valid_function_call(
 158         &self,
 159         bb: BasicBlock,
 160         bb_data: &BasicBlockData<'tcx>,
 161         caller_body: &Body<'tcx>,
 162     ) -> Option<CallSite<'tcx>> {
 163         // Don't inline calls that are in cleanup blocks.
 164         if bb_data.is_cleanup {
 165             return None;
 166         }
 167
 168         // Only consider direct calls to functions
 169         let terminator = bb_data.terminator();
 170         if let TerminatorKind::Call { ref func, ref destination, .. } = terminator.kind {
 171             let func_ty = func.ty(caller_body, self.tcx);
 172             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 173                 // To resolve an instance its substs have to be fully normalized.
 174                 let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 175                 let callee =
 176                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 177
 178                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 179                     return None;
 180                 }
 181
 182                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 183
 184                 return Some(CallSite {
 185                     callee,
 186                     fn_sig,
 187                     block: bb,
 188                     target: destination.map(|(_, target)| target),
 189                     source_info: terminator.source_info,
 190                 });
 191             }
 192         }
 193
 194         None
 195     }
 196
 197     fn should_inline(&self, callsite: CallSite<'tcx>, callee_body: &Body<'tcx>) -> bool {
 198         debug!("should_inline({:?})", callsite);
 199         let tcx = self.tcx;
 200
 201         if callsite.fn_sig.c_variadic() {
 202             debug!("callee is variadic - not inlining");
 203             return false;
 204         }
 205
 206         let codegen_fn_attrs = tcx.codegen_fn_attrs(callsite.callee.def_id());
 207
 208         let self_features = &self.codegen_fn_attrs.target_features;
 209         let callee_features = &codegen_fn_attrs.target_features;
 210         if callee_features.iter().any(|feature| !self_features.contains(feature)) {
 211             debug!("`callee has extra target features - not inlining");
 212             return false;
 213         }
 214
 215         if self.codegen_fn_attrs.no_sanitize != codegen_fn_attrs.no_sanitize {
 216             debug!("`callee has incompatible no_sanitize attribute - not inlining");
 217             return false;
 218         }
 219
 220         let hinted = match codegen_fn_attrs.inline {
 221             // Just treat inline(always) as a hint for now,
 222             // there are cases that prevent inlining that we
 223             // need to check for first.
 224             attr::InlineAttr::Always => true,
 225             attr::InlineAttr::Never => {
 226                 debug!("`#[inline(never)]` present - not inlining");
 227                 return false;
 228             }
 229             attr::InlineAttr::Hint => true,
 230             attr::InlineAttr::None => false,
 231         };
 232
 233         // Only inline local functions if they would be eligible for cross-crate
 234         // inlining. This is to ensure that the final crate doesn't have MIR that
 235         // reference unexported symbols
 236         if callsite.callee.def_id().is_local() {
 237             if callsite.callee.substs.non_erasable_generics().count() == 0 && !hinted {
 238                 debug!("    callee is an exported function - not inlining");
 239                 return false;
 240             }
 241         }
 242
 243         let mut threshold = if hinted {
 244             self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold
 245         } else {
 246             self.tcx.sess.opts.debugging_opts.inline_mir_threshold
 247         };
 248
 249         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 250             debug!("#[naked] present - not inlining");
 251             return false;
 252         }
 253
 254         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 255             debug!("#[cold] present - not inlining");
 256             return false;
 257         }
 258
 259         // Give a bonus functions with a small number of blocks,
 260         // We normally have two or three blocks for even
 261         // very small functions.
 262         if callee_body.basic_blocks().len() <= 3 {
 263             threshold += threshold / 4;
 264         }
 265         debug!("    final inline threshold = {}", threshold);
 266
 267         // FIXME: Give a bonus to functions with only a single caller
 268         let mut first_block = true;
 269         let mut cost = 0;
 270
 271         // Traverse the MIR manually so we can account for the effects of
 272         // inlining on the CFG.
 273         let mut work_list = vec![START_BLOCK];
 274         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 275         while let Some(bb) = work_list.pop() {
 276             if !visited.insert(bb.index()) {
 277                 continue;
 278             }
 279             let blk = &callee_body.basic_blocks()[bb];
 280
 281             for stmt in &blk.statements {
 282                 // Don't count StorageLive/StorageDead in the inlining cost.
 283                 match stmt.kind {
 284                     StatementKind::StorageLive(_)
 285                     | StatementKind::StorageDead(_)
 286                     | StatementKind::Nop => {}
 287                     _ => cost += INSTR_COST,
 288                 }
 289             }
 290             let term = blk.terminator();
 291             let mut is_drop = false;
 292             match term.kind {
 293                 TerminatorKind::Drop { ref place, target, unwind }
 294                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 295                     is_drop = true;
 296                     work_list.push(target);
 297                     // If the place doesn't actually need dropping, treat it like
 298                     // a regular goto.
 299                     let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 300                     if ty.needs_drop(tcx, self.param_env) {
 301                         cost += CALL_PENALTY;
 302                         if let Some(unwind) = unwind {
 303                             cost += LANDINGPAD_PENALTY;
 304                             work_list.push(unwind);
 305                         }
 306                     } else {
 307                         cost += INSTR_COST;
 308                     }
 309                 }
 310
 311                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 312                     if first_block =>
 313                 {
 314                     // If the function always diverges, don't inline
 315                     // unless the cost is zero
 316                     threshold = 0;
 317                 }
 318
 319                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 320                     if let ty::FnDef(def_id, substs) =
 321                         *callsite.callee.subst_mir(self.tcx, &f.literal.ty).kind()
 322                     {
 323                         let substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 324                         if let Ok(Some(instance)) =
 325                             Instance::resolve(self.tcx, self.param_env, def_id, substs)
 326                         {
 327                             if callsite.callee == instance || self.history.contains(&instance) {
 328                                 debug!("`callee is recursive - not inlining");
 329                                 return false;
 330                             }
 331                         }
 332                         // Don't give intrinsics the extra penalty for calls
 333                         let f = tcx.fn_sig(def_id);
 334                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 335                             cost += INSTR_COST;
 336                         } else {
 337                             cost += CALL_PENALTY;
 338                         }
 339                     } else {
 340                         cost += CALL_PENALTY;
 341                     }
 342                     if cleanup.is_some() {
 343                         cost += LANDINGPAD_PENALTY;
 344                     }
 345                 }
 346                 TerminatorKind::Assert { cleanup, .. } => {
 347                     cost += CALL_PENALTY;
 348
 349                     if cleanup.is_some() {
 350                         cost += LANDINGPAD_PENALTY;
 351                     }
 352                 }
 353                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 354                 _ => cost += INSTR_COST,
 355             }
 356
 357             if !is_drop {
 358                 for &succ in term.successors() {
 359                     work_list.push(succ);
 360                 }
 361             }
 362
 363             first_block = false;
 364         }
 365
 366         // Count up the cost of local variables and temps, if we know the size
 367         // use that, otherwise we use a moderately-large dummy cost.
 368
 369         let ptr_size = tcx.data_layout.pointer_size.bytes();
 370
 371         for v in callee_body.vars_and_temps_iter() {
 372             let ty = callsite.callee.subst_mir(self.tcx, &callee_body.local_decls[v].ty);
 373             // Cost of the var is the size in machine-words, if we know
 374             // it.
 375             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 376                 cost += (size / ptr_size) as usize;
 377             } else {
 378                 cost += UNKNOWN_SIZE_COST;
 379             }
 380         }
 381
 382         if let attr::InlineAttr::Always = codegen_fn_attrs.inline {
 383             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 384             true
 385         } else {
 386             if cost <= threshold {
 387                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 388                 true
 389             } else {
 390                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 391                 false
 392             }
 393         }
 394     }
 395
 396     fn inline_call(
 397         &self,
 398         callsite: CallSite<'tcx>,
 399         caller_body: &mut Body<'tcx>,
 400         mut callee_body: Body<'tcx>,
 401     ) {
 402         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 403         match terminator.kind {
 404             TerminatorKind::Call { args, destination, cleanup, .. } => {
 405                 // If the call is something like `a[*i] = f(i)`, where
 406                 // `i : &mut usize`, then just duplicating the `a[*i]`
 407                 // Place could result in two different locations if `f`
 408                 // writes to `i`. To prevent this we need to create a temporary
 409                 // borrow of the place and pass the destination as `*temp` instead.
 410                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 411                     for elem in place.projection.iter() {
 412                         match elem {
 413                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 414                             _ => {}
 415                         }
 416                     }
 417
 418                     false
 419                 }
 420
 421                 let dest = if let Some((destination_place, _)) = destination {
 422                     if dest_needs_borrow(destination_place) {
 423                         trace!("creating temp for return destination");
 424                         let dest = Rvalue::Ref(
 425                             self.tcx.lifetimes.re_erased,
 426                             BorrowKind::Mut { allow_two_phase_borrow: false },
 427                             destination_place,
 428                         );
 429                         let dest_ty = dest.ty(caller_body, self.tcx);
 430                         let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 431                         caller_body[callsite.block].statements.push(Statement {
 432                             source_info: callsite.source_info,
 433                             kind: StatementKind::Assign(box (temp, dest)),
 434                         });
 435                         self.tcx.mk_place_deref(temp)
 436                     } else {
 437                         destination_place
 438                     }
 439                 } else {
 440                     trace!("creating temp for return place");
 441                     Place::from(self.new_call_temp(caller_body, &callsite, callee_body.return_ty()))
 442                 };
 443
 444                 // Copy the arguments if needed.
 445                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 446
 447                 let mut integrator = Integrator {
 448                     args: &args,
 449                     new_locals: Local::new(caller_body.local_decls.len())..,
 450                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 451                     new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
 452                     destination: dest,
 453                     return_block: callsite.target,
 454                     cleanup_block: cleanup,
 455                     in_cleanup_block: false,
 456                     tcx: self.tcx,
 457                     callsite_span: callsite.source_info.span,
 458                     body_span: callee_body.span,
 459                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 460                 };
 461
 462                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 463                 // (or existing ones, in a few special cases) in the caller.
 464                 integrator.visit_body(&mut callee_body);
 465
 466                 for scope in &mut callee_body.source_scopes {
 467                     // FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
 468                     if scope.parent_scope.is_none() {
 469                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 470
 471                         // Attach the outermost callee scope as a child of the callsite
 472                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 473                         scope.parent_scope = Some(callsite.source_info.scope);
 474                         assert_eq!(scope.inlined_parent_scope, None);
 475                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 476                             Some(callsite.source_info.scope)
 477                         } else {
 478                             callsite_scope.inlined_parent_scope
 479                         };
 480
 481                         // Mark the outermost callee scope as an inlined one.
 482                         assert_eq!(scope.inlined, None);
 483                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 484                     } else if scope.inlined_parent_scope.is_none() {
 485                         // Make it easy to find the scope with `inlined` set above.
 486                         scope.inlined_parent_scope =
 487                             Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
 488                     }
 489                 }
 490
 491                 // If there are any locals without storage markers, give them storage only for the
 492                 // duration of the call.
 493                 for local in callee_body.vars_and_temps_iter() {
 494                     if integrator.always_live_locals.contains(local) {
 495                         let new_local = integrator.map_local(local);
 496                         caller_body[callsite.block].statements.push(Statement {
 497                             source_info: callsite.source_info,
 498                             kind: StatementKind::StorageLive(new_local),
 499                         });
 500                     }
 501                 }
 502                 if let Some(block) = callsite.target {
 503                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 504                     // the slice once.
 505                     let mut n = 0;
 506                     for local in callee_body.vars_and_temps_iter().rev() {
 507                         if integrator.always_live_locals.contains(local) {
 508                             let new_local = integrator.map_local(local);
 509                             caller_body[block].statements.push(Statement {
 510                                 source_info: callsite.source_info,
 511                                 kind: StatementKind::StorageDead(new_local),
 512                             });
 513                             n += 1;
 514                         }
 515                     }
 516                     caller_body[block].statements.rotate_right(n);
 517                 }
 518
 519                 // Insert all of the (mapped) parts of the callee body into the caller.
 520                 caller_body.local_decls.extend(
 521                     // FIXME(eddyb) make `Range<Local>` iterable so that we can use
 522                     // `callee_body.local_decls.drain(callee_body.vars_and_temps())`
 523                     callee_body
 524                         .vars_and_temps_iter()
 525                         .map(|local| callee_body.local_decls[local].clone()),
 526                 );
 527                 caller_body.source_scopes.extend(callee_body.source_scopes.drain(..));
 528                 caller_body.var_debug_info.extend(callee_body.var_debug_info.drain(..));
 529                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 530
 531                 caller_body[callsite.block].terminator = Some(Terminator {
 532                     source_info: callsite.source_info,
 533                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 534                 });
 535
 536                 // Copy only unevaluated constants from the callee_body into the caller_body.
 537                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 538                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 539                 // because we are calling `subst_and_normalize_erasing_regions`.
 540                 caller_body.required_consts.extend(
 541                     callee_body.required_consts.iter().copied().filter(|&constant| {
 542                         matches!(constant.literal.val, ConstKind::Unevaluated(_, _, _))
 543                     }),
 544                 );
 545             }
 546             kind => bug!("unexpected terminator kind {:?}", kind),
 547         }
 548     }
 549
 550     fn make_call_args(
 551         &self,
 552         args: Vec<Operand<'tcx>>,
 553         callsite: &CallSite<'tcx>,
 554         caller_body: &mut Body<'tcx>,
 555         callee_body: &Body<'tcx>,
 556     ) -> Vec<Local> {
 557         let tcx = self.tcx;
 558
 559         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 560         // The caller provides the arguments wrapped up in a tuple:
 561         //
 562         //     tuple_tmp = (a, b, c)
 563         //     Fn::call(closure_ref, tuple_tmp)
 564         //
 565         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 566         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 567         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 568         // a vector like
 569         //
 570         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 571         //
 572         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 573         // if we "spill" that into *another* temporary, so that we can map the argument
 574         // variable in the callee MIR directly to an argument variable on our side.
 575         // So we introduce temporaries like:
 576         //
 577         //     tmp0 = tuple_tmp.0
 578         //     tmp1 = tuple_tmp.1
 579         //     tmp2 = tuple_tmp.2
 580         //
 581         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 582         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 583             let mut args = args.into_iter();
 584             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 585             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 586             assert!(args.next().is_none());
 587
 588             let tuple = Place::from(tuple);
 589             let tuple_tys = if let ty::Tuple(s) = tuple.ty(caller_body, tcx).ty.kind() {
 590                 s
 591             } else {
 592                 bug!("Closure arguments are not passed as a tuple");
 593             };
 594
 595             // The `closure_ref` in our example above.
 596             let closure_ref_arg = iter::once(self_);
 597
 598             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 599             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 600                 // This is e.g., `tuple_tmp.0` in our example above.
 601                 let tuple_field =
 602                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 603
 604                 // Spill to a local to make e.g., `tmp0`.
 605                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 606             });
 607
 608             closure_ref_arg.chain(tuple_tmp_args).collect()
 609         } else {
 610             args.into_iter()
 611                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 612                 .collect()
 613         }
 614     }
 615
 616     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 617     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 618     fn create_temp_if_necessary(
 619         &self,
 620         arg: Operand<'tcx>,
 621         callsite: &CallSite<'tcx>,
 622         caller_body: &mut Body<'tcx>,
 623     ) -> Local {
 624         // Reuse the operand if it is a moved temporary.
 625         if let Operand::Move(place) = &arg {
 626             if let Some(local) = place.as_local() {
 627                 if caller_body.local_kind(local) == LocalKind::Temp {
 628                     return local;
 629                 }
 630             }
 631         }
 632
 633         // Otherwise, create a temporary for the argument.
 634         trace!("creating temp for argument {:?}", arg);
 635         let arg_ty = arg.ty(caller_body, self.tcx);
 636         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 637         caller_body[callsite.block].statements.push(Statement {
 638             source_info: callsite.source_info,
 639             kind: StatementKind::Assign(box (Place::from(local), Rvalue::Use(arg))),
 640         });
 641         local
 642     }
 643
 644     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 645     fn new_call_temp(
 646         &self,
 647         caller_body: &mut Body<'tcx>,
 648         callsite: &CallSite<'tcx>,
 649         ty: Ty<'tcx>,
 650     ) -> Local {
 651         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 652
 653         caller_body[callsite.block].statements.push(Statement {
 654             source_info: callsite.source_info,
 655             kind: StatementKind::StorageLive(local),
 656         });
 657
 658         if let Some(block) = callsite.target {
 659             caller_body[block].statements.insert(
 660                 0,
 661                 Statement {
 662                     source_info: callsite.source_info,
 663                     kind: StatementKind::StorageDead(local),
 664                 },
 665             );
 666         }
 667
 668         local
 669     }
 670 }
 671
 672 fn type_size_of<'tcx>(
 673     tcx: TyCtxt<'tcx>,
 674     param_env: ty::ParamEnv<'tcx>,
 675     ty: Ty<'tcx>,
 676 ) -> Option<u64> {
 677     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 678 }
 679
 680 /**
 681  * Integrator.
 682  *
 683  * Integrates blocks from the callee function into the calling function.
 684  * Updates block indices, references to locals and other control flow
 685  * stuff.
 686 */
 687 struct Integrator<'a, 'tcx> {
 688     args: &'a [Local],
 689     new_locals: RangeFrom<Local>,
 690     new_scopes: RangeFrom<SourceScope>,
 691     new_blocks: RangeFrom<BasicBlock>,
 692     destination: Place<'tcx>,
 693     return_block: Option<BasicBlock>,
 694     cleanup_block: Option<BasicBlock>,
 695     in_cleanup_block: bool,
 696     tcx: TyCtxt<'tcx>,
 697     callsite_span: Span,
 698     body_span: Span,
 699     always_live_locals: BitSet<Local>,
 700 }
 701
 702 impl<'a, 'tcx> Integrator<'a, 'tcx> {
 703     fn map_local(&self, local: Local) -> Local {
 704         let new = if local == RETURN_PLACE {
 705             self.destination.local
 706         } else {
 707             let idx = local.index() - 1;
 708             if idx < self.args.len() {
 709                 self.args[idx]
 710             } else {
 711                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
 712             }
 713         };
 714         trace!("mapping local `{:?}` to `{:?}`", local, new);
 715         new
 716     }
 717
 718     fn map_scope(&self, scope: SourceScope) -> SourceScope {
 719         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
 720         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
 721         new
 722     }
 723
 724     fn map_block(&self, block: BasicBlock) -> BasicBlock {
 725         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
 726         trace!("mapping block `{:?}` to `{:?}`", block, new);
 727         new
 728     }
 729 }
 730
 731 impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
 732     fn tcx(&self) -> TyCtxt<'tcx> {
 733         self.tcx
 734     }
 735
 736     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 737         *local = self.map_local(*local);
 738     }
 739
 740     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 741         *scope = self.map_scope(*scope);
 742     }
 743
 744     fn visit_span(&mut self, span: &mut Span) {
 745         let mut expn_data =
 746             ExpnData::default(ExpnKind::Inlined, *span, self.tcx.sess.edition(), None);
 747         expn_data.def_site = self.body_span;
 748         // Make sure that all spans track the fact that they were inlined.
 749         *span = self.callsite_span.fresh_expansion(expn_data);
 750     }
 751
 752     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 753         for elem in place.projection {
 754             // FIXME: Make sure that return place is not used in an indexing projection, since it
 755             // won't be rebased as it is supposed to be.
 756             assert_ne!(ProjectionElem::Index(RETURN_PLACE), elem);
 757         }
 758
 759         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 760         let dest_proj_len = self.destination.projection.len();
 761         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 762             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 763             projs.extend(self.destination.projection);
 764             projs.extend(place.projection);
 765
 766             place.projection = self.tcx.intern_place_elems(&*projs);
 767         }
 768         // Handles integrating any locals that occur in the base
 769         // or projections
 770         self.super_place(place, context, location)
 771     }
 772
 773     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 774         self.in_cleanup_block = data.is_cleanup;
 775         self.super_basic_block_data(block, data);
 776         self.in_cleanup_block = false;
 777     }
 778
 779     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 780         self.super_retag(kind, place, loc);
 781
 782         // We have to patch all inlined retags to be aware that they are no longer
 783         // happening on function entry.
 784         if *kind == RetagKind::FnEntry {
 785             *kind = RetagKind::Default;
 786         }
 787     }
 788
 789     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
 790         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
 791             statement.kind
 792         {
 793             self.always_live_locals.remove(local);
 794         }
 795         self.super_statement(statement, location);
 796     }
 797
 798     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 799         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 800         // replaced down below anyways).
 801         if !matches!(terminator.kind, TerminatorKind::Return) {
 802             self.super_terminator(terminator, loc);
 803         }
 804
 805         match terminator.kind {
 806             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 807             TerminatorKind::Goto { ref mut target } => {
 808                 *target = self.map_block(*target);
 809             }
 810             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 811                 for tgt in targets.all_targets_mut() {
 812                     *tgt = self.map_block(*tgt);
 813                 }
 814             }
 815             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 816             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 817                 *target = self.map_block(*target);
 818                 if let Some(tgt) = *unwind {
 819                     *unwind = Some(self.map_block(tgt));
 820                 } else if !self.in_cleanup_block {
 821                     // Unless this drop is in a cleanup block, add an unwind edge to
 822                     // the original call's cleanup block
 823                     *unwind = self.cleanup_block;
 824                 }
 825             }
 826             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 827                 if let Some((_, ref mut tgt)) = *destination {
 828                     *tgt = self.map_block(*tgt);
 829                 }
 830                 if let Some(tgt) = *cleanup {
 831                     *cleanup = Some(self.map_block(tgt));
 832                 } else if !self.in_cleanup_block {
 833                     // Unless this call is in a cleanup block, add an unwind edge to
 834                     // the original call's cleanup block
 835                     *cleanup = self.cleanup_block;
 836                 }
 837             }
 838             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 839                 *target = self.map_block(*target);
 840                 if let Some(tgt) = *cleanup {
 841                     *cleanup = Some(self.map_block(tgt));
 842                 } else if !self.in_cleanup_block {
 843                     // Unless this assert is in a cleanup block, add an unwind edge to
 844                     // the original call's cleanup block
 845                     *cleanup = self.cleanup_block;
 846                 }
 847             }
 848             TerminatorKind::Return => {
 849                 terminator.kind = if let Some(tgt) = self.return_block {
 850                     TerminatorKind::Goto { target: tgt }
 851                 } else {
 852                     TerminatorKind::Unreachable
 853                 }
 854             }
 855             TerminatorKind::Resume => {
 856                 if let Some(tgt) = self.cleanup_block {
 857                     terminator.kind = TerminatorKind::Goto { target: tgt }
 858                 }
 859             }
 860             TerminatorKind::Abort => {}
 861             TerminatorKind::Unreachable => {}
 862             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 863                 *real_target = self.map_block(*real_target);
 864                 *imaginary_target = self.map_block(*imaginary_target);
 865             }
 866             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 867             // see the ordering of passes in the optimized_mir query.
 868             {
 869                 bug!("False unwinds should have been removed before inlining")
 870             }
 871             TerminatorKind::InlineAsm { ref mut destination, .. } => {
 872                 if let Some(ref mut tgt) = *destination {
 873                     *tgt = self.map_block(*tgt);
 874                 }
 875             }
 876         }
 877     }
 878 }