compiler/rustc_mir/src/transform/inline.rs

   1 //! Inlining pass for MIR functions
   2
   3 use rustc_attr as attr;
   4 use rustc_index::bit_set::BitSet;
   5 use rustc_index::vec::{Idx, IndexVec};
   6 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
   7 use rustc_middle::mir::visit::*;
   8 use rustc_middle::mir::*;
   9 use rustc_middle::ty::subst::Subst;
  10 use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
  11 use rustc_target::spec::abi::Abi;
  12
  13 use super::simplify::{remove_dead_blocks, CfgSimplifier};
  14 use crate::transform::MirPass;
  15 use std::collections::VecDeque;
  16 use std::iter;
  17
  18 const DEFAULT_THRESHOLD: usize = 50;
  19 const HINT_THRESHOLD: usize = 100;
  20
  21 const INSTR_COST: usize = 5;
  22 const CALL_PENALTY: usize = 25;
  23 const LANDINGPAD_PENALTY: usize = 50;
  24 const RESUME_PENALTY: usize = 45;
  25
  26 const UNKNOWN_SIZE_COST: usize = 10;
  27
  28 pub struct Inline;
  29
  30 #[derive(Copy, Clone, Debug)]
  31 struct CallSite<'tcx> {
  32     callee: Instance<'tcx>,
  33     bb: BasicBlock,
  34     source_info: SourceInfo,
  35 }
  36
  37 impl<'tcx> MirPass<'tcx> for Inline {
  38     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  39         if tcx.sess.opts.debugging_opts.mir_opt_level >= 2 {
  40             if tcx.sess.opts.debugging_opts.instrument_coverage {
  41                 // The current implementation of source code coverage injects code region counters
  42                 // into the MIR, and assumes a 1-to-1 correspondence between MIR and source-code-
  43                 // based function.
  44                 debug!("function inlining is disabled when compiling with `instrument_coverage`");
  45             } else {
  46                 Inliner {
  47                     tcx,
  48                     param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()),
  49                     codegen_fn_attrs: tcx.codegen_fn_attrs(body.source.def_id()),
  50                 }
  51                 .run_pass(body);
  52             }
  53         }
  54     }
  55 }
  56
  57 struct Inliner<'tcx> {
  58     tcx: TyCtxt<'tcx>,
  59     param_env: ParamEnv<'tcx>,
  60     codegen_fn_attrs: &'tcx CodegenFnAttrs,
  61 }
  62
  63 impl Inliner<'tcx> {
  64     fn run_pass(&self, caller_body: &mut Body<'tcx>) {
  65         // Keep a queue of callsites to try inlining on. We take
  66         // advantage of the fact that queries detect cycles here to
  67         // allow us to try and fetch the fully optimized MIR of a
  68         // call; if it succeeds, we can inline it and we know that
  69         // they do not call us.  Otherwise, we just don't try to
  70         // inline.
  71         //
  72         // We use a queue so that we inline "broadly" before we inline
  73         // in depth. It is unclear if this is the best heuristic,
  74         // really, but that's true of all the heuristics in this
  75         // file. =)
  76
  77         let mut callsites = VecDeque::new();
  78
  79         let def_id = caller_body.source.def_id();
  80
  81         // Only do inlining into fn bodies.
  82         let self_hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
  83         if self.tcx.hir().body_owner_kind(self_hir_id).is_fn_or_closure()
  84             && caller_body.source.promoted.is_none()
  85         {
  86             for (bb, bb_data) in caller_body.basic_blocks().iter_enumerated() {
  87                 if let Some(callsite) = self.get_valid_function_call(bb, bb_data, caller_body) {
  88                     callsites.push_back(callsite);
  89                 }
  90             }
  91         } else {
  92             return;
  93         }
  94
  95         let mut local_change;
  96         let mut changed = false;
  97
  98         loop {
  99             local_change = false;
 100             while let Some(callsite) = callsites.pop_front() {
 101                 debug!("checking whether to inline callsite {:?}", callsite);
 102
 103                 if let InstanceDef::Item(_) = callsite.callee.def {
 104                     if !self.tcx.is_mir_available(callsite.callee.def_id()) {
 105                         debug!(
 106                             "checking whether to inline callsite {:?} - MIR unavailable",
 107                             callsite,
 108                         );
 109                         continue;
 110                     }
 111                 }
 112
 113                 let callee_body = if let Some(callee_def_id) = callsite.callee.def_id().as_local() {
 114                     let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
 115                     // Avoid a cycle here by only using `instance_mir` only if we have
 116                     // a lower `HirId` than the callee. This ensures that the callee will
 117                     // not inline us. This trick only works without incremental compilation.
 118                     // So don't do it if that is enabled. Also avoid inlining into generators,
 119                     // since their `optimized_mir` is used for layout computation, which can
 120                     // create a cycle, even when no attempt is made to inline the function
 121                     // in the other direction.
 122                     if !self.tcx.dep_graph.is_fully_enabled()
 123                         && self_hir_id < callee_hir_id
 124                         && caller_body.generator_kind.is_none()
 125                     {
 126                         self.tcx.instance_mir(callsite.callee.def)
 127                     } else {
 128                         continue;
 129                     }
 130                 } else {
 131                     // This cannot result in a cycle since the callee MIR is from another crate
 132                     // and is already optimized.
 133                     self.tcx.instance_mir(callsite.callee.def)
 134                 };
 135
 136                 let callee_body: &Body<'tcx> = &*callee_body;
 137
 138                 let callee_body = if self.consider_optimizing(callsite, callee_body) {
 139                     self.tcx.subst_and_normalize_erasing_regions(
 140                         &callsite.callee.substs,
 141                         self.param_env,
 142                         callee_body,
 143                     )
 144                 } else {
 145                     continue;
 146                 };
 147
 148                 // Copy only unevaluated constants from the callee_body into the caller_body.
 149                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 150                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 151                 // because we are calling `subst_and_normalize_erasing_regions`.
 152                 caller_body.required_consts.extend(
 153                     callee_body.required_consts.iter().copied().filter(|&constant| {
 154                         matches!(constant.literal.val, ConstKind::Unevaluated(_, _, _))
 155                     }),
 156                 );
 157
 158                 let start = caller_body.basic_blocks().len();
 159                 debug!("attempting to inline callsite {:?} - body={:?}", callsite, callee_body);
 160                 if !self.inline_call(callsite, caller_body, callee_body) {
 161                     debug!("attempting to inline callsite {:?} - failure", callsite);
 162                     continue;
 163                 }
 164                 debug!("attempting to inline callsite {:?} - success", callsite);
 165
 166                 // Add callsites from inlined function
 167                 for (bb, bb_data) in caller_body.basic_blocks().iter_enumerated().skip(start) {
 168                     if let Some(new_callsite) =
 169                         self.get_valid_function_call(bb, bb_data, caller_body)
 170                     {
 171                         // Don't inline the same function multiple times.
 172                         if callsite.callee != new_callsite.callee {
 173                             callsites.push_back(new_callsite);
 174                         }
 175                     }
 176                 }
 177
 178                 local_change = true;
 179                 changed = true;
 180             }
 181
 182             if !local_change {
 183                 break;
 184             }
 185         }
 186
 187         // Simplify if we inlined anything.
 188         if changed {
 189             debug!("running simplify cfg on {:?}", caller_body.source);
 190             CfgSimplifier::new(caller_body).simplify();
 191             remove_dead_blocks(caller_body);
 192         }
 193     }
 194
 195     fn get_valid_function_call(
 196         &self,
 197         bb: BasicBlock,
 198         bb_data: &BasicBlockData<'tcx>,
 199         caller_body: &Body<'tcx>,
 200     ) -> Option<CallSite<'tcx>> {
 201         // Don't inline calls that are in cleanup blocks.
 202         if bb_data.is_cleanup {
 203             return None;
 204         }
 205
 206         // Only consider direct calls to functions
 207         let terminator = bb_data.terminator();
 208         if let TerminatorKind::Call { func: ref op, .. } = terminator.kind {
 209             if let ty::FnDef(callee_def_id, substs) = *op.ty(caller_body, self.tcx).kind() {
 210                 // To resolve an instance its substs have to be fully normalized, so
 211                 // we do this here.
 212                 let normalized_substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
 213                 let callee =
 214                     Instance::resolve(self.tcx, self.param_env, callee_def_id, normalized_substs)
 215                         .ok()
 216                         .flatten()?;
 217
 218                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 219                     return None;
 220                 }
 221
 222                 return Some(CallSite { callee, bb, source_info: terminator.source_info });
 223             }
 224         }
 225
 226         None
 227     }
 228
 229     fn consider_optimizing(&self, callsite: CallSite<'tcx>, callee_body: &Body<'tcx>) -> bool {
 230         debug!("consider_optimizing({:?})", callsite);
 231         self.should_inline(callsite, callee_body)
 232             && self.tcx.consider_optimizing(|| {
 233                 format!("Inline {:?} into {:?}", callee_body.span, callsite)
 234             })
 235     }
 236
 237     fn should_inline(&self, callsite: CallSite<'tcx>, callee_body: &Body<'tcx>) -> bool {
 238         debug!("should_inline({:?})", callsite);
 239         let tcx = self.tcx;
 240
 241         // Cannot inline generators which haven't been transformed yet
 242         if callee_body.yield_ty.is_some() {
 243             debug!("    yield ty present - not inlining");
 244             return false;
 245         }
 246
 247         let codegen_fn_attrs = tcx.codegen_fn_attrs(callsite.callee.def_id());
 248
 249         let self_features = &self.codegen_fn_attrs.target_features;
 250         let callee_features = &codegen_fn_attrs.target_features;
 251         if callee_features.iter().any(|feature| !self_features.contains(feature)) {
 252             debug!("`callee has extra target features - not inlining");
 253             return false;
 254         }
 255
 256         let self_no_sanitize =
 257             self.codegen_fn_attrs.no_sanitize & self.tcx.sess.opts.debugging_opts.sanitizer;
 258         let callee_no_sanitize =
 259             codegen_fn_attrs.no_sanitize & self.tcx.sess.opts.debugging_opts.sanitizer;
 260         if self_no_sanitize != callee_no_sanitize {
 261             debug!("`callee has incompatible no_sanitize attribute - not inlining");
 262             return false;
 263         }
 264
 265         let hinted = match codegen_fn_attrs.inline {
 266             // Just treat inline(always) as a hint for now,
 267             // there are cases that prevent inlining that we
 268             // need to check for first.
 269             attr::InlineAttr::Always => true,
 270             attr::InlineAttr::Never => {
 271                 debug!("`#[inline(never)]` present - not inlining");
 272                 return false;
 273             }
 274             attr::InlineAttr::Hint => true,
 275             attr::InlineAttr::None => false,
 276         };
 277
 278         // Only inline local functions if they would be eligible for cross-crate
 279         // inlining. This is to ensure that the final crate doesn't have MIR that
 280         // reference unexported symbols
 281         if callsite.callee.def_id().is_local() {
 282             if callsite.callee.substs.non_erasable_generics().count() == 0 && !hinted {
 283                 debug!("    callee is an exported function - not inlining");
 284                 return false;
 285             }
 286         }
 287
 288         let mut threshold = if hinted { HINT_THRESHOLD } else { DEFAULT_THRESHOLD };
 289
 290         // Significantly lower the threshold for inlining cold functions
 291         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 292             threshold /= 5;
 293         }
 294
 295         // Give a bonus functions with a small number of blocks,
 296         // We normally have two or three blocks for even
 297         // very small functions.
 298         if callee_body.basic_blocks().len() <= 3 {
 299             threshold += threshold / 4;
 300         }
 301         debug!("    final inline threshold = {}", threshold);
 302
 303         // FIXME: Give a bonus to functions with only a single caller
 304         let mut first_block = true;
 305         let mut cost = 0;
 306
 307         // Traverse the MIR manually so we can account for the effects of
 308         // inlining on the CFG.
 309         let mut work_list = vec![START_BLOCK];
 310         let mut visited = BitSet::new_empty(callee_body.basic_blocks().len());
 311         while let Some(bb) = work_list.pop() {
 312             if !visited.insert(bb.index()) {
 313                 continue;
 314             }
 315             let blk = &callee_body.basic_blocks()[bb];
 316
 317             for stmt in &blk.statements {
 318                 // Don't count StorageLive/StorageDead in the inlining cost.
 319                 match stmt.kind {
 320                     StatementKind::StorageLive(_)
 321                     | StatementKind::StorageDead(_)
 322                     | StatementKind::Nop => {}
 323                     _ => cost += INSTR_COST,
 324                 }
 325             }
 326             let term = blk.terminator();
 327             let mut is_drop = false;
 328             match term.kind {
 329                 TerminatorKind::Drop { ref place, target, unwind }
 330                 | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } => {
 331                     is_drop = true;
 332                     work_list.push(target);
 333                     // If the place doesn't actually need dropping, treat it like
 334                     // a regular goto.
 335                     let ty = place.ty(callee_body, tcx).subst(tcx, callsite.callee.substs).ty;
 336                     if ty.needs_drop(tcx, self.param_env) {
 337                         cost += CALL_PENALTY;
 338                         if let Some(unwind) = unwind {
 339                             cost += LANDINGPAD_PENALTY;
 340                             work_list.push(unwind);
 341                         }
 342                     } else {
 343                         cost += INSTR_COST;
 344                     }
 345                 }
 346
 347                 TerminatorKind::Unreachable | TerminatorKind::Call { destination: None, .. }
 348                     if first_block =>
 349                 {
 350                     // If the function always diverges, don't inline
 351                     // unless the cost is zero
 352                     threshold = 0;
 353                 }
 354
 355                 TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 356                     if let ty::FnDef(def_id, _) = *f.literal.ty.kind() {
 357                         // Don't give intrinsics the extra penalty for calls
 358                         let f = tcx.fn_sig(def_id);
 359                         if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
 360                             cost += INSTR_COST;
 361                         } else {
 362                             cost += CALL_PENALTY;
 363                         }
 364                     } else {
 365                         cost += CALL_PENALTY;
 366                     }
 367                     if cleanup.is_some() {
 368                         cost += LANDINGPAD_PENALTY;
 369                     }
 370                 }
 371                 TerminatorKind::Assert { cleanup, .. } => {
 372                     cost += CALL_PENALTY;
 373
 374                     if cleanup.is_some() {
 375                         cost += LANDINGPAD_PENALTY;
 376                     }
 377                 }
 378                 TerminatorKind::Resume => cost += RESUME_PENALTY,
 379                 _ => cost += INSTR_COST,
 380             }
 381
 382             if !is_drop {
 383                 for &succ in term.successors() {
 384                     work_list.push(succ);
 385                 }
 386             }
 387
 388             first_block = false;
 389         }
 390
 391         // Count up the cost of local variables and temps, if we know the size
 392         // use that, otherwise we use a moderately-large dummy cost.
 393
 394         let ptr_size = tcx.data_layout.pointer_size.bytes();
 395
 396         for v in callee_body.vars_and_temps_iter() {
 397             let v = &callee_body.local_decls[v];
 398             let ty = v.ty.subst(tcx, callsite.callee.substs);
 399             // Cost of the var is the size in machine-words, if we know
 400             // it.
 401             if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 402                 cost += (size / ptr_size) as usize;
 403             } else {
 404                 cost += UNKNOWN_SIZE_COST;
 405             }
 406         }
 407
 408         if let attr::InlineAttr::Always = codegen_fn_attrs.inline {
 409             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 410             true
 411         } else {
 412             if cost <= threshold {
 413                 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 414                 true
 415             } else {
 416                 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 417                 false
 418             }
 419         }
 420     }
 421
 422     fn inline_call(
 423         &self,
 424         callsite: CallSite<'tcx>,
 425         caller_body: &mut Body<'tcx>,
 426         mut callee_body: Body<'tcx>,
 427     ) -> bool {
 428         let terminator = caller_body[callsite.bb].terminator.take().unwrap();
 429         match terminator.kind {
 430             // FIXME: Handle inlining of diverging calls
 431             TerminatorKind::Call { args, destination: Some(destination), cleanup, .. } => {
 432                 debug!("inlined {:?} into {:?}", callsite.callee, caller_body.source);
 433
 434                 let mut local_map = IndexVec::with_capacity(callee_body.local_decls.len());
 435                 let mut scope_map = IndexVec::with_capacity(callee_body.source_scopes.len());
 436
 437                 for mut scope in callee_body.source_scopes.iter().cloned() {
 438                     // Map the callee scopes into the caller.
 439                     // FIXME(eddyb) this may ICE if the scopes are out of order.
 440                     scope.parent_scope = scope.parent_scope.map(|s| scope_map[s]);
 441                     scope.inlined_parent_scope = scope.inlined_parent_scope.map(|s| scope_map[s]);
 442
 443                     if scope.parent_scope.is_none() {
 444                         let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
 445
 446                         // Attach the outermost callee scope as a child of the callsite
 447                         // scope, via the `parent_scope` and `inlined_parent_scope` chains.
 448                         scope.parent_scope = Some(callsite.source_info.scope);
 449                         assert_eq!(scope.inlined_parent_scope, None);
 450                         scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
 451                             Some(callsite.source_info.scope)
 452                         } else {
 453                             callsite_scope.inlined_parent_scope
 454                         };
 455
 456                         // Mark the outermost callee scope as an inlined one.
 457                         assert_eq!(scope.inlined, None);
 458                         scope.inlined = Some((callsite.callee, callsite.source_info.span));
 459                     } else if scope.inlined_parent_scope.is_none() {
 460                         // Make it easy to find the scope with `inlined` set above.
 461                         scope.inlined_parent_scope = Some(scope_map[OUTERMOST_SOURCE_SCOPE]);
 462                     }
 463
 464                     let idx = caller_body.source_scopes.push(scope);
 465                     scope_map.push(idx);
 466                 }
 467
 468                 for loc in callee_body.vars_and_temps_iter() {
 469                     let mut local = callee_body.local_decls[loc].clone();
 470
 471                     local.source_info.scope = scope_map[local.source_info.scope];
 472                     local.source_info.span = callsite.source_info.span;
 473
 474                     let idx = caller_body.local_decls.push(local);
 475                     local_map.push(idx);
 476                 }
 477
 478                 // If the call is something like `a[*i] = f(i)`, where
 479                 // `i : &mut usize`, then just duplicating the `a[*i]`
 480                 // Place could result in two different locations if `f`
 481                 // writes to `i`. To prevent this we need to create a temporary
 482                 // borrow of the place and pass the destination as `*temp` instead.
 483                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 484                     for elem in place.projection.iter() {
 485                         match elem {
 486                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 487                             _ => {}
 488                         }
 489                     }
 490
 491                     false
 492                 }
 493
 494                 let dest = if dest_needs_borrow(destination.0) {
 495                     debug!("creating temp for return destination");
 496                     let dest = Rvalue::Ref(
 497                         self.tcx.lifetimes.re_erased,
 498                         BorrowKind::Mut { allow_two_phase_borrow: false },
 499                         destination.0,
 500                     );
 501
 502                     let ty = dest.ty(caller_body, self.tcx);
 503
 504                     let temp = LocalDecl::new(ty, callsite.source_info.span);
 505
 506                     let tmp = caller_body.local_decls.push(temp);
 507                     let tmp = Place::from(tmp);
 508
 509                     let stmt = Statement {
 510                         source_info: callsite.source_info,
 511                         kind: StatementKind::Assign(box (tmp, dest)),
 512                     };
 513                     caller_body[callsite.bb].statements.push(stmt);
 514                     self.tcx.mk_place_deref(tmp)
 515                 } else {
 516                     destination.0
 517                 };
 518
 519                 let return_block = destination.1;
 520
 521                 // Copy the arguments if needed.
 522                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, return_block);
 523
 524                 let bb_len = caller_body.basic_blocks().len();
 525                 let mut integrator = Integrator {
 526                     block_idx: bb_len,
 527                     args: &args,
 528                     local_map,
 529                     scope_map,
 530                     destination: dest,
 531                     return_block,
 532                     cleanup_block: cleanup,
 533                     in_cleanup_block: false,
 534                     tcx: self.tcx,
 535                 };
 536
 537                 for mut var_debug_info in callee_body.var_debug_info.drain(..) {
 538                     integrator.visit_var_debug_info(&mut var_debug_info);
 539                     caller_body.var_debug_info.push(var_debug_info);
 540                 }
 541
 542                 for (bb, mut block) in callee_body.basic_blocks_mut().drain_enumerated(..) {
 543                     integrator.visit_basic_block_data(bb, &mut block);
 544                     caller_body.basic_blocks_mut().push(block);
 545                 }
 546
 547                 let terminator = Terminator {
 548                     source_info: callsite.source_info,
 549                     kind: TerminatorKind::Goto { target: BasicBlock::new(bb_len) },
 550                 };
 551
 552                 caller_body[callsite.bb].terminator = Some(terminator);
 553
 554                 true
 555             }
 556             kind => {
 557                 caller_body[callsite.bb].terminator =
 558                     Some(Terminator { source_info: terminator.source_info, kind });
 559                 false
 560             }
 561         }
 562     }
 563
 564     fn make_call_args(
 565         &self,
 566         args: Vec<Operand<'tcx>>,
 567         callsite: &CallSite<'tcx>,
 568         caller_body: &mut Body<'tcx>,
 569         return_block: BasicBlock,
 570     ) -> Vec<Local> {
 571         let tcx = self.tcx;
 572
 573         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 574         // The caller provides the arguments wrapped up in a tuple:
 575         //
 576         //     tuple_tmp = (a, b, c)
 577         //     Fn::call(closure_ref, tuple_tmp)
 578         //
 579         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 580         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 581         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 582         // a vector like
 583         //
 584         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 585         //
 586         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 587         // if we "spill" that into *another* temporary, so that we can map the argument
 588         // variable in the callee MIR directly to an argument variable on our side.
 589         // So we introduce temporaries like:
 590         //
 591         //     tmp0 = tuple_tmp.0
 592         //     tmp1 = tuple_tmp.1
 593         //     tmp2 = tuple_tmp.2
 594         //
 595         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 596         // FIXME(eddyb) make this check for `"rust-call"` ABI combined with
 597         // `callee_body.spread_arg == None`, instead of special-casing closures.
 598         if tcx.is_closure(callsite.callee.def_id()) {
 599             let mut args = args.into_iter();
 600             let self_ = self.create_temp_if_necessary(
 601                 args.next().unwrap(),
 602                 callsite,
 603                 caller_body,
 604                 return_block,
 605             );
 606             let tuple = self.create_temp_if_necessary(
 607                 args.next().unwrap(),
 608                 callsite,
 609                 caller_body,
 610                 return_block,
 611             );
 612             assert!(args.next().is_none());
 613
 614             let tuple = Place::from(tuple);
 615             let tuple_tys = if let ty::Tuple(s) = tuple.ty(caller_body, tcx).ty.kind() {
 616                 s
 617             } else {
 618                 bug!("Closure arguments are not passed as a tuple");
 619             };
 620
 621             // The `closure_ref` in our example above.
 622             let closure_ref_arg = iter::once(self_);
 623
 624             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 625             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 626                 // This is e.g., `tuple_tmp.0` in our example above.
 627                 let tuple_field =
 628                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 629
 630                 // Spill to a local to make e.g., `tmp0`.
 631                 self.create_temp_if_necessary(tuple_field, callsite, caller_body, return_block)
 632             });
 633
 634             closure_ref_arg.chain(tuple_tmp_args).collect()
 635         } else {
 636             args.into_iter()
 637                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body, return_block))
 638                 .collect()
 639         }
 640     }
 641
 642     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 643     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 644     fn create_temp_if_necessary(
 645         &self,
 646         arg: Operand<'tcx>,
 647         callsite: &CallSite<'tcx>,
 648         caller_body: &mut Body<'tcx>,
 649         return_block: BasicBlock,
 650     ) -> Local {
 651         // FIXME: Analysis of the usage of the arguments to avoid
 652         // unnecessary temporaries.
 653
 654         if let Operand::Move(place) = &arg {
 655             if let Some(local) = place.as_local() {
 656                 if caller_body.local_kind(local) == LocalKind::Temp {
 657                     // Reuse the operand if it's a temporary already
 658                     return local;
 659                 }
 660             }
 661         }
 662
 663         debug!("creating temp for argument {:?}", arg);
 664         // Otherwise, create a temporary for the arg
 665         let arg = Rvalue::Use(arg);
 666
 667         let ty = arg.ty(caller_body, self.tcx);
 668
 669         let arg_tmp = LocalDecl::new(ty, callsite.source_info.span);
 670         let arg_tmp = caller_body.local_decls.push(arg_tmp);
 671
 672         caller_body[callsite.bb].statements.push(Statement {
 673             source_info: callsite.source_info,
 674             kind: StatementKind::StorageLive(arg_tmp),
 675         });
 676         caller_body[callsite.bb].statements.push(Statement {
 677             source_info: callsite.source_info,
 678             kind: StatementKind::Assign(box (Place::from(arg_tmp), arg)),
 679         });
 680         caller_body[return_block].statements.insert(
 681             0,
 682             Statement {
 683                 source_info: callsite.source_info,
 684                 kind: StatementKind::StorageDead(arg_tmp),
 685             },
 686         );
 687
 688         arg_tmp
 689     }
 690 }
 691
 692 fn type_size_of<'tcx>(
 693     tcx: TyCtxt<'tcx>,
 694     param_env: ty::ParamEnv<'tcx>,
 695     ty: Ty<'tcx>,
 696 ) -> Option<u64> {
 697     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 698 }
 699
 700 /**
 701  * Integrator.
 702  *
 703  * Integrates blocks from the callee function into the calling function.
 704  * Updates block indices, references to locals and other control flow
 705  * stuff.
 706 */
 707 struct Integrator<'a, 'tcx> {
 708     block_idx: usize,
 709     args: &'a [Local],
 710     local_map: IndexVec<Local, Local>,
 711     scope_map: IndexVec<SourceScope, SourceScope>,
 712     destination: Place<'tcx>,
 713     return_block: BasicBlock,
 714     cleanup_block: Option<BasicBlock>,
 715     in_cleanup_block: bool,
 716     tcx: TyCtxt<'tcx>,
 717 }
 718
 719 impl<'a, 'tcx> Integrator<'a, 'tcx> {
 720     fn update_target(&self, tgt: BasicBlock) -> BasicBlock {
 721         let new = BasicBlock::new(tgt.index() + self.block_idx);
 722         debug!("updating target `{:?}`, new: `{:?}`", tgt, new);
 723         new
 724     }
 725
 726     fn make_integrate_local(&self, local: Local) -> Local {
 727         if local == RETURN_PLACE {
 728             return self.destination.local;
 729         }
 730
 731         let idx = local.index() - 1;
 732         if idx < self.args.len() {
 733             return self.args[idx];
 734         }
 735
 736         self.local_map[Local::new(idx - self.args.len())]
 737     }
 738 }
 739
 740 impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
 741     fn tcx(&self) -> TyCtxt<'tcx> {
 742         self.tcx
 743     }
 744
 745     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 746         *local = self.make_integrate_local(*local);
 747     }
 748
 749     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 750         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 751         let dest_proj_len = self.destination.projection.len();
 752         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 753             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 754             projs.extend(self.destination.projection);
 755             projs.extend(place.projection);
 756
 757             place.projection = self.tcx.intern_place_elems(&*projs);
 758         }
 759         // Handles integrating any locals that occur in the base
 760         // or projections
 761         self.super_place(place, context, location)
 762     }
 763
 764     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 765         self.in_cleanup_block = data.is_cleanup;
 766         self.super_basic_block_data(block, data);
 767         self.in_cleanup_block = false;
 768     }
 769
 770     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 771         self.super_retag(kind, place, loc);
 772
 773         // We have to patch all inlined retags to be aware that they are no longer
 774         // happening on function entry.
 775         if *kind == RetagKind::FnEntry {
 776             *kind = RetagKind::Default;
 777         }
 778     }
 779
 780     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 781         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 782         // replaced down below anyways).
 783         if !matches!(terminator.kind, TerminatorKind::Return) {
 784             self.super_terminator(terminator, loc);
 785         }
 786
 787         match terminator.kind {
 788             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 789             TerminatorKind::Goto { ref mut target } => {
 790                 *target = self.update_target(*target);
 791             }
 792             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 793                 for tgt in targets.all_targets_mut() {
 794                     *tgt = self.update_target(*tgt);
 795                 }
 796             }
 797             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 798             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 799                 *target = self.update_target(*target);
 800                 if let Some(tgt) = *unwind {
 801                     *unwind = Some(self.update_target(tgt));
 802                 } else if !self.in_cleanup_block {
 803                     // Unless this drop is in a cleanup block, add an unwind edge to
 804                     // the original call's cleanup block
 805                     *unwind = self.cleanup_block;
 806                 }
 807             }
 808             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 809                 if let Some((_, ref mut tgt)) = *destination {
 810                     *tgt = self.update_target(*tgt);
 811                 }
 812                 if let Some(tgt) = *cleanup {
 813                     *cleanup = Some(self.update_target(tgt));
 814                 } else if !self.in_cleanup_block {
 815                     // Unless this call is in a cleanup block, add an unwind edge to
 816                     // the original call's cleanup block
 817                     *cleanup = self.cleanup_block;
 818                 }
 819             }
 820             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 821                 *target = self.update_target(*target);
 822                 if let Some(tgt) = *cleanup {
 823                     *cleanup = Some(self.update_target(tgt));
 824                 } else if !self.in_cleanup_block {
 825                     // Unless this assert is in a cleanup block, add an unwind edge to
 826                     // the original call's cleanup block
 827                     *cleanup = self.cleanup_block;
 828                 }
 829             }
 830             TerminatorKind::Return => {
 831                 terminator.kind = TerminatorKind::Goto { target: self.return_block };
 832             }
 833             TerminatorKind::Resume => {
 834                 if let Some(tgt) = self.cleanup_block {
 835                     terminator.kind = TerminatorKind::Goto { target: tgt }
 836                 }
 837             }
 838             TerminatorKind::Abort => {}
 839             TerminatorKind::Unreachable => {}
 840             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 841                 *real_target = self.update_target(*real_target);
 842                 *imaginary_target = self.update_target(*imaginary_target);
 843             }
 844             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 845             // see the ordering of passes in the optimized_mir query.
 846             {
 847                 bug!("False unwinds should have been removed before inlining")
 848             }
 849             TerminatorKind::InlineAsm { ref mut destination, .. } => {
 850                 if let Some(ref mut tgt) = *destination {
 851                     *tgt = self.update_target(*tgt);
 852                 }
 853             }
 854         }
 855     }
 856
 857     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 858         *scope = self.scope_map[*scope];
 859     }
 860 }