compiler/rustc_mir/src/transform/inline.rs

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