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                 let instance = Instance::resolve(self.tcx, self.param_env, callee_def_id, substs)
 205                     .ok()
 206                     .flatten()?;
 207
 208                 if let InstanceDef::Virtual(..) = instance.def {
 209                     return None;
 210                 }
 211
 212                 return Some(CallSite {
 213                     callee: instance.def_id(),
 214                     substs: instance.substs,
 215                     bb,
 216                     location: terminator.source_info,
 217                 });
 218             }
 219         }
 220
 221         None
 222     }
 223
 224     fn consider_optimizing(&self, callsite: CallSite<'tcx>, callee_body: &Body<'tcx>) -> bool {
 225         debug!("consider_optimizing({:?})", callsite);
 226         self.should_inline(callsite, callee_body)
 227             && self.tcx.consider_optimizing(|| {
 228                 format!("Inline {:?} into {:?}", callee_body.span, callsite)
 229             })
 230     }
 231
 232     fn should_inline(&self, callsite: CallSite<'tcx>, callee_body: &Body<'tcx>) -> bool {
 233         debug!("should_inline({:?})", callsite);
 234         let tcx = self.tcx;
 235
 236         // Cannot inline generators which haven't been transformed yet
 237         if callee_body.yield_ty.is_some() {
 238             debug!("    yield ty present - not inlining");
 239             return false;
 240         }
 241
 242         let codegen_fn_attrs = tcx.codegen_fn_attrs(callsite.callee);
 243
 244         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::TRACK_CALLER) {
 245             debug!("`#[track_caller]` present - not inlining");
 246             return false;
 247         }
 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.is_local() {
 282             if callsite.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.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.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                     if scope.parent_scope.is_none() {
 439                         scope.parent_scope = Some(callsite.location.scope);
 440                         // FIXME(eddyb) is this really needed?
 441                         // (also note that it's always overwritten below)
 442                         scope.span = callee_body.span;
 443                     }
 444
 445                     // FIXME(eddyb) this doesn't seem right at all.
 446                     // The inlined source scopes should probably be annotated as
 447                     // such, but also contain all of the original information.
 448                     scope.span = callsite.location.span;
 449
 450                     let idx = caller_body.source_scopes.push(scope);
 451                     scope_map.push(idx);
 452                 }
 453
 454                 for loc in callee_body.vars_and_temps_iter() {
 455                     let mut local = callee_body.local_decls[loc].clone();
 456
 457                     local.source_info.scope = scope_map[local.source_info.scope];
 458                     local.source_info.span = callsite.location.span;
 459
 460                     let idx = caller_body.local_decls.push(local);
 461                     local_map.push(idx);
 462                 }
 463
 464                 // If the call is something like `a[*i] = f(i)`, where
 465                 // `i : &mut usize`, then just duplicating the `a[*i]`
 466                 // Place could result in two different locations if `f`
 467                 // writes to `i`. To prevent this we need to create a temporary
 468                 // borrow of the place and pass the destination as `*temp` instead.
 469                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 470                     for elem in place.projection.iter() {
 471                         match elem {
 472                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 473                             _ => {}
 474                         }
 475                     }
 476
 477                     false
 478                 }
 479
 480                 let dest = if dest_needs_borrow(destination.0) {
 481                     debug!("creating temp for return destination");
 482                     let dest = Rvalue::Ref(
 483                         self.tcx.lifetimes.re_erased,
 484                         BorrowKind::Mut { allow_two_phase_borrow: false },
 485                         destination.0,
 486                     );
 487
 488                     let ty = dest.ty(caller_body, self.tcx);
 489
 490                     let temp = LocalDecl::new(ty, callsite.location.span);
 491
 492                     let tmp = caller_body.local_decls.push(temp);
 493                     let tmp = Place::from(tmp);
 494
 495                     let stmt = Statement {
 496                         source_info: callsite.location,
 497                         kind: StatementKind::Assign(box (tmp, dest)),
 498                     };
 499                     caller_body[callsite.bb].statements.push(stmt);
 500                     self.tcx.mk_place_deref(tmp)
 501                 } else {
 502                     destination.0
 503                 };
 504
 505                 let return_block = destination.1;
 506
 507                 // Copy the arguments if needed.
 508                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, return_block);
 509
 510                 let bb_len = caller_body.basic_blocks().len();
 511                 let mut integrator = Integrator {
 512                     block_idx: bb_len,
 513                     args: &args,
 514                     local_map,
 515                     scope_map,
 516                     destination: dest,
 517                     return_block,
 518                     cleanup_block: cleanup,
 519                     in_cleanup_block: false,
 520                     tcx: self.tcx,
 521                 };
 522
 523                 for mut var_debug_info in callee_body.var_debug_info.drain(..) {
 524                     integrator.visit_var_debug_info(&mut var_debug_info);
 525                     caller_body.var_debug_info.push(var_debug_info);
 526                 }
 527
 528                 for (bb, mut block) in callee_body.basic_blocks_mut().drain_enumerated(..) {
 529                     integrator.visit_basic_block_data(bb, &mut block);
 530                     caller_body.basic_blocks_mut().push(block);
 531                 }
 532
 533                 let terminator = Terminator {
 534                     source_info: callsite.location,
 535                     kind: TerminatorKind::Goto { target: BasicBlock::new(bb_len) },
 536                 };
 537
 538                 caller_body[callsite.bb].terminator = Some(terminator);
 539
 540                 true
 541             }
 542             kind => {
 543                 caller_body[callsite.bb].terminator =
 544                     Some(Terminator { source_info: terminator.source_info, kind });
 545                 false
 546             }
 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         return_block: BasicBlock,
 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 tcx.is_closure(callsite.callee) {
 583             let mut args = args.into_iter();
 584             let self_ = self.create_temp_if_necessary(
 585                 args.next().unwrap(),
 586                 callsite,
 587                 caller_body,
 588                 return_block,
 589             );
 590             let tuple = self.create_temp_if_necessary(
 591                 args.next().unwrap(),
 592                 callsite,
 593                 caller_body,
 594                 return_block,
 595             );
 596             assert!(args.next().is_none());
 597
 598             let tuple = Place::from(tuple);
 599             let tuple_tys = if let ty::Tuple(s) = tuple.ty(caller_body, tcx).ty.kind() {
 600                 s
 601             } else {
 602                 bug!("Closure arguments are not passed as a tuple");
 603             };
 604
 605             // The `closure_ref` in our example above.
 606             let closure_ref_arg = iter::once(self_);
 607
 608             // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
 609             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 610                 // This is e.g., `tuple_tmp.0` in our example above.
 611                 let tuple_field =
 612                     Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty.expect_ty()));
 613
 614                 // Spill to a local to make e.g., `tmp0`.
 615                 self.create_temp_if_necessary(tuple_field, callsite, caller_body, return_block)
 616             });
 617
 618             closure_ref_arg.chain(tuple_tmp_args).collect()
 619         } else {
 620             args.into_iter()
 621                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body, return_block))
 622                 .collect()
 623         }
 624     }
 625
 626     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 627     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 628     fn create_temp_if_necessary(
 629         &self,
 630         arg: Operand<'tcx>,
 631         callsite: &CallSite<'tcx>,
 632         caller_body: &mut Body<'tcx>,
 633         return_block: BasicBlock,
 634     ) -> Local {
 635         // FIXME: Analysis of the usage of the arguments to avoid
 636         // unnecessary temporaries.
 637
 638         if let Operand::Move(place) = &arg {
 639             if let Some(local) = place.as_local() {
 640                 if caller_body.local_kind(local) == LocalKind::Temp {
 641                     // Reuse the operand if it's a temporary already
 642                     return local;
 643                 }
 644             }
 645         }
 646
 647         debug!("creating temp for argument {:?}", arg);
 648         // Otherwise, create a temporary for the arg
 649         let arg = Rvalue::Use(arg);
 650
 651         let ty = arg.ty(caller_body, self.tcx);
 652
 653         let arg_tmp = LocalDecl::new(ty, callsite.location.span);
 654         let arg_tmp = caller_body.local_decls.push(arg_tmp);
 655
 656         caller_body[callsite.bb].statements.push(Statement {
 657             source_info: callsite.location,
 658             kind: StatementKind::StorageLive(arg_tmp),
 659         });
 660         caller_body[callsite.bb].statements.push(Statement {
 661             source_info: callsite.location,
 662             kind: StatementKind::Assign(box (Place::from(arg_tmp), arg)),
 663         });
 664         caller_body[return_block].statements.insert(
 665             0,
 666             Statement { source_info: callsite.location, kind: StatementKind::StorageDead(arg_tmp) },
 667         );
 668
 669         arg_tmp
 670     }
 671 }
 672
 673 fn type_size_of<'tcx>(
 674     tcx: TyCtxt<'tcx>,
 675     param_env: ty::ParamEnv<'tcx>,
 676     ty: Ty<'tcx>,
 677 ) -> Option<u64> {
 678     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 679 }
 680
 681 /**
 682  * Integrator.
 683  *
 684  * Integrates blocks from the callee function into the calling function.
 685  * Updates block indices, references to locals and other control flow
 686  * stuff.
 687 */
 688 struct Integrator<'a, 'tcx> {
 689     block_idx: usize,
 690     args: &'a [Local],
 691     local_map: IndexVec<Local, Local>,
 692     scope_map: IndexVec<SourceScope, SourceScope>,
 693     destination: Place<'tcx>,
 694     return_block: BasicBlock,
 695     cleanup_block: Option<BasicBlock>,
 696     in_cleanup_block: bool,
 697     tcx: TyCtxt<'tcx>,
 698 }
 699
 700 impl<'a, 'tcx> Integrator<'a, 'tcx> {
 701     fn update_target(&self, tgt: BasicBlock) -> BasicBlock {
 702         let new = BasicBlock::new(tgt.index() + self.block_idx);
 703         debug!("updating target `{:?}`, new: `{:?}`", tgt, new);
 704         new
 705     }
 706
 707     fn make_integrate_local(&self, local: Local) -> Local {
 708         if local == RETURN_PLACE {
 709             return self.destination.local;
 710         }
 711
 712         let idx = local.index() - 1;
 713         if idx < self.args.len() {
 714             return self.args[idx];
 715         }
 716
 717         self.local_map[Local::new(idx - self.args.len())]
 718     }
 719 }
 720
 721 impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
 722     fn tcx(&self) -> TyCtxt<'tcx> {
 723         self.tcx
 724     }
 725
 726     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
 727         *local = self.make_integrate_local(*local);
 728     }
 729
 730     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
 731         // If this is the `RETURN_PLACE`, we need to rebase any projections onto it.
 732         let dest_proj_len = self.destination.projection.len();
 733         if place.local == RETURN_PLACE && dest_proj_len > 0 {
 734             let mut projs = Vec::with_capacity(dest_proj_len + place.projection.len());
 735             projs.extend(self.destination.projection);
 736             projs.extend(place.projection);
 737
 738             place.projection = self.tcx.intern_place_elems(&*projs);
 739         }
 740         // Handles integrating any locals that occur in the base
 741         // or projections
 742         self.super_place(place, context, location)
 743     }
 744
 745     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
 746         self.in_cleanup_block = data.is_cleanup;
 747         self.super_basic_block_data(block, data);
 748         self.in_cleanup_block = false;
 749     }
 750
 751     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
 752         self.super_retag(kind, place, loc);
 753
 754         // We have to patch all inlined retags to be aware that they are no longer
 755         // happening on function entry.
 756         if *kind == RetagKind::FnEntry {
 757             *kind = RetagKind::Default;
 758         }
 759     }
 760
 761     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
 762         // Don't try to modify the implicit `_0` access on return (`return` terminators are
 763         // replaced down below anyways).
 764         if !matches!(terminator.kind, TerminatorKind::Return) {
 765             self.super_terminator(terminator, loc);
 766         }
 767
 768         match terminator.kind {
 769             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
 770             TerminatorKind::Goto { ref mut target } => {
 771                 *target = self.update_target(*target);
 772             }
 773             TerminatorKind::SwitchInt { ref mut targets, .. } => {
 774                 for tgt in targets.all_targets_mut() {
 775                     *tgt = self.update_target(*tgt);
 776                 }
 777             }
 778             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
 779             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
 780                 *target = self.update_target(*target);
 781                 if let Some(tgt) = *unwind {
 782                     *unwind = Some(self.update_target(tgt));
 783                 } else if !self.in_cleanup_block {
 784                     // Unless this drop is in a cleanup block, add an unwind edge to
 785                     // the original call's cleanup block
 786                     *unwind = self.cleanup_block;
 787                 }
 788             }
 789             TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
 790                 if let Some((_, ref mut tgt)) = *destination {
 791                     *tgt = self.update_target(*tgt);
 792                 }
 793                 if let Some(tgt) = *cleanup {
 794                     *cleanup = Some(self.update_target(tgt));
 795                 } else if !self.in_cleanup_block {
 796                     // Unless this call is in a cleanup block, add an unwind edge to
 797                     // the original call's cleanup block
 798                     *cleanup = self.cleanup_block;
 799                 }
 800             }
 801             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
 802                 *target = self.update_target(*target);
 803                 if let Some(tgt) = *cleanup {
 804                     *cleanup = Some(self.update_target(tgt));
 805                 } else if !self.in_cleanup_block {
 806                     // Unless this assert is in a cleanup block, add an unwind edge to
 807                     // the original call's cleanup block
 808                     *cleanup = self.cleanup_block;
 809                 }
 810             }
 811             TerminatorKind::Return => {
 812                 terminator.kind = TerminatorKind::Goto { target: self.return_block };
 813             }
 814             TerminatorKind::Resume => {
 815                 if let Some(tgt) = self.cleanup_block {
 816                     terminator.kind = TerminatorKind::Goto { target: tgt }
 817                 }
 818             }
 819             TerminatorKind::Abort => {}
 820             TerminatorKind::Unreachable => {}
 821             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
 822                 *real_target = self.update_target(*real_target);
 823                 *imaginary_target = self.update_target(*imaginary_target);
 824             }
 825             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
 826             // see the ordering of passes in the optimized_mir query.
 827             {
 828                 bug!("False unwinds should have been removed before inlining")
 829             }
 830             TerminatorKind::InlineAsm { ref mut destination, .. } => {
 831                 if let Some(ref mut tgt) = *destination {
 832                     *tgt = self.update_target(*tgt);
 833                 }
 834             }
 835         }
 836     }
 837
 838     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
 839         *scope = self.scope_map[*scope];
 840     }
 841 }