compiler/rustc_mir_transform/src/inline.rs

   1 //! Inlining pass for MIR functions
   2 use crate::deref_separator::deref_finder;
   3 use rustc_attr::InlineAttr;
   4 use rustc_hir::def_id::DefId;
   5 use rustc_index::bit_set::BitSet;
   6 use rustc_index::vec::Idx;
   7 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
   8 use rustc_middle::mir::visit::*;
   9 use rustc_middle::mir::*;
  10 use rustc_middle::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
  11 use rustc_session::config::OptLevel;
  12 use rustc_span::{hygiene::ExpnKind, ExpnData, LocalExpnId, Span};
  13 use rustc_target::abi::VariantIdx;
  14 use rustc_target::spec::abi::Abi;
  15
  16 use crate::simplify::{remove_dead_blocks, CfgSimplifier};
  17 use crate::util;
  18 use crate::MirPass;
  19 use std::iter;
  20 use std::ops::{Range, RangeFrom};
  21
  22 pub(crate) mod cycle;
  23
  24 const INSTR_COST: usize = 5;
  25 const CALL_PENALTY: usize = 25;
  26 const LANDINGPAD_PENALTY: usize = 50;
  27 const RESUME_PENALTY: usize = 45;
  28
  29 const UNKNOWN_SIZE_COST: usize = 10;
  30
  31 const TOP_DOWN_DEPTH_LIMIT: usize = 5;
  32
  33 pub struct Inline;
  34
  35 #[derive(Copy, Clone, Debug)]
  36 struct CallSite<'tcx> {
  37     callee: Instance<'tcx>,
  38     fn_sig: ty::PolyFnSig<'tcx>,
  39     block: BasicBlock,
  40     target: Option<BasicBlock>,
  41     source_info: SourceInfo,
  42 }
  43
  44 impl<'tcx> MirPass<'tcx> for Inline {
  45     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
  46         if let Some(enabled) = sess.opts.unstable_opts.inline_mir {
  47             return enabled;
  48         }
  49
  50         match sess.mir_opt_level() {
  51             0 | 1 => false,
  52             2 => {
  53                 (sess.opts.optimize == OptLevel::Default
  54                     || sess.opts.optimize == OptLevel::Aggressive)
  55                     && sess.opts.incremental == None
  56             }
  57             _ => true,
  58         }
  59     }
  60
  61     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
  62         let span = trace_span!("inline", body = %tcx.def_path_str(body.source.def_id()));
  63         let _guard = span.enter();
  64         if inline(tcx, body) {
  65             debug!("running simplify cfg on {:?}", body.source);
  66             CfgSimplifier::new(body).simplify();
  67             remove_dead_blocks(tcx, body);
  68             deref_finder(tcx, body);
  69         }
  70     }
  71 }
  72
  73 fn inline<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
  74     let def_id = body.source.def_id().expect_local();
  75
  76     // Only do inlining into fn bodies.
  77     if !tcx.hir().body_owner_kind(def_id).is_fn_or_closure() {
  78         return false;
  79     }
  80     if body.source.promoted.is_some() {
  81         return false;
  82     }
  83     // Avoid inlining into generators, since their `optimized_mir` is used for layout computation,
  84     // which can create a cycle, even when no attempt is made to inline the function in the other
  85     // direction.
  86     if body.generator.is_some() {
  87         return false;
  88     }
  89
  90     let param_env = tcx.param_env_reveal_all_normalized(def_id);
  91
  92     let mut this = Inliner {
  93         tcx,
  94         param_env,
  95         codegen_fn_attrs: tcx.codegen_fn_attrs(def_id),
  96         history: Vec::new(),
  97         changed: false,
  98     };
  99     let blocks = BasicBlock::new(0)..body.basic_blocks.next_index();
 100     this.process_blocks(body, blocks);
 101     this.changed
 102 }
 103
 104 struct Inliner<'tcx> {
 105     tcx: TyCtxt<'tcx>,
 106     param_env: ParamEnv<'tcx>,
 107     /// Caller codegen attributes.
 108     codegen_fn_attrs: &'tcx CodegenFnAttrs,
 109     /// Stack of inlined instances.
 110     /// We only check the `DefId` and not the substs because we want to
 111     /// avoid inlining cases of polymorphic recursion.
 112     /// The number of `DefId`s is finite, so checking history is enough
 113     /// to ensure that we do not loop endlessly while inlining.
 114     history: Vec<DefId>,
 115     /// Indicates that the caller body has been modified.
 116     changed: bool,
 117 }
 118
 119 impl<'tcx> Inliner<'tcx> {
 120     fn process_blocks(&mut self, caller_body: &mut Body<'tcx>, blocks: Range<BasicBlock>) {
 121         // How many callsites in this body are we allowed to inline? We need to limit this in order
 122         // to prevent super-linear growth in MIR size
 123         let inline_limit = match self.history.len() {
 124             0 => usize::MAX,
 125             1..=TOP_DOWN_DEPTH_LIMIT => 1,
 126             _ => return,
 127         };
 128         let mut inlined_count = 0;
 129         for bb in blocks {
 130             let bb_data = &caller_body[bb];
 131             if bb_data.is_cleanup {
 132                 continue;
 133             }
 134
 135             let Some(callsite) = self.resolve_callsite(caller_body, bb, bb_data) else {
 136                 continue;
 137             };
 138
 139             let span = trace_span!("process_blocks", %callsite.callee, ?bb);
 140             let _guard = span.enter();
 141
 142             match self.try_inlining(caller_body, &callsite) {
 143                 Err(reason) => {
 144                     debug!("not-inlined {} [{}]", callsite.callee, reason);
 145                     continue;
 146                 }
 147                 Ok(new_blocks) => {
 148                     debug!("inlined {}", callsite.callee);
 149                     self.changed = true;
 150                     inlined_count += 1;
 151                     if inlined_count == inline_limit {
 152                         return;
 153                     }
 154                     self.history.push(callsite.callee.def_id());
 155                     self.process_blocks(caller_body, new_blocks);
 156                     self.history.pop();
 157                 }
 158             }
 159         }
 160     }
 161
 162     /// Attempts to inline a callsite into the caller body. When successful returns basic blocks
 163     /// containing the inlined body. Otherwise returns an error describing why inlining didn't take
 164     /// place.
 165     fn try_inlining(
 166         &self,
 167         caller_body: &mut Body<'tcx>,
 168         callsite: &CallSite<'tcx>,
 169     ) -> Result<std::ops::Range<BasicBlock>, &'static str> {
 170         let callee_attrs = self.tcx.codegen_fn_attrs(callsite.callee.def_id());
 171         self.check_codegen_attributes(callsite, callee_attrs)?;
 172         self.check_mir_is_available(caller_body, &callsite.callee)?;
 173         let callee_body = self.tcx.instance_mir(callsite.callee.def);
 174         self.check_mir_body(callsite, callee_body, callee_attrs)?;
 175
 176         if !self.tcx.consider_optimizing(|| {
 177             format!("Inline {:?} into {:?}", callsite.callee, caller_body.source)
 178         }) {
 179             return Err("optimization fuel exhausted");
 180         }
 181
 182         let Ok(callee_body) = callsite.callee.try_subst_mir_and_normalize_erasing_regions(
 183             self.tcx,
 184             self.param_env,
 185             callee_body.clone(),
 186         ) else {
 187             return Err("failed to normalize callee body");
 188         };
 189
 190         // Check call signature compatibility.
 191         // Normally, this shouldn't be required, but trait normalization failure can create a
 192         // validation ICE.
 193         let terminator = caller_body[callsite.block].terminator.as_ref().unwrap();
 194         let TerminatorKind::Call { args, destination, .. } = &terminator.kind else { bug!() };
 195         let destination_ty = destination.ty(&caller_body.local_decls, self.tcx).ty;
 196         let output_type = callee_body.return_ty();
 197         if !util::is_subtype(self.tcx, self.param_env, output_type, destination_ty) {
 198             trace!(?output_type, ?destination_ty);
 199             return Err("failed to normalize return type");
 200         }
 201         if callsite.fn_sig.abi() == Abi::RustCall {
 202             let (arg_tuple, skipped_args) = match &args[..] {
 203                 [arg_tuple] => (arg_tuple, 0),
 204                 [_, arg_tuple] => (arg_tuple, 1),
 205                 _ => bug!("Expected `rust-call` to have 1 or 2 args"),
 206             };
 207
 208             let arg_tuple_ty = arg_tuple.ty(&caller_body.local_decls, self.tcx);
 209             let ty::Tuple(arg_tuple_tys) = arg_tuple_ty.kind() else {
 210                 bug!("Closure arguments are not passed as a tuple");
 211             };
 212
 213             for (arg_ty, input) in
 214                 arg_tuple_tys.iter().zip(callee_body.args_iter().skip(skipped_args))
 215             {
 216                 let input_type = callee_body.local_decls[input].ty;
 217                 if !util::is_subtype(self.tcx, self.param_env, input_type, arg_ty) {
 218                     trace!(?arg_ty, ?input_type);
 219                     return Err("failed to normalize tuple argument type");
 220                 }
 221             }
 222         } else {
 223             for (arg, input) in args.iter().zip(callee_body.args_iter()) {
 224                 let input_type = callee_body.local_decls[input].ty;
 225                 let arg_ty = arg.ty(&caller_body.local_decls, self.tcx);
 226                 if !util::is_subtype(self.tcx, self.param_env, input_type, arg_ty) {
 227                     trace!(?arg_ty, ?input_type);
 228                     return Err("failed to normalize argument type");
 229                 }
 230             }
 231         }
 232
 233         let old_blocks = caller_body.basic_blocks.next_index();
 234         self.inline_call(caller_body, &callsite, callee_body);
 235         let new_blocks = old_blocks..caller_body.basic_blocks.next_index();
 236
 237         Ok(new_blocks)
 238     }
 239
 240     fn check_mir_is_available(
 241         &self,
 242         caller_body: &Body<'tcx>,
 243         callee: &Instance<'tcx>,
 244     ) -> Result<(), &'static str> {
 245         let caller_def_id = caller_body.source.def_id();
 246         let callee_def_id = callee.def_id();
 247         if callee_def_id == caller_def_id {
 248             return Err("self-recursion");
 249         }
 250
 251         match callee.def {
 252             InstanceDef::Item(_) => {
 253                 // If there is no MIR available (either because it was not in metadata or
 254                 // because it has no MIR because it's an extern function), then the inliner
 255                 // won't cause cycles on this.
 256                 if !self.tcx.is_mir_available(callee_def_id) {
 257                     return Err("item MIR unavailable");
 258                 }
 259             }
 260             // These have no own callable MIR.
 261             InstanceDef::Intrinsic(_) | InstanceDef::Virtual(..) => {
 262                 return Err("instance without MIR (intrinsic / virtual)");
 263             }
 264             // This cannot result in an immediate cycle since the callee MIR is a shim, which does
 265             // not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
 266             // do not need to catch this here, we can wait until the inliner decides to continue
 267             // inlining a second time.
 268             InstanceDef::VTableShim(_)
 269             | InstanceDef::ReifyShim(_)
 270             | InstanceDef::FnPtrShim(..)
 271             | InstanceDef::ClosureOnceShim { .. }
 272             | InstanceDef::DropGlue(..)
 273             | InstanceDef::CloneShim(..) => return Ok(()),
 274         }
 275
 276         if self.tcx.is_constructor(callee_def_id) {
 277             trace!("constructors always have MIR");
 278             // Constructor functions cannot cause a query cycle.
 279             return Ok(());
 280         }
 281
 282         if callee_def_id.is_local() {
 283             // Avoid a cycle here by only using `instance_mir` only if we have
 284             // a lower `DefPathHash` than the callee. This ensures that the callee will
 285             // not inline us. This trick even works with incremental compilation,
 286             // since `DefPathHash` is stable.
 287             if self.tcx.def_path_hash(caller_def_id).local_hash()
 288                 < self.tcx.def_path_hash(callee_def_id).local_hash()
 289             {
 290                 return Ok(());
 291             }
 292
 293             // If we know for sure that the function we're calling will itself try to
 294             // call us, then we avoid inlining that function.
 295             if self.tcx.mir_callgraph_reachable((*callee, caller_def_id.expect_local())) {
 296                 return Err("caller might be reachable from callee (query cycle avoidance)");
 297             }
 298
 299             Ok(())
 300         } else {
 301             // This cannot result in an immediate cycle since the callee MIR is from another crate
 302             // and is already optimized. Any subsequent inlining may cause cycles, but we do
 303             // not need to catch this here, we can wait until the inliner decides to continue
 304             // inlining a second time.
 305             trace!("functions from other crates always have MIR");
 306             Ok(())
 307         }
 308     }
 309
 310     fn resolve_callsite(
 311         &self,
 312         caller_body: &Body<'tcx>,
 313         bb: BasicBlock,
 314         bb_data: &BasicBlockData<'tcx>,
 315     ) -> Option<CallSite<'tcx>> {
 316         // Only consider direct calls to functions
 317         let terminator = bb_data.terminator();
 318         if let TerminatorKind::Call { ref func, target, fn_span, .. } = terminator.kind {
 319             let func_ty = func.ty(caller_body, self.tcx);
 320             if let ty::FnDef(def_id, substs) = *func_ty.kind() {
 321                 // To resolve an instance its substs have to be fully normalized.
 322                 let substs = self.tcx.try_normalize_erasing_regions(self.param_env, substs).ok()?;
 323                 let callee =
 324                     Instance::resolve(self.tcx, self.param_env, def_id, substs).ok().flatten()?;
 325
 326                 if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
 327                     return None;
 328                 }
 329
 330                 if self.history.contains(&callee.def_id()) {
 331                     return None;
 332                 }
 333
 334                 let fn_sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 335                 let source_info = SourceInfo { span: fn_span, ..terminator.source_info };
 336
 337                 return Some(CallSite { callee, fn_sig, block: bb, target, source_info });
 338             }
 339         }
 340
 341         None
 342     }
 343
 344     /// Returns an error if inlining is not possible based on codegen attributes alone. A success
 345     /// indicates that inlining decision should be based on other criteria.
 346     fn check_codegen_attributes(
 347         &self,
 348         callsite: &CallSite<'tcx>,
 349         callee_attrs: &CodegenFnAttrs,
 350     ) -> Result<(), &'static str> {
 351         match callee_attrs.inline {
 352             InlineAttr::Never => return Err("never inline hint"),
 353             InlineAttr::Always | InlineAttr::Hint => {}
 354             InlineAttr::None => {
 355                 if self.tcx.sess.mir_opt_level() <= 2 {
 356                     return Err("at mir-opt-level=2, only #[inline] is inlined");
 357                 }
 358             }
 359         }
 360
 361         // Only inline local functions if they would be eligible for cross-crate
 362         // inlining. This is to ensure that the final crate doesn't have MIR that
 363         // reference unexported symbols
 364         if callsite.callee.def_id().is_local() {
 365             let is_generic = callsite.callee.substs.non_erasable_generics().next().is_some();
 366             if !is_generic && !callee_attrs.requests_inline() {
 367                 return Err("not exported");
 368             }
 369         }
 370
 371         if callsite.fn_sig.c_variadic() {
 372             return Err("C variadic");
 373         }
 374
 375         if callee_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
 376             return Err("cold");
 377         }
 378
 379         if callee_attrs.no_sanitize != self.codegen_fn_attrs.no_sanitize {
 380             return Err("incompatible sanitizer set");
 381         }
 382
 383         // Two functions are compatible if the callee has no attribute (meaning
 384         // that it's codegen agnostic), or sets an attribute that is identical
 385         // to this function's attribute.
 386         if callee_attrs.instruction_set.is_some()
 387             && callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set
 388         {
 389             return Err("incompatible instruction set");
 390         }
 391
 392         for feature in &callee_attrs.target_features {
 393             if !self.codegen_fn_attrs.target_features.contains(feature) {
 394                 return Err("incompatible target feature");
 395             }
 396         }
 397
 398         Ok(())
 399     }
 400
 401     /// Returns inlining decision that is based on the examination of callee MIR body.
 402     /// Assumes that codegen attributes have been checked for compatibility already.
 403     #[instrument(level = "debug", skip(self, callee_body))]
 404     fn check_mir_body(
 405         &self,
 406         callsite: &CallSite<'tcx>,
 407         callee_body: &Body<'tcx>,
 408         callee_attrs: &CodegenFnAttrs,
 409     ) -> Result<(), &'static str> {
 410         let tcx = self.tcx;
 411
 412         let mut threshold = if callee_attrs.requests_inline() {
 413             self.tcx.sess.opts.unstable_opts.inline_mir_hint_threshold.unwrap_or(100)
 414         } else {
 415             self.tcx.sess.opts.unstable_opts.inline_mir_threshold.unwrap_or(50)
 416         };
 417
 418         // Give a bonus functions with a small number of blocks,
 419         // We normally have two or three blocks for even
 420         // very small functions.
 421         if callee_body.basic_blocks.len() <= 3 {
 422             threshold += threshold / 4;
 423         }
 424         debug!("    final inline threshold = {}", threshold);
 425
 426         // FIXME: Give a bonus to functions with only a single caller
 427         let diverges = matches!(
 428             callee_body.basic_blocks[START_BLOCK].terminator().kind,
 429             TerminatorKind::Unreachable | TerminatorKind::Call { target: None, .. }
 430         );
 431         if diverges && !matches!(callee_attrs.inline, InlineAttr::Always) {
 432             return Err("callee diverges unconditionally");
 433         }
 434
 435         let mut checker = CostChecker {
 436             tcx: self.tcx,
 437             param_env: self.param_env,
 438             instance: callsite.callee,
 439             callee_body,
 440             cost: 0,
 441             validation: Ok(()),
 442         };
 443
 444         // Traverse the MIR manually so we can account for the effects of inlining on the CFG.
 445         let mut work_list = vec![START_BLOCK];
 446         let mut visited = BitSet::new_empty(callee_body.basic_blocks.len());
 447         while let Some(bb) = work_list.pop() {
 448             if !visited.insert(bb.index()) {
 449                 continue;
 450             }
 451
 452             let blk = &callee_body.basic_blocks[bb];
 453             checker.visit_basic_block_data(bb, blk);
 454
 455             let term = blk.terminator();
 456             if let TerminatorKind::Drop { ref place, target, unwind }
 457             | TerminatorKind::DropAndReplace { ref place, target, unwind, .. } = term.kind
 458             {
 459                 work_list.push(target);
 460
 461                 // If the place doesn't actually need dropping, treat it like a regular goto.
 462                 let ty = callsite.callee.subst_mir(self.tcx, &place.ty(callee_body, tcx).ty);
 463                 if ty.needs_drop(tcx, self.param_env) && let Some(unwind) = unwind {
 464                         work_list.push(unwind);
 465                     }
 466             } else if callee_attrs.instruction_set != self.codegen_fn_attrs.instruction_set
 467                 && matches!(term.kind, TerminatorKind::InlineAsm { .. })
 468             {
 469                 // During the attribute checking stage we allow a callee with no
 470                 // instruction_set assigned to count as compatible with a function that does
 471                 // assign one. However, during this stage we require an exact match when any
 472                 // inline-asm is detected. LLVM will still possibly do an inline later on
 473                 // if the no-attribute function ends up with the same instruction set anyway.
 474                 return Err("Cannot move inline-asm across instruction sets");
 475             } else {
 476                 work_list.extend(term.successors())
 477             }
 478         }
 479
 480         // Count up the cost of local variables and temps, if we know the size
 481         // use that, otherwise we use a moderately-large dummy cost.
 482         for v in callee_body.vars_and_temps_iter() {
 483             checker.visit_local_decl(v, &callee_body.local_decls[v]);
 484         }
 485
 486         // Abort if type validation found anything fishy.
 487         checker.validation?;
 488
 489         let cost = checker.cost;
 490         if let InlineAttr::Always = callee_attrs.inline {
 491             debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
 492             Ok(())
 493         } else if cost <= threshold {
 494             debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
 495             Ok(())
 496         } else {
 497             debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
 498             Err("cost above threshold")
 499         }
 500     }
 501
 502     fn inline_call(
 503         &self,
 504         caller_body: &mut Body<'tcx>,
 505         callsite: &CallSite<'tcx>,
 506         mut callee_body: Body<'tcx>,
 507     ) {
 508         let terminator = caller_body[callsite.block].terminator.take().unwrap();
 509         match terminator.kind {
 510             TerminatorKind::Call { args, destination, cleanup, .. } => {
 511                 // If the call is something like `a[*i] = f(i)`, where
 512                 // `i : &mut usize`, then just duplicating the `a[*i]`
 513                 // Place could result in two different locations if `f`
 514                 // writes to `i`. To prevent this we need to create a temporary
 515                 // borrow of the place and pass the destination as `*temp` instead.
 516                 fn dest_needs_borrow(place: Place<'_>) -> bool {
 517                     for elem in place.projection.iter() {
 518                         match elem {
 519                             ProjectionElem::Deref | ProjectionElem::Index(_) => return true,
 520                             _ => {}
 521                         }
 522                     }
 523
 524                     false
 525                 }
 526
 527                 let dest = if dest_needs_borrow(destination) {
 528                     trace!("creating temp for return destination");
 529                     let dest = Rvalue::Ref(
 530                         self.tcx.lifetimes.re_erased,
 531                         BorrowKind::Mut { allow_two_phase_borrow: false },
 532                         destination,
 533                     );
 534                     let dest_ty = dest.ty(caller_body, self.tcx);
 535                     let temp = Place::from(self.new_call_temp(caller_body, &callsite, dest_ty));
 536                     caller_body[callsite.block].statements.push(Statement {
 537                         source_info: callsite.source_info,
 538                         kind: StatementKind::Assign(Box::new((temp, dest))),
 539                     });
 540                     self.tcx.mk_place_deref(temp)
 541                 } else {
 542                     destination
 543                 };
 544
 545                 // Always create a local to hold the destination, as `RETURN_PLACE` may appear
 546                 // where a full `Place` is not allowed.
 547                 let (remap_destination, destination_local) = if let Some(d) = dest.as_local() {
 548                     (false, d)
 549                 } else {
 550                     (
 551                         true,
 552                         self.new_call_temp(
 553                             caller_body,
 554                             &callsite,
 555                             destination.ty(caller_body, self.tcx).ty,
 556                         ),
 557                     )
 558                 };
 559
 560                 // Copy the arguments if needed.
 561                 let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, &callee_body);
 562
 563                 let mut expn_data = ExpnData::default(
 564                     ExpnKind::Inlined,
 565                     callsite.source_info.span,
 566                     self.tcx.sess.edition(),
 567                     None,
 568                     None,
 569                 );
 570                 expn_data.def_site = callee_body.span;
 571                 let expn_data =
 572                     self.tcx.with_stable_hashing_context(|hcx| LocalExpnId::fresh(expn_data, hcx));
 573                 let mut integrator = Integrator {
 574                     args: &args,
 575                     new_locals: Local::new(caller_body.local_decls.len())..,
 576                     new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
 577                     new_blocks: BasicBlock::new(caller_body.basic_blocks.len())..,
 578                     destination: destination_local,
 579                     callsite_scope: caller_body.source_scopes[callsite.source_info.scope].clone(),
 580                     callsite,
 581                     cleanup_block: cleanup,
 582                     in_cleanup_block: false,
 583                     tcx: self.tcx,
 584                     expn_data,
 585                     always_live_locals: BitSet::new_filled(callee_body.local_decls.len()),
 586                 };
 587
 588                 // Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
 589                 // (or existing ones, in a few special cases) in the caller.
 590                 integrator.visit_body(&mut callee_body);
 591
 592                 // If there are any locals without storage markers, give them storage only for the
 593                 // duration of the call.
 594                 for local in callee_body.vars_and_temps_iter() {
 595                     if !callee_body.local_decls[local].internal
 596                         && integrator.always_live_locals.contains(local)
 597                     {
 598                         let new_local = integrator.map_local(local);
 599                         caller_body[callsite.block].statements.push(Statement {
 600                             source_info: callsite.source_info,
 601                             kind: StatementKind::StorageLive(new_local),
 602                         });
 603                     }
 604                 }
 605                 if let Some(block) = callsite.target {
 606                     // To avoid repeated O(n) insert, push any new statements to the end and rotate
 607                     // the slice once.
 608                     let mut n = 0;
 609                     if remap_destination {
 610                         caller_body[block].statements.push(Statement {
 611                             source_info: callsite.source_info,
 612                             kind: StatementKind::Assign(Box::new((
 613                                 dest,
 614                                 Rvalue::Use(Operand::Move(destination_local.into())),
 615                             ))),
 616                         });
 617                         n += 1;
 618                     }
 619                     for local in callee_body.vars_and_temps_iter().rev() {
 620                         if !callee_body.local_decls[local].internal
 621                             && integrator.always_live_locals.contains(local)
 622                         {
 623                             let new_local = integrator.map_local(local);
 624                             caller_body[block].statements.push(Statement {
 625                                 source_info: callsite.source_info,
 626                                 kind: StatementKind::StorageDead(new_local),
 627                             });
 628                             n += 1;
 629                         }
 630                     }
 631                     caller_body[block].statements.rotate_right(n);
 632                 }
 633
 634                 // Insert all of the (mapped) parts of the callee body into the caller.
 635                 caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
 636                 caller_body.source_scopes.extend(&mut callee_body.source_scopes.drain(..));
 637                 caller_body.var_debug_info.append(&mut callee_body.var_debug_info);
 638                 caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
 639
 640                 caller_body[callsite.block].terminator = Some(Terminator {
 641                     source_info: callsite.source_info,
 642                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
 643                 });
 644
 645                 // Copy only unevaluated constants from the callee_body into the caller_body.
 646                 // Although we are only pushing `ConstKind::Unevaluated` consts to
 647                 // `required_consts`, here we may not only have `ConstKind::Unevaluated`
 648                 // because we are calling `subst_and_normalize_erasing_regions`.
 649                 caller_body.required_consts.extend(
 650                     callee_body.required_consts.iter().copied().filter(|&ct| match ct.literal {
 651                         ConstantKind::Ty(_) => {
 652                             bug!("should never encounter ty::UnevaluatedConst in `required_consts`")
 653                         }
 654                         ConstantKind::Val(..) | ConstantKind::Unevaluated(..) => true,
 655                     }),
 656                 );
 657             }
 658             kind => bug!("unexpected terminator kind {:?}", kind),
 659         }
 660     }
 661
 662     fn make_call_args(
 663         &self,
 664         args: Vec<Operand<'tcx>>,
 665         callsite: &CallSite<'tcx>,
 666         caller_body: &mut Body<'tcx>,
 667         callee_body: &Body<'tcx>,
 668     ) -> Vec<Local> {
 669         let tcx = self.tcx;
 670
 671         // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
 672         // The caller provides the arguments wrapped up in a tuple:
 673         //
 674         //     tuple_tmp = (a, b, c)
 675         //     Fn::call(closure_ref, tuple_tmp)
 676         //
 677         // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
 678         // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
 679         // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
 680         // a vector like
 681         //
 682         //     [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
 683         //
 684         // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
 685         // if we "spill" that into *another* temporary, so that we can map the argument
 686         // variable in the callee MIR directly to an argument variable on our side.
 687         // So we introduce temporaries like:
 688         //
 689         //     tmp0 = tuple_tmp.0
 690         //     tmp1 = tuple_tmp.1
 691         //     tmp2 = tuple_tmp.2
 692         //
 693         // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
 694         if callsite.fn_sig.abi() == Abi::RustCall && callee_body.spread_arg.is_none() {
 695             let mut args = args.into_iter();
 696             let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 697             let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_body);
 698             assert!(args.next().is_none());
 699
 700             let tuple = Place::from(tuple);
 701             let ty::Tuple(tuple_tys) = tuple.ty(caller_body, tcx).ty.kind() else {
 702                 bug!("Closure arguments are not passed as a tuple");
 703             };
 704
 705             // The `closure_ref` in our example above.
 706             let closure_ref_arg = iter::once(self_);
 707
 708             // The `tmp0`, `tmp1`, and `tmp2` in our example above.
 709             let tuple_tmp_args = tuple_tys.iter().enumerate().map(|(i, ty)| {
 710                 // This is e.g., `tuple_tmp.0` in our example above.
 711                 let tuple_field = Operand::Move(tcx.mk_place_field(tuple, Field::new(i), ty));
 712
 713                 // Spill to a local to make e.g., `tmp0`.
 714                 self.create_temp_if_necessary(tuple_field, callsite, caller_body)
 715             });
 716
 717             closure_ref_arg.chain(tuple_tmp_args).collect()
 718         } else {
 719             args.into_iter()
 720                 .map(|a| self.create_temp_if_necessary(a, callsite, caller_body))
 721                 .collect()
 722         }
 723     }
 724
 725     /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
 726     /// temporary `T` and an instruction `T = arg`, and returns `T`.
 727     fn create_temp_if_necessary(
 728         &self,
 729         arg: Operand<'tcx>,
 730         callsite: &CallSite<'tcx>,
 731         caller_body: &mut Body<'tcx>,
 732     ) -> Local {
 733         // Reuse the operand if it is a moved temporary.
 734         if let Operand::Move(place) = &arg
 735             && let Some(local) = place.as_local()
 736             && caller_body.local_kind(local) == LocalKind::Temp
 737         {
 738             return local;
 739         }
 740
 741         // Otherwise, create a temporary for the argument.
 742         trace!("creating temp for argument {:?}", arg);
 743         let arg_ty = arg.ty(caller_body, self.tcx);
 744         let local = self.new_call_temp(caller_body, callsite, arg_ty);
 745         caller_body[callsite.block].statements.push(Statement {
 746             source_info: callsite.source_info,
 747             kind: StatementKind::Assign(Box::new((Place::from(local), Rvalue::Use(arg)))),
 748         });
 749         local
 750     }
 751
 752     /// Introduces a new temporary into the caller body that is live for the duration of the call.
 753     fn new_call_temp(
 754         &self,
 755         caller_body: &mut Body<'tcx>,
 756         callsite: &CallSite<'tcx>,
 757         ty: Ty<'tcx>,
 758     ) -> Local {
 759         let local = caller_body.local_decls.push(LocalDecl::new(ty, callsite.source_info.span));
 760
 761         caller_body[callsite.block].statements.push(Statement {
 762             source_info: callsite.source_info,
 763             kind: StatementKind::StorageLive(local),
 764         });
 765
 766         if let Some(block) = callsite.target {
 767             caller_body[block].statements.insert(
 768                 0,
 769                 Statement {
 770                     source_info: callsite.source_info,
 771                     kind: StatementKind::StorageDead(local),
 772                 },
 773             );
 774         }
 775
 776         local
 777     }
 778 }
 779
 780 fn type_size_of<'tcx>(
 781     tcx: TyCtxt<'tcx>,
 782     param_env: ty::ParamEnv<'tcx>,
 783     ty: Ty<'tcx>,
 784 ) -> Option<u64> {
 785     tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
 786 }
 787
 788 /// Verify that the callee body is compatible with the caller.
 789 ///
 790 /// This visitor mostly computes the inlining cost,
 791 /// but also needs to verify that types match because of normalization failure.
 792 struct CostChecker<'b, 'tcx> {
 793     tcx: TyCtxt<'tcx>,
 794     param_env: ParamEnv<'tcx>,
 795     cost: usize,
 796     callee_body: &'b Body<'tcx>,
 797     instance: ty::Instance<'tcx>,
 798     validation: Result<(), &'static str>,
 799 }
 800
 801 impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
 802     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 803         // Don't count StorageLive/StorageDead in the inlining cost.
 804         match statement.kind {
 805             StatementKind::StorageLive(_)
 806             | StatementKind::StorageDead(_)
 807             | StatementKind::Deinit(_)
 808             | StatementKind::Nop => {}
 809             _ => self.cost += INSTR_COST,
 810         }
 811
 812         self.super_statement(statement, location);
 813     }
 814
 815     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
 816         let tcx = self.tcx;
 817         match terminator.kind {
 818             TerminatorKind::Drop { ref place, unwind, .. }
 819             | TerminatorKind::DropAndReplace { ref place, unwind, .. } => {
 820                 // If the place doesn't actually need dropping, treat it like a regular goto.
 821                 let ty = self.instance.subst_mir(tcx, &place.ty(self.callee_body, tcx).ty);
 822                 if ty.needs_drop(tcx, self.param_env) {
 823                     self.cost += CALL_PENALTY;
 824                     if unwind.is_some() {
 825                         self.cost += LANDINGPAD_PENALTY;
 826                     }
 827                 } else {
 828                     self.cost += INSTR_COST;
 829                 }
 830             }
 831             TerminatorKind::Call { func: Operand::Constant(ref f), cleanup, .. } => {
 832                 let fn_ty = self.instance.subst_mir(tcx, &f.literal.ty());
 833                 self.cost += if let ty::FnDef(def_id, _) = *fn_ty.kind() && tcx.is_intrinsic(def_id) {
 834                     // Don't give intrinsics the extra penalty for calls
 835                     INSTR_COST
 836                 } else {
 837                     CALL_PENALTY
 838                 };
 839                 if cleanup.is_some() {
 840                     self.cost += LANDINGPAD_PENALTY;
 841                 }
 842             }
 843             TerminatorKind::Assert { cleanup, .. } => {
 844                 self.cost += CALL_PENALTY;
 845                 if cleanup.is_some() {
 846                     self.cost += LANDINGPAD_PENALTY;
 847                 }
 848             }
 849             TerminatorKind::Resume => self.cost += RESUME_PENALTY,
 850             TerminatorKind::InlineAsm { cleanup, .. } => {
 851                 self.cost += INSTR_COST;
 852                 if cleanup.is_some() {
 853                     self.cost += LANDINGPAD_PENALTY;
 854                 }
 855             }
 856             _ => self.cost += INSTR_COST,
 857         }
 858
 859         self.super_terminator(terminator, location);
 860     }
 861
 862     /// Count up the cost of local variables and temps, if we know the size
 863     /// use that, otherwise we use a moderately-large dummy cost.
 864     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
 865         let tcx = self.tcx;
 866         let ptr_size = tcx.data_layout.pointer_size.bytes();
 867
 868         let ty = self.instance.subst_mir(tcx, &local_decl.ty);
 869         // Cost of the var is the size in machine-words, if we know
 870         // it.
 871         if let Some(size) = type_size_of(tcx, self.param_env, ty) {
 872             self.cost += ((size + ptr_size - 1) / ptr_size) as usize;
 873         } else {
 874             self.cost += UNKNOWN_SIZE_COST;
 875         }
 876
 877         self.super_local_decl(local, local_decl)
 878     }
 879
 880     /// This method duplicates code from MIR validation in an attempt to detect type mismatches due
 881     /// to normalization failure.
 882     fn visit_projection_elem(
 883         &mut self,
 884         local: Local,
 885         proj_base: &[PlaceElem<'tcx>],
 886         elem: PlaceElem<'tcx>,
 887         context: PlaceContext,
 888         location: Location,
 889     ) {
 890         if let ProjectionElem::Field(f, ty) = elem {
 891             let parent = Place { local, projection: self.tcx.intern_place_elems(proj_base) };
 892             let parent_ty = parent.ty(&self.callee_body.local_decls, self.tcx);
 893             let check_equal = |this: &mut Self, f_ty| {
 894                 if !util::is_equal_up_to_subtyping(this.tcx, this.param_env, ty, f_ty) {
 895                     trace!(?ty, ?f_ty);
 896                     this.validation = Err("failed to normalize projection type");
 897                     return;
 898                 }
 899             };
 900
 901             let kind = match parent_ty.ty.kind() {
 902                 &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
 903                     self.tcx.bound_type_of(def_id).subst(self.tcx, substs).kind()
 904                 }
 905                 kind => kind,
 906             };
 907
 908             match kind {
 909                 ty::Tuple(fields) => {
 910                     let Some(f_ty) = fields.get(f.as_usize()) else {
 911                         self.validation = Err("malformed MIR");
 912                         return;
 913                     };
 914                     check_equal(self, *f_ty);
 915                 }
 916                 ty::Adt(adt_def, substs) => {
 917                     let var = parent_ty.variant_index.unwrap_or(VariantIdx::from_u32(0));
 918                     let Some(field) = adt_def.variant(var).fields.get(f.as_usize()) else {
 919                         self.validation = Err("malformed MIR");
 920                         return;
 921                     };
 922                     check_equal(self, field.ty(self.tcx, substs));
 923                 }
 924                 ty::Closure(_, substs) => {
 925                     let substs = substs.as_closure();
 926                     let Some(f_ty) = substs.upvar_tys().nth(f.as_usize()) else {
 927                         self.validation = Err("malformed MIR");
 928                         return;
 929                     };
 930                     check_equal(self, f_ty);
 931                 }
 932                 &ty::Generator(def_id, substs, _) => {
 933                     let f_ty = if let Some(var) = parent_ty.variant_index {
 934                         let gen_body = if def_id == self.callee_body.source.def_id() {
 935                             self.callee_body
 936                         } else {
 937                             self.tcx.optimized_mir(def_id)
 938                         };
 939
 940                         let Some(layout) = gen_body.generator_layout() else {
 941                             self.validation = Err("malformed MIR");
 942                             return;
 943                         };
 944
 945                         let Some(&local) = layout.variant_fields[var].get(f) else {
 946                             self.validation = Err("malformed MIR");
 947                             return;
 948                         };
 949
 950                         let Some(f_ty) = layout.field_tys.get(local) else {
 951                             self.validation = Err("malformed MIR");
 952                             return;
 953                         };
 954
 955                         f_ty.ty
 956                     } else {
 957                         let Some(f_ty) = substs.as_generator().prefix_tys().nth(f.index()) else {
 958                             self.validation = Err("malformed MIR");
 959                             return;
 960                         };
 961
 962                         f_ty
 963                     };
 964
 965                     check_equal(self, f_ty);
 966                 }
 967                 _ => self.validation = Err("malformed MIR"),
 968             }
 969         }
 970
 971         self.super_projection_elem(local, proj_base, elem, context, location);
 972     }
 973 }
 974
 975 /**
 976  * Integrator.
 977  *
 978  * Integrates blocks from the callee function into the calling function.
 979  * Updates block indices, references to locals and other control flow
 980  * stuff.
 981 */
 982 struct Integrator<'a, 'tcx> {
 983     args: &'a [Local],
 984     new_locals: RangeFrom<Local>,
 985     new_scopes: RangeFrom<SourceScope>,
 986     new_blocks: RangeFrom<BasicBlock>,
 987     destination: Local,
 988     callsite_scope: SourceScopeData<'tcx>,
 989     callsite: &'a CallSite<'tcx>,
 990     cleanup_block: Option<BasicBlock>,
 991     in_cleanup_block: bool,
 992     tcx: TyCtxt<'tcx>,
 993     expn_data: LocalExpnId,
 994     always_live_locals: BitSet<Local>,
 995 }
 996
 997 impl Integrator<'_, '_> {
 998     fn map_local(&self, local: Local) -> Local {
 999         let new = if local == RETURN_PLACE {
1000             self.destination
1001         } else {
1002             let idx = local.index() - 1;
1003             if idx < self.args.len() {
1004                 self.args[idx]
1005             } else {
1006                 Local::new(self.new_locals.start.index() + (idx - self.args.len()))
1007             }
1008         };
1009         trace!("mapping local `{:?}` to `{:?}`", local, new);
1010         new
1011     }
1012
1013     fn map_scope(&self, scope: SourceScope) -> SourceScope {
1014         let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
1015         trace!("mapping scope `{:?}` to `{:?}`", scope, new);
1016         new
1017     }
1018
1019     fn map_block(&self, block: BasicBlock) -> BasicBlock {
1020         let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
1021         trace!("mapping block `{:?}` to `{:?}`", block, new);
1022         new
1023     }
1024
1025     fn map_unwind(&self, unwind: Option<BasicBlock>) -> Option<BasicBlock> {
1026         if self.in_cleanup_block {
1027             if unwind.is_some() {
1028                 bug!("cleanup on cleanup block");
1029             }
1030             return unwind;
1031         }
1032
1033         match unwind {
1034             Some(target) => Some(self.map_block(target)),
1035             // Add an unwind edge to the original call's cleanup block
1036             None => self.cleanup_block,
1037         }
1038     }
1039 }
1040
1041 impl<'tcx> MutVisitor<'tcx> for Integrator<'_, 'tcx> {
1042     fn tcx(&self) -> TyCtxt<'tcx> {
1043         self.tcx
1044     }
1045
1046     fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
1047         *local = self.map_local(*local);
1048     }
1049
1050     fn visit_source_scope_data(&mut self, scope_data: &mut SourceScopeData<'tcx>) {
1051         self.super_source_scope_data(scope_data);
1052         if scope_data.parent_scope.is_none() {
1053             // Attach the outermost callee scope as a child of the callsite
1054             // scope, via the `parent_scope` and `inlined_parent_scope` chains.
1055             scope_data.parent_scope = Some(self.callsite.source_info.scope);
1056             assert_eq!(scope_data.inlined_parent_scope, None);
1057             scope_data.inlined_parent_scope = if self.callsite_scope.inlined.is_some() {
1058                 Some(self.callsite.source_info.scope)
1059             } else {
1060                 self.callsite_scope.inlined_parent_scope
1061             };
1062
1063             // Mark the outermost callee scope as an inlined one.
1064             assert_eq!(scope_data.inlined, None);
1065             scope_data.inlined = Some((self.callsite.callee, self.callsite.source_info.span));
1066         } else if scope_data.inlined_parent_scope.is_none() {
1067             // Make it easy to find the scope with `inlined` set above.
1068             scope_data.inlined_parent_scope = Some(self.map_scope(OUTERMOST_SOURCE_SCOPE));
1069         }
1070     }
1071
1072     fn visit_source_scope(&mut self, scope: &mut SourceScope) {
1073         *scope = self.map_scope(*scope);
1074     }
1075
1076     fn visit_span(&mut self, span: &mut Span) {
1077         // Make sure that all spans track the fact that they were inlined.
1078         *span = span.fresh_expansion(self.expn_data);
1079     }
1080
1081     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
1082         self.in_cleanup_block = data.is_cleanup;
1083         self.super_basic_block_data(block, data);
1084         self.in_cleanup_block = false;
1085     }
1086
1087     fn visit_retag(&mut self, kind: &mut RetagKind, place: &mut Place<'tcx>, loc: Location) {
1088         self.super_retag(kind, place, loc);
1089
1090         // We have to patch all inlined retags to be aware that they are no longer
1091         // happening on function entry.
1092         if *kind == RetagKind::FnEntry {
1093             *kind = RetagKind::Default;
1094         }
1095     }
1096
1097     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
1098         if let StatementKind::StorageLive(local) | StatementKind::StorageDead(local) =
1099             statement.kind
1100         {
1101             self.always_live_locals.remove(local);
1102         }
1103         self.super_statement(statement, location);
1104     }
1105
1106     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, loc: Location) {
1107         // Don't try to modify the implicit `_0` access on return (`return` terminators are
1108         // replaced down below anyways).
1109         if !matches!(terminator.kind, TerminatorKind::Return) {
1110             self.super_terminator(terminator, loc);
1111         }
1112
1113         match terminator.kind {
1114             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
1115             TerminatorKind::Goto { ref mut target } => {
1116                 *target = self.map_block(*target);
1117             }
1118             TerminatorKind::SwitchInt { ref mut targets, .. } => {
1119                 for tgt in targets.all_targets_mut() {
1120                     *tgt = self.map_block(*tgt);
1121                 }
1122             }
1123             TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
1124             | TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
1125                 *target = self.map_block(*target);
1126                 *unwind = self.map_unwind(*unwind);
1127             }
1128             TerminatorKind::Call { ref mut target, ref mut cleanup, .. } => {
1129                 if let Some(ref mut tgt) = *target {
1130                     *tgt = self.map_block(*tgt);
1131                 }
1132                 *cleanup = self.map_unwind(*cleanup);
1133             }
1134             TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
1135                 *target = self.map_block(*target);
1136                 *cleanup = self.map_unwind(*cleanup);
1137             }
1138             TerminatorKind::Return => {
1139                 terminator.kind = if let Some(tgt) = self.callsite.target {
1140                     TerminatorKind::Goto { target: tgt }
1141                 } else {
1142                     TerminatorKind::Unreachable
1143                 }
1144             }
1145             TerminatorKind::Resume => {
1146                 if let Some(tgt) = self.cleanup_block {
1147                     terminator.kind = TerminatorKind::Goto { target: tgt }
1148                 }
1149             }
1150             TerminatorKind::Abort => {}
1151             TerminatorKind::Unreachable => {}
1152             TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
1153                 *real_target = self.map_block(*real_target);
1154                 *imaginary_target = self.map_block(*imaginary_target);
1155             }
1156             TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
1157             // see the ordering of passes in the optimized_mir query.
1158             {
1159                 bug!("False unwinds should have been removed before inlining")
1160             }
1161             TerminatorKind::InlineAsm { ref mut destination, ref mut cleanup, .. } => {
1162                 if let Some(ref mut tgt) = *destination {
1163                     *tgt = self.map_block(*tgt);
1164                 }
1165                 *cleanup = self.map_unwind(*cleanup);
1166             }
1167         }
1168     }
1169 }