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