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