1 //! Inlining pass for MIR functions
3 use rustc::hir::CodegenFnAttrFlags;
4 use rustc::hir::def_id::DefId;
6 use rustc_data_structures::bit_set::BitSet;
7 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
10 use rustc::mir::visit::*;
11 use rustc::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
12 use rustc::ty::subst::{Subst, SubstsRef};
14 use std::collections::VecDeque;
16 use crate::transform::{MirPass, MirSource};
17 use super::simplify::{remove_dead_blocks, CfgSimplifier};
20 use rustc_target::spec::abi::Abi;
22 const DEFAULT_THRESHOLD: usize = 50;
23 const HINT_THRESHOLD: usize = 100;
25 const INSTR_COST: usize = 5;
26 const CALL_PENALTY: usize = 25;
28 const UNKNOWN_SIZE_COST: usize = 10;
32 #[derive(Copy, Clone, Debug)]
33 struct CallSite<'tcx> {
35 substs: SubstsRef<'tcx>,
40 impl MirPass for Inline {
41 fn run_pass<'a, 'tcx>(&self,
42 tcx: TyCtxt<'a, 'tcx, 'tcx>,
43 source: MirSource<'tcx>,
44 mir: &mut Mir<'tcx>) {
45 if tcx.sess.opts.debugging_opts.mir_opt_level >= 2 {
46 Inliner { tcx, source }.run_pass(mir);
51 struct Inliner<'a, 'tcx: 'a> {
52 tcx: TyCtxt<'a, 'tcx, 'tcx>,
53 source: MirSource<'tcx>,
56 impl<'a, 'tcx> Inliner<'a, 'tcx> {
57 fn run_pass(&self, caller_mir: &mut Mir<'tcx>) {
58 // Keep a queue of callsites to try inlining on. We take
59 // advantage of the fact that queries detect cycles here to
60 // allow us to try and fetch the fully optimized MIR of a
61 // call; if it succeeds, we can inline it and we know that
62 // they do not call us. Otherwise, we just don't try to
65 // We use a queue so that we inline "broadly" before we inline
66 // in depth. It is unclear if this is the best heuristic,
67 // really, but that's true of all the heuristics in this
70 let mut callsites = VecDeque::new();
72 let param_env = self.tcx.param_env(self.source.def_id());
74 // Only do inlining into fn bodies.
75 let id = self.tcx.hir().as_local_hir_id(self.source.def_id()).unwrap();
76 if self.tcx.hir().body_owner_kind_by_hir_id(id).is_fn_or_closure()
77 && self.source.promoted.is_none()
79 for (bb, bb_data) in caller_mir.basic_blocks().iter_enumerated() {
80 if let Some(callsite) = self.get_valid_function_call(bb,
84 callsites.push_back(callsite);
92 let mut changed = false;
96 while let Some(callsite) = callsites.pop_front() {
97 debug!("checking whether to inline callsite {:?}", callsite);
98 if !self.tcx.is_mir_available(callsite.callee) {
99 debug!("checking whether to inline callsite {:?} - MIR unavailable", callsite);
103 let self_node_id = self.tcx.hir().as_local_node_id(self.source.def_id()).unwrap();
104 let callee_node_id = self.tcx.hir().as_local_node_id(callsite.callee);
106 let callee_mir = if let Some(callee_node_id) = callee_node_id {
107 // Avoid a cycle here by only using `optimized_mir` only if we have
108 // a lower node id than the callee. This ensures that the callee will
109 // not inline us. This trick only works without incremental compilation.
110 // So don't do it if that is enabled.
111 if !self.tcx.dep_graph.is_fully_enabled()
112 && self_node_id.as_u32() < callee_node_id.as_u32() {
113 self.tcx.optimized_mir(callsite.callee)
118 // This cannot result in a cycle since the callee MIR is from another crate
119 // and is already optimized.
120 self.tcx.optimized_mir(callsite.callee)
123 let callee_mir = if self.consider_optimizing(callsite, callee_mir) {
124 self.tcx.subst_and_normalize_erasing_regions(
133 let start = caller_mir.basic_blocks().len();
134 debug!("attempting to inline callsite {:?} - mir={:?}", callsite, callee_mir);
135 if !self.inline_call(callsite, caller_mir, callee_mir) {
136 debug!("attempting to inline callsite {:?} - failure", callsite);
139 debug!("attempting to inline callsite {:?} - success", callsite);
141 // Add callsites from inlined function
142 for (bb, bb_data) in caller_mir.basic_blocks().iter_enumerated().skip(start) {
143 if let Some(new_callsite) = self.get_valid_function_call(bb,
147 // Don't inline the same function multiple times.
148 if callsite.callee != new_callsite.callee {
149 callsites.push_back(new_callsite);
163 // Simplify if we inlined anything.
165 debug!("Running simplify cfg on {:?}", self.source);
166 CfgSimplifier::new(caller_mir).simplify();
167 remove_dead_blocks(caller_mir);
171 fn get_valid_function_call(&self,
173 bb_data: &BasicBlockData<'tcx>,
174 caller_mir: &Mir<'tcx>,
175 param_env: ParamEnv<'tcx>,
176 ) -> Option<CallSite<'tcx>> {
177 // Don't inline calls that are in cleanup blocks.
178 if bb_data.is_cleanup { return None; }
180 // Only consider direct calls to functions
181 let terminator = bb_data.terminator();
182 if let TerminatorKind::Call { func: ref op, .. } = terminator.kind {
183 if let ty::FnDef(callee_def_id, substs) = op.ty(caller_mir, self.tcx).sty {
184 let instance = Instance::resolve(self.tcx,
189 if let InstanceDef::Virtual(..) = instance.def {
193 return Some(CallSite {
194 callee: instance.def_id(),
195 substs: instance.substs,
197 location: terminator.source_info
205 fn consider_optimizing(&self,
206 callsite: CallSite<'tcx>,
207 callee_mir: &Mir<'tcx>)
210 debug!("consider_optimizing({:?})", callsite);
211 self.should_inline(callsite, callee_mir)
212 && self.tcx.consider_optimizing(|| format!("Inline {:?} into {:?}",
217 fn should_inline(&self,
218 callsite: CallSite<'tcx>,
219 callee_mir: &Mir<'tcx>)
222 debug!("should_inline({:?})", callsite);
225 // Don't inline closures that have capture debuginfo
226 // FIXME: Handle closures better
227 if callee_mir.__upvar_debuginfo_codegen_only_do_not_use.len() > 0 {
228 debug!(" upvar debuginfo present - not inlining");
232 // Cannot inline generators which haven't been transformed yet
233 if callee_mir.yield_ty.is_some() {
234 debug!(" yield ty present - not inlining");
238 // Do not inline {u,i}128 lang items, codegen const eval depends
239 // on detecting calls to these lang items and intercepting them
240 if tcx.is_binop_lang_item(callsite.callee).is_some() {
241 debug!(" not inlining 128bit integer lang item");
245 let codegen_fn_attrs = tcx.codegen_fn_attrs(callsite.callee);
247 let hinted = match codegen_fn_attrs.inline {
248 // Just treat inline(always) as a hint for now,
249 // there are cases that prevent inlining that we
250 // need to check for first.
251 attr::InlineAttr::Always => true,
252 attr::InlineAttr::Never => {
253 debug!("#[inline(never)] present - not inlining");
256 attr::InlineAttr::Hint => true,
257 attr::InlineAttr::None => false,
260 // Only inline local functions if they would be eligible for cross-crate
261 // inlining. This is to ensure that the final crate doesn't have MIR that
262 // reference unexported symbols
263 if callsite.callee.is_local() {
264 if callsite.substs.non_erasable_generics().count() == 0 && !hinted {
265 debug!(" callee is an exported function - not inlining");
270 let mut threshold = if hinted {
276 // Significantly lower the threshold for inlining cold functions
277 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
281 // Give a bonus functions with a small number of blocks,
282 // We normally have two or three blocks for even
283 // very small functions.
284 if callee_mir.basic_blocks().len() <= 3 {
285 threshold += threshold / 4;
287 debug!(" final inline threshold = {}", threshold);
289 // FIXME: Give a bonus to functions with only a single caller
291 let param_env = tcx.param_env(self.source.def_id());
293 let mut first_block = true;
296 // Traverse the MIR manually so we can account for the effects of
297 // inlining on the CFG.
298 let mut work_list = vec![START_BLOCK];
299 let mut visited = BitSet::new_empty(callee_mir.basic_blocks().len());
300 while let Some(bb) = work_list.pop() {
301 if !visited.insert(bb.index()) { continue; }
302 let blk = &callee_mir.basic_blocks()[bb];
304 for stmt in &blk.statements {
305 // Don't count StorageLive/StorageDead in the inlining cost.
307 StatementKind::StorageLive(_) |
308 StatementKind::StorageDead(_) |
309 StatementKind::Nop => {}
310 _ => cost += INSTR_COST
313 let term = blk.terminator();
314 let mut is_drop = false;
316 TerminatorKind::Drop { ref location, target, unwind } |
317 TerminatorKind::DropAndReplace { ref location, target, unwind, .. } => {
319 work_list.push(target);
320 // If the location doesn't actually need dropping, treat it like
322 let ty = location.ty(callee_mir, tcx).subst(tcx, callsite.substs).ty;
323 if ty.needs_drop(tcx, param_env) {
324 cost += CALL_PENALTY;
325 if let Some(unwind) = unwind {
326 work_list.push(unwind);
333 TerminatorKind::Unreachable |
334 TerminatorKind::Call { destination: None, .. } if first_block => {
335 // If the function always diverges, don't inline
336 // unless the cost is zero
340 TerminatorKind::Call {func: Operand::Constant(ref f), .. } => {
341 if let ty::FnDef(def_id, _) = f.ty.sty {
342 // Don't give intrinsics the extra penalty for calls
343 let f = tcx.fn_sig(def_id);
344 if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
347 cost += CALL_PENALTY;
351 TerminatorKind::Assert { .. } => cost += CALL_PENALTY,
352 _ => cost += INSTR_COST
356 for &succ in term.successors() {
357 work_list.push(succ);
364 // Count up the cost of local variables and temps, if we know the size
365 // use that, otherwise we use a moderately-large dummy cost.
367 let ptr_size = tcx.data_layout.pointer_size.bytes();
369 for v in callee_mir.vars_and_temps_iter() {
370 let v = &callee_mir.local_decls[v];
371 let ty = v.ty.subst(tcx, callsite.substs);
372 // Cost of the var is the size in machine-words, if we know
374 if let Some(size) = type_size_of(tcx, param_env.clone(), ty) {
375 cost += (size / ptr_size) as usize;
377 cost += UNKNOWN_SIZE_COST;
381 if let attr::InlineAttr::Always = codegen_fn_attrs.inline {
382 debug!("INLINING {:?} because inline(always) [cost={}]", callsite, cost);
385 if cost <= threshold {
386 debug!("INLINING {:?} [cost={} <= threshold={}]", callsite, cost, threshold);
389 debug!("NOT inlining {:?} [cost={} > threshold={}]", callsite, cost, threshold);
395 fn inline_call(&self,
396 callsite: CallSite<'tcx>,
397 caller_mir: &mut Mir<'tcx>,
398 mut callee_mir: Mir<'tcx>) -> bool {
399 let terminator = caller_mir[callsite.bb].terminator.take().unwrap();
400 match terminator.kind {
401 // FIXME: Handle inlining of diverging calls
402 TerminatorKind::Call { args, destination: Some(destination), cleanup, .. } => {
403 debug!("Inlined {:?} into {:?}", callsite.callee, self.source);
405 let mut local_map = IndexVec::with_capacity(callee_mir.local_decls.len());
406 let mut scope_map = IndexVec::with_capacity(callee_mir.source_scopes.len());
407 let mut promoted_map = IndexVec::with_capacity(callee_mir.promoted.len());
409 for mut scope in callee_mir.source_scopes.iter().cloned() {
410 if scope.parent_scope.is_none() {
411 scope.parent_scope = Some(callsite.location.scope);
412 scope.span = callee_mir.span;
415 scope.span = callsite.location.span;
417 let idx = caller_mir.source_scopes.push(scope);
421 for loc in callee_mir.vars_and_temps_iter() {
422 let mut local = callee_mir.local_decls[loc].clone();
424 local.source_info.scope =
425 scope_map[local.source_info.scope];
426 local.source_info.span = callsite.location.span;
427 local.visibility_scope = scope_map[local.visibility_scope];
429 let idx = caller_mir.local_decls.push(local);
434 callee_mir.promoted.iter().cloned().map(|p| caller_mir.promoted.push(p))
437 // If the call is something like `a[*i] = f(i)`, where
438 // `i : &mut usize`, then just duplicating the `a[*i]`
439 // Place could result in two different locations if `f`
440 // writes to `i`. To prevent this we need to create a temporary
441 // borrow of the place and pass the destination as `*temp` instead.
442 fn dest_needs_borrow(place: &Place<'_>) -> bool {
444 Place::Projection(ref p) => {
446 ProjectionElem::Deref |
447 ProjectionElem::Index(_) => true,
448 _ => dest_needs_borrow(&p.base)
451 // Static variables need a borrow because the callee
452 // might modify the same static.
453 Place::Base(PlaceBase::Static(_)) => true,
458 let dest = if dest_needs_borrow(&destination.0) {
459 debug!("Creating temp for return destination");
460 let dest = Rvalue::Ref(
461 self.tcx.lifetimes.re_erased,
462 BorrowKind::Mut { allow_two_phase_borrow: false },
465 let ty = dest.ty(caller_mir, self.tcx);
467 let temp = LocalDecl::new_temp(ty, callsite.location.span);
469 let tmp = caller_mir.local_decls.push(temp);
470 let tmp = Place::Base(PlaceBase::Local(tmp));
472 let stmt = Statement {
473 source_info: callsite.location,
474 kind: StatementKind::Assign(tmp.clone(), box dest)
476 caller_mir[callsite.bb]
477 .statements.push(stmt);
483 let return_block = destination.1;
485 // Copy the arguments if needed.
486 let args: Vec<_> = self.make_call_args(args, &callsite, caller_mir);
488 let bb_len = caller_mir.basic_blocks().len();
489 let mut integrator = Integrator {
498 cleanup_block: cleanup,
499 in_cleanup_block: false
503 for (bb, mut block) in callee_mir.basic_blocks_mut().drain_enumerated(..) {
504 integrator.visit_basic_block_data(bb, &mut block);
505 caller_mir.basic_blocks_mut().push(block);
508 let terminator = Terminator {
509 source_info: callsite.location,
510 kind: TerminatorKind::Goto { target: BasicBlock::new(bb_len) }
513 caller_mir[callsite.bb].terminator = Some(terminator);
518 caller_mir[callsite.bb].terminator = Some(Terminator {
519 source_info: terminator.source_info,
529 args: Vec<Operand<'tcx>>,
530 callsite: &CallSite<'tcx>,
531 caller_mir: &mut Mir<'tcx>,
535 // There is a bit of a mismatch between the *caller* of a closure and the *callee*.
536 // The caller provides the arguments wrapped up in a tuple:
538 // tuple_tmp = (a, b, c)
539 // Fn::call(closure_ref, tuple_tmp)
541 // meanwhile the closure body expects the arguments (here, `a`, `b`, and `c`)
542 // as distinct arguments. (This is the "rust-call" ABI hack.) Normally, codegen has
543 // the job of unpacking this tuple. But here, we are codegen. =) So we want to create
546 // [closure_ref, tuple_tmp.0, tuple_tmp.1, tuple_tmp.2]
548 // Except for one tiny wrinkle: we don't actually want `tuple_tmp.0`. It's more convenient
549 // if we "spill" that into *another* temporary, so that we can map the argument
550 // variable in the callee MIR directly to an argument variable on our side.
551 // So we introduce temporaries like:
553 // tmp0 = tuple_tmp.0
554 // tmp1 = tuple_tmp.1
555 // tmp2 = tuple_tmp.2
557 // and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
558 if tcx.is_closure(callsite.callee) {
559 let mut args = args.into_iter();
560 let self_ = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_mir);
561 let tuple = self.create_temp_if_necessary(args.next().unwrap(), callsite, caller_mir);
562 assert!(args.next().is_none());
564 let tuple = Place::Base(PlaceBase::Local(tuple));
565 let tuple_tys = if let ty::Tuple(s) = tuple.ty(caller_mir, tcx).ty.sty {
568 bug!("Closure arguments are not passed as a tuple");
571 // The `closure_ref` in our example above.
572 let closure_ref_arg = iter::once(self_);
574 // The `tmp0`, `tmp1`, and `tmp2` in our example abonve.
576 tuple_tys.iter().enumerate().map(|(i, ty)| {
577 // This is e.g., `tuple_tmp.0` in our example above.
578 let tuple_field = Operand::Move(tuple.clone().field(
583 // Spill to a local to make e.g., `tmp0`.
584 self.create_temp_if_necessary(tuple_field, callsite, caller_mir)
587 closure_ref_arg.chain(tuple_tmp_args).collect()
590 .map(|a| self.create_temp_if_necessary(a, callsite, caller_mir))
595 /// If `arg` is already a temporary, returns it. Otherwise, introduces a fresh
596 /// temporary `T` and an instruction `T = arg`, and returns `T`.
597 fn create_temp_if_necessary(
600 callsite: &CallSite<'tcx>,
601 caller_mir: &mut Mir<'tcx>,
603 // FIXME: Analysis of the usage of the arguments to avoid
604 // unnecessary temporaries.
606 if let Operand::Move(Place::Base(PlaceBase::Local(local))) = arg {
607 if caller_mir.local_kind(local) == LocalKind::Temp {
608 // Reuse the operand if it's a temporary already
613 debug!("Creating temp for argument {:?}", arg);
614 // Otherwise, create a temporary for the arg
615 let arg = Rvalue::Use(arg);
617 let ty = arg.ty(caller_mir, self.tcx);
619 let arg_tmp = LocalDecl::new_temp(ty, callsite.location.span);
620 let arg_tmp = caller_mir.local_decls.push(arg_tmp);
622 let stmt = Statement {
623 source_info: callsite.location,
624 kind: StatementKind::Assign(Place::Base(PlaceBase::Local(arg_tmp)), box arg),
626 caller_mir[callsite.bb].statements.push(stmt);
631 fn type_size_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
632 param_env: ty::ParamEnv<'tcx>,
633 ty: Ty<'tcx>) -> Option<u64> {
634 tcx.layout_of(param_env.and(ty)).ok().map(|layout| layout.size.bytes())
640 * Integrates blocks from the callee function into the calling function.
641 * Updates block indices, references to locals and other control flow
644 struct Integrator<'a, 'tcx: 'a> {
647 local_map: IndexVec<Local, Local>,
648 scope_map: IndexVec<SourceScope, SourceScope>,
649 promoted_map: IndexVec<Promoted, Promoted>,
650 _callsite: CallSite<'tcx>,
651 destination: Place<'tcx>,
652 return_block: BasicBlock,
653 cleanup_block: Option<BasicBlock>,
654 in_cleanup_block: bool,
657 impl<'a, 'tcx> Integrator<'a, 'tcx> {
658 fn update_target(&self, tgt: BasicBlock) -> BasicBlock {
659 let new = BasicBlock::new(tgt.index() + self.block_idx);
660 debug!("Updating target `{:?}`, new: `{:?}`", tgt, new);
665 impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
666 fn visit_local(&mut self,
669 _location: Location) {
670 if *local == RETURN_PLACE {
671 match self.destination {
672 Place::Base(PlaceBase::Local(l)) => {
676 ref place => bug!("Return place is {:?}, not local", place)
679 let idx = local.index() - 1;
680 if idx < self.args.len() {
681 *local = self.args[idx];
684 *local = self.local_map[Local::new(idx - self.args.len())];
687 fn visit_place(&mut self,
688 place: &mut Place<'tcx>,
690 _location: Location) {
693 Place::Base(PlaceBase::Local(RETURN_PLACE)) => {
694 // Return pointer; update the place itself
695 *place = self.destination.clone();
698 PlaceBase::Static(box Static { kind: StaticKind::Promoted(promoted), .. })
700 if let Some(p) = self.promoted_map.get(*promoted).cloned() {
704 _ => self.super_place(place, _ctxt, _location)
708 fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
709 self.in_cleanup_block = data.is_cleanup;
710 self.super_basic_block_data(block, data);
711 self.in_cleanup_block = false;
716 kind: &mut RetagKind,
717 place: &mut Place<'tcx>,
720 self.super_retag(kind, place, loc);
722 // We have to patch all inlined retags to be aware that they are no longer
723 // happening on function entry.
724 if *kind == RetagKind::FnEntry {
725 *kind = RetagKind::Default;
729 fn visit_terminator_kind(&mut self,
730 kind: &mut TerminatorKind<'tcx>, loc: Location) {
731 self.super_terminator_kind(kind, loc);
734 TerminatorKind::GeneratorDrop |
735 TerminatorKind::Yield { .. } => bug!(),
736 TerminatorKind::Goto { ref mut target} => {
737 *target = self.update_target(*target);
739 TerminatorKind::SwitchInt { ref mut targets, .. } => {
741 *tgt = self.update_target(*tgt);
744 TerminatorKind::Drop { ref mut target, ref mut unwind, .. } |
745 TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
746 *target = self.update_target(*target);
747 if let Some(tgt) = *unwind {
748 *unwind = Some(self.update_target(tgt));
749 } else if !self.in_cleanup_block {
750 // Unless this drop is in a cleanup block, add an unwind edge to
751 // the original call's cleanup block
752 *unwind = self.cleanup_block;
755 TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
756 if let Some((_, ref mut tgt)) = *destination {
757 *tgt = self.update_target(*tgt);
759 if let Some(tgt) = *cleanup {
760 *cleanup = Some(self.update_target(tgt));
761 } else if !self.in_cleanup_block {
762 // Unless this call is in a cleanup block, add an unwind edge to
763 // the original call's cleanup block
764 *cleanup = self.cleanup_block;
767 TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
768 *target = self.update_target(*target);
769 if let Some(tgt) = *cleanup {
770 *cleanup = Some(self.update_target(tgt));
771 } else if !self.in_cleanup_block {
772 // Unless this assert is in a cleanup block, add an unwind edge to
773 // the original call's cleanup block
774 *cleanup = self.cleanup_block;
777 TerminatorKind::Return => {
778 *kind = TerminatorKind::Goto { target: self.return_block };
780 TerminatorKind::Resume => {
781 if let Some(tgt) = self.cleanup_block {
782 *kind = TerminatorKind::Goto { target: tgt }
785 TerminatorKind::Abort => { }
786 TerminatorKind::Unreachable => { }
787 TerminatorKind::FalseEdges { ref mut real_target, ref mut imaginary_targets } => {
788 *real_target = self.update_target(*real_target);
789 for target in imaginary_targets {
790 *target = self.update_target(*target);
793 TerminatorKind::FalseUnwind { real_target: _ , unwind: _ } =>
794 // see the ordering of passes in the optimized_mir query.
795 bug!("False unwinds should have been removed before inlining")
799 fn visit_source_scope(&mut self, scope: &mut SourceScope) {
800 *scope = self.scope_map[*scope];