1 //===- Inliner.cpp - Code common to all inliners --------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the mechanics required to implement inlining without
11 // missing any calls and updating the call graph. The decisions of which calls
12 // are profitable to inline are implemented elsewhere.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Transforms/IPO/Inliner.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/None.h"
19 #include "llvm/ADT/Optional.h"
20 #include "llvm/ADT/STLExtras.h"
21 #include "llvm/ADT/SetVector.h"
22 #include "llvm/ADT/SmallPtrSet.h"
23 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/ADT/Statistic.h"
25 #include "llvm/ADT/StringRef.h"
26 #include "llvm/Analysis/AliasAnalysis.h"
27 #include "llvm/Analysis/AssumptionCache.h"
28 #include "llvm/Analysis/BasicAliasAnalysis.h"
29 #include "llvm/Analysis/BlockFrequencyInfo.h"
30 #include "llvm/Analysis/CGSCCPassManager.h"
31 #include "llvm/Analysis/CallGraph.h"
32 #include "llvm/Analysis/InlineCost.h"
33 #include "llvm/Analysis/LazyCallGraph.h"
34 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
35 #include "llvm/Analysis/ProfileSummaryInfo.h"
36 #include "llvm/Analysis/TargetLibraryInfo.h"
37 #include "llvm/Analysis/TargetTransformInfo.h"
38 #include "llvm/Transforms/Utils/Local.h"
39 #include "llvm/IR/Attributes.h"
40 #include "llvm/IR/BasicBlock.h"
41 #include "llvm/IR/CallSite.h"
42 #include "llvm/IR/DataLayout.h"
43 #include "llvm/IR/DebugLoc.h"
44 #include "llvm/IR/DerivedTypes.h"
45 #include "llvm/IR/DiagnosticInfo.h"
46 #include "llvm/IR/Function.h"
47 #include "llvm/IR/InstIterator.h"
48 #include "llvm/IR/Instruction.h"
49 #include "llvm/IR/Instructions.h"
50 #include "llvm/IR/IntrinsicInst.h"
51 #include "llvm/IR/Metadata.h"
52 #include "llvm/IR/Module.h"
53 #include "llvm/IR/PassManager.h"
54 #include "llvm/IR/User.h"
55 #include "llvm/IR/Value.h"
56 #include "llvm/Pass.h"
57 #include "llvm/Support/Casting.h"
58 #include "llvm/Support/CommandLine.h"
59 #include "llvm/Support/Debug.h"
60 #include "llvm/Support/raw_ostream.h"
61 #include "llvm/Transforms/Utils/Cloning.h"
62 #include "llvm/Transforms/Utils/ImportedFunctionsInliningStatistics.h"
63 #include "llvm/Transforms/Utils/ModuleUtils.h"
74 #define DEBUG_TYPE "inline"
76 STATISTIC(NumInlined, "Number of functions inlined");
77 STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined");
78 STATISTIC(NumDeleted, "Number of functions deleted because all callers found");
79 STATISTIC(NumMergedAllocas, "Number of allocas merged together");
81 // This weirdly named statistic tracks the number of times that, when attempting
82 // to inline a function A into B, we analyze the callers of B in order to see
83 // if those would be more profitable and blocked inline steps.
84 STATISTIC(NumCallerCallersAnalyzed, "Number of caller-callers analyzed");
86 /// Flag to disable manual alloca merging.
88 /// Merging of allocas was originally done as a stack-size saving technique
89 /// prior to LLVM's code generator having support for stack coloring based on
90 /// lifetime markers. It is now in the process of being removed. To experiment
91 /// with disabling it and relying fully on lifetime marker based stack
92 /// coloring, you can pass this flag to LLVM.
94 DisableInlinedAllocaMerging("disable-inlined-alloca-merging",
95 cl::init(false), cl::Hidden);
99 enum class InlinerFunctionImportStatsOpts {
105 } // end anonymous namespace
107 static cl::opt<InlinerFunctionImportStatsOpts> InlinerFunctionImportStats(
108 "inliner-function-import-stats",
109 cl::init(InlinerFunctionImportStatsOpts::No),
110 cl::values(clEnumValN(InlinerFunctionImportStatsOpts::Basic, "basic",
112 clEnumValN(InlinerFunctionImportStatsOpts::Verbose, "verbose",
113 "printing of statistics for each inlined function")),
114 cl::Hidden, cl::desc("Enable inliner stats for imported functions"));
116 /// Flag to add inline messages as callsite attributes 'inline-remark'.
118 InlineRemarkAttribute("inline-remark-attribute", cl::init(false),
120 cl::desc("Enable adding inline-remark attribute to"
121 " callsites processed by inliner but decided"
122 " to be not inlined"));
124 LegacyInlinerBase::LegacyInlinerBase(char &ID) : CallGraphSCCPass(ID) {}
126 LegacyInlinerBase::LegacyInlinerBase(char &ID, bool InsertLifetime)
127 : CallGraphSCCPass(ID), InsertLifetime(InsertLifetime) {}
129 /// For this class, we declare that we require and preserve the call graph.
130 /// If the derived class implements this method, it should
131 /// always explicitly call the implementation here.
132 void LegacyInlinerBase::getAnalysisUsage(AnalysisUsage &AU) const {
133 AU.addRequired<AssumptionCacheTracker>();
134 AU.addRequired<ProfileSummaryInfoWrapperPass>();
135 AU.addRequired<TargetLibraryInfoWrapperPass>();
136 getAAResultsAnalysisUsage(AU);
137 CallGraphSCCPass::getAnalysisUsage(AU);
140 using InlinedArrayAllocasTy = DenseMap<ArrayType *, std::vector<AllocaInst *>>;
142 /// Look at all of the allocas that we inlined through this call site. If we
143 /// have already inlined other allocas through other calls into this function,
144 /// then we know that they have disjoint lifetimes and that we can merge them.
146 /// There are many heuristics possible for merging these allocas, and the
147 /// different options have different tradeoffs. One thing that we *really*
148 /// don't want to hurt is SRoA: once inlining happens, often allocas are no
149 /// longer address taken and so they can be promoted.
151 /// Our "solution" for that is to only merge allocas whose outermost type is an
152 /// array type. These are usually not promoted because someone is using a
153 /// variable index into them. These are also often the most important ones to
156 /// A better solution would be to have real memory lifetime markers in the IR
157 /// and not have the inliner do any merging of allocas at all. This would
158 /// allow the backend to do proper stack slot coloring of all allocas that
159 /// *actually make it to the backend*, which is really what we want.
161 /// Because we don't have this information, we do this simple and useful hack.
162 static void mergeInlinedArrayAllocas(
163 Function *Caller, InlineFunctionInfo &IFI,
164 InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory) {
165 SmallPtrSet<AllocaInst *, 16> UsedAllocas;
167 // When processing our SCC, check to see if CS was inlined from some other
168 // call site. For example, if we're processing "A" in this code:
170 // B() { x = alloca ... C() }
171 // C() { y = alloca ... }
172 // Assume that C was not inlined into B initially, and so we're processing A
173 // and decide to inline B into A. Doing this makes an alloca available for
174 // reuse and makes a callsite (C) available for inlining. When we process
175 // the C call site we don't want to do any alloca merging between X and Y
176 // because their scopes are not disjoint. We could make this smarter by
177 // keeping track of the inline history for each alloca in the
178 // InlinedArrayAllocas but this isn't likely to be a significant win.
179 if (InlineHistory != -1) // Only do merging for top-level call sites in SCC.
182 // Loop over all the allocas we have so far and see if they can be merged with
183 // a previously inlined alloca. If not, remember that we had it.
184 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size(); AllocaNo != e;
186 AllocaInst *AI = IFI.StaticAllocas[AllocaNo];
188 // Don't bother trying to merge array allocations (they will usually be
189 // canonicalized to be an allocation *of* an array), or allocations whose
190 // type is not itself an array (because we're afraid of pessimizing SRoA).
191 ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType());
192 if (!ATy || AI->isArrayAllocation())
195 // Get the list of all available allocas for this array type.
196 std::vector<AllocaInst *> &AllocasForType = InlinedArrayAllocas[ATy];
198 // Loop over the allocas in AllocasForType to see if we can reuse one. Note
199 // that we have to be careful not to reuse the same "available" alloca for
200 // multiple different allocas that we just inlined, we use the 'UsedAllocas'
201 // set to keep track of which "available" allocas are being used by this
202 // function. Also, AllocasForType can be empty of course!
203 bool MergedAwayAlloca = false;
204 for (AllocaInst *AvailableAlloca : AllocasForType) {
205 unsigned Align1 = AI->getAlignment(),
206 Align2 = AvailableAlloca->getAlignment();
208 // The available alloca has to be in the right function, not in some other
209 // function in this SCC.
210 if (AvailableAlloca->getParent() != AI->getParent())
213 // If the inlined function already uses this alloca then we can't reuse
215 if (!UsedAllocas.insert(AvailableAlloca).second)
218 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare
220 LLVM_DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI
221 << "\n\t\tINTO: " << *AvailableAlloca << '\n');
223 // Move affected dbg.declare calls immediately after the new alloca to
224 // avoid the situation when a dbg.declare precedes its alloca.
225 if (auto *L = LocalAsMetadata::getIfExists(AI))
226 if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
227 for (User *U : MDV->users())
228 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
229 DDI->moveBefore(AvailableAlloca->getNextNode());
231 AI->replaceAllUsesWith(AvailableAlloca);
233 if (Align1 != Align2) {
234 if (!Align1 || !Align2) {
235 const DataLayout &DL = Caller->getParent()->getDataLayout();
236 unsigned TypeAlign = DL.getABITypeAlignment(AI->getAllocatedType());
238 Align1 = Align1 ? Align1 : TypeAlign;
239 Align2 = Align2 ? Align2 : TypeAlign;
243 AvailableAlloca->setAlignment(AI->getAlignment());
246 AI->eraseFromParent();
247 MergedAwayAlloca = true;
249 IFI.StaticAllocas[AllocaNo] = nullptr;
253 // If we already nuked the alloca, we're done with it.
254 if (MergedAwayAlloca)
257 // If we were unable to merge away the alloca either because there are no
258 // allocas of the right type available or because we reused them all
259 // already, remember that this alloca came from an inlined function and mark
260 // it used so we don't reuse it for other allocas from this inline
262 AllocasForType.push_back(AI);
263 UsedAllocas.insert(AI);
267 /// If it is possible to inline the specified call site,
268 /// do so and update the CallGraph for this operation.
270 /// This function also does some basic book-keeping to update the IR. The
271 /// InlinedArrayAllocas map keeps track of any allocas that are already
272 /// available from other functions inlined into the caller. If we are able to
273 /// inline this call site we attempt to reuse already available allocas or add
274 /// any new allocas to the set if not possible.
275 static InlineResult InlineCallIfPossible(
276 CallSite CS, InlineFunctionInfo &IFI,
277 InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory,
278 bool InsertLifetime, function_ref<AAResults &(Function &)> &AARGetter,
279 ImportedFunctionsInliningStatistics &ImportedFunctionsStats) {
280 Function *Callee = CS.getCalledFunction();
281 Function *Caller = CS.getCaller();
283 AAResults &AAR = AARGetter(*Callee);
285 // Try to inline the function. Get the list of static allocas that were
287 InlineResult IR = InlineFunction(CS, IFI, &AAR, InsertLifetime);
291 if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
292 ImportedFunctionsStats.recordInline(*Caller, *Callee);
294 AttributeFuncs::mergeAttributesForInlining(*Caller, *Callee);
296 if (!DisableInlinedAllocaMerging)
297 mergeInlinedArrayAllocas(Caller, IFI, InlinedArrayAllocas, InlineHistory);
299 return IR; // success
302 /// Return true if inlining of CS can block the caller from being
303 /// inlined which is proved to be more beneficial. \p IC is the
304 /// estimated inline cost associated with callsite \p CS.
305 /// \p TotalSecondaryCost will be set to the estimated cost of inlining the
306 /// caller if \p CS is suppressed for inlining.
308 shouldBeDeferred(Function *Caller, CallSite CS, InlineCost IC,
309 int &TotalSecondaryCost,
310 function_ref<InlineCost(CallSite CS)> GetInlineCost) {
311 // For now we only handle local or inline functions.
312 if (!Caller->hasLocalLinkage() && !Caller->hasLinkOnceODRLinkage())
314 // If the cost of inlining CS is non-positive, it is not going to prevent the
315 // caller from being inlined into its callers and hence we don't need to
317 if (IC.getCost() <= 0)
319 // Try to detect the case where the current inlining candidate caller (call
320 // it B) is a static or linkonce-ODR function and is an inlining candidate
321 // elsewhere, and the current candidate callee (call it C) is large enough
322 // that inlining it into B would make B too big to inline later. In these
323 // circumstances it may be best not to inline C into B, but to inline B into
326 // This only applies to static and linkonce-ODR functions because those are
327 // expected to be available for inlining in the translation units where they
328 // are used. Thus we will always have the opportunity to make local inlining
329 // decisions. Importantly the linkonce-ODR linkage covers inline functions
330 // and templates in C++.
332 // FIXME: All of this logic should be sunk into getInlineCost. It relies on
333 // the internal implementation of the inline cost metrics rather than
334 // treating them as truly abstract units etc.
335 TotalSecondaryCost = 0;
336 // The candidate cost to be imposed upon the current function.
337 int CandidateCost = IC.getCost() - 1;
338 // If the caller has local linkage and can be inlined to all its callers, we
339 // can apply a huge negative bonus to TotalSecondaryCost.
340 bool ApplyLastCallBonus = Caller->hasLocalLinkage() && !Caller->hasOneUse();
341 // This bool tracks what happens if we DO inline C into B.
342 bool inliningPreventsSomeOuterInline = false;
343 for (User *U : Caller->users()) {
344 // If the caller will not be removed (either because it does not have a
345 // local linkage or because the LastCallToStaticBonus has been already
346 // applied), then we can exit the loop early.
347 if (!ApplyLastCallBonus && TotalSecondaryCost >= IC.getCost())
351 // If this isn't a call to Caller (it could be some other sort
352 // of reference) skip it. Such references will prevent the caller
353 // from being removed.
354 if (!CS2 || CS2.getCalledFunction() != Caller) {
355 ApplyLastCallBonus = false;
359 InlineCost IC2 = GetInlineCost(CS2);
360 ++NumCallerCallersAnalyzed;
362 ApplyLastCallBonus = false;
368 // See if inlining of the original callsite would erase the cost delta of
369 // this callsite. We subtract off the penalty for the call instruction,
370 // which we would be deleting.
371 if (IC2.getCostDelta() <= CandidateCost) {
372 inliningPreventsSomeOuterInline = true;
373 TotalSecondaryCost += IC2.getCost();
376 // If all outer calls to Caller would get inlined, the cost for the last
377 // one is set very low by getInlineCost, in anticipation that Caller will
378 // be removed entirely. We did not account for this above unless there
379 // is only one caller of Caller.
380 if (ApplyLastCallBonus)
381 TotalSecondaryCost -= InlineConstants::LastCallToStaticBonus;
383 if (inliningPreventsSomeOuterInline && TotalSecondaryCost < IC.getCost())
389 static std::basic_ostream<char> &operator<<(std::basic_ostream<char> &R,
390 const ore::NV &Arg) {
394 template <class RemarkT>
395 RemarkT &operator<<(RemarkT &&R, const InlineCost &IC) {
398 R << "(cost=always)";
399 } else if (IC.isNever()) {
402 R << "(cost=" << ore::NV("Cost", IC.getCost())
403 << ", threshold=" << ore::NV("Threshold", IC.getThreshold()) << ")";
405 if (const char *Reason = IC.getReason())
406 R << ": " << ore::NV("Reason", Reason);
410 static std::string inlineCostStr(const InlineCost &IC) {
411 std::stringstream Remark;
416 /// Return the cost only if the inliner should attempt to inline at the given
417 /// CallSite. If we return the cost, we will emit an optimisation remark later
418 /// using that cost, so we won't do so from this function.
419 static Optional<InlineCost>
420 shouldInline(CallSite CS, function_ref<InlineCost(CallSite CS)> GetInlineCost,
421 OptimizationRemarkEmitter &ORE) {
424 InlineCost IC = GetInlineCost(CS);
425 Instruction *Call = CS.getInstruction();
426 Function *Callee = CS.getCalledFunction();
427 Function *Caller = CS.getCaller();
430 LLVM_DEBUG(dbgs() << " Inlining " << inlineCostStr(IC)
431 << ", Call: " << *CS.getInstruction() << "\n");
436 LLVM_DEBUG(dbgs() << " NOT Inlining " << inlineCostStr(IC)
437 << ", Call: " << *CS.getInstruction() << "\n");
439 return OptimizationRemarkMissed(DEBUG_TYPE, "NeverInline", Call)
440 << NV("Callee", Callee) << " not inlined into "
441 << NV("Caller", Caller) << " because it should never be inlined "
448 LLVM_DEBUG(dbgs() << " NOT Inlining " << inlineCostStr(IC)
449 << ", Call: " << *CS.getInstruction() << "\n");
451 return OptimizationRemarkMissed(DEBUG_TYPE, "TooCostly", Call)
452 << NV("Callee", Callee) << " not inlined into "
453 << NV("Caller", Caller) << " because too costly to inline " << IC;
458 int TotalSecondaryCost = 0;
459 if (shouldBeDeferred(Caller, CS, IC, TotalSecondaryCost, GetInlineCost)) {
460 LLVM_DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction()
461 << " Cost = " << IC.getCost()
462 << ", outer Cost = " << TotalSecondaryCost << '\n');
464 return OptimizationRemarkMissed(DEBUG_TYPE, "IncreaseCostInOtherContexts",
466 << "Not inlining. Cost of inlining " << NV("Callee", Callee)
467 << " increases the cost of inlining " << NV("Caller", Caller)
468 << " in other contexts";
471 // IC does not bool() to false, so get an InlineCost that will.
472 // This will not be inspected to make an error message.
476 LLVM_DEBUG(dbgs() << " Inlining " << inlineCostStr(IC)
477 << ", Call: " << *CS.getInstruction() << '\n');
481 /// Return true if the specified inline history ID
482 /// indicates an inline history that includes the specified function.
483 static bool InlineHistoryIncludes(
484 Function *F, int InlineHistoryID,
485 const SmallVectorImpl<std::pair<Function *, int>> &InlineHistory) {
486 while (InlineHistoryID != -1) {
487 assert(unsigned(InlineHistoryID) < InlineHistory.size() &&
488 "Invalid inline history ID");
489 if (InlineHistory[InlineHistoryID].first == F)
491 InlineHistoryID = InlineHistory[InlineHistoryID].second;
496 bool LegacyInlinerBase::doInitialization(CallGraph &CG) {
497 if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
498 ImportedFunctionsStats.setModuleInfo(CG.getModule());
499 return false; // No changes to CallGraph.
502 bool LegacyInlinerBase::runOnSCC(CallGraphSCC &SCC) {
505 return inlineCalls(SCC);
508 static void emit_inlined_into(OptimizationRemarkEmitter &ORE, DebugLoc &DLoc,
509 const BasicBlock *Block, const Function &Callee,
510 const Function &Caller, const InlineCost &IC) {
512 bool AlwaysInline = IC.isAlways();
513 StringRef RemarkName = AlwaysInline ? "AlwaysInline" : "Inlined";
514 return OptimizationRemark(DEBUG_TYPE, RemarkName, DLoc, Block)
515 << ore::NV("Callee", &Callee) << " inlined into "
516 << ore::NV("Caller", &Caller) << " with " << IC;
520 static void setInlineRemark(CallSite &CS, StringRef message) {
521 if (!InlineRemarkAttribute)
524 Attribute attr = Attribute::get(CS->getContext(), "inline-remark", message);
525 CS.addAttribute(AttributeList::FunctionIndex, attr);
529 inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG,
530 std::function<AssumptionCache &(Function &)> GetAssumptionCache,
531 ProfileSummaryInfo *PSI, TargetLibraryInfo &TLI,
533 function_ref<InlineCost(CallSite CS)> GetInlineCost,
534 function_ref<AAResults &(Function &)> AARGetter,
535 ImportedFunctionsInliningStatistics &ImportedFunctionsStats) {
536 SmallPtrSet<Function *, 8> SCCFunctions;
537 LLVM_DEBUG(dbgs() << "Inliner visiting SCC:");
538 for (CallGraphNode *Node : SCC) {
539 Function *F = Node->getFunction();
541 SCCFunctions.insert(F);
542 LLVM_DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE"));
545 // Scan through and identify all call sites ahead of time so that we only
546 // inline call sites in the original functions, not call sites that result
547 // from inlining other functions.
548 SmallVector<std::pair<CallSite, int>, 16> CallSites;
550 // When inlining a callee produces new call sites, we want to keep track of
551 // the fact that they were inlined from the callee. This allows us to avoid
552 // infinite inlining in some obscure cases. To represent this, we use an
553 // index into the InlineHistory vector.
554 SmallVector<std::pair<Function *, int>, 8> InlineHistory;
556 for (CallGraphNode *Node : SCC) {
557 Function *F = Node->getFunction();
558 if (!F || F->isDeclaration())
561 OptimizationRemarkEmitter ORE(F);
562 for (BasicBlock &BB : *F)
563 for (Instruction &I : BB) {
564 CallSite CS(cast<Value>(&I));
565 // If this isn't a call, or it is a call to an intrinsic, it can
567 if (!CS || isa<IntrinsicInst>(I))
570 // If this is a direct call to an external function, we can never inline
571 // it. If it is an indirect call, inlining may resolve it to be a
572 // direct call, so we keep it.
573 if (Function *Callee = CS.getCalledFunction())
574 if (Callee->isDeclaration()) {
577 setInlineRemark(CS, "unavailable definition");
579 return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
580 << NV("Callee", Callee) << " will not be inlined into "
581 << NV("Caller", CS.getCaller())
582 << " because its definition is unavailable"
588 CallSites.push_back(std::make_pair(CS, -1));
592 LLVM_DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n");
594 // If there are no calls in this function, exit early.
595 if (CallSites.empty())
598 // Now that we have all of the call sites, move the ones to functions in the
599 // current SCC to the end of the list.
600 unsigned FirstCallInSCC = CallSites.size();
601 for (unsigned i = 0; i < FirstCallInSCC; ++i)
602 if (Function *F = CallSites[i].first.getCalledFunction())
603 if (SCCFunctions.count(F))
604 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
606 InlinedArrayAllocasTy InlinedArrayAllocas;
607 InlineFunctionInfo InlineInfo(&CG, &GetAssumptionCache, PSI);
609 // Now that we have all of the call sites, loop over them and inline them if
610 // it looks profitable to do so.
611 bool Changed = false;
615 // Iterate over the outer loop because inlining functions can cause indirect
616 // calls to become direct calls.
617 // CallSites may be modified inside so ranged for loop can not be used.
618 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
619 CallSite CS = CallSites[CSi].first;
621 Function *Caller = CS.getCaller();
622 Function *Callee = CS.getCalledFunction();
624 // We can only inline direct calls to non-declarations.
625 if (!Callee || Callee->isDeclaration())
628 Instruction *Instr = CS.getInstruction();
630 bool IsTriviallyDead = isInstructionTriviallyDead(Instr, &TLI);
633 if (!IsTriviallyDead) {
634 // If this call site was obtained by inlining another function, verify
635 // that the include path for the function did not include the callee
636 // itself. If so, we'd be recursively inlining the same function,
637 // which would provide the same callsites, which would cause us to
638 // infinitely inline.
639 InlineHistoryID = CallSites[CSi].second;
640 if (InlineHistoryID != -1 &&
641 InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) {
642 setInlineRemark(CS, "recursive");
647 // FIXME for new PM: because of the old PM we currently generate ORE and
648 // in turn BFI on demand. With the new PM, the ORE dependency should
649 // just become a regular analysis dependency.
650 OptimizationRemarkEmitter ORE(Caller);
652 Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
653 // If the policy determines that we should inline this function,
654 // delete the call instead.
655 if (!OIC.hasValue()) {
656 setInlineRemark(CS, "deferred");
660 if (!OIC.getValue()) {
661 // shouldInline() call returned a negative inline cost that explains
662 // why this callsite should not be inlined.
663 setInlineRemark(CS, inlineCostStr(*OIC));
667 // If this call site is dead and it is to a readonly function, we should
668 // just delete the call instead of trying to inline it, regardless of
669 // size. This happens because IPSCCP propagates the result out of the
670 // call and then we're left with the dead call.
671 if (IsTriviallyDead) {
672 LLVM_DEBUG(dbgs() << " -> Deleting dead call: " << *Instr << "\n");
673 // Update the call graph by deleting the edge from Callee to Caller.
674 setInlineRemark(CS, "trivially dead");
675 CG[Caller]->removeCallEdgeFor(CS);
676 Instr->eraseFromParent();
679 // Get DebugLoc to report. CS will be invalid after Inliner.
680 DebugLoc DLoc = CS->getDebugLoc();
681 BasicBlock *Block = CS.getParent();
683 // Attempt to inline the function.
686 InlineResult IR = InlineCallIfPossible(
687 CS, InlineInfo, InlinedArrayAllocas, InlineHistoryID,
688 InsertLifetime, AARGetter, ImportedFunctionsStats);
690 setInlineRemark(CS, std::string(IR) + "; " + inlineCostStr(*OIC));
692 return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc,
694 << NV("Callee", Callee) << " will not be inlined into "
695 << NV("Caller", Caller) << ": " << NV("Reason", IR.message);
701 emit_inlined_into(ORE, DLoc, Block, *Callee, *Caller, *OIC);
703 // If inlining this function gave us any new call sites, throw them
704 // onto our worklist to process. They are useful inline candidates.
705 if (!InlineInfo.InlinedCalls.empty()) {
706 // Create a new inline history entry for this, so that we remember
707 // that these new callsites came about due to inlining Callee.
708 int NewHistoryID = InlineHistory.size();
709 InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID));
711 for (Value *Ptr : InlineInfo.InlinedCalls)
712 CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID));
716 // If we inlined or deleted the last possible call site to the function,
717 // delete the function body now.
718 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() &&
719 // TODO: Can remove if in SCC now.
720 !SCCFunctions.count(Callee) &&
721 // The function may be apparently dead, but if there are indirect
722 // callgraph references to the node, we cannot delete it yet, this
723 // could invalidate the CGSCC iterator.
724 CG[Callee]->getNumReferences() == 0) {
725 LLVM_DEBUG(dbgs() << " -> Deleting dead function: "
726 << Callee->getName() << "\n");
727 CallGraphNode *CalleeNode = CG[Callee];
729 // Remove any call graph edges from the callee to its callees.
730 CalleeNode->removeAllCalledFunctions();
732 // Removing the node for callee from the call graph and delete it.
733 delete CG.removeFunctionFromModule(CalleeNode);
737 // Remove this call site from the list. If possible, use
738 // swap/pop_back for efficiency, but do not use it if doing so would
739 // move a call site to a function in this SCC before the
740 // 'FirstCallInSCC' barrier.
741 if (SCC.isSingular()) {
742 CallSites[CSi] = CallSites.back();
743 CallSites.pop_back();
745 CallSites.erase(CallSites.begin() + CSi);
752 } while (LocalChange);
757 bool LegacyInlinerBase::inlineCalls(CallGraphSCC &SCC) {
758 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
759 ACT = &getAnalysis<AssumptionCacheTracker>();
760 PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
761 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
762 auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
763 return ACT->getAssumptionCache(F);
765 return inlineCallsImpl(SCC, CG, GetAssumptionCache, PSI, TLI, InsertLifetime,
766 [this](CallSite CS) { return getInlineCost(CS); },
767 LegacyAARGetter(*this), ImportedFunctionsStats);
770 /// Remove now-dead linkonce functions at the end of
771 /// processing to avoid breaking the SCC traversal.
772 bool LegacyInlinerBase::doFinalization(CallGraph &CG) {
773 if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
774 ImportedFunctionsStats.dump(InlinerFunctionImportStats ==
775 InlinerFunctionImportStatsOpts::Verbose);
776 return removeDeadFunctions(CG);
779 /// Remove dead functions that are not included in DNR (Do Not Remove) list.
780 bool LegacyInlinerBase::removeDeadFunctions(CallGraph &CG,
781 bool AlwaysInlineOnly) {
782 SmallVector<CallGraphNode *, 16> FunctionsToRemove;
783 SmallVector<Function *, 16> DeadFunctionsInComdats;
785 auto RemoveCGN = [&](CallGraphNode *CGN) {
786 // Remove any call graph edges from the function to its callees.
787 CGN->removeAllCalledFunctions();
789 // Remove any edges from the external node to the function's call graph
790 // node. These edges might have been made irrelegant due to
791 // optimization of the program.
792 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
794 // Removing the node for callee from the call graph and delete it.
795 FunctionsToRemove.push_back(CGN);
798 // Scan for all of the functions, looking for ones that should now be removed
799 // from the program. Insert the dead ones in the FunctionsToRemove set.
800 for (const auto &I : CG) {
801 CallGraphNode *CGN = I.second.get();
802 Function *F = CGN->getFunction();
803 if (!F || F->isDeclaration())
806 // Handle the case when this function is called and we only want to care
807 // about always-inline functions. This is a bit of a hack to share code
808 // between here and the InlineAlways pass.
809 if (AlwaysInlineOnly && !F->hasFnAttribute(Attribute::AlwaysInline))
812 // If the only remaining users of the function are dead constants, remove
814 F->removeDeadConstantUsers();
816 if (!F->isDefTriviallyDead())
819 // It is unsafe to drop a function with discardable linkage from a COMDAT
820 // without also dropping the other members of the COMDAT.
821 // The inliner doesn't visit non-function entities which are in COMDAT
822 // groups so it is unsafe to do so *unless* the linkage is local.
823 if (!F->hasLocalLinkage()) {
824 if (F->hasComdat()) {
825 DeadFunctionsInComdats.push_back(F);
832 if (!DeadFunctionsInComdats.empty()) {
833 // Filter out the functions whose comdats remain alive.
834 filterDeadComdatFunctions(CG.getModule(), DeadFunctionsInComdats);
836 for (Function *F : DeadFunctionsInComdats)
840 if (FunctionsToRemove.empty())
843 // Now that we know which functions to delete, do so. We didn't want to do
844 // this inline, because that would invalidate our CallGraph::iterator
847 // Note that it doesn't matter that we are iterating over a non-stable order
848 // here to do this, it doesn't matter which order the functions are deleted
850 array_pod_sort(FunctionsToRemove.begin(), FunctionsToRemove.end());
851 FunctionsToRemove.erase(
852 std::unique(FunctionsToRemove.begin(), FunctionsToRemove.end()),
853 FunctionsToRemove.end());
854 for (CallGraphNode *CGN : FunctionsToRemove) {
855 delete CG.removeFunctionFromModule(CGN);
861 InlinerPass::~InlinerPass() {
862 if (ImportedFunctionsStats) {
863 assert(InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No);
864 ImportedFunctionsStats->dump(InlinerFunctionImportStats ==
865 InlinerFunctionImportStatsOpts::Verbose);
869 PreservedAnalyses InlinerPass::run(LazyCallGraph::SCC &InitialC,
870 CGSCCAnalysisManager &AM, LazyCallGraph &CG,
871 CGSCCUpdateResult &UR) {
872 const ModuleAnalysisManager &MAM =
873 AM.getResult<ModuleAnalysisManagerCGSCCProxy>(InitialC, CG).getManager();
874 bool Changed = false;
876 assert(InitialC.size() > 0 && "Cannot handle an empty SCC!");
877 Module &M = *InitialC.begin()->getFunction().getParent();
878 ProfileSummaryInfo *PSI = MAM.getCachedResult<ProfileSummaryAnalysis>(M);
880 if (!ImportedFunctionsStats &&
881 InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No) {
882 ImportedFunctionsStats =
883 llvm::make_unique<ImportedFunctionsInliningStatistics>();
884 ImportedFunctionsStats->setModuleInfo(M);
887 // We use a single common worklist for calls across the entire SCC. We
888 // process these in-order and append new calls introduced during inlining to
891 // Note that this particular order of processing is actually critical to
892 // avoid very bad behaviors. Consider *highly connected* call graphs where
893 // each function contains a small amonut of code and a couple of calls to
894 // other functions. Because the LLVM inliner is fundamentally a bottom-up
895 // inliner, it can handle gracefully the fact that these all appear to be
896 // reasonable inlining candidates as it will flatten things until they become
897 // too big to inline, and then move on and flatten another batch.
899 // However, when processing call edges *within* an SCC we cannot rely on this
900 // bottom-up behavior. As a consequence, with heavily connected *SCCs* of
901 // functions we can end up incrementally inlining N calls into each of
902 // N functions because each incremental inlining decision looks good and we
903 // don't have a topological ordering to prevent explosions.
905 // To compensate for this, we don't process transitive edges made immediate
906 // by inlining until we've done one pass of inlining across the entire SCC.
907 // Large, highly connected SCCs still lead to some amount of code bloat in
908 // this model, but it is uniformly spread across all the functions in the SCC
909 // and eventually they all become too large to inline, rather than
910 // incrementally maknig a single function grow in a super linear fashion.
911 SmallVector<std::pair<CallSite, int>, 16> Calls;
913 FunctionAnalysisManager &FAM =
914 AM.getResult<FunctionAnalysisManagerCGSCCProxy>(InitialC, CG)
917 // Populate the initial list of calls in this SCC.
918 for (auto &N : InitialC) {
920 FAM.getResult<OptimizationRemarkEmitterAnalysis>(N.getFunction());
921 // We want to generally process call sites top-down in order for
922 // simplifications stemming from replacing the call with the returned value
923 // after inlining to be visible to subsequent inlining decisions.
924 // FIXME: Using instructions sequence is a really bad way to do this.
925 // Instead we should do an actual RPO walk of the function body.
926 for (Instruction &I : instructions(N.getFunction()))
927 if (auto CS = CallSite(&I))
928 if (Function *Callee = CS.getCalledFunction()) {
929 if (!Callee->isDeclaration())
930 Calls.push_back({CS, -1});
931 else if (!isa<IntrinsicInst>(I)) {
933 setInlineRemark(CS, "unavailable definition");
935 return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
936 << NV("Callee", Callee) << " will not be inlined into "
937 << NV("Caller", CS.getCaller())
938 << " because its definition is unavailable"
945 return PreservedAnalyses::all();
947 // Capture updatable variables for the current SCC and RefSCC.
949 auto *RC = &C->getOuterRefSCC();
951 // When inlining a callee produces new call sites, we want to keep track of
952 // the fact that they were inlined from the callee. This allows us to avoid
953 // infinite inlining in some obscure cases. To represent this, we use an
954 // index into the InlineHistory vector.
955 SmallVector<std::pair<Function *, int>, 16> InlineHistory;
957 // Track a set vector of inlined callees so that we can augment the caller
958 // with all of their edges in the call graph before pruning out the ones that
959 // got simplified away.
960 SmallSetVector<Function *, 4> InlinedCallees;
962 // Track the dead functions to delete once finished with inlining calls. We
963 // defer deleting these to make it easier to handle the call graph updates.
964 SmallVector<Function *, 4> DeadFunctions;
966 // Loop forward over all of the calls. Note that we cannot cache the size as
967 // inlining can introduce new calls that need to be processed.
968 for (int i = 0; i < (int)Calls.size(); ++i) {
969 // We expect the calls to typically be batched with sequences of calls that
970 // have the same caller, so we first set up some shared infrastructure for
971 // this caller. We also do any pruning we can at this layer on the caller
973 Function &F = *Calls[i].first.getCaller();
974 LazyCallGraph::Node &N = *CG.lookup(F);
975 if (CG.lookupSCC(N) != C)
977 if (F.hasFnAttribute(Attribute::OptimizeNone)) {
978 setInlineRemark(Calls[i].first, "optnone attribute");
982 LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n");
984 // Get a FunctionAnalysisManager via a proxy for this particular node. We
985 // do this each time we visit a node as the SCC may have changed and as
986 // we're going to mutate this particular function we want to make sure the
987 // proxy is in place to forward any invalidation events. We can use the
988 // manager we get here for looking up results for functions other than this
989 // node however because those functions aren't going to be mutated by this
991 FunctionAnalysisManager &FAM =
992 AM.getResult<FunctionAnalysisManagerCGSCCProxy>(*C, CG)
995 // Get the remarks emission analysis for the caller.
996 auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
998 std::function<AssumptionCache &(Function &)> GetAssumptionCache =
999 [&](Function &F) -> AssumptionCache & {
1000 return FAM.getResult<AssumptionAnalysis>(F);
1002 auto GetBFI = [&](Function &F) -> BlockFrequencyInfo & {
1003 return FAM.getResult<BlockFrequencyAnalysis>(F);
1006 auto GetInlineCost = [&](CallSite CS) {
1007 Function &Callee = *CS.getCalledFunction();
1008 auto &CalleeTTI = FAM.getResult<TargetIRAnalysis>(Callee);
1009 return getInlineCost(CS, Params, CalleeTTI, GetAssumptionCache, {GetBFI},
1013 // Now process as many calls as we have within this caller in the sequnece.
1014 // We bail out as soon as the caller has to change so we can update the
1015 // call graph and prepare the context of that new caller.
1016 bool DidInline = false;
1017 for (; i < (int)Calls.size() && Calls[i].first.getCaller() == &F; ++i) {
1018 int InlineHistoryID;
1020 std::tie(CS, InlineHistoryID) = Calls[i];
1021 Function &Callee = *CS.getCalledFunction();
1023 if (InlineHistoryID != -1 &&
1024 InlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory)) {
1025 setInlineRemark(CS, "recursive");
1029 // Check if this inlining may repeat breaking an SCC apart that has
1030 // already been split once before. In that case, inlining here may
1031 // trigger infinite inlining, much like is prevented within the inliner
1032 // itself by the InlineHistory above, but spread across CGSCC iterations
1033 // and thus hidden from the full inline history.
1034 if (CG.lookupSCC(*CG.lookup(Callee)) == C &&
1035 UR.InlinedInternalEdges.count({&N, C})) {
1036 LLVM_DEBUG(dbgs() << "Skipping inlining internal SCC edge from a node "
1037 "previously split out of this SCC by inlining: "
1038 << F.getName() << " -> " << Callee.getName() << "\n");
1039 setInlineRemark(CS, "recursive SCC split");
1043 Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
1044 // Check whether we want to inline this callsite.
1045 if (!OIC.hasValue()) {
1046 setInlineRemark(CS, "deferred");
1050 if (!OIC.getValue()) {
1051 // shouldInline() call returned a negative inline cost that explains
1052 // why this callsite should not be inlined.
1053 setInlineRemark(CS, inlineCostStr(*OIC));
1057 // Setup the data structure used to plumb customization into the
1058 // `InlineFunction` routine.
1059 InlineFunctionInfo IFI(
1060 /*cg=*/nullptr, &GetAssumptionCache, PSI,
1061 &FAM.getResult<BlockFrequencyAnalysis>(*(CS.getCaller())),
1062 &FAM.getResult<BlockFrequencyAnalysis>(Callee));
1064 // Get DebugLoc to report. CS will be invalid after Inliner.
1065 DebugLoc DLoc = CS->getDebugLoc();
1066 BasicBlock *Block = CS.getParent();
1068 using namespace ore;
1070 InlineResult IR = InlineFunction(CS, IFI);
1072 setInlineRemark(CS, std::string(IR) + "; " + inlineCostStr(*OIC));
1074 return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc, Block)
1075 << NV("Callee", &Callee) << " will not be inlined into "
1076 << NV("Caller", &F) << ": " << NV("Reason", IR.message);
1081 InlinedCallees.insert(&Callee);
1085 emit_inlined_into(ORE, DLoc, Block, Callee, F, *OIC);
1087 // Add any new callsites to defined functions to the worklist.
1088 if (!IFI.InlinedCallSites.empty()) {
1089 int NewHistoryID = InlineHistory.size();
1090 InlineHistory.push_back({&Callee, InlineHistoryID});
1091 for (CallSite &CS : reverse(IFI.InlinedCallSites))
1092 if (Function *NewCallee = CS.getCalledFunction())
1093 if (!NewCallee->isDeclaration())
1094 Calls.push_back({CS, NewHistoryID});
1097 if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
1098 ImportedFunctionsStats->recordInline(F, Callee);
1100 // Merge the attributes based on the inlining.
1101 AttributeFuncs::mergeAttributesForInlining(F, Callee);
1103 // For local functions, check whether this makes the callee trivially
1104 // dead. In that case, we can drop the body of the function eagerly
1105 // which may reduce the number of callers of other functions to one,
1106 // changing inline cost thresholds.
1107 if (Callee.hasLocalLinkage()) {
1108 // To check this we also need to nuke any dead constant uses (perhaps
1109 // made dead by this operation on other functions).
1110 Callee.removeDeadConstantUsers();
1111 if (Callee.use_empty() && !CG.isLibFunction(Callee)) {
1113 std::remove_if(Calls.begin() + i + 1, Calls.end(),
1114 [&Callee](const std::pair<CallSite, int> &Call) {
1115 return Call.first.getCaller() == &Callee;
1118 // Clear the body and queue the function itself for deletion when we
1119 // finish inlining and call graph updates.
1120 // Note that after this point, it is an error to do anything other
1121 // than use the callee's address or delete it.
1122 Callee.dropAllReferences();
1123 assert(find(DeadFunctions, &Callee) == DeadFunctions.end() &&
1124 "Cannot put cause a function to become dead twice!");
1125 DeadFunctions.push_back(&Callee);
1130 // Back the call index up by one to put us in a good position to go around
1138 // Add all the inlined callees' edges as ref edges to the caller. These are
1139 // by definition trivial edges as we always have *some* transitive ref edge
1140 // chain. While in some cases these edges are direct calls inside the
1141 // callee, they have to be modeled in the inliner as reference edges as
1142 // there may be a reference edge anywhere along the chain from the current
1143 // caller to the callee that causes the whole thing to appear like
1144 // a (transitive) reference edge that will require promotion to a call edge
1146 for (Function *InlinedCallee : InlinedCallees) {
1147 LazyCallGraph::Node &CalleeN = *CG.lookup(*InlinedCallee);
1148 for (LazyCallGraph::Edge &E : *CalleeN)
1149 RC->insertTrivialRefEdge(N, E.getNode());
1152 // At this point, since we have made changes we have at least removed
1153 // a call instruction. However, in the process we do some incremental
1154 // simplification of the surrounding code. This simplification can
1155 // essentially do all of the same things as a function pass and we can
1156 // re-use the exact same logic for updating the call graph to reflect the
1158 LazyCallGraph::SCC *OldC = C;
1159 C = &updateCGAndAnalysisManagerForFunctionPass(CG, *C, N, AM, UR);
1160 LLVM_DEBUG(dbgs() << "Updated inlining SCC: " << *C << "\n");
1161 RC = &C->getOuterRefSCC();
1163 // If this causes an SCC to split apart into multiple smaller SCCs, there
1164 // is a subtle risk we need to prepare for. Other transformations may
1165 // expose an "infinite inlining" opportunity later, and because of the SCC
1166 // mutation, we will revisit this function and potentially re-inline. If we
1167 // do, and that re-inlining also has the potentially to mutate the SCC
1168 // structure, the infinite inlining problem can manifest through infinite
1169 // SCC splits and merges. To avoid this, we capture the originating caller
1170 // node and the SCC containing the call edge. This is a slight over
1171 // approximation of the possible inlining decisions that must be avoided,
1172 // but is relatively efficient to store. We use C != OldC to know when
1173 // a new SCC is generated and the original SCC may be generated via merge
1174 // in later iterations.
1176 // It is also possible that even if no new SCC is generated
1177 // (i.e., C == OldC), the original SCC could be split and then merged
1178 // into the same one as itself. and the original SCC will be added into
1179 // UR.CWorklist again, we want to catch such cases too.
1181 // FIXME: This seems like a very heavyweight way of retaining the inline
1182 // history, we should look for a more efficient way of tracking it.
1183 if ((C != OldC || UR.CWorklist.count(OldC)) &&
1184 llvm::any_of(InlinedCallees, [&](Function *Callee) {
1185 return CG.lookupSCC(*CG.lookup(*Callee)) == OldC;
1187 LLVM_DEBUG(dbgs() << "Inlined an internal call edge and split an SCC, "
1188 "retaining this to avoid infinite inlining.\n");
1189 UR.InlinedInternalEdges.insert({&N, OldC});
1191 InlinedCallees.clear();
1194 // Now that we've finished inlining all of the calls across this SCC, delete
1195 // all of the trivially dead functions, updating the call graph and the CGSCC
1196 // pass manager in the process.
1198 // Note that this walks a pointer set which has non-deterministic order but
1199 // that is OK as all we do is delete things and add pointers to unordered
1201 for (Function *DeadF : DeadFunctions) {
1202 // Get the necessary information out of the call graph and nuke the
1203 // function there. Also, cclear out any cached analyses.
1204 auto &DeadC = *CG.lookupSCC(*CG.lookup(*DeadF));
1205 FunctionAnalysisManager &FAM =
1206 AM.getResult<FunctionAnalysisManagerCGSCCProxy>(DeadC, CG)
1208 FAM.clear(*DeadF, DeadF->getName());
1209 AM.clear(DeadC, DeadC.getName());
1210 auto &DeadRC = DeadC.getOuterRefSCC();
1211 CG.removeDeadFunction(*DeadF);
1213 // Mark the relevant parts of the call graph as invalid so we don't visit
1215 UR.InvalidatedSCCs.insert(&DeadC);
1216 UR.InvalidatedRefSCCs.insert(&DeadRC);
1218 // And delete the actual function from the module.
1219 M.getFunctionList().erase(DeadF);
1224 return PreservedAnalyses::all();
1226 // Even if we change the IR, we update the core CGSCC data structures and so
1227 // can preserve the proxy to the function analysis manager.
1228 PreservedAnalyses PA;
1229 PA.preserve<FunctionAnalysisManagerCGSCCProxy>();