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Diffstat (limited to 'contrib/llvm-project/llvm/lib/Transforms/IPO/Inliner.cpp')
| -rw-r--r-- | contrib/llvm-project/llvm/lib/Transforms/IPO/Inliner.cpp | 1038 |
1 files changed, 1038 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/IPO/Inliner.cpp b/contrib/llvm-project/llvm/lib/Transforms/IPO/Inliner.cpp new file mode 100644 index 000000000000..e91b6c9b1d26 --- /dev/null +++ b/contrib/llvm-project/llvm/lib/Transforms/IPO/Inliner.cpp @@ -0,0 +1,1038 @@ +//===- Inliner.cpp - Code common to all inliners --------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file implements the mechanics required to implement inlining without +// missing any calls and updating the call graph. The decisions of which calls +// are profitable to inline are implemented elsewhere. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/IPO/Inliner.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/None.h" +#include "llvm/ADT/Optional.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/ScopeExit.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/BasicAliasAnalysis.h" +#include "llvm/Analysis/BlockFrequencyInfo.h" +#include "llvm/Analysis/CGSCCPassManager.h" +#include "llvm/Analysis/CallGraph.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/InlineAdvisor.h" +#include "llvm/Analysis/InlineCost.h" +#include "llvm/Analysis/LazyCallGraph.h" +#include "llvm/Analysis/OptimizationRemarkEmitter.h" +#include "llvm/Analysis/ProfileSummaryInfo.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/Analysis/Utils/ImportedFunctionsInliningStatistics.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DebugLoc.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/DiagnosticInfo.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/PassManager.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Utils/CallPromotionUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/ModuleUtils.h" +#include <algorithm> +#include <cassert> +#include <functional> +#include <sstream> +#include <tuple> +#include <utility> +#include <vector> + +using namespace llvm; + +#define DEBUG_TYPE "inline" + +STATISTIC(NumInlined, "Number of functions inlined"); +STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined"); +STATISTIC(NumDeleted, "Number of functions deleted because all callers found"); +STATISTIC(NumMergedAllocas, "Number of allocas merged together"); + +/// Flag to disable manual alloca merging. +/// +/// Merging of allocas was originally done as a stack-size saving technique +/// prior to LLVM's code generator having support for stack coloring based on +/// lifetime markers. It is now in the process of being removed. To experiment +/// with disabling it and relying fully on lifetime marker based stack +/// coloring, you can pass this flag to LLVM. +static cl::opt<bool> + DisableInlinedAllocaMerging("disable-inlined-alloca-merging", + cl::init(false), cl::Hidden); + +extern cl::opt<InlinerFunctionImportStatsOpts> InlinerFunctionImportStats; + +static cl::opt<std::string> CGSCCInlineReplayFile( + "cgscc-inline-replay", cl::init(""), cl::value_desc("filename"), + cl::desc( + "Optimization remarks file containing inline remarks to be replayed " + "by inlining from cgscc inline remarks."), + cl::Hidden); + +LegacyInlinerBase::LegacyInlinerBase(char &ID) : CallGraphSCCPass(ID) {} + +LegacyInlinerBase::LegacyInlinerBase(char &ID, bool InsertLifetime) + : CallGraphSCCPass(ID), InsertLifetime(InsertLifetime) {} + +/// For this class, we declare that we require and preserve the call graph. +/// If the derived class implements this method, it should +/// always explicitly call the implementation here. +void LegacyInlinerBase::getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<ProfileSummaryInfoWrapperPass>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + getAAResultsAnalysisUsage(AU); + CallGraphSCCPass::getAnalysisUsage(AU); +} + +using InlinedArrayAllocasTy = DenseMap<ArrayType *, std::vector<AllocaInst *>>; + +/// Look at all of the allocas that we inlined through this call site. If we +/// have already inlined other allocas through other calls into this function, +/// then we know that they have disjoint lifetimes and that we can merge them. +/// +/// There are many heuristics possible for merging these allocas, and the +/// different options have different tradeoffs. One thing that we *really* +/// don't want to hurt is SRoA: once inlining happens, often allocas are no +/// longer address taken and so they can be promoted. +/// +/// Our "solution" for that is to only merge allocas whose outermost type is an +/// array type. These are usually not promoted because someone is using a +/// variable index into them. These are also often the most important ones to +/// merge. +/// +/// A better solution would be to have real memory lifetime markers in the IR +/// and not have the inliner do any merging of allocas at all. This would +/// allow the backend to do proper stack slot coloring of all allocas that +/// *actually make it to the backend*, which is really what we want. +/// +/// Because we don't have this information, we do this simple and useful hack. +static void mergeInlinedArrayAllocas(Function *Caller, InlineFunctionInfo &IFI, + InlinedArrayAllocasTy &InlinedArrayAllocas, + int InlineHistory) { + SmallPtrSet<AllocaInst *, 16> UsedAllocas; + + // When processing our SCC, check to see if the call site was inlined from + // some other call site. For example, if we're processing "A" in this code: + // A() { B() } + // B() { x = alloca ... C() } + // C() { y = alloca ... } + // Assume that C was not inlined into B initially, and so we're processing A + // and decide to inline B into A. Doing this makes an alloca available for + // reuse and makes a callsite (C) available for inlining. When we process + // the C call site we don't want to do any alloca merging between X and Y + // because their scopes are not disjoint. We could make this smarter by + // keeping track of the inline history for each alloca in the + // InlinedArrayAllocas but this isn't likely to be a significant win. + if (InlineHistory != -1) // Only do merging for top-level call sites in SCC. + return; + + // Loop over all the allocas we have so far and see if they can be merged with + // a previously inlined alloca. If not, remember that we had it. + for (unsigned AllocaNo = 0, E = IFI.StaticAllocas.size(); AllocaNo != E; + ++AllocaNo) { + AllocaInst *AI = IFI.StaticAllocas[AllocaNo]; + + // Don't bother trying to merge array allocations (they will usually be + // canonicalized to be an allocation *of* an array), or allocations whose + // type is not itself an array (because we're afraid of pessimizing SRoA). + ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType()); + if (!ATy || AI->isArrayAllocation()) + continue; + + // Get the list of all available allocas for this array type. + std::vector<AllocaInst *> &AllocasForType = InlinedArrayAllocas[ATy]; + + // Loop over the allocas in AllocasForType to see if we can reuse one. Note + // that we have to be careful not to reuse the same "available" alloca for + // multiple different allocas that we just inlined, we use the 'UsedAllocas' + // set to keep track of which "available" allocas are being used by this + // function. Also, AllocasForType can be empty of course! + bool MergedAwayAlloca = false; + for (AllocaInst *AvailableAlloca : AllocasForType) { + Align Align1 = AI->getAlign(); + Align Align2 = AvailableAlloca->getAlign(); + + // The available alloca has to be in the right function, not in some other + // function in this SCC. + if (AvailableAlloca->getParent() != AI->getParent()) + continue; + + // If the inlined function already uses this alloca then we can't reuse + // it. + if (!UsedAllocas.insert(AvailableAlloca).second) + continue; + + // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare + // success! + LLVM_DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI + << "\n\t\tINTO: " << *AvailableAlloca << '\n'); + + // Move affected dbg.declare calls immediately after the new alloca to + // avoid the situation when a dbg.declare precedes its alloca. + if (auto *L = LocalAsMetadata::getIfExists(AI)) + if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L)) + for (User *U : MDV->users()) + if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U)) + DDI->moveBefore(AvailableAlloca->getNextNode()); + + AI->replaceAllUsesWith(AvailableAlloca); + + if (Align1 > Align2) + AvailableAlloca->setAlignment(AI->getAlign()); + + AI->eraseFromParent(); + MergedAwayAlloca = true; + ++NumMergedAllocas; + IFI.StaticAllocas[AllocaNo] = nullptr; + break; + } + + // If we already nuked the alloca, we're done with it. + if (MergedAwayAlloca) + continue; + + // If we were unable to merge away the alloca either because there are no + // allocas of the right type available or because we reused them all + // already, remember that this alloca came from an inlined function and mark + // it used so we don't reuse it for other allocas from this inline + // operation. + AllocasForType.push_back(AI); + UsedAllocas.insert(AI); + } +} + +/// If it is possible to inline the specified call site, +/// do so and update the CallGraph for this operation. +/// +/// This function also does some basic book-keeping to update the IR. The +/// InlinedArrayAllocas map keeps track of any allocas that are already +/// available from other functions inlined into the caller. If we are able to +/// inline this call site we attempt to reuse already available allocas or add +/// any new allocas to the set if not possible. +static InlineResult inlineCallIfPossible( + CallBase &CB, InlineFunctionInfo &IFI, + InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory, + bool InsertLifetime, function_ref<AAResults &(Function &)> &AARGetter, + ImportedFunctionsInliningStatistics &ImportedFunctionsStats) { + Function *Callee = CB.getCalledFunction(); + Function *Caller = CB.getCaller(); + + AAResults &AAR = AARGetter(*Callee); + + // Try to inline the function. Get the list of static allocas that were + // inlined. + InlineResult IR = InlineFunction(CB, IFI, &AAR, InsertLifetime); + if (!IR.isSuccess()) + return IR; + + if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No) + ImportedFunctionsStats.recordInline(*Caller, *Callee); + + AttributeFuncs::mergeAttributesForInlining(*Caller, *Callee); + + if (!DisableInlinedAllocaMerging) + mergeInlinedArrayAllocas(Caller, IFI, InlinedArrayAllocas, InlineHistory); + + return IR; // success +} + +/// Return true if the specified inline history ID +/// indicates an inline history that includes the specified function. +static bool inlineHistoryIncludes( + Function *F, int InlineHistoryID, + const SmallVectorImpl<std::pair<Function *, int>> &InlineHistory) { + while (InlineHistoryID != -1) { + assert(unsigned(InlineHistoryID) < InlineHistory.size() && + "Invalid inline history ID"); + if (InlineHistory[InlineHistoryID].first == F) + return true; + InlineHistoryID = InlineHistory[InlineHistoryID].second; + } + return false; +} + +bool LegacyInlinerBase::doInitialization(CallGraph &CG) { + if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No) + ImportedFunctionsStats.setModuleInfo(CG.getModule()); + return false; // No changes to CallGraph. +} + +bool LegacyInlinerBase::runOnSCC(CallGraphSCC &SCC) { + if (skipSCC(SCC)) + return false; + return inlineCalls(SCC); +} + +static bool +inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG, + std::function<AssumptionCache &(Function &)> GetAssumptionCache, + ProfileSummaryInfo *PSI, + std::function<const TargetLibraryInfo &(Function &)> GetTLI, + bool InsertLifetime, + function_ref<InlineCost(CallBase &CB)> GetInlineCost, + function_ref<AAResults &(Function &)> AARGetter, + ImportedFunctionsInliningStatistics &ImportedFunctionsStats) { + SmallPtrSet<Function *, 8> SCCFunctions; + LLVM_DEBUG(dbgs() << "Inliner visiting SCC:"); + for (CallGraphNode *Node : SCC) { + Function *F = Node->getFunction(); + if (F) + SCCFunctions.insert(F); + LLVM_DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE")); + } + + // Scan through and identify all call sites ahead of time so that we only + // inline call sites in the original functions, not call sites that result + // from inlining other functions. + SmallVector<std::pair<CallBase *, int>, 16> CallSites; + + // When inlining a callee produces new call sites, we want to keep track of + // the fact that they were inlined from the callee. This allows us to avoid + // infinite inlining in some obscure cases. To represent this, we use an + // index into the InlineHistory vector. + SmallVector<std::pair<Function *, int>, 8> InlineHistory; + + for (CallGraphNode *Node : SCC) { + Function *F = Node->getFunction(); + if (!F || F->isDeclaration()) + continue; + + OptimizationRemarkEmitter ORE(F); + for (BasicBlock &BB : *F) + for (Instruction &I : BB) { + auto *CB = dyn_cast<CallBase>(&I); + // If this isn't a call, or it is a call to an intrinsic, it can + // never be inlined. + if (!CB || isa<IntrinsicInst>(I)) + continue; + + // If this is a direct call to an external function, we can never inline + // it. If it is an indirect call, inlining may resolve it to be a + // direct call, so we keep it. + if (Function *Callee = CB->getCalledFunction()) + if (Callee->isDeclaration()) { + using namespace ore; + + setInlineRemark(*CB, "unavailable definition"); + ORE.emit([&]() { + return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I) + << NV("Callee", Callee) << " will not be inlined into " + << NV("Caller", CB->getCaller()) + << " because its definition is unavailable" + << setIsVerbose(); + }); + continue; + } + + CallSites.push_back(std::make_pair(CB, -1)); + } + } + + LLVM_DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n"); + + // If there are no calls in this function, exit early. + if (CallSites.empty()) + return false; + + // Now that we have all of the call sites, move the ones to functions in the + // current SCC to the end of the list. + unsigned FirstCallInSCC = CallSites.size(); + for (unsigned I = 0; I < FirstCallInSCC; ++I) + if (Function *F = CallSites[I].first->getCalledFunction()) + if (SCCFunctions.count(F)) + std::swap(CallSites[I--], CallSites[--FirstCallInSCC]); + + InlinedArrayAllocasTy InlinedArrayAllocas; + InlineFunctionInfo InlineInfo(&CG, GetAssumptionCache, PSI); + + // Now that we have all of the call sites, loop over them and inline them if + // it looks profitable to do so. + bool Changed = false; + bool LocalChange; + do { + LocalChange = false; + // Iterate over the outer loop because inlining functions can cause indirect + // calls to become direct calls. + // CallSites may be modified inside so ranged for loop can not be used. + for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { + auto &P = CallSites[CSi]; + CallBase &CB = *P.first; + const int InlineHistoryID = P.second; + + Function *Caller = CB.getCaller(); + Function *Callee = CB.getCalledFunction(); + + // We can only inline direct calls to non-declarations. + if (!Callee || Callee->isDeclaration()) + continue; + + bool IsTriviallyDead = isInstructionTriviallyDead(&CB, &GetTLI(*Caller)); + + if (!IsTriviallyDead) { + // If this call site was obtained by inlining another function, verify + // that the include path for the function did not include the callee + // itself. If so, we'd be recursively inlining the same function, + // which would provide the same callsites, which would cause us to + // infinitely inline. + if (InlineHistoryID != -1 && + inlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) { + setInlineRemark(CB, "recursive"); + continue; + } + } + + // FIXME for new PM: because of the old PM we currently generate ORE and + // in turn BFI on demand. With the new PM, the ORE dependency should + // just become a regular analysis dependency. + OptimizationRemarkEmitter ORE(Caller); + + auto OIC = shouldInline(CB, GetInlineCost, ORE); + // If the policy determines that we should inline this function, + // delete the call instead. + if (!OIC) + continue; + + // If this call site is dead and it is to a readonly function, we should + // just delete the call instead of trying to inline it, regardless of + // size. This happens because IPSCCP propagates the result out of the + // call and then we're left with the dead call. + if (IsTriviallyDead) { + LLVM_DEBUG(dbgs() << " -> Deleting dead call: " << CB << "\n"); + // Update the call graph by deleting the edge from Callee to Caller. + setInlineRemark(CB, "trivially dead"); + CG[Caller]->removeCallEdgeFor(CB); + CB.eraseFromParent(); + ++NumCallsDeleted; + } else { + // Get DebugLoc to report. CB will be invalid after Inliner. + DebugLoc DLoc = CB.getDebugLoc(); + BasicBlock *Block = CB.getParent(); + + // Attempt to inline the function. + using namespace ore; + + InlineResult IR = inlineCallIfPossible( + CB, InlineInfo, InlinedArrayAllocas, InlineHistoryID, + InsertLifetime, AARGetter, ImportedFunctionsStats); + if (!IR.isSuccess()) { + setInlineRemark(CB, std::string(IR.getFailureReason()) + "; " + + inlineCostStr(*OIC)); + ORE.emit([&]() { + return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc, + Block) + << NV("Callee", Callee) << " will not be inlined into " + << NV("Caller", Caller) << ": " + << NV("Reason", IR.getFailureReason()); + }); + continue; + } + ++NumInlined; + + emitInlinedInto(ORE, DLoc, Block, *Callee, *Caller, *OIC); + + // If inlining this function gave us any new call sites, throw them + // onto our worklist to process. They are useful inline candidates. + if (!InlineInfo.InlinedCalls.empty()) { + // Create a new inline history entry for this, so that we remember + // that these new callsites came about due to inlining Callee. + int NewHistoryID = InlineHistory.size(); + InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID)); + +#ifndef NDEBUG + // Make sure no dupplicates in the inline candidates. This could + // happen when a callsite is simpilfied to reusing the return value + // of another callsite during function cloning, thus the other + // callsite will be reconsidered here. + DenseSet<CallBase *> DbgCallSites; + for (auto &II : CallSites) + DbgCallSites.insert(II.first); +#endif + + for (Value *Ptr : InlineInfo.InlinedCalls) { +#ifndef NDEBUG + assert(DbgCallSites.count(dyn_cast<CallBase>(Ptr)) == 0); +#endif + CallSites.push_back( + std::make_pair(dyn_cast<CallBase>(Ptr), NewHistoryID)); + } + } + } + + // If we inlined or deleted the last possible call site to the function, + // delete the function body now. + if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() && + // TODO: Can remove if in SCC now. + !SCCFunctions.count(Callee) && + // The function may be apparently dead, but if there are indirect + // callgraph references to the node, we cannot delete it yet, this + // could invalidate the CGSCC iterator. + CG[Callee]->getNumReferences() == 0) { + LLVM_DEBUG(dbgs() << " -> Deleting dead function: " + << Callee->getName() << "\n"); + CallGraphNode *CalleeNode = CG[Callee]; + + // Remove any call graph edges from the callee to its callees. + CalleeNode->removeAllCalledFunctions(); + + // Removing the node for callee from the call graph and delete it. + delete CG.removeFunctionFromModule(CalleeNode); + ++NumDeleted; + } + + // Remove this call site from the list. If possible, use + // swap/pop_back for efficiency, but do not use it if doing so would + // move a call site to a function in this SCC before the + // 'FirstCallInSCC' barrier. + if (SCC.isSingular()) { + CallSites[CSi] = CallSites.back(); + CallSites.pop_back(); + } else { + CallSites.erase(CallSites.begin() + CSi); + } + --CSi; + + Changed = true; + LocalChange = true; + } + } while (LocalChange); + + return Changed; +} + +bool LegacyInlinerBase::inlineCalls(CallGraphSCC &SCC) { + CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph(); + ACT = &getAnalysis<AssumptionCacheTracker>(); + PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI(); + GetTLI = [&](Function &F) -> const TargetLibraryInfo & { + return getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); + }; + auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & { + return ACT->getAssumptionCache(F); + }; + return inlineCallsImpl( + SCC, CG, GetAssumptionCache, PSI, GetTLI, InsertLifetime, + [&](CallBase &CB) { return getInlineCost(CB); }, LegacyAARGetter(*this), + ImportedFunctionsStats); +} + +/// Remove now-dead linkonce functions at the end of +/// processing to avoid breaking the SCC traversal. +bool LegacyInlinerBase::doFinalization(CallGraph &CG) { + if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No) + ImportedFunctionsStats.dump(InlinerFunctionImportStats == + InlinerFunctionImportStatsOpts::Verbose); + return removeDeadFunctions(CG); +} + +/// Remove dead functions that are not included in DNR (Do Not Remove) list. +bool LegacyInlinerBase::removeDeadFunctions(CallGraph &CG, + bool AlwaysInlineOnly) { + SmallVector<CallGraphNode *, 16> FunctionsToRemove; + SmallVector<Function *, 16> DeadFunctionsInComdats; + + auto RemoveCGN = [&](CallGraphNode *CGN) { + // Remove any call graph edges from the function to its callees. + CGN->removeAllCalledFunctions(); + + // Remove any edges from the external node to the function's call graph + // node. These edges might have been made irrelegant due to + // optimization of the program. + CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN); + + // Removing the node for callee from the call graph and delete it. + FunctionsToRemove.push_back(CGN); + }; + + // Scan for all of the functions, looking for ones that should now be removed + // from the program. Insert the dead ones in the FunctionsToRemove set. + for (const auto &I : CG) { + CallGraphNode *CGN = I.second.get(); + Function *F = CGN->getFunction(); + if (!F || F->isDeclaration()) + continue; + + // Handle the case when this function is called and we only want to care + // about always-inline functions. This is a bit of a hack to share code + // between here and the InlineAlways pass. + if (AlwaysInlineOnly && !F->hasFnAttribute(Attribute::AlwaysInline)) + continue; + + // If the only remaining users of the function are dead constants, remove + // them. + F->removeDeadConstantUsers(); + + if (!F->isDefTriviallyDead()) + continue; + + // It is unsafe to drop a function with discardable linkage from a COMDAT + // without also dropping the other members of the COMDAT. + // The inliner doesn't visit non-function entities which are in COMDAT + // groups so it is unsafe to do so *unless* the linkage is local. + if (!F->hasLocalLinkage()) { + if (F->hasComdat()) { + DeadFunctionsInComdats.push_back(F); + continue; + } + } + + RemoveCGN(CGN); + } + if (!DeadFunctionsInComdats.empty()) { + // Filter out the functions whose comdats remain alive. + filterDeadComdatFunctions(CG.getModule(), DeadFunctionsInComdats); + // Remove the rest. + for (Function *F : DeadFunctionsInComdats) + RemoveCGN(CG[F]); + } + + if (FunctionsToRemove.empty()) + return false; + + // Now that we know which functions to delete, do so. We didn't want to do + // this inline, because that would invalidate our CallGraph::iterator + // objects. :( + // + // Note that it doesn't matter that we are iterating over a non-stable order + // here to do this, it doesn't matter which order the functions are deleted + // in. + array_pod_sort(FunctionsToRemove.begin(), FunctionsToRemove.end()); + FunctionsToRemove.erase( + std::unique(FunctionsToRemove.begin(), FunctionsToRemove.end()), + FunctionsToRemove.end()); + for (CallGraphNode *CGN : FunctionsToRemove) { + delete CG.removeFunctionFromModule(CGN); + ++NumDeleted; + } + return true; +} + +InlineAdvisor & +InlinerPass::getAdvisor(const ModuleAnalysisManagerCGSCCProxy::Result &MAM, + FunctionAnalysisManager &FAM, Module &M) { + if (OwnedAdvisor) + return *OwnedAdvisor; + + auto *IAA = MAM.getCachedResult<InlineAdvisorAnalysis>(M); + if (!IAA) { + // It should still be possible to run the inliner as a stand-alone SCC pass, + // for test scenarios. In that case, we default to the + // DefaultInlineAdvisor, which doesn't need to keep state between SCC pass + // runs. It also uses just the default InlineParams. + // In this case, we need to use the provided FAM, which is valid for the + // duration of the inliner pass, and thus the lifetime of the owned advisor. + // The one we would get from the MAM can be invalidated as a result of the + // inliner's activity. + OwnedAdvisor = + std::make_unique<DefaultInlineAdvisor>(M, FAM, getInlineParams()); + + if (!CGSCCInlineReplayFile.empty()) + OwnedAdvisor = std::make_unique<ReplayInlineAdvisor>( + M, FAM, M.getContext(), std::move(OwnedAdvisor), + CGSCCInlineReplayFile, + /*EmitRemarks=*/true); + + return *OwnedAdvisor; + } + assert(IAA->getAdvisor() && + "Expected a present InlineAdvisorAnalysis also have an " + "InlineAdvisor initialized"); + return *IAA->getAdvisor(); +} + +PreservedAnalyses InlinerPass::run(LazyCallGraph::SCC &InitialC, + CGSCCAnalysisManager &AM, LazyCallGraph &CG, + CGSCCUpdateResult &UR) { + const auto &MAMProxy = + AM.getResult<ModuleAnalysisManagerCGSCCProxy>(InitialC, CG); + bool Changed = false; + + assert(InitialC.size() > 0 && "Cannot handle an empty SCC!"); + Module &M = *InitialC.begin()->getFunction().getParent(); + ProfileSummaryInfo *PSI = MAMProxy.getCachedResult<ProfileSummaryAnalysis>(M); + + FunctionAnalysisManager &FAM = + AM.getResult<FunctionAnalysisManagerCGSCCProxy>(InitialC, CG) + .getManager(); + + InlineAdvisor &Advisor = getAdvisor(MAMProxy, FAM, M); + Advisor.onPassEntry(); + + auto AdvisorOnExit = make_scope_exit([&] { Advisor.onPassExit(); }); + + // We use a single common worklist for calls across the entire SCC. We + // process these in-order and append new calls introduced during inlining to + // the end. + // + // Note that this particular order of processing is actually critical to + // avoid very bad behaviors. Consider *highly connected* call graphs where + // each function contains a small amount of code and a couple of calls to + // other functions. Because the LLVM inliner is fundamentally a bottom-up + // inliner, it can handle gracefully the fact that these all appear to be + // reasonable inlining candidates as it will flatten things until they become + // too big to inline, and then move on and flatten another batch. + // + // However, when processing call edges *within* an SCC we cannot rely on this + // bottom-up behavior. As a consequence, with heavily connected *SCCs* of + // functions we can end up incrementally inlining N calls into each of + // N functions because each incremental inlining decision looks good and we + // don't have a topological ordering to prevent explosions. + // + // To compensate for this, we don't process transitive edges made immediate + // by inlining until we've done one pass of inlining across the entire SCC. + // Large, highly connected SCCs still lead to some amount of code bloat in + // this model, but it is uniformly spread across all the functions in the SCC + // and eventually they all become too large to inline, rather than + // incrementally maknig a single function grow in a super linear fashion. + SmallVector<std::pair<CallBase *, int>, 16> Calls; + + // Populate the initial list of calls in this SCC. + for (auto &N : InitialC) { + auto &ORE = + FAM.getResult<OptimizationRemarkEmitterAnalysis>(N.getFunction()); + // We want to generally process call sites top-down in order for + // simplifications stemming from replacing the call with the returned value + // after inlining to be visible to subsequent inlining decisions. + // FIXME: Using instructions sequence is a really bad way to do this. + // Instead we should do an actual RPO walk of the function body. + for (Instruction &I : instructions(N.getFunction())) + if (auto *CB = dyn_cast<CallBase>(&I)) + if (Function *Callee = CB->getCalledFunction()) { + if (!Callee->isDeclaration()) + Calls.push_back({CB, -1}); + else if (!isa<IntrinsicInst>(I)) { + using namespace ore; + setInlineRemark(*CB, "unavailable definition"); + ORE.emit([&]() { + return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I) + << NV("Callee", Callee) << " will not be inlined into " + << NV("Caller", CB->getCaller()) + << " because its definition is unavailable" + << setIsVerbose(); + }); + } + } + } + if (Calls.empty()) + return PreservedAnalyses::all(); + + // Capture updatable variable for the current SCC. + auto *C = &InitialC; + + // When inlining a callee produces new call sites, we want to keep track of + // the fact that they were inlined from the callee. This allows us to avoid + // infinite inlining in some obscure cases. To represent this, we use an + // index into the InlineHistory vector. + SmallVector<std::pair<Function *, int>, 16> InlineHistory; + + // Track a set vector of inlined callees so that we can augment the caller + // with all of their edges in the call graph before pruning out the ones that + // got simplified away. + SmallSetVector<Function *, 4> InlinedCallees; + + // Track the dead functions to delete once finished with inlining calls. We + // defer deleting these to make it easier to handle the call graph updates. + SmallVector<Function *, 4> DeadFunctions; + + // Loop forward over all of the calls. Note that we cannot cache the size as + // inlining can introduce new calls that need to be processed. + for (int I = 0; I < (int)Calls.size(); ++I) { + // We expect the calls to typically be batched with sequences of calls that + // have the same caller, so we first set up some shared infrastructure for + // this caller. We also do any pruning we can at this layer on the caller + // alone. + Function &F = *Calls[I].first->getCaller(); + LazyCallGraph::Node &N = *CG.lookup(F); + if (CG.lookupSCC(N) != C) + continue; + + LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n"); + + auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & { + return FAM.getResult<AssumptionAnalysis>(F); + }; + + // Now process as many calls as we have within this caller in the sequence. + // We bail out as soon as the caller has to change so we can update the + // call graph and prepare the context of that new caller. + bool DidInline = false; + for (; I < (int)Calls.size() && Calls[I].first->getCaller() == &F; ++I) { + auto &P = Calls[I]; + CallBase *CB = P.first; + const int InlineHistoryID = P.second; + Function &Callee = *CB->getCalledFunction(); + + if (InlineHistoryID != -1 && + inlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory)) { + setInlineRemark(*CB, "recursive"); + continue; + } + + // Check if this inlining may repeat breaking an SCC apart that has + // already been split once before. In that case, inlining here may + // trigger infinite inlining, much like is prevented within the inliner + // itself by the InlineHistory above, but spread across CGSCC iterations + // and thus hidden from the full inline history. + if (CG.lookupSCC(*CG.lookup(Callee)) == C && + UR.InlinedInternalEdges.count({&N, C})) { + LLVM_DEBUG(dbgs() << "Skipping inlining internal SCC edge from a node " + "previously split out of this SCC by inlining: " + << F.getName() << " -> " << Callee.getName() << "\n"); + setInlineRemark(*CB, "recursive SCC split"); + continue; + } + + auto Advice = Advisor.getAdvice(*CB, OnlyMandatory); + // Check whether we want to inline this callsite. + if (!Advice->isInliningRecommended()) { + Advice->recordUnattemptedInlining(); + continue; + } + + // Setup the data structure used to plumb customization into the + // `InlineFunction` routine. + InlineFunctionInfo IFI( + /*cg=*/nullptr, GetAssumptionCache, PSI, + &FAM.getResult<BlockFrequencyAnalysis>(*(CB->getCaller())), + &FAM.getResult<BlockFrequencyAnalysis>(Callee)); + + InlineResult IR = + InlineFunction(*CB, IFI, &FAM.getResult<AAManager>(*CB->getCaller())); + if (!IR.isSuccess()) { + Advice->recordUnsuccessfulInlining(IR); + continue; + } + + DidInline = true; + InlinedCallees.insert(&Callee); + ++NumInlined; + + // Add any new callsites to defined functions to the worklist. + if (!IFI.InlinedCallSites.empty()) { + int NewHistoryID = InlineHistory.size(); + InlineHistory.push_back({&Callee, InlineHistoryID}); + + for (CallBase *ICB : reverse(IFI.InlinedCallSites)) { + Function *NewCallee = ICB->getCalledFunction(); + if (!NewCallee) { + // Try to promote an indirect (virtual) call without waiting for + // the post-inline cleanup and the next DevirtSCCRepeatedPass + // iteration because the next iteration may not happen and we may + // miss inlining it. + if (tryPromoteCall(*ICB)) + NewCallee = ICB->getCalledFunction(); + } + if (NewCallee) + if (!NewCallee->isDeclaration()) + Calls.push_back({ICB, NewHistoryID}); + } + } + + // Merge the attributes based on the inlining. + AttributeFuncs::mergeAttributesForInlining(F, Callee); + + // For local functions, check whether this makes the callee trivially + // dead. In that case, we can drop the body of the function eagerly + // which may reduce the number of callers of other functions to one, + // changing inline cost thresholds. + bool CalleeWasDeleted = false; + if (Callee.hasLocalLinkage()) { + // To check this we also need to nuke any dead constant uses (perhaps + // made dead by this operation on other functions). + Callee.removeDeadConstantUsers(); + if (Callee.use_empty() && !CG.isLibFunction(Callee)) { + Calls.erase( + std::remove_if(Calls.begin() + I + 1, Calls.end(), + [&](const std::pair<CallBase *, int> &Call) { + return Call.first->getCaller() == &Callee; + }), + Calls.end()); + // Clear the body and queue the function itself for deletion when we + // finish inlining and call graph updates. + // Note that after this point, it is an error to do anything other + // than use the callee's address or delete it. + Callee.dropAllReferences(); + assert(!is_contained(DeadFunctions, &Callee) && + "Cannot put cause a function to become dead twice!"); + DeadFunctions.push_back(&Callee); + CalleeWasDeleted = true; + } + } + if (CalleeWasDeleted) + Advice->recordInliningWithCalleeDeleted(); + else + Advice->recordInlining(); + } + + // Back the call index up by one to put us in a good position to go around + // the outer loop. + --I; + + if (!DidInline) + continue; + Changed = true; + + // At this point, since we have made changes we have at least removed + // a call instruction. However, in the process we do some incremental + // simplification of the surrounding code. This simplification can + // essentially do all of the same things as a function pass and we can + // re-use the exact same logic for updating the call graph to reflect the + // change. + + // Inside the update, we also update the FunctionAnalysisManager in the + // proxy for this particular SCC. We do this as the SCC may have changed and + // as we're going to mutate this particular function we want to make sure + // the proxy is in place to forward any invalidation events. + LazyCallGraph::SCC *OldC = C; + C = &updateCGAndAnalysisManagerForCGSCCPass(CG, *C, N, AM, UR, FAM); + LLVM_DEBUG(dbgs() << "Updated inlining SCC: " << *C << "\n"); + + // If this causes an SCC to split apart into multiple smaller SCCs, there + // is a subtle risk we need to prepare for. Other transformations may + // expose an "infinite inlining" opportunity later, and because of the SCC + // mutation, we will revisit this function and potentially re-inline. If we + // do, and that re-inlining also has the potentially to mutate the SCC + // structure, the infinite inlining problem can manifest through infinite + // SCC splits and merges. To avoid this, we capture the originating caller + // node and the SCC containing the call edge. This is a slight over + // approximation of the possible inlining decisions that must be avoided, + // but is relatively efficient to store. We use C != OldC to know when + // a new SCC is generated and the original SCC may be generated via merge + // in later iterations. + // + // It is also possible that even if no new SCC is generated + // (i.e., C == OldC), the original SCC could be split and then merged + // into the same one as itself. and the original SCC will be added into + // UR.CWorklist again, we want to catch such cases too. + // + // FIXME: This seems like a very heavyweight way of retaining the inline + // history, we should look for a more efficient way of tracking it. + if ((C != OldC || UR.CWorklist.count(OldC)) && + llvm::any_of(InlinedCallees, [&](Function *Callee) { + return CG.lookupSCC(*CG.lookup(*Callee)) == OldC; + })) { + LLVM_DEBUG(dbgs() << "Inlined an internal call edge and split an SCC, " + "retaining this to avoid infinite inlining.\n"); + UR.InlinedInternalEdges.insert({&N, OldC}); + } + InlinedCallees.clear(); + } + + // Now that we've finished inlining all of the calls across this SCC, delete + // all of the trivially dead functions, updating the call graph and the CGSCC + // pass manager in the process. + // + // Note that this walks a pointer set which has non-deterministic order but + // that is OK as all we do is delete things and add pointers to unordered + // sets. + for (Function *DeadF : DeadFunctions) { + // Get the necessary information out of the call graph and nuke the + // function there. Also, clear out any cached analyses. + auto &DeadC = *CG.lookupSCC(*CG.lookup(*DeadF)); + FAM.clear(*DeadF, DeadF->getName()); + AM.clear(DeadC, DeadC.getName()); + auto &DeadRC = DeadC.getOuterRefSCC(); + CG.removeDeadFunction(*DeadF); + + // Mark the relevant parts of the call graph as invalid so we don't visit + // them. + UR.InvalidatedSCCs.insert(&DeadC); + UR.InvalidatedRefSCCs.insert(&DeadRC); + + // And delete the actual function from the module. + // The Advisor may use Function pointers to efficiently index various + // internal maps, e.g. for memoization. Function cleanup passes like + // argument promotion create new functions. It is possible for a new + // function to be allocated at the address of a deleted function. We could + // index using names, but that's inefficient. Alternatively, we let the + // Advisor free the functions when it sees fit. + DeadF->getBasicBlockList().clear(); + M.getFunctionList().remove(DeadF); + + ++NumDeleted; + } + + if (!Changed) + return PreservedAnalyses::all(); + + // Even if we change the IR, we update the core CGSCC data structures and so + // can preserve the proxy to the function analysis manager. + PreservedAnalyses PA; + PA.preserve<FunctionAnalysisManagerCGSCCProxy>(); + return PA; +} + +ModuleInlinerWrapperPass::ModuleInlinerWrapperPass(InlineParams Params, + bool Debugging, + bool MandatoryFirst, + InliningAdvisorMode Mode, + unsigned MaxDevirtIterations) + : Params(Params), Mode(Mode), MaxDevirtIterations(MaxDevirtIterations), + PM(Debugging), MPM(Debugging) { + // Run the inliner first. The theory is that we are walking bottom-up and so + // the callees have already been fully optimized, and we want to inline them + // into the callers so that our optimizations can reflect that. + // For PreLinkThinLTO pass, we disable hot-caller heuristic for sample PGO + // because it makes profile annotation in the backend inaccurate. + if (MandatoryFirst) + PM.addPass(InlinerPass(/*OnlyMandatory*/ true)); + PM.addPass(InlinerPass()); +} + +PreservedAnalyses ModuleInlinerWrapperPass::run(Module &M, + ModuleAnalysisManager &MAM) { + auto &IAA = MAM.getResult<InlineAdvisorAnalysis>(M); + if (!IAA.tryCreate(Params, Mode, CGSCCInlineReplayFile)) { + M.getContext().emitError( + "Could not setup Inlining Advisor for the requested " + "mode and/or options"); + return PreservedAnalyses::all(); + } + + // We wrap the CGSCC pipeline in a devirtualization repeater. This will try + // to detect when we devirtualize indirect calls and iterate the SCC passes + // in that case to try and catch knock-on inlining or function attrs + // opportunities. Then we add it to the module pipeline by walking the SCCs + // in postorder (or bottom-up). + // If MaxDevirtIterations is 0, we just don't use the devirtualization + // wrapper. + if (MaxDevirtIterations == 0) + MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(std::move(PM))); + else + MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor( + createDevirtSCCRepeatedPass(std::move(PM), MaxDevirtIterations))); + auto Ret = MPM.run(M, MAM); + + IAA.clear(); + return Ret; +} |