//===- Inliner.cpp - Code common to all inliners --------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // 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. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "inline" #include "llvm/Module.h" #include "llvm/Instructions.h" #include "llvm/IntrinsicInst.h" #include "llvm/Analysis/CallGraph.h" #include "llvm/Analysis/InlineCost.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetLibraryInfo.h" #include "llvm/Transforms/IPO/InlinerPass.h" #include "llvm/Transforms/Utils/Cloning.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Support/CallSite.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" using namespace llvm; 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"); // This weirdly named statistic tracks the number of times that, when attempting // to inline a function A into B, we analyze the callers of B in order to see // if those would be more profitable and blocked inline steps. STATISTIC(NumCallerCallersAnalyzed, "Number of caller-callers analyzed"); static cl::opt<int> InlineLimit("inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore, cl::desc("Control the amount of inlining to perform (default = 225)")); static cl::opt<int> HintThreshold("inlinehint-threshold", cl::Hidden, cl::init(325), cl::desc("Threshold for inlining functions with inline hint")); // Threshold to use when optsize is specified (and there is no -inline-limit). const int OptSizeThreshold = 75; Inliner::Inliner(char &ID) : CallGraphSCCPass(ID), InlineThreshold(InlineLimit), InsertLifetime(true) {} Inliner::Inliner(char &ID, int Threshold, bool InsertLifetime) : CallGraphSCCPass(ID), InlineThreshold(InlineLimit.getNumOccurrences() > 0 ? InlineLimit : Threshold), InsertLifetime(InsertLifetime) {} /// getAnalysisUsage - 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 Inliner::getAnalysisUsage(AnalysisUsage &Info) const { CallGraphSCCPass::getAnalysisUsage(Info); } typedef DenseMap<ArrayType*, std::vector<AllocaInst*> > InlinedArrayAllocasTy; /// InlineCallIfPossible - 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 bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI, InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory, bool InsertLifetime) { Function *Callee = CS.getCalledFunction(); Function *Caller = CS.getCaller(); // Try to inline the function. Get the list of static allocas that were // inlined. if (!InlineFunction(CS, IFI, InsertLifetime)) return false; // If the inlined function had a higher stack protection level than the // calling function, then bump up the caller's stack protection level. if (Callee->getFnAttributes().hasStackProtectReqAttr()) Caller->addFnAttr(Attribute::StackProtectReq); else if (Callee->getFnAttributes().hasStackProtectAttr() && !Caller->getFnAttributes().hasStackProtectReqAttr()) Caller->addFnAttr(Attribute::StackProtect); // 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. // SmallPtrSet<AllocaInst*, 16> UsedAllocas; // When processing our SCC, check to see if CS 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 true; // 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 == 0 || 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 (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) { AllocaInst *AvailableAlloca = AllocasForType[i]; // 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)) continue; // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare // success! DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI << "\n\t\tINTO: " << *AvailableAlloca << '\n'); AI->replaceAllUsesWith(AvailableAlloca); AI->eraseFromParent(); MergedAwayAlloca = true; ++NumMergedAllocas; IFI.StaticAllocas[AllocaNo] = 0; 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); } return true; } unsigned Inliner::getInlineThreshold(CallSite CS) const { int thres = InlineThreshold; // -inline-threshold or else selected by // overall opt level // If -inline-threshold is not given, listen to the optsize attribute when it // would decrease the threshold. Function *Caller = CS.getCaller(); bool OptSize = Caller && !Caller->isDeclaration() && Caller->getFnAttributes().hasOptimizeForSizeAttr(); if (!(InlineLimit.getNumOccurrences() > 0) && OptSize && OptSizeThreshold < thres) thres = OptSizeThreshold; // Listen to the inlinehint attribute when it would increase the threshold. Function *Callee = CS.getCalledFunction(); bool InlineHint = Callee && !Callee->isDeclaration() && Callee->getFnAttributes().hasInlineHintAttr(); if (InlineHint && HintThreshold > thres) thres = HintThreshold; return thres; } /// shouldInline - Return true if the inliner should attempt to inline /// at the given CallSite. bool Inliner::shouldInline(CallSite CS) { InlineCost IC = getInlineCost(CS); if (IC.isAlways()) { DEBUG(dbgs() << " Inlining: cost=always" << ", Call: " << *CS.getInstruction() << "\n"); return true; } if (IC.isNever()) { DEBUG(dbgs() << " NOT Inlining: cost=never" << ", Call: " << *CS.getInstruction() << "\n"); return false; } Function *Caller = CS.getCaller(); if (!IC) { DEBUG(dbgs() << " NOT Inlining: cost=" << IC.getCost() << ", thres=" << (IC.getCostDelta() + IC.getCost()) << ", Call: " << *CS.getInstruction() << "\n"); return false; } // Try to detect the case where the current inlining candidate caller (call // it B) is a static or linkonce-ODR function and is an inlining candidate // elsewhere, and the current candidate callee (call it C) is large enough // that inlining it into B would make B too big to inline later. In these // circumstances it may be best not to inline C into B, but to inline B into // its callers. // // This only applies to static and linkonce-ODR functions because those are // expected to be available for inlining in the translation units where they // are used. Thus we will always have the opportunity to make local inlining // decisions. Importantly the linkonce-ODR linkage covers inline functions // and templates in C++. // // FIXME: All of this logic should be sunk into getInlineCost. It relies on // the internal implementation of the inline cost metrics rather than // treating them as truly abstract units etc. if (Caller->hasLocalLinkage() || Caller->getLinkage() == GlobalValue::LinkOnceODRLinkage) { int TotalSecondaryCost = 0; // The candidate cost to be imposed upon the current function. int CandidateCost = IC.getCost() - (InlineConstants::CallPenalty + 1); // This bool tracks what happens if we do NOT inline C into B. bool callerWillBeRemoved = Caller->hasLocalLinkage(); // This bool tracks what happens if we DO inline C into B. bool inliningPreventsSomeOuterInline = false; for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end(); I != E; ++I) { CallSite CS2(*I); // If this isn't a call to Caller (it could be some other sort // of reference) skip it. Such references will prevent the caller // from being removed. if (!CS2 || CS2.getCalledFunction() != Caller) { callerWillBeRemoved = false; continue; } InlineCost IC2 = getInlineCost(CS2); ++NumCallerCallersAnalyzed; if (!IC2) { callerWillBeRemoved = false; continue; } if (IC2.isAlways()) continue; // See if inlining or original callsite would erase the cost delta of // this callsite. We subtract off the penalty for the call instruction, // which we would be deleting. if (IC2.getCostDelta() <= CandidateCost) { inliningPreventsSomeOuterInline = true; TotalSecondaryCost += IC2.getCost(); } } // If all outer calls to Caller would get inlined, the cost for the last // one is set very low by getInlineCost, in anticipation that Caller will // be removed entirely. We did not account for this above unless there // is only one caller of Caller. if (callerWillBeRemoved && Caller->use_begin() != Caller->use_end()) TotalSecondaryCost += InlineConstants::LastCallToStaticBonus; if (inliningPreventsSomeOuterInline && TotalSecondaryCost < IC.getCost()) { DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() << " Cost = " << IC.getCost() << ", outer Cost = " << TotalSecondaryCost << '\n'); return false; } } DEBUG(dbgs() << " Inlining: cost=" << IC.getCost() << ", thres=" << (IC.getCostDelta() + IC.getCost()) << ", Call: " << *CS.getInstruction() << '\n'); return true; } /// InlineHistoryIncludes - 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 Inliner::runOnSCC(CallGraphSCC &SCC) { CallGraph &CG = getAnalysis<CallGraph>(); const TargetData *TD = getAnalysisIfAvailable<TargetData>(); const TargetLibraryInfo *TLI = getAnalysisIfAvailable<TargetLibraryInfo>(); SmallPtrSet<Function*, 8> SCCFunctions; DEBUG(dbgs() << "Inliner visiting SCC:"); for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { Function *F = (*I)->getFunction(); if (F) SCCFunctions.insert(F); 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<CallSite, 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 (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { Function *F = (*I)->getFunction(); if (!F) continue; for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { CallSite CS(cast<Value>(I)); // If this isn't a call, or it is a call to an intrinsic, it can // never be inlined. if (!CS || 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 (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration()) continue; CallSites.push_back(std::make_pair(CS, -1)); } } 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, TD); // 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. for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) { CallSite CS = CallSites[CSi].first; Function *Caller = CS.getCaller(); Function *Callee = CS.getCalledFunction(); // 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 (isInstructionTriviallyDead(CS.getInstruction(), TLI)) { DEBUG(dbgs() << " -> Deleting dead call: " << *CS.getInstruction() << "\n"); // Update the call graph by deleting the edge from Callee to Caller. CG[Caller]->removeCallEdgeFor(CS); CS.getInstruction()->eraseFromParent(); ++NumCallsDeleted; } else { // We can only inline direct calls to non-declarations. if (Callee == 0 || Callee->isDeclaration()) continue; // 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. int InlineHistoryID = CallSites[CSi].second; if (InlineHistoryID != -1 && InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) continue; // If the policy determines that we should inline this function, // try to do so. if (!shouldInline(CS)) continue; // Attempt to inline the function. if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas, InlineHistoryID, InsertLifetime)) continue; ++NumInlined; // 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)); for (unsigned i = 0, e = InlineInfo.InlinedCalls.size(); i != e; ++i) { Value *Ptr = InlineInfo.InlinedCalls[i]; CallSites.push_back(std::make_pair(CallSite(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) { 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; } // doFinalization - Remove now-dead linkonce functions at the end of // processing to avoid breaking the SCC traversal. bool Inliner::doFinalization(CallGraph &CG) { return removeDeadFunctions(CG); } /// removeDeadFunctions - Remove dead functions that are not included in /// DNR (Do Not Remove) list. bool Inliner::removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly) { SmallVector<CallGraphNode*, 16> FunctionsToRemove; // 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 (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) { CallGraphNode *CGN = I->second; 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->getFnAttributes().hasAlwaysInlineAttr()) continue; // If the only remaining users of the function are dead constants, remove // them. F->removeDeadConstantUsers(); if (!F->isDefTriviallyDead()) continue; // 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); } 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 (SmallVectorImpl<CallGraphNode *>::iterator I = FunctionsToRemove.begin(), E = FunctionsToRemove.end(); I != E; ++I) { delete CG.removeFunctionFromModule(*I); ++NumDeleted; } return true; }