1 //===-- IndirectCallPromotionAnalysis.cpp - Find promotion candidates ===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // Helper methods for identifying profitable indirect call promotion 10 // candidates for an instruction when the indirect-call value profile metadata 11 // is available. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Analysis/IndirectCallPromotionAnalysis.h" 16 #include "llvm/IR/Instruction.h" 17 #include "llvm/ProfileData/InstrProf.h" 18 #include "llvm/Support/CommandLine.h" 19 #include "llvm/Support/Debug.h" 20 21 using namespace llvm; 22 23 #define DEBUG_TYPE "pgo-icall-prom-analysis" 24 25 // The percent threshold for the direct-call target (this call site vs the 26 // remaining call count) for it to be considered as the promotion target. 27 static cl::opt<unsigned> ICPRemainingPercentThreshold( 28 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, 29 cl::desc("The percentage threshold against remaining unpromoted indirect " 30 "call count for the promotion")); 31 32 // The percent threshold for the direct-call target (this call site vs the 33 // total call count) for it to be considered as the promotion target. 34 static cl::opt<uint64_t> 35 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5), 36 cl::Hidden, 37 cl::desc("The percentage threshold against total " 38 "count for the promotion")); 39 40 // Set the minimum absolute count threshold for indirect call promotion. 41 // Candidates with counts below this threshold will not be promoted. 42 static cl::opt<unsigned> ICPMinimumCountThreshold( 43 "icp-minimum-count-threshold", cl::init(0), cl::Hidden, 44 cl::desc("Minimum absolute count for promotion candidate")); 45 46 // Set the maximum number of targets to promote for a single indirect-call 47 // callsite. 48 static cl::opt<unsigned> 49 MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, 50 cl::desc("Max number of promotions for a single indirect " 51 "call callsite")); 52 53 cl::opt<unsigned> MaxNumVTableAnnotations( 54 "icp-max-num-vtables", cl::init(6), cl::Hidden, 55 cl::desc("Max number of vtables annotated for a vtable load instruction.")); 56 57 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count, 58 uint64_t TotalCount, 59 uint64_t RemainingCount) { 60 return Count >= ICPMinimumCountThreshold && 61 Count * 100 >= ICPRemainingPercentThreshold * RemainingCount && 62 Count * 100 >= ICPTotalPercentThreshold * TotalCount; 63 } 64 65 // Indirect-call promotion heuristic. The direct targets are sorted based on 66 // the count. Stop at the first target that is not promoted. Returns the 67 // number of candidates deemed profitable. 68 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates( 69 const Instruction *Inst, uint64_t TotalCount) { 70 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst 71 << " Num_targets: " << ValueDataArray.size() << "\n"); 72 73 uint32_t I = 0; 74 uint64_t RemainingCount = TotalCount; 75 for (; I < MaxNumPromotions && I < ValueDataArray.size(); I++) { 76 uint64_t Count = ValueDataArray[I].Count; 77 assert(Count <= RemainingCount); 78 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count 79 << " Target_func: " << ValueDataArray[I].Value << "\n"); 80 81 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) { 82 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n"); 83 return I; 84 } 85 RemainingCount -= Count; 86 } 87 return I; 88 } 89 90 MutableArrayRef<InstrProfValueData> 91 ICallPromotionAnalysis::getPromotionCandidatesForInstruction( 92 const Instruction *I, uint64_t &TotalCount, uint32_t &NumCandidates) { 93 ValueDataArray = getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, 94 MaxNumPromotions, TotalCount); 95 if (ValueDataArray.empty()) { 96 NumCandidates = 0; 97 return MutableArrayRef<InstrProfValueData>(); 98 } 99 NumCandidates = getProfitablePromotionCandidates(I, TotalCount); 100 return ValueDataArray; 101 } 102