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 #include <memory> 21 22 using namespace llvm; 23 24 #define DEBUG_TYPE "pgo-icall-prom-analysis" 25 26 // The percent threshold for the direct-call target (this call site vs the 27 // remaining call count) for it to be considered as the promotion target. 28 static cl::opt<unsigned> ICPRemainingPercentThreshold( 29 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, 30 cl::desc("The percentage threshold against remaining unpromoted indirect " 31 "call count for the promotion")); 32 33 // The percent threshold for the direct-call target (this call site vs the 34 // total call count) for it to be considered as the promotion target. 35 static cl::opt<unsigned> 36 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5), 37 cl::Hidden, 38 cl::desc("The percentage threshold against total " 39 "count for the promotion")); 40 41 // Set the maximum number of targets to promote for a single indirect-call 42 // callsite. 43 static cl::opt<unsigned> 44 MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, 45 cl::desc("Max number of promotions for a single indirect " 46 "call callsite")); 47 48 cl::opt<unsigned> MaxNumVTableAnnotations( 49 "icp-max-num-vtables", cl::init(6), cl::Hidden, 50 cl::desc("Max number of vtables annotated for a vtable load instruction.")); 51 52 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count, 53 uint64_t TotalCount, 54 uint64_t RemainingCount) { 55 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount && 56 Count * 100 >= ICPTotalPercentThreshold * TotalCount; 57 } 58 59 // Indirect-call promotion heuristic. The direct targets are sorted based on 60 // the count. Stop at the first target that is not promoted. Returns the 61 // number of candidates deemed profitable. 62 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates( 63 const Instruction *Inst, uint64_t TotalCount) { 64 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst 65 << " Num_targets: " << ValueDataArray.size() << "\n"); 66 67 uint32_t I = 0; 68 uint64_t RemainingCount = TotalCount; 69 for (; I < MaxNumPromotions && I < ValueDataArray.size(); I++) { 70 uint64_t Count = ValueDataArray[I].Count; 71 assert(Count <= RemainingCount); 72 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count 73 << " Target_func: " << ValueDataArray[I].Value << "\n"); 74 75 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) { 76 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n"); 77 return I; 78 } 79 RemainingCount -= Count; 80 } 81 return I; 82 } 83 84 MutableArrayRef<InstrProfValueData> 85 ICallPromotionAnalysis::getPromotionCandidatesForInstruction( 86 const Instruction *I, uint64_t &TotalCount, uint32_t &NumCandidates) { 87 ValueDataArray = getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, 88 MaxNumPromotions, TotalCount); 89 if (ValueDataArray.empty()) { 90 NumCandidates = 0; 91 return MutableArrayRef<InstrProfValueData>(); 92 } 93 NumCandidates = getProfitablePromotionCandidates(I, TotalCount); 94 return ValueDataArray; 95 } 96