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/ADT/STLExtras.h" 17 #include "llvm/Analysis/IndirectCallVisitor.h" 18 #include "llvm/IR/InstIterator.h" 19 #include "llvm/IR/InstVisitor.h" 20 #include "llvm/IR/Instructions.h" 21 #include "llvm/IR/IntrinsicInst.h" 22 #include "llvm/ProfileData/InstrProf.h" 23 #include "llvm/Support/CommandLine.h" 24 #include "llvm/Support/Debug.h" 25 #include <memory> 26 27 using namespace llvm; 28 29 #define DEBUG_TYPE "pgo-icall-prom-analysis" 30 31 // The percent threshold for the direct-call target (this call site vs the 32 // remaining call count) for it to be considered as the promotion target. 33 static cl::opt<unsigned> ICPRemainingPercentThreshold( 34 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore, 35 cl::desc("The percentage threshold against remaining unpromoted indirect " 36 "call count for the promotion")); 37 38 // The percent threshold for the direct-call target (this call site vs the 39 // total call count) for it to be considered as the promotion target. 40 static cl::opt<unsigned> 41 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5), 42 cl::Hidden, cl::ZeroOrMore, 43 cl::desc("The percentage threshold against total " 44 "count for the promotion")); 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, cl::ZeroOrMore, 50 cl::desc("Max number of promotions for a single indirect " 51 "call callsite")); 52 53 ICallPromotionAnalysis::ICallPromotionAnalysis() { 54 ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions); 55 } 56 57 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count, 58 uint64_t TotalCount, 59 uint64_t RemainingCount) { 60 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount && 61 Count * 100 >= ICPTotalPercentThreshold * TotalCount; 62 } 63 64 // Indirect-call promotion heuristic. The direct targets are sorted based on 65 // the count. Stop at the first target that is not promoted. Returns the 66 // number of candidates deemed profitable. 67 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates( 68 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) { 69 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals); 70 71 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst 72 << " Num_targets: " << NumVals << "\n"); 73 74 uint32_t I = 0; 75 uint64_t RemainingCount = TotalCount; 76 for (; I < MaxNumPromotions && I < NumVals; I++) { 77 uint64_t Count = ValueDataRef[I].Count; 78 assert(Count <= RemainingCount); 79 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count 80 << " Target_func: " << ValueDataRef[I].Value << "\n"); 81 82 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) { 83 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n"); 84 return I; 85 } 86 RemainingCount -= Count; 87 } 88 return I; 89 } 90 91 ArrayRef<InstrProfValueData> 92 ICallPromotionAnalysis::getPromotionCandidatesForInstruction( 93 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount, 94 uint32_t &NumCandidates) { 95 bool Res = 96 getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions, 97 ValueDataArray.get(), NumVals, TotalCount); 98 if (!Res) { 99 NumCandidates = 0; 100 return ArrayRef<InstrProfValueData>(); 101 } 102 NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount); 103 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals); 104 } 105