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 <string> 26 #include <utility> 27 #include <vector> 28 29 using namespace llvm; 30 31 #define DEBUG_TYPE "pgo-icall-prom-analysis" 32 33 // The percent threshold for the direct-call target (this call site vs the 34 // remaining call count) for it to be considered as the promotion target. 35 static cl::opt<unsigned> ICPRemainingPercentThreshold( 36 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore, 37 cl::desc("The percentage threshold against remaining unpromoted indirect " 38 "call count for the promotion")); 39 40 // The percent threshold for the direct-call target (this call site vs the 41 // total call count) for it to be considered as the promotion target. 42 static cl::opt<unsigned> 43 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5), 44 cl::Hidden, cl::ZeroOrMore, 45 cl::desc("The percentage threshold against total " 46 "count for the promotion")); 47 48 // Set the maximum number of targets to promote for a single indirect-call 49 // callsite. 50 static cl::opt<unsigned> 51 MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore, 52 cl::desc("Max number of promotions for a single indirect " 53 "call callsite")); 54 55 ICallPromotionAnalysis::ICallPromotionAnalysis() { 56 ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions); 57 } 58 59 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count, 60 uint64_t TotalCount, 61 uint64_t RemainingCount) { 62 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount && 63 Count * 100 >= ICPTotalPercentThreshold * TotalCount; 64 } 65 66 // Indirect-call promotion heuristic. The direct targets are sorted based on 67 // the count. Stop at the first target that is not promoted. Returns the 68 // number of candidates deemed profitable. 69 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates( 70 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) { 71 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals); 72 73 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst 74 << " Num_targets: " << NumVals << "\n"); 75 76 uint32_t I = 0; 77 uint64_t RemainingCount = TotalCount; 78 for (; I < MaxNumPromotions && I < NumVals; I++) { 79 uint64_t Count = ValueDataRef[I].Count; 80 assert(Count <= RemainingCount); 81 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count 82 << " Target_func: " << ValueDataRef[I].Value << "\n"); 83 84 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) { 85 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n"); 86 return I; 87 } 88 RemainingCount -= Count; 89 } 90 return I; 91 } 92 93 ArrayRef<InstrProfValueData> 94 ICallPromotionAnalysis::getPromotionCandidatesForInstruction( 95 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount, 96 uint32_t &NumCandidates) { 97 bool Res = 98 getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions, 99 ValueDataArray.get(), NumVals, TotalCount); 100 if (!Res) { 101 NumCandidates = 0; 102 return ArrayRef<InstrProfValueData>(); 103 } 104 NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount); 105 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals); 106 } 107