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/CallSite.h" 19 #include "llvm/IR/InstIterator.h" 20 #include "llvm/IR/InstVisitor.h" 21 #include "llvm/IR/Instructions.h" 22 #include "llvm/IR/IntrinsicInst.h" 23 #include "llvm/ProfileData/InstrProf.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Support/Debug.h" 26 #include <string> 27 #include <utility> 28 #include <vector> 29 30 using namespace llvm; 31 32 #define DEBUG_TYPE "pgo-icall-prom-analysis" 33 34 // The percent threshold for the direct-call target (this call site vs the 35 // remaining call count) for it to be considered as the promotion target. 36 static cl::opt<unsigned> ICPRemainingPercentThreshold( 37 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore, 38 cl::desc("The percentage threshold against remaining unpromoted indirect " 39 "call count for the promotion")); 40 41 // The percent threshold for the direct-call target (this call site vs the 42 // total call count) for it to be considered as the promotion target. 43 static cl::opt<unsigned> 44 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5), 45 cl::Hidden, cl::ZeroOrMore, 46 cl::desc("The percentage threshold against total " 47 "count for the promotion")); 48 49 // Set the maximum number of targets to promote for a single indirect-call 50 // callsite. 51 static cl::opt<unsigned> 52 MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore, 53 cl::desc("Max number of promotions for a single indirect " 54 "call callsite")); 55 56 ICallPromotionAnalysis::ICallPromotionAnalysis() { 57 ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions); 58 } 59 60 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count, 61 uint64_t TotalCount, 62 uint64_t RemainingCount) { 63 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount && 64 Count * 100 >= ICPTotalPercentThreshold * TotalCount; 65 } 66 67 // Indirect-call promotion heuristic. The direct targets are sorted based on 68 // the count. Stop at the first target that is not promoted. Returns the 69 // number of candidates deemed profitable. 70 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates( 71 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) { 72 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals); 73 74 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst 75 << " Num_targets: " << NumVals << "\n"); 76 77 uint32_t I = 0; 78 uint64_t RemainingCount = TotalCount; 79 for (; I < MaxNumPromotions && I < NumVals; I++) { 80 uint64_t Count = ValueDataRef[I].Count; 81 assert(Count <= RemainingCount); 82 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count 83 << " Target_func: " << ValueDataRef[I].Value << "\n"); 84 85 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) { 86 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n"); 87 return I; 88 } 89 RemainingCount -= Count; 90 } 91 return I; 92 } 93 94 ArrayRef<InstrProfValueData> 95 ICallPromotionAnalysis::getPromotionCandidatesForInstruction( 96 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount, 97 uint32_t &NumCandidates) { 98 bool Res = 99 getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions, 100 ValueDataArray.get(), NumVals, TotalCount); 101 if (!Res) { 102 NumCandidates = 0; 103 return ArrayRef<InstrProfValueData>(); 104 } 105 NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount); 106 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals); 107 } 108