llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp

   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<unsigned>
  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 maximum number of targets to promote for a single indirect-call
  41 // callsite.
  42 static cl::opt<unsigned>
  43     MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden,
  44                      cl::desc("Max number of promotions for a single indirect "
  45                               "call callsite"));
  46
  47 cl::opt<unsigned> MaxNumVTableAnnotations(
  48     "icp-max-num-vtables", cl::init(6), cl::Hidden,
  49     cl::desc("Max number of vtables annotated for a vtable load instruction."));
  50
  51 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
  52                                                    uint64_t TotalCount,
  53                                                    uint64_t RemainingCount) {
  54   return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
  55          Count * 100 >= ICPTotalPercentThreshold * TotalCount;
  56 }
  57
  58 // Indirect-call promotion heuristic. The direct targets are sorted based on
  59 // the count. Stop at the first target that is not promoted. Returns the
  60 // number of candidates deemed profitable.
  61 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
  62     const Instruction *Inst, uint64_t TotalCount) {
  63   LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
  64                     << " Num_targets: " << ValueDataArray.size() << "\n");
  65
  66   uint32_t I = 0;
  67   uint64_t RemainingCount = TotalCount;
  68   for (; I < MaxNumPromotions && I < ValueDataArray.size(); I++) {
  69     uint64_t Count = ValueDataArray[I].Count;
  70     assert(Count <= RemainingCount);
  71     LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
  72                       << "  Target_func: " << ValueDataArray[I].Value << "\n");
  73
  74     if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
  75       LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
  76       return I;
  77     }
  78     RemainingCount -= Count;
  79   }
  80   return I;
  81 }
  82
  83 MutableArrayRef<InstrProfValueData>
  84 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
  85     const Instruction *I, uint64_t &TotalCount, uint32_t &NumCandidates) {
  86   ValueDataArray = getValueProfDataFromInst(*I, IPVK_IndirectCallTarget,
  87                                             MaxNumPromotions, TotalCount);
  88   if (ValueDataArray.empty()) {
  89     NumCandidates = 0;
  90     return MutableArrayRef<InstrProfValueData>();
  91   }
  92   NumCandidates = getProfitablePromotionCandidates(I, TotalCount);
  93   return ValueDataArray;
  94 }