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 #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 }