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 ICallPromotionAnalysis::ICallPromotionAnalysis() {
  49   ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions);
  50 }
  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, uint32_t NumVals, uint64_t TotalCount) {
  64   ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
  65
  66   LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
  67                     << " Num_targets: " << NumVals << "\n");
  68
  69   uint32_t I = 0;
  70   uint64_t RemainingCount = TotalCount;
  71   for (; I < MaxNumPromotions && I < NumVals; I++) {
  72     uint64_t Count = ValueDataRef[I].Count;
  73     assert(Count <= RemainingCount);
  74     LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
  75                       << "  Target_func: " << ValueDataRef[I].Value << "\n");
  76
  77     if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
  78       LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
  79       return I;
  80     }
  81     RemainingCount -= Count;
  82   }
  83   return I;
  84 }
  85
  86 ArrayRef<InstrProfValueData>
  87 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
  88     const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
  89     uint32_t &NumCandidates) {
  90   bool Res =
  91       getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
  92                                ValueDataArray.get(), NumVals, TotalCount);
  93   if (!Res) {
  94     NumCandidates = 0;
  95     return ArrayRef<InstrProfValueData>();
  96   }
  97   NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
  98   return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
  99 }