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