lib/Analysis/IndirectCallPromotionAnalysis.cpp

   1 //===-- IndirectCallPromotionAnalysis.cpp - Find promotion candidates ===//
   2 //
   3 //                      The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // Helper methods for identifying profitable indirect call promotion
  11 // candidates for an instruction when the indirect-call value profile metadata
  12 // is available.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
  17 #include "llvm/ADT/STLExtras.h"
  18 #include "llvm/Analysis/IndirectCallSiteVisitor.h"
  19 #include "llvm/IR/CallSite.h"
  20 #include "llvm/IR/InstIterator.h"
  21 #include "llvm/IR/InstVisitor.h"
  22 #include "llvm/IR/Instructions.h"
  23 #include "llvm/IR/IntrinsicInst.h"
  24 #include "llvm/ProfileData/InstrProf.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 = llvm::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 }