contrib/llvm/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/DiagnosticInfo.h"
  21 #include "llvm/IR/InstIterator.h"
  22 #include "llvm/IR/InstVisitor.h"
  23 #include "llvm/IR/Instructions.h"
  24 #include "llvm/IR/IntrinsicInst.h"
  25 #include "llvm/ProfileData/InstrProf.h"
  26 #include "llvm/Support/Debug.h"
  27 #include <string>
  28 #include <utility>
  29 #include <vector>
  30
  31 using namespace llvm;
  32
  33 #define DEBUG_TYPE "pgo-icall-prom-analysis"
  34
  35 // The minimum call count for the direct-call target to be considered as the
  36 // promotion candidate.
  37 static cl::opt<unsigned>
  38     ICPCountThreshold("icp-count-threshold", cl::Hidden, cl::ZeroOrMore,
  39                       cl::init(1000),
  40                       cl::desc("The minimum count to the direct call target "
  41                                "for the promotion"));
  42
  43 // The percent threshold for the direct-call target (this call site vs the
  44 // total call count) for it to be considered as the promotion target.
  45 static cl::opt<unsigned>
  46     ICPPercentThreshold("icp-percent-threshold", cl::init(30), cl::Hidden,
  47                         cl::ZeroOrMore,
  48                         cl::desc("The percentage threshold for the promotion"));
  49
  50 // Set the maximum number of targets to promote for a single indirect-call
  51 // callsite.
  52 static cl::opt<unsigned>
  53     MaxNumPromotions("icp-max-prom", cl::init(2), cl::Hidden, cl::ZeroOrMore,
  54                      cl::desc("Max number of promotions for a single indirect "
  55                               "call callsite"));
  56
  57 ICallPromotionAnalysis::ICallPromotionAnalysis() {
  58   ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
  59 }
  60
  61 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
  62                                                    uint64_t TotalCount) {
  63   if (Count < ICPCountThreshold)
  64     return false;
  65
  66   unsigned Percentage = (Count * 100) / TotalCount;
  67   return (Percentage >= ICPPercentThreshold);
  68 }
  69
  70 // Indirect-call promotion heuristic. The direct targets are sorted based on
  71 // the count. Stop at the first target that is not promoted. Returns the
  72 // number of candidates deemed profitable.
  73 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
  74     const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
  75   ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
  76
  77   DEBUG(dbgs() << " \nWork on callsite " << *Inst << " Num_targets: " << NumVals
  78                << "\n");
  79
  80   uint32_t I = 0;
  81   for (; I < MaxNumPromotions && I < NumVals; I++) {
  82     uint64_t Count = ValueDataRef[I].Count;
  83     assert(Count <= TotalCount);
  84     DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
  85                  << "  Target_func: " << ValueDataRef[I].Value << "\n");
  86
  87     if (!isPromotionProfitable(Count, TotalCount)) {
  88       DEBUG(dbgs() << " Not promote: Cold target.\n");
  89       return I;
  90     }
  91     TotalCount -= Count;
  92   }
  93   return I;
  94 }
  95
  96 ArrayRef<InstrProfValueData>
  97 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
  98     const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
  99     uint32_t &NumCandidates) {
 100   bool Res =
 101       getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
 102                                ValueDataArray.get(), NumVals, TotalCount);
 103   if (!Res) {
 104     NumCandidates = 0;
 105     return ArrayRef<InstrProfValueData>();
 106   }
 107   NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
 108   return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
 109 }