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/CallSite.h"
  19 #include "llvm/IR/InstIterator.h"
  20 #include "llvm/IR/InstVisitor.h"
  21 #include "llvm/IR/Instructions.h"
  22 #include "llvm/IR/IntrinsicInst.h"
  23 #include "llvm/ProfileData/InstrProf.h"
  24 #include "llvm/Support/Debug.h"
  25 #include <string>
  26 #include <utility>
  27 #include <vector>
  28
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "pgo-icall-prom-analysis"
  32
  33 // The percent threshold for the direct-call target (this call site vs the
  34 // remaining call count) for it to be considered as the promotion target.
  35 static cl::opt<unsigned> ICPRemainingPercentThreshold(
  36     "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
  37     cl::desc("The percentage threshold against remaining unpromoted indirect "
  38              "call count for the promotion"));
  39
  40 // The percent threshold for the direct-call target (this call site vs the
  41 // total call count) for it to be considered as the promotion target.
  42 static cl::opt<unsigned>
  43     ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
  44                              cl::Hidden, cl::ZeroOrMore,
  45                              cl::desc("The percentage threshold against total "
  46                                       "count for the promotion"));
  47
  48 // Set the maximum number of targets to promote for a single indirect-call
  49 // callsite.
  50 static cl::opt<unsigned>
  51     MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
  52                      cl::desc("Max number of promotions for a single indirect "
  53                               "call callsite"));
  54
  55 ICallPromotionAnalysis::ICallPromotionAnalysis() {
  56   ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions);
  57 }
  58
  59 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
  60                                                    uint64_t TotalCount,
  61                                                    uint64_t RemainingCount) {
  62   return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
  63          Count * 100 >= ICPTotalPercentThreshold * TotalCount;
  64 }
  65
  66 // Indirect-call promotion heuristic. The direct targets are sorted based on
  67 // the count. Stop at the first target that is not promoted. Returns the
  68 // number of candidates deemed profitable.
  69 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
  70     const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
  71   ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
  72
  73   LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
  74                     << " Num_targets: " << NumVals << "\n");
  75
  76   uint32_t I = 0;
  77   uint64_t RemainingCount = TotalCount;
  78   for (; I < MaxNumPromotions && I < NumVals; I++) {
  79     uint64_t Count = ValueDataRef[I].Count;
  80     assert(Count <= RemainingCount);
  81     LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
  82                       << "  Target_func: " << ValueDataRef[I].Value << "\n");
  83
  84     if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
  85       LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
  86       return I;
  87     }
  88     RemainingCount -= Count;
  89   }
  90   return I;
  91 }
  92
  93 ArrayRef<InstrProfValueData>
  94 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
  95     const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
  96     uint32_t &NumCandidates) {
  97   bool Res =
  98       getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
  99                                ValueDataArray.get(), NumVals, TotalCount);
 100   if (!Res) {
 101     NumCandidates = 0;
 102     return ArrayRef<InstrProfValueData>();
 103   }
 104   NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
 105   return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
 106 }