IndirectCallPromotionAnalysis.cpp revision 360784 
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/CommandLine.h"
25#include "llvm/Support/Debug.h"
26#include <string>
27#include <utility>
28#include <vector>
29
30using 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.
36static 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.
43static 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.
51static 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
56ICallPromotionAnalysis::ICallPromotionAnalysis() {
57  ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions);
58}
59
60bool 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.
70uint32_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
94ArrayRef<InstrProfValueData>
95ICallPromotionAnalysis::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}
108