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/IR/Instruction.h"
17#include "llvm/ProfileData/InstrProf.h"
18#include "llvm/Support/CommandLine.h"
19#include "llvm/Support/Debug.h"
20
21using namespace llvm;
22
23#define DEBUG_TYPE "pgo-icall-prom-analysis"
24
25namespace llvm {
26
27// The percent threshold for the direct-call target (this call site vs the
28// remaining call count) for it to be considered as the promotion target.
29static cl::opt<unsigned> ICPRemainingPercentThreshold(
30 "icp-remaining-percent-threshold", cl::init(Val: 30), cl::Hidden,
31 cl::desc("The percentage threshold against remaining unpromoted indirect "
32 "call count for the promotion"));
33
34// The percent threshold for the direct-call target (this call site vs the
35// total call count) for it to be considered as the promotion target.
36static cl::opt<uint64_t>
37 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(Val: 5),
38 cl::Hidden,
39 cl::desc("The percentage threshold against total "
40 "count for the promotion"));
41
42// Set the minimum absolute count threshold for indirect call promotion.
43// Candidates with counts below this threshold will not be promoted.
44static cl::opt<unsigned> ICPMinimumCountThreshold(
45 "icp-minimum-count-threshold", cl::init(Val: 0), cl::Hidden,
46 cl::desc("Minimum absolute count for promotion candidate"));
47
48// Set the maximum number of targets to promote for a single indirect-call
49// callsite.
50static cl::opt<unsigned>
51 MaxNumPromotions("icp-max-prom", cl::init(Val: 3), cl::Hidden,
52 cl::desc("Max number of promotions for a single indirect "
53 "call callsite"));
54
55cl::opt<unsigned> MaxNumVTableAnnotations(
56 "icp-max-num-vtables", cl::init(Val: 6), cl::Hidden,
57 cl::desc("Max number of vtables annotated for a vtable load instruction."));
58
59} // end namespace llvm
60
61bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
62 uint64_t TotalCount,
63 uint64_t RemainingCount) {
64 return Count >= ICPMinimumCountThreshold &&
65 Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
66 Count * 100 >= ICPTotalPercentThreshold * TotalCount;
67}
68
69// Indirect-call promotion heuristic. The direct targets are sorted based on
70// the count. Stop at the first target that is not promoted. Returns the
71// number of candidates deemed profitable.
72uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
73 const Instruction *Inst, uint64_t TotalCount) {
74 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
75 << " Num_targets: " << ValueDataArray.size() << "\n");
76
77 uint32_t I = 0;
78 uint64_t RemainingCount = TotalCount;
79 for (; I < MaxNumPromotions && I < ValueDataArray.size(); I++) {
80 uint64_t Count = ValueDataArray[I].Count;
81 assert(Count <= RemainingCount);
82 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
83 << " Target_func: " << ValueDataArray[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
94MutableArrayRef<InstrProfValueData>
95ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
96 const Instruction *I, uint64_t &TotalCount, uint32_t &NumCandidates,
97 unsigned MaxNumValueData) {
98 // Use the max of the values specified by -icp-max-prom and the provided
99 // MaxNumValueData parameter.
100 if (MaxNumPromotions > MaxNumValueData)
101 MaxNumValueData = MaxNumPromotions;
102 ValueDataArray = getValueProfDataFromInst(Inst: *I, ValueKind: IPVK_IndirectCallTarget,
103 MaxNumValueData, TotalC&: TotalCount);
104 if (ValueDataArray.empty()) {
105 NumCandidates = 0;
106 return MutableArrayRef<InstrProfValueData>();
107 }
108 NumCandidates = getProfitablePromotionCandidates(Inst: I, TotalCount);
109 return ValueDataArray;
110}
111