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
25// The percent threshold for the direct-call target (this call site vs the
26// remaining call count) for it to be considered as the promotion target.
27static cl::opt<unsigned> ICPRemainingPercentThreshold(
28 "icp-remaining-percent-threshold", cl::init(Val: 30), cl::Hidden,
29 cl::desc("The percentage threshold against remaining unpromoted indirect "
30 "call count for the promotion"));
31
32// The percent threshold for the direct-call target (this call site vs the
33// total call count) for it to be considered as the promotion target.
34static cl::opt<uint64_t>
35 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(Val: 5),
36 cl::Hidden,
37 cl::desc("The percentage threshold against total "
38 "count for the promotion"));
39
40// Set the minimum absolute count threshold for indirect call promotion.
41// Candidates with counts below this threshold will not be promoted.
42static cl::opt<unsigned> ICPMinimumCountThreshold(
43 "icp-minimum-count-threshold", cl::init(Val: 0), cl::Hidden,
44 cl::desc("Minimum absolute count for promotion candidate"));
45
46// Set the maximum number of targets to promote for a single indirect-call
47// callsite.
48static cl::opt<unsigned>
49 MaxNumPromotions("icp-max-prom", cl::init(Val: 3), cl::Hidden,
50 cl::desc("Max number of promotions for a single indirect "
51 "call callsite"));
52
53cl::opt<unsigned> MaxNumVTableAnnotations(
54 "icp-max-num-vtables", cl::init(Val: 6), cl::Hidden,
55 cl::desc("Max number of vtables annotated for a vtable load instruction."));
56
57bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
58 uint64_t TotalCount,
59 uint64_t RemainingCount) {
60 return Count >= ICPMinimumCountThreshold &&
61 Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
62 Count * 100 >= ICPTotalPercentThreshold * TotalCount;
63}
64
65// Indirect-call promotion heuristic. The direct targets are sorted based on
66// the count. Stop at the first target that is not promoted. Returns the
67// number of candidates deemed profitable.
68uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
69 const Instruction *Inst, uint64_t TotalCount) {
70 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
71 << " Num_targets: " << ValueDataArray.size() << "\n");
72
73 uint32_t I = 0;
74 uint64_t RemainingCount = TotalCount;
75 for (; I < MaxNumPromotions && I < ValueDataArray.size(); I++) {
76 uint64_t Count = ValueDataArray[I].Count;
77 assert(Count <= RemainingCount);
78 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
79 << " Target_func: " << ValueDataArray[I].Value << "\n");
80
81 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
82 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
83 return I;
84 }
85 RemainingCount -= Count;
86 }
87 return I;
88}
89
90MutableArrayRef<InstrProfValueData>
91ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
92 const Instruction *I, uint64_t &TotalCount, uint32_t &NumCandidates) {
93 ValueDataArray = getValueProfDataFromInst(Inst: *I, ValueKind: IPVK_IndirectCallTarget,
94 MaxNumValueData: MaxNumPromotions, TotalC&: TotalCount);
95 if (ValueDataArray.empty()) {
96 NumCandidates = 0;
97 return MutableArrayRef<InstrProfValueData>();
98 }
99 NumCandidates = getProfitablePromotionCandidates(Inst: I, TotalCount);
100 return ValueDataArray;
101}
102