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#include <memory>
21
22using namespace llvm;
23
24#define DEBUG_TYPE "pgo-icall-prom-analysis"
25
26// The percent threshold for the direct-call target (this call site vs the
27// remaining call count) for it to be considered as the promotion target.
28static cl::opt<unsigned> ICPRemainingPercentThreshold(
29 "icp-remaining-percent-threshold", cl::init(Val: 30), cl::Hidden,
30 cl::desc("The percentage threshold against remaining unpromoted indirect "
31 "call count for the promotion"));
32
33// The percent threshold for the direct-call target (this call site vs the
34// total call count) for it to be considered as the promotion target.
35static cl::opt<unsigned>
36 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(Val: 5),
37 cl::Hidden,
38 cl::desc("The percentage threshold against total "
39 "count for the promotion"));
40
41// Set the maximum number of targets to promote for a single indirect-call
42// callsite.
43static cl::opt<unsigned>
44 MaxNumPromotions("icp-max-prom", cl::init(Val: 3), cl::Hidden,
45 cl::desc("Max number of promotions for a single indirect "
46 "call callsite"));
47
48cl::opt<unsigned> MaxNumVTableAnnotations(
49 "icp-max-num-vtables", cl::init(Val: 6), cl::Hidden,
50 cl::desc("Max number of vtables annotated for a vtable load instruction."));
51
52ICallPromotionAnalysis::ICallPromotionAnalysis() {
53 ValueDataArray = std::make_unique<InstrProfValueData[]>(num: MaxNumPromotions);
54}
55
56bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
57 uint64_t TotalCount,
58 uint64_t RemainingCount) {
59 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
60 Count * 100 >= ICPTotalPercentThreshold * TotalCount;
61}
62
63// Indirect-call promotion heuristic. The direct targets are sorted based on
64// the count. Stop at the first target that is not promoted. Returns the
65// number of candidates deemed profitable.
66uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
67 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
68 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
69
70 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
71 << " Num_targets: " << NumVals << "\n");
72
73 uint32_t I = 0;
74 uint64_t RemainingCount = TotalCount;
75 for (; I < MaxNumPromotions && I < NumVals; I++) {
76 uint64_t Count = ValueDataRef[I].Count;
77 assert(Count <= RemainingCount);
78 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
79 << " Target_func: " << ValueDataRef[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
90ArrayRef<InstrProfValueData>
91ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
92 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
93 uint32_t &NumCandidates) {
94 bool Res =
95 getValueProfDataFromInst(Inst: *I, ValueKind: IPVK_IndirectCallTarget, MaxNumValueData: MaxNumPromotions,
96 ValueData: ValueDataArray.get(), ActualNumValueData&: NumVals, TotalC&: TotalCount);
97 if (!Res) {
98 NumCandidates = 0;
99 return ArrayRef<InstrProfValueData>();
100 }
101 NumCandidates = getProfitablePromotionCandidates(Inst: I, NumVals, TotalCount);
102 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
103}
104

source code of llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp