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
52bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
53 uint64_t TotalCount,
54 uint64_t RemainingCount) {
55 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
56 Count * 100 >= ICPTotalPercentThreshold * TotalCount;
57}
58
59// Indirect-call promotion heuristic. The direct targets are sorted based on
60// the count. Stop at the first target that is not promoted. Returns the
61// number of candidates deemed profitable.
62uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
63 const Instruction *Inst, uint64_t TotalCount) {
64 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
65 << " Num_targets: " << ValueDataArray.size() << "\n");
66
67 uint32_t I = 0;
68 uint64_t RemainingCount = TotalCount;
69 for (; I < MaxNumPromotions && I < ValueDataArray.size(); I++) {
70 uint64_t Count = ValueDataArray[I].Count;
71 assert(Count <= RemainingCount);
72 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
73 << " Target_func: " << ValueDataArray[I].Value << "\n");
74
75 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
76 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
77 return I;
78 }
79 RemainingCount -= Count;
80 }
81 return I;
82}
83
84MutableArrayRef<InstrProfValueData>
85ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
86 const Instruction *I, uint64_t &TotalCount, uint32_t &NumCandidates) {
87 ValueDataArray = getValueProfDataFromInst(Inst: *I, ValueKind: IPVK_IndirectCallTarget,
88 MaxNumValueData: MaxNumPromotions, TotalC&: TotalCount);
89 if (ValueDataArray.empty()) {
90 NumCandidates = 0;
91 return MutableArrayRef<InstrProfValueData>();
92 }
93 NumCandidates = getProfitablePromotionCandidates(Inst: I, TotalCount);
94 return ValueDataArray;
95}
96