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 | |
22 | using 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. |
28 | static 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. |
35 | static 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. |
43 | static 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 | |
48 | cl::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 | |
52 | ICallPromotionAnalysis::ICallPromotionAnalysis() { |
53 | ValueDataArray = std::make_unique<InstrProfValueData[]>(num: MaxNumPromotions); |
54 | } |
55 | |
56 | bool 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. |
66 | uint32_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 | |
90 | ArrayRef<InstrProfValueData> |
91 | ICallPromotionAnalysis::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 | |