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/ADT/STLExtras.h"
17 #include "llvm/Analysis/IndirectCallVisitor.h"
18 #include "llvm/IR/InstIterator.h"
19 #include "llvm/IR/InstVisitor.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/IntrinsicInst.h"
22 #include "llvm/ProfileData/InstrProf.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include <memory>
26
27 using namespace llvm;
28
29 #define DEBUG_TYPE "pgo-icall-prom-analysis"
30
31 // The percent threshold for the direct-call target (this call site vs the
32 // remaining call count) for it to be considered as the promotion target.
33 static cl::opt<unsigned> ICPRemainingPercentThreshold(
34 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
35 cl::desc("The percentage threshold against remaining unpromoted indirect "
36 "call count for the promotion"));
37
38 // The percent threshold for the direct-call target (this call site vs the
39 // total call count) for it to be considered as the promotion target.
40 static cl::opt<unsigned>
41 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
42 cl::Hidden, cl::ZeroOrMore,
43 cl::desc("The percentage threshold against total "
44 "count for the promotion"));
45
46 // Set the maximum number of targets to promote for a single indirect-call
47 // callsite.
48 static cl::opt<unsigned>
49 MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
50 cl::desc("Max number of promotions for a single indirect "
51 "call callsite"));
52
ICallPromotionAnalysis()53 ICallPromotionAnalysis::ICallPromotionAnalysis() {
54 ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions);
55 }
56
isPromotionProfitable(uint64_t Count,uint64_t TotalCount,uint64_t RemainingCount)57 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
58 uint64_t TotalCount,
59 uint64_t RemainingCount) {
60 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
61 Count * 100 >= ICPTotalPercentThreshold * TotalCount;
62 }
63
64 // Indirect-call promotion heuristic. The direct targets are sorted based on
65 // the count. Stop at the first target that is not promoted. Returns the
66 // number of candidates deemed profitable.
getProfitablePromotionCandidates(const Instruction * Inst,uint32_t NumVals,uint64_t TotalCount)67 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
68 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
69 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
70
71 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
72 << " Num_targets: " << NumVals << "\n");
73
74 uint32_t I = 0;
75 uint64_t RemainingCount = TotalCount;
76 for (; I < MaxNumPromotions && I < NumVals; I++) {
77 uint64_t Count = ValueDataRef[I].Count;
78 assert(Count <= RemainingCount);
79 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
80 << " Target_func: " << ValueDataRef[I].Value << "\n");
81
82 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
83 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
84 return I;
85 }
86 RemainingCount -= Count;
87 }
88 return I;
89 }
90
91 ArrayRef<InstrProfValueData>
getPromotionCandidatesForInstruction(const Instruction * I,uint32_t & NumVals,uint64_t & TotalCount,uint32_t & NumCandidates)92 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
93 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
94 uint32_t &NumCandidates) {
95 bool Res =
96 getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
97 ValueDataArray.get(), NumVals, TotalCount);
98 if (!Res) {
99 NumCandidates = 0;
100 return ArrayRef<InstrProfValueData>();
101 }
102 NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
103 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
104 }
105