1 //===-- IndirectCallPromotionAnalysis.cpp - Find promotion candidates ===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Helper methods for identifying profitable indirect call promotion
11 // candidates for an instruction when the indirect-call value profile metadata
12 // is available.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/Analysis/IndirectCallSiteVisitor.h"
19 #include "llvm/IR/CallSite.h"
20 #include "llvm/IR/DiagnosticInfo.h"
21 #include "llvm/IR/InstIterator.h"
22 #include "llvm/IR/InstVisitor.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/IntrinsicInst.h"
25 #include "llvm/ProfileData/InstrProf.h"
26 #include "llvm/Support/Debug.h"
27 #include <string>
28 #include <utility>
29 #include <vector>
30
31 using namespace llvm;
32
33 #define DEBUG_TYPE "pgo-icall-prom-analysis"
34
35 // The minimum call count for the direct-call target to be considered as the
36 // promotion candidate.
37 static cl::opt<unsigned>
38 ICPCountThreshold("icp-count-threshold", cl::Hidden, cl::ZeroOrMore,
39 cl::init(1000),
40 cl::desc("The minimum count to the direct call target "
41 "for the promotion"));
42
43 // The percent threshold for the direct-call target (this call site vs the
44 // total call count) for it to be considered as the promotion target.
45 static cl::opt<unsigned>
46 ICPPercentThreshold("icp-percent-threshold", cl::init(33), cl::Hidden,
47 cl::ZeroOrMore,
48 cl::desc("The percentage threshold for the promotion"));
49
50 // Set the maximum number of targets to promote for a single indirect-call
51 // callsite.
52 static cl::opt<unsigned>
53 MaxNumPromotions("icp-max-prom", cl::init(2), cl::Hidden, cl::ZeroOrMore,
54 cl::desc("Max number of promotions for a single indirect "
55 "call callsite"));
56
ICallPromotionAnalysis()57 ICallPromotionAnalysis::ICallPromotionAnalysis() {
58 ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
59 }
60
isPromotionProfitable(uint64_t Count,uint64_t TotalCount)61 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
62 uint64_t TotalCount) {
63 if (Count < ICPCountThreshold)
64 return false;
65
66 unsigned Percentage = (Count * 100) / TotalCount;
67 return (Percentage >= ICPPercentThreshold);
68 }
69
70 // Indirect-call promotion heuristic. The direct targets are sorted based on
71 // the count. Stop at the first target that is not promoted. Returns the
72 // number of candidates deemed profitable.
getProfitablePromotionCandidates(const Instruction * Inst,uint32_t NumVals,uint64_t TotalCount)73 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
74 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
75 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
76
77 DEBUG(dbgs() << " \nWork on callsite " << *Inst << " Num_targets: " << NumVals
78 << "\n");
79
80 uint32_t I = 0;
81 for (; I < MaxNumPromotions && I < NumVals; I++) {
82 uint64_t Count = ValueDataRef[I].Count;
83 assert(Count <= TotalCount);
84 DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
85 << " Target_func: " << ValueDataRef[I].Value << "\n");
86
87 if (!isPromotionProfitable(Count, TotalCount)) {
88 DEBUG(dbgs() << " Not promote: Cold target.\n");
89 return I;
90 }
91 TotalCount -= Count;
92 }
93 return I;
94 }
95
96 ArrayRef<InstrProfValueData>
getPromotionCandidatesForInstruction(const Instruction * I,uint32_t & NumVals,uint64_t & TotalCount,uint32_t & NumCandidates)97 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
98 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
99 uint32_t &NumCandidates) {
100 bool Res =
101 getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
102 ValueDataArray.get(), NumVals, TotalCount);
103 if (!Res) {
104 NumCandidates = 0;
105 return ArrayRef<InstrProfValueData>();
106 }
107 NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
108 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
109 }
110