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/InstIterator.h"
21 #include "llvm/IR/InstVisitor.h"
22 #include "llvm/IR/Instructions.h"
23 #include "llvm/IR/IntrinsicInst.h"
24 #include "llvm/ProfileData/InstrProf.h"
25 #include "llvm/Support/Debug.h"
26 #include <string>
27 #include <utility>
28 #include <vector>
29
30 using namespace llvm;
31
32 #define DEBUG_TYPE "pgo-icall-prom-analysis"
33
34 // The percent threshold for the direct-call target (this call site vs the
35 // remaining call count) for it to be considered as the promotion target.
36 static cl::opt<unsigned> ICPRemainingPercentThreshold(
37 "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
38 cl::desc("The percentage threshold against remaining unpromoted indirect "
39 "call count for the promotion"));
40
41 // The percent threshold for the direct-call target (this call site vs the
42 // total call count) for it to be considered as the promotion target.
43 static cl::opt<unsigned>
44 ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
45 cl::Hidden, cl::ZeroOrMore,
46 cl::desc("The percentage threshold against total "
47 "count for the promotion"));
48
49 // Set the maximum number of targets to promote for a single indirect-call
50 // callsite.
51 static cl::opt<unsigned>
52 MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
53 cl::desc("Max number of promotions for a single indirect "
54 "call callsite"));
55
ICallPromotionAnalysis()56 ICallPromotionAnalysis::ICallPromotionAnalysis() {
57 ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
58 }
59
isPromotionProfitable(uint64_t Count,uint64_t TotalCount,uint64_t RemainingCount)60 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
61 uint64_t TotalCount,
62 uint64_t RemainingCount) {
63 return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
64 Count * 100 >= ICPTotalPercentThreshold * TotalCount;
65 }
66
67 // Indirect-call promotion heuristic. The direct targets are sorted based on
68 // the count. Stop at the first target that is not promoted. Returns the
69 // number of candidates deemed profitable.
getProfitablePromotionCandidates(const Instruction * Inst,uint32_t NumVals,uint64_t TotalCount)70 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
71 const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
72 ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
73
74 LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
75 << " Num_targets: " << NumVals << "\n");
76
77 uint32_t I = 0;
78 uint64_t RemainingCount = TotalCount;
79 for (; I < MaxNumPromotions && I < NumVals; I++) {
80 uint64_t Count = ValueDataRef[I].Count;
81 assert(Count <= RemainingCount);
82 LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
83 << " Target_func: " << ValueDataRef[I].Value << "\n");
84
85 if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
86 LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
87 return I;
88 }
89 RemainingCount -= Count;
90 }
91 return I;
92 }
93
94 ArrayRef<InstrProfValueData>
getPromotionCandidatesForInstruction(const Instruction * I,uint32_t & NumVals,uint64_t & TotalCount,uint32_t & NumCandidates)95 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
96 const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
97 uint32_t &NumCandidates) {
98 bool Res =
99 getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
100 ValueDataArray.get(), NumVals, TotalCount);
101 if (!Res) {
102 NumCandidates = 0;
103 return ArrayRef<InstrProfValueData>();
104 }
105 NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
106 return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
107 }
108