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 // remaining call count) for it to be considered as the promotion target.
45 static cl::opt<unsigned> ICPRemainingPercentThreshold(
46     "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
47     cl::desc("The percentage threshold against remaining unpromoted indirect "
48              "call count for the promotion"));
49 
50 // The percent threshold for the direct-call target (this call site vs the
51 // total call count) for it to be considered as the promotion target.
52 static cl::opt<unsigned>
53     ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
54                              cl::Hidden, cl::ZeroOrMore,
55                              cl::desc("The percentage threshold against total "
56                                       "count for the promotion"));
57 
58 // Set the maximum number of targets to promote for a single indirect-call
59 // callsite.
60 static cl::opt<unsigned>
61     MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
62                      cl::desc("Max number of promotions for a single indirect "
63                               "call callsite"));
64 
65 ICallPromotionAnalysis::ICallPromotionAnalysis() {
66   ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
67 }
68 
69 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
70                                                    uint64_t TotalCount,
71                                                    uint64_t RemainingCount) {
72   return Count >= ICPCountThreshold &&
73          Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
74          Count * 100 >= ICPTotalPercentThreshold * TotalCount;
75 }
76 
77 // Indirect-call promotion heuristic. The direct targets are sorted based on
78 // the count. Stop at the first target that is not promoted. Returns the
79 // number of candidates deemed profitable.
80 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
81     const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
82   ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
83 
84   DEBUG(dbgs() << " \nWork on callsite " << *Inst << " Num_targets: " << NumVals
85                << "\n");
86 
87   uint32_t I = 0;
88   uint64_t RemainingCount = TotalCount;
89   for (; I < MaxNumPromotions && I < NumVals; I++) {
90     uint64_t Count = ValueDataRef[I].Count;
91     assert(Count <= RemainingCount);
92     DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
93                  << "  Target_func: " << ValueDataRef[I].Value << "\n");
94 
95     if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
96       DEBUG(dbgs() << " Not promote: Cold target.\n");
97       return I;
98     }
99     RemainingCount -= Count;
100   }
101   return I;
102 }
103 
104 ArrayRef<InstrProfValueData>
105 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
106     const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
107     uint32_t &NumCandidates) {
108   bool Res =
109       getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
110                                ValueDataArray.get(), NumVals, TotalCount);
111   if (!Res) {
112     NumCandidates = 0;
113     return ArrayRef<InstrProfValueData>();
114   }
115   NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
116   return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
117 }
118