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 percent threshold for the direct-call target (this call site vs the
36 // remaining call count) for it to be considered as the promotion target.
37 static cl::opt<unsigned> ICPRemainingPercentThreshold(
38     "icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
39     cl::desc("The percentage threshold against remaining unpromoted indirect "
40              "call count for the promotion"));
41 
42 // The percent threshold for the direct-call target (this call site vs the
43 // total call count) for it to be considered as the promotion target.
44 static cl::opt<unsigned>
45     ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
46                              cl::Hidden, cl::ZeroOrMore,
47                              cl::desc("The percentage threshold against total "
48                                       "count 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(3), cl::Hidden, cl::ZeroOrMore,
54                      cl::desc("Max number of promotions for a single indirect "
55                               "call callsite"));
56 
57 ICallPromotionAnalysis::ICallPromotionAnalysis() {
58   ValueDataArray = llvm::make_unique<InstrProfValueData[]>(MaxNumPromotions);
59 }
60 
61 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
62                                                    uint64_t TotalCount,
63                                                    uint64_t RemainingCount) {
64   return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
65          Count * 100 >= ICPTotalPercentThreshold * TotalCount;
66 }
67 
68 // Indirect-call promotion heuristic. The direct targets are sorted based on
69 // the count. Stop at the first target that is not promoted. Returns the
70 // number of candidates deemed profitable.
71 uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
72     const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
73   ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
74 
75   DEBUG(dbgs() << " \nWork on callsite " << *Inst << " Num_targets: " << NumVals
76                << "\n");
77 
78   uint32_t I = 0;
79   uint64_t RemainingCount = TotalCount;
80   for (; I < MaxNumPromotions && I < NumVals; I++) {
81     uint64_t Count = ValueDataRef[I].Count;
82     assert(Count <= RemainingCount);
83     DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
84                  << "  Target_func: " << ValueDataRef[I].Value << "\n");
85 
86     if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
87       DEBUG(dbgs() << " Not promote: Cold target.\n");
88       return I;
89     }
90     RemainingCount -= Count;
91   }
92   return I;
93 }
94 
95 ArrayRef<InstrProfValueData>
96 ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
97     const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
98     uint32_t &NumCandidates) {
99   bool Res =
100       getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
101                                ValueDataArray.get(), NumVals, TotalCount);
102   if (!Res) {
103     NumCandidates = 0;
104     return ArrayRef<InstrProfValueData>();
105   }
106   NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
107   return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
108 }
109