1 //===- Transforms/IPO/SampleProfileProbe.h ----------*- C++ -*-===//
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 /// \file
10 /// This file provides the interface for the pseudo probe implementation for
11 /// AutoFDO.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_TRANSFORMS_IPO_SAMPLEPROFILEPROBE_H
16 #define LLVM_TRANSFORMS_IPO_SAMPLEPROFILEPROBE_H
17 
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/Analysis/LazyCallGraph.h"
20 #include "llvm/IR/PassManager.h"
21 #include "llvm/ProfileData/SampleProf.h"
22 #include <unordered_map>
23 
24 namespace llvm {
25 class Any;
26 class BasicBlock;
27 class Function;
28 class Instruction;
29 class Loop;
30 class PassInstrumentationCallbacks;
31 class TargetMachine;
32 
33 class Module;
34 
35 using namespace sampleprof;
36 using BlockIdMap = std::unordered_map<BasicBlock *, uint32_t>;
37 using InstructionIdMap = std::unordered_map<Instruction *, uint32_t>;
38 // Map from tuples of Probe id and inline stack hash code to distribution
39 // factors.
40 using ProbeFactorMap = std::unordered_map<std::pair<uint64_t, uint64_t>, float,
41                                           pair_hash<uint64_t, uint64_t>>;
42 using FuncProbeFactorMap = StringMap<ProbeFactorMap>;
43 
44 class PseudoProbeDescriptor {
45   uint64_t FunctionGUID;
46   uint64_t FunctionHash;
47 
48 public:
49   PseudoProbeDescriptor(uint64_t GUID, uint64_t Hash)
50       : FunctionGUID(GUID), FunctionHash(Hash) {}
51   uint64_t getFunctionGUID() const { return FunctionGUID; }
52   uint64_t getFunctionHash() const { return FunctionHash; }
53 };
54 
55 // A pseudo probe verifier that can be run after each IR passes to detect the
56 // violation of updating probe factors. In principle, the sum of distribution
57 // factor for a probe should be identical before and after a pass. For a
58 // function pass, the factor sum for a probe would be typically 100%.
59 class PseudoProbeVerifier {
60 public:
61   void registerCallbacks(PassInstrumentationCallbacks &PIC);
62 
63   // Implementation of pass instrumentation callbacks for new pass manager.
64   void runAfterPass(StringRef PassID, Any IR);
65 
66 private:
67   // Allow a little bias due the rounding to integral factors.
68   constexpr static float DistributionFactorVariance = 0.02f;
69   // Distribution factors from last pass.
70   FuncProbeFactorMap FunctionProbeFactors;
71 
72   void collectProbeFactors(const BasicBlock *BB, ProbeFactorMap &ProbeFactors);
73   void runAfterPass(const Module *M);
74   void runAfterPass(const LazyCallGraph::SCC *C);
75   void runAfterPass(const Function *F);
76   void runAfterPass(const Loop *L);
77   bool shouldVerifyFunction(const Function *F);
78   void verifyProbeFactors(const Function *F,
79                           const ProbeFactorMap &ProbeFactors);
80 };
81 
82 // This class serves sample counts correlation for SampleProfileLoader by
83 // analyzing pseudo probes and their function descriptors injected by
84 // SampleProfileProber.
85 class PseudoProbeManager {
86   DenseMap<uint64_t, PseudoProbeDescriptor> GUIDToProbeDescMap;
87 
88   const PseudoProbeDescriptor *getDesc(const Function &F) const;
89 
90 public:
91   PseudoProbeManager(const Module &M);
92   bool moduleIsProbed(const Module &M) const;
93   bool profileIsValid(const Function &F, const FunctionSamples &Samples) const;
94 };
95 
96 /// Sample profile pseudo prober.
97 ///
98 /// Insert pseudo probes for block sampling and value sampling.
99 class SampleProfileProber {
100 public:
101   // Give an empty module id when the prober is not used for instrumentation.
102   SampleProfileProber(Function &F, const std::string &CurModuleUniqueId);
103   void instrumentOneFunc(Function &F, TargetMachine *TM);
104 
105 private:
106   Function *getFunction() const { return F; }
107   uint64_t getFunctionHash() const { return FunctionHash; }
108   uint32_t getBlockId(const BasicBlock *BB) const;
109   uint32_t getCallsiteId(const Instruction *Call) const;
110   void computeCFGHash();
111   void computeProbeIdForBlocks();
112   void computeProbeIdForCallsites();
113 
114   Function *F;
115 
116   /// The current module ID that is used to name a static object as a comdat
117   /// group.
118   std::string CurModuleUniqueId;
119 
120   /// A CFG hash code used to identify a function code changes.
121   uint64_t FunctionHash;
122 
123   /// Map basic blocks to the their pseudo probe ids.
124   BlockIdMap BlockProbeIds;
125 
126   /// Map indirect calls to the their pseudo probe ids.
127   InstructionIdMap CallProbeIds;
128 
129   /// The ID of the last probe, Can be used to number a new probe.
130   uint32_t LastProbeId;
131 };
132 
133 class SampleProfileProbePass : public PassInfoMixin<SampleProfileProbePass> {
134   TargetMachine *TM;
135 
136 public:
137   SampleProfileProbePass(TargetMachine *TM) : TM(TM) {}
138   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
139 };
140 
141 // Pseudo probe distribution factor updater.
142 // Sample profile annotation can happen in both LTO prelink and postlink. The
143 // postlink-time re-annotation can degrade profile quality because of prelink
144 // code duplication transformation, such as loop unrolling, jump threading,
145 // indirect call promotion etc. As such, samples corresponding to a source
146 // location may be aggregated multiple times in postlink. With a concept of
147 // distribution factor for pseudo probes, samples can be distributed among
148 // duplicated probes reasonable based on the assumption that optimizations
149 // duplicating code well-maintain the branch frequency information (BFI). This
150 // pass updates distribution factors for each pseudo probe at the end of the
151 // prelink pipeline, to reflect an estimated portion of the real execution
152 // count.
153 class PseudoProbeUpdatePass : public PassInfoMixin<PseudoProbeUpdatePass> {
154   void runOnFunction(Function &F, FunctionAnalysisManager &FAM);
155 
156 public:
157   PseudoProbeUpdatePass() = default;
158   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
159 };
160 
161 } // end namespace llvm
162 #endif // LLVM_TRANSFORMS_IPO_SAMPLEPROFILEPROBE_H
163