1//===- ValueProfileCollector.h - determine what to value profile ----------===//
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// This file contains a utility class, ValueProfileCollector, that is used to
10// determine what kind of llvm::Value's are worth value-profiling, at which
11// point in the program, and which instruction holds the Value Profile metadata.
12// Currently, the only users of this utility is the PGOInstrumentation[Gen|Use]
13// passes.
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H
17#define LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H
18
19#include "llvm/Analysis/TargetLibraryInfo.h"
20#include "llvm/IR/Function.h"
21#include "llvm/IR/PassManager.h"
22#include "llvm/Pass.h"
23#include "llvm/ProfileData/InstrProf.h"
24
25namespace llvm {
26
27/// Utility analysis that determines what values are worth profiling.
28/// The actual logic is inside the ValueProfileCollectorImpl, whose job is to
29/// populate the Candidates vector.
30///
31/// Value profiling an expression means to track the values that this expression
32/// takes at runtime and the frequency of each value.
33/// It is important to distinguish between two sets of value profiles for a
34/// particular expression:
35///  1) The set of values at the point of evaluation.
36///  2) The set of values at the point of use.
37/// In some cases, the two sets are identical, but it's not unusual for the two
38/// to differ.
39///
40/// To elaborate more, consider this C code, and focus on the expression `nn`:
41///  void foo(int nn, bool b) {
42///    if (b)  memcpy(x, y, nn);
43///  }
44/// The point of evaluation can be as early as the start of the function, and
45/// let's say the value profile for `nn` is:
46///     total=100; (value,freq) set = {(8,10), (32,50)}
47/// The point of use is right before we call memcpy, and since we execute the
48/// memcpy conditionally, the value profile of `nn` can be:
49///     total=15; (value,freq) set = {(8,10), (4,5)}
50///
51/// For this reason, a plugin is responsible for computing the insertion point
52/// for each value to be profiled. The `CandidateInfo` structure encapsulates
53/// all the information needed for each value profile site.
54class ValueProfileCollector {
55public:
56  struct CandidateInfo {
57    Value *V;                   // The value to profile.
58    Instruction *InsertPt;      // Insert the VP lib call before this instr.
59    Instruction *AnnotatedInst; // Where metadata is attached.
60  };
61
62  ValueProfileCollector(Function &Fn, TargetLibraryInfo &TLI);
63  ValueProfileCollector(ValueProfileCollector &&) = delete;
64  ValueProfileCollector &operator=(ValueProfileCollector &&) = delete;
65
66  ValueProfileCollector(const ValueProfileCollector &) = delete;
67  ValueProfileCollector &operator=(const ValueProfileCollector &) = delete;
68  ~ValueProfileCollector();
69
70  /// returns a list of value profiling candidates of the given kind
71  std::vector<CandidateInfo> get(InstrProfValueKind Kind) const;
72
73private:
74  class ValueProfileCollectorImpl;
75  std::unique_ptr<ValueProfileCollectorImpl> PImpl;
76};
77
78} // namespace llvm
79
80#endif
81