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