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/ProfileData/InstrProf.h"
20#include <memory>
21#include <vector>
22
23namespace llvm {
24
25class Function;
26class Instruction;
27class TargetLibraryInfo;
28class Value;
29
30/// Utility analysis that determines what values are worth profiling.
31/// The actual logic is inside the ValueProfileCollectorImpl, whose job is to
32/// populate the Candidates vector.
33///
34/// Value profiling an expression means to track the values that this expression
35/// takes at runtime and the frequency of each value.
36/// It is important to distinguish between two sets of value profiles for a
37/// particular expression:
38/// 1) The set of values at the point of evaluation.
39/// 2) The set of values at the point of use.
40/// In some cases, the two sets are identical, but it's not unusual for the two
41/// to differ.
42///
43/// To elaborate more, consider this C code, and focus on the expression `nn`:
44/// void foo(int nn, bool b) {
45/// if (b) memcpy(x, y, nn);
46/// }
47/// The point of evaluation can be as early as the start of the function, and
48/// let's say the value profile for `nn` is:
49/// total=100; (value,freq) set = {(8,10), (32,50)}
50/// The point of use is right before we call memcpy, and since we execute the
51/// memcpy conditionally, the value profile of `nn` can be:
52/// total=15; (value,freq) set = {(8,10), (4,5)}
53///
54/// For this reason, a plugin is responsible for computing the insertion point
55/// for each value to be profiled. The `CandidateInfo` structure encapsulates
56/// all the information needed for each value profile site.
57class ValueProfileCollector {
58public:
59 struct CandidateInfo {
60 Value *V; // The value to profile.
61 Instruction *InsertPt; // Insert the VP lib call before this instr.
62 Instruction *AnnotatedInst; // Where metadata is attached.
63 };
64
65 ValueProfileCollector(Function &Fn, TargetLibraryInfo &TLI);
66 ValueProfileCollector(ValueProfileCollector &&) = delete;
67 ValueProfileCollector &operator=(ValueProfileCollector &&) = delete;
68
69 ValueProfileCollector(const ValueProfileCollector &) = delete;
70 ValueProfileCollector &operator=(const ValueProfileCollector &) = delete;
71 ~ValueProfileCollector();
72
73 /// returns a list of value profiling candidates of the given kind
74 std::vector<CandidateInfo> get(InstrProfValueKind Kind) const;
75
76private:
77 class ValueProfileCollectorImpl;
78 std::unique_ptr<ValueProfileCollectorImpl> PImpl;
79};
80
81} // namespace llvm
82
83#endif
84

source code of llvm/lib/Transforms/Instrumentation/ValueProfileCollector.h