1 //===- ValueProfileCollector.h - determine what to value profile ----------===//
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
7 //===----------------------------------------------------------------------===//
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]
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H
17 #define LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H
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"
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.
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
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);
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)}
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.
54 class ValueProfileCollector {
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.
62 ValueProfileCollector(Function &Fn, TargetLibraryInfo &TLI);
63 ValueProfileCollector(ValueProfileCollector &&) = delete;
64 ValueProfileCollector &operator=(ValueProfileCollector &&) = delete;
66 ValueProfileCollector(const ValueProfileCollector &) = delete;
67 ValueProfileCollector &operator=(const ValueProfileCollector &) = delete;
68 ~ValueProfileCollector();
70 /// returns a list of value profiling candidates of the given kind
71 std::vector<CandidateInfo> get(InstrProfValueKind Kind) const;
74 class ValueProfileCollectorImpl;
75 std::unique_ptr<ValueProfileCollectorImpl> PImpl;