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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-exception6//7//===----------------------------------------------------------------------===//8//9// This file contains a utility class, ValueProfileCollector, that is used to10// determine what kind of llvm::Value's are worth value-profiling, at which11// 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_H17#define LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H18 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 to32/// populate the Candidates vector.33///34/// Value profiling an expression means to track the values that this expression35/// takes at runtime and the frequency of each value.36/// It is important to distinguish between two sets of value profiles for a37/// 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 two41/// 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, and48/// 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 the51/// 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 point55/// for each value to be profiled. The `CandidateInfo` structure encapsulates56/// 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 kind74 std::vector<CandidateInfo> get(InstrProfValueKind Kind) const;75 76private:77 class ValueProfileCollectorImpl;78 std::unique_ptr<ValueProfileCollectorImpl> PImpl;79};80 81} // namespace llvm82 83#endif84