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