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