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/Analysis/TargetLibraryInfo.h" 20 #include "llvm/ProfileData/InstrProf.h" 21 #include <memory> 22 #include <vector> 23 24 namespace llvm { 25 26 class Function; 27 class Instruction; 28 class 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. 57 class ValueProfileCollector { 58 public: 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 76 private: 77 class ValueProfileCollectorImpl; 78 std::unique_ptr<ValueProfileCollectorImpl> PImpl; 79 }; 80 81 } // namespace llvm 82 83 #endif 84