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 24 namespace 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. 53 class ValueProfileCollector { 54 public: 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 72 private: 73 class ValueProfileCollectorImpl; 74 std::unique_ptr<ValueProfileCollectorImpl> PImpl; 75 }; 76 77 } // namespace llvm 78 79 #endif 80