//===- ValueProfileCollector.h - determine what to value profile ----------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file contains a utility class, ValueProfileCollector, that is used to // determine what kind of llvm::Value's are worth value-profiling, at which // point in the program, and which instruction holds the Value Profile metadata. // Currently, the only users of this utility is the PGOInstrumentation[Gen|Use] // passes. //===----------------------------------------------------------------------===// #ifndef LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H #define LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H #include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/ProfileData/InstrProf.h" #include #include namespace llvm { class Function; class Instruction; class Value; /// Utility analysis that determines what values are worth profiling. /// The actual logic is inside the ValueProfileCollectorImpl, whose job is to /// populate the Candidates vector. /// /// Value profiling an expression means to track the values that this expression /// takes at runtime and the frequency of each value. /// It is important to distinguish between two sets of value profiles for a /// particular expression: /// 1) The set of values at the point of evaluation. /// 2) The set of values at the point of use. /// In some cases, the two sets are identical, but it's not unusual for the two /// to differ. /// /// To elaborate more, consider this C code, and focus on the expression `nn`: /// void foo(int nn, bool b) { /// if (b) memcpy(x, y, nn); /// } /// The point of evaluation can be as early as the start of the function, and /// let's say the value profile for `nn` is: /// total=100; (value,freq) set = {(8,10), (32,50)} /// The point of use is right before we call memcpy, and since we execute the /// memcpy conditionally, the value profile of `nn` can be: /// total=15; (value,freq) set = {(8,10), (4,5)} /// /// For this reason, a plugin is responsible for computing the insertion point /// for each value to be profiled. The `CandidateInfo` structure encapsulates /// all the information needed for each value profile site. class ValueProfileCollector { public: struct CandidateInfo { Value *V; // The value to profile. Instruction *InsertPt; // Insert the VP lib call before this instr. Instruction *AnnotatedInst; // Where metadata is attached. }; ValueProfileCollector(Function &Fn, TargetLibraryInfo &TLI); ValueProfileCollector(ValueProfileCollector &&) = delete; ValueProfileCollector &operator=(ValueProfileCollector &&) = delete; ValueProfileCollector(const ValueProfileCollector &) = delete; ValueProfileCollector &operator=(const ValueProfileCollector &) = delete; ~ValueProfileCollector(); /// returns a list of value profiling candidates of the given kind std::vector get(InstrProfValueKind Kind) const; private: class ValueProfileCollectorImpl; std::unique_ptr PImpl; }; } // namespace llvm #endif