| //===- 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 <memory> |
| #include <vector> |
| |
| 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<CandidateInfo> get(InstrProfValueKind Kind) const; |
| |
| private: |
| class ValueProfileCollectorImpl; |
| std::unique_ptr<ValueProfileCollectorImpl> PImpl; |
| }; |
| |
| } // namespace llvm |
| |
| #endif |