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| //===- 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/IR/Function.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include "llvm/ProfileData/InstrProf.h"
namespace llvm {
/// 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);
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
|