llvm/llvm/include/llvm/Analysis/LazyBlockFrequencyInfo.h

//===- LazyBlockFrequencyInfo.h - Lazy Block Frequency Analysis -*- C++ -*-===//
//
// 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 is an alternative analysis pass to BlockFrequencyInfoWrapperPass.  The
// difference is that with this pass the block frequencies are not computed when
// the analysis pass is executed but rather when the BFI result is explicitly
// requested by the analysis client.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
#define LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H

#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/LazyBranchProbabilityInfo.h"
#include "llvm/Pass.h"

namespace llvm {
class Function;
class LoopInfo;

/// Wraps a BFI to allow lazy computation of the block frequencies.
///
/// A pass that only conditionally uses BFI can uncondtionally require the
/// analysis without paying for the overhead if BFI doesn't end up being used.
template <typename FunctionT, typename BranchProbabilityInfoPassT,
          typename LoopInfoT, typename BlockFrequencyInfoT>
class LazyBlockFrequencyInfo { … };

/// This is an alternative analysis pass to
/// BlockFrequencyInfoWrapperPass.  The difference is that with this pass the
/// block frequencies are not computed when the analysis pass is executed but
/// rather when the BFI result is explicitly requested by the analysis client.
///
/// There are some additional requirements for any client pass that wants to use
/// the analysis:
///
/// 1. The pass needs to initialize dependent passes with:
///
///   INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
///
/// 2. Similarly, getAnalysisUsage should call:
///
///   LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU)
///
/// 3. The computed BFI should be requested with
///    getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() before either LoopInfo
///    or BPI could be invalidated for example by changing the CFG.
///
/// Note that it is expected that we wouldn't need this functionality for the
/// new PM since with the new PM, analyses are executed on demand.

class LazyBlockFrequencyInfoPass : public FunctionPass { … };

/// Helper for client passes to initialize dependent passes for LBFI.
void initializeLazyBFIPassPass(PassRegistry &Registry);
} // namespace llvm
#endif