llvm/llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h

//===- llvm/Transforms/Vectorize/LoopVectorizationLegality.h ----*- 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
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This file defines the LoopVectorizationLegality class. Original code
/// in Loop Vectorizer has been moved out to its own file for modularity
/// and reusability.
///
/// Currently, it works for innermost loop vectorization. Extending this to
/// outer loop vectorization is a TODO item.
///
/// Also provides:
/// 1) LoopVectorizeHints class which keeps a number of loop annotations
/// locally for easy look up. It has the ability to write them back as
/// loop metadata, upon request.
/// 2) LoopVectorizationRequirements class for lazy bail out for the purpose
/// of reporting useful failure to vectorize message.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZATIONLEGALITY_H
#define LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZATIONLEGALITY_H

#include "llvm/ADT/MapVector.h"
#include "llvm/Analysis/LoopAccessAnalysis.h"
#include "llvm/Support/TypeSize.h"
#include "llvm/Transforms/Utils/LoopUtils.h"

namespace llvm {
class AssumptionCache;
class BasicBlock;
class BlockFrequencyInfo;
class DemandedBits;
class DominatorTree;
class Function;
class Loop;
class LoopInfo;
class Metadata;
class OptimizationRemarkEmitter;
class PredicatedScalarEvolution;
class ProfileSummaryInfo;
class TargetLibraryInfo;
class TargetTransformInfo;
class Type;

/// Utility class for getting and setting loop vectorizer hints in the form
/// of loop metadata.
/// This class keeps a number of loop annotations locally (as member variables)
/// and can, upon request, write them back as metadata on the loop. It will
/// initially scan the loop for existing metadata, and will update the local
/// values based on information in the loop.
/// We cannot write all values to metadata, as the mere presence of some info,
/// for example 'force', means a decision has been made. So, we need to be
/// careful NOT to add them if the user hasn't specifically asked so.
class LoopVectorizeHints { … };

/// This holds vectorization requirements that must be verified late in
/// the process. The requirements are set by legalize and costmodel. Once
/// vectorization has been determined to be possible and profitable the
/// requirements can be verified by looking for metadata or compiler options.
/// For example, some loops require FP commutativity which is only allowed if
/// vectorization is explicitly specified or if the fast-math compiler option
/// has been provided.
/// Late evaluation of these requirements allows helpful diagnostics to be
/// composed that tells the user what need to be done to vectorize the loop. For
/// example, by specifying #pragma clang loop vectorize or -ffast-math. Late
/// evaluation should be used only when diagnostics can generated that can be
/// followed by a non-expert user.
class LoopVectorizationRequirements { … };

/// This holds details about a histogram operation -- a load -> update -> store
/// sequence where each lane in a vector might be updating the same element as
/// another lane.
struct HistogramInfo { … };

/// LoopVectorizationLegality checks if it is legal to vectorize a loop, and
/// to what vectorization factor.
/// This class does not look at the profitability of vectorization, only the
/// legality. This class has two main kinds of checks:
/// * Memory checks - The code in canVectorizeMemory checks if vectorization
///   will change the order of memory accesses in a way that will change the
///   correctness of the program.
/// * Scalars checks - The code in canVectorizeInstrs and canVectorizeMemory
/// checks for a number of different conditions, such as the availability of a
/// single induction variable, that all types are supported and vectorize-able,
/// etc. This code reflects the capabilities of InnerLoopVectorizer.
/// This class is also used by InnerLoopVectorizer for identifying
/// induction variable and the different reduction variables.
class LoopVectorizationLegality { … };

} // namespace llvm

#endif // LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZATIONLEGALITY_H