llvm/llvm/include/llvm/SandboxIR/Region.h

//===- Region.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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_REGION_H
#define LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_REGION_H

#include <memory>

#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/SandboxIR/Instruction.h"
#include "llvm/Support/raw_ostream.h"

namespace llvm::sandboxir {

/// The main job of the Region is to point to new instructions generated by
/// vectorization passes. It is the unit that RegionPasses operate on with their
/// runOnRegion() function.
///
/// The region allows us to stack transformations horizontally, meaning that
/// each transformation operates on a single region and the resulting region is
/// the input to the next transformation, as opposed to vertically, which is the
/// common way of applying a transformation across the whole function. This
/// enables us to check for profitability and decide whether we accept or
/// rollback at a region granularity, which is much better than doing this at
/// the function level.
///
//  Traditional approach: transformations applied vertically for the whole
//  function
//    F
//  +----+
//  |    |
//  |    |
//  |    | -> Transform1 ->  ... -> TransformN -> Check Cost
//  |    |
//  |    |
//  +----+
//
//  Region-based approach: transformations applied horizontally, for each Region
//    F
//  +----+
//  |Rgn1| -> Transform1 ->  ... -> TransformN -> Check Cost
//  |    |
//  |Rgn2| -> Transform1 ->  ... -> TransformN -> Check Cost
//  |    |
//  |Rgn3| -> Transform1 ->  ... -> TransformN -> Check Cost
//  +----+

class Region { … };

} // namespace llvm::sandboxir

#endif // LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_REGION_H