llvm/llvm/include/llvm/Analysis/LoopUnrollAnalyzer.h

//===- llvm/Analysis/LoopUnrollAnalyzer.h - Loop Unroll Analyzer-*- 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 file implements UnrolledInstAnalyzer class. It's used for predicting
// potential effects that loop unrolling might have, such as enabling constant
// propagation and other optimizations.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_LOOPUNROLLANALYZER_H
#define LLVM_ANALYSIS_LOOPUNROLLANALYZER_H

#include "llvm/ADT/APInt.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/IR/InstVisitor.h"

// This class is used to get an estimate of the optimization effects that we
// could get from complete loop unrolling. It comes from the fact that some
// loads might be replaced with concrete constant values and that could trigger
// a chain of instruction simplifications.
//
// E.g. we might have:
//   int a[] = {0, 1, 0};
//   v = 0;
//   for (i = 0; i < 3; i ++)
//     v += b[i]*a[i];
// If we completely unroll the loop, we would get:
//   v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2]
// Which then will be simplified to:
//   v = b[0]* 0 + b[1]* 1 + b[2]* 0
// And finally:
//   v = b[1]
namespace llvm {
class Instruction;

class UnrolledInstAnalyzer : private InstVisitor<UnrolledInstAnalyzer, bool> { … };
}
#endif