llvm/mlir/lib/Dialect/SCF/Transforms/ParallelLoopFusion.cpp

//===- ParallelLoopFusion.cpp - Code to perform loop fusion ---------------===//
//
// 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 loop fusion on parallel loops.
//
//===----------------------------------------------------------------------===//

#include "mlir/Dialect/SCF/Transforms/Passes.h"

#include "mlir/Analysis/AliasAnalysis.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Dialect/SCF/Transforms/Transforms.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/IRMapping.h"
#include "mlir/IR/OpDefinition.h"
#include "mlir/IR/OperationSupport.h"
#include "mlir/Interfaces/SideEffectInterfaces.h"

namespace mlir {
#define GEN_PASS_DEF_SCFPARALLELLOOPFUSION
#include "mlir/Dialect/SCF/Transforms/Passes.h.inc"
} // namespace mlir

usingnamespacemlir;
usingnamespacemlir::scf;

/// Verify there are no nested ParallelOps.
static bool hasNestedParallelOp(ParallelOp ploop) { … }

/// Verify equal iteration spaces.
static bool equalIterationSpaces(ParallelOp firstPloop,
                                 ParallelOp secondPloop) { … }

/// Checks if the parallel loops have mixed access to the same buffers. Returns
/// `true` if the first parallel loop writes to the same indices that the second
/// loop reads.
static bool haveNoReadsAfterWriteExceptSameIndex(
    ParallelOp firstPloop, ParallelOp secondPloop,
    const IRMapping &firstToSecondPloopIndices,
    llvm::function_ref<bool(Value, Value)> mayAlias) { … }

/// Analyzes dependencies in the most primitive way by checking simple read and
/// write patterns.
static LogicalResult
verifyDependencies(ParallelOp firstPloop, ParallelOp secondPloop,
                   const IRMapping &firstToSecondPloopIndices,
                   llvm::function_ref<bool(Value, Value)> mayAlias) { … }

static bool isFusionLegal(ParallelOp firstPloop, ParallelOp secondPloop,
                          const IRMapping &firstToSecondPloopIndices,
                          llvm::function_ref<bool(Value, Value)> mayAlias) { … }

/// Prepends operations of firstPloop's body into secondPloop's body.
/// Updates secondPloop with new loop.
static void fuseIfLegal(ParallelOp firstPloop, ParallelOp &secondPloop,
                        OpBuilder builder,
                        llvm::function_ref<bool(Value, Value)> mayAlias) { … }

void mlir::scf::naivelyFuseParallelOps(
    Region &region, llvm::function_ref<bool(Value, Value)> mayAlias) { … }

namespace {
struct ParallelLoopFusion
    : public impl::SCFParallelLoopFusionBase<ParallelLoopFusion> { … };
} // namespace

std::unique_ptr<Pass> mlir::createParallelLoopFusionPass() { … }