ControlFlowSink.cpp

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//===- ControlFlowSink.cpp - Code to perform control-flow sinking ---------===//
//
// 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 a basic control-flow sink pass. Control-flow sinking
// moves operations whose only uses are in conditionally-executed blocks in to
// those blocks so that they aren't executed on paths where their results are
// not needed.
//
//===----------------------------------------------------------------------===//

#include "PassDetail.h"
#include "mlir/IR/Dominance.h"
#include "mlir/Interfaces/ControlFlowInterfaces.h"
#include "mlir/Interfaces/SideEffectInterfaces.h"
#include "mlir/Transforms/ControlFlowSinkUtils.h"
#include "mlir/Transforms/Passes.h"
#include "mlir/Transforms/SideEffectUtils.h"

using namespace mlir;

namespace {
/// A control-flow sink pass.
struct ControlFlowSink : public ControlFlowSinkBase<ControlFlowSink> {
  void runOnOperation() override;
};
} // end anonymous namespace

void ControlFlowSink::runOnOperation() {
  auto &domInfo = getAnalysis<DominanceInfo>();
  getOperation()->walk([&](RegionBranchOpInterface branch) {
    SmallVector<Region *> regionsToSink;
    // Get the regions are that known to be executed at most once.
    getSinglyExecutedRegionsToSink(branch, regionsToSink);
    // Sink side-effect free operations.
    numSunk = controlFlowSink(
        regionsToSink, domInfo,
        [](Operation *op, Region *) { return isSideEffectFree(op); },
        [](Operation *op, Region *region) {
          // Move the operation to the beginning of the region's entry block.
          // This guarantees the preservation of SSA dominance of all of the
          // operation's uses are in the region.
          op->moveBefore(&region->front(), region->front().begin());
        });
  });
}

std::unique_ptr<Pass> mlir::createControlFlowSinkPass() {
  return std::make_unique<ControlFlowSink>();
}