ForallToParallel.cpp

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//===- ForallToParallel.cpp - scf.forall to scf.parallel loop conversion --===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Transforms SCF.ForallOp's into SCF.ParallelOps's.
//
//===----------------------------------------------------------------------===//
 
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Dialect/SCF/Transforms/Passes.h"
#include "mlir/Dialect/SCF/Transforms/Transforms.h"
#include "mlir/IR/PatternMatch.h"
 
namespace mlir {
#define GEN_PASS_DEF_SCFFORALLTOPARALLELLOOP
#include "mlir/Dialect/SCF/Transforms/Passes.h.inc"
} // namespace mlir
 
using namespace mlir;
 
LogicalResult mlir::scf::forallToParallelLoop(RewriterBase &rewriter,
                                              scf::ForallOp forallOp,
                                              scf::ParallelOp *result) {
  OpBuilder::InsertionGuard guard(rewriter);
  rewriter.setInsertionPoint(forallOp);
 
  Location loc = forallOp.getLoc();
  if (!forallOp.getOutputs().empty())
    return rewriter.notifyMatchFailure(
        forallOp,
        "only fully bufferized scf.forall ops can be lowered to scf.parallel");
 
  // Convert mixed bounds and steps to SSA values.
  SmallVector<Value> lbs = forallOp.getLowerBound(rewriter);
  SmallVector<Value> ubs = forallOp.getUpperBound(rewriter);
  SmallVector<Value> steps = forallOp.getStep(rewriter);
 
  // Create empty scf.parallel op.
  auto parallelOp = rewriter.create<scf::ParallelOp>(loc, lbs, ubs, steps);
  rewriter.eraseBlock(&parallelOp.getRegion().front());
  rewriter.inlineRegionBefore(forallOp.getRegion(), parallelOp.getRegion(),
                              parallelOp.getRegion().begin());
  // Replace the terminator.
  rewriter.setInsertionPointToEnd(&parallelOp.getRegion().front());
  rewriter.replaceOpWithNewOp<scf::ReduceOp>(
      parallelOp.getRegion().front().getTerminator());
 
  // If the mapping attribute is present, propagate to the new parallelOp.
  if (forallOp.getMapping())
    parallelOp->setAttr("mapping", *forallOp.getMapping());
 
  // Erase the scf.forall op.
  rewriter.replaceOp(forallOp, parallelOp);
 
  if (result)
    *result = parallelOp;
 
  return success();
}
 
namespace {
struct ForallToParallelLoop final
    : public impl::SCFForallToParallelLoopBase<ForallToParallelLoop> {
  void runOnOperation() override {
    Operation *parentOp = getOperation();
    IRRewriter rewriter(parentOp->getContext());
 
    parentOp->walk([&](scf::ForallOp forallOp) {
      if (failed(scf::forallToParallelLoop(rewriter, forallOp))) {
        return signalPassFailure();
      }
    });
  }
};
} // namespace
 
std::unique_ptr<Pass> mlir::createForallToParallelLoopPass() {
  return std::make_unique<ForallToParallelLoop>();
}