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There is currently no path to lower scf.forall to scf.parallel with the goal of targeting the OpenMP dialect. In the SCF->ControlFlow conversion, scf.forall is briefly converted to scf.parallel, but the scf.parallel is lowered directly to a sequential loop. This makes experimenting with scf.forall for CPU execution difficult. This change factors out the rewrite in the SCF->ControlFlow pass into a utility function that can then be used in the SCF->ControlFlow lowering and via a separate -scf-forall-to-parallel pass. --------- Co-authored-by: Spenser Bauman <sabauma@fastmail>
87 lines
3.0 KiB
C++
87 lines
3.0 KiB
C++
//===- ForallToParallel.cpp - scf.forall to scf.parallel loop conversion --===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Transforms SCF.ForallOp's into SCF.ParallelOps's.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/SCF/IR/SCF.h"
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#include "mlir/Dialect/SCF/Transforms/Passes.h"
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#include "mlir/Dialect/SCF/Transforms/Transforms.h"
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#include "mlir/IR/PatternMatch.h"
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namespace mlir {
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#define GEN_PASS_DEF_SCFFORALLTOPARALLELLOOP
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#include "mlir/Dialect/SCF/Transforms/Passes.h.inc"
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} // namespace mlir
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using namespace mlir;
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LogicalResult mlir::scf::forallToParallelLoop(RewriterBase &rewriter,
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scf::ForallOp forallOp,
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scf::ParallelOp *result) {
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OpBuilder::InsertionGuard guard(rewriter);
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rewriter.setInsertionPoint(forallOp);
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Location loc = forallOp.getLoc();
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if (!forallOp.getOutputs().empty())
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return rewriter.notifyMatchFailure(
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forallOp,
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"only fully bufferized scf.forall ops can be lowered to scf.parallel");
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// Convert mixed bounds and steps to SSA values.
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SmallVector<Value> lbs = getValueOrCreateConstantIndexOp(
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rewriter, loc, forallOp.getMixedLowerBound());
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SmallVector<Value> ubs = getValueOrCreateConstantIndexOp(
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rewriter, loc, forallOp.getMixedUpperBound());
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SmallVector<Value> steps =
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getValueOrCreateConstantIndexOp(rewriter, loc, forallOp.getMixedStep());
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// Create empty scf.parallel op.
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auto parallelOp = rewriter.create<scf::ParallelOp>(loc, lbs, ubs, steps);
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rewriter.eraseBlock(¶llelOp.getRegion().front());
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rewriter.inlineRegionBefore(forallOp.getRegion(), parallelOp.getRegion(),
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parallelOp.getRegion().begin());
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// Replace the terminator.
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rewriter.setInsertionPointToEnd(¶llelOp.getRegion().front());
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rewriter.replaceOpWithNewOp<scf::ReduceOp>(
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parallelOp.getRegion().front().getTerminator());
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// If the mapping attribute is present, propagate to the new parallelOp.
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if (forallOp.getMapping())
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parallelOp->setAttr("mapping", *forallOp.getMapping());
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// Erase the scf.forall op.
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rewriter.replaceOp(forallOp, parallelOp);
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if (result)
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*result = parallelOp;
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return success();
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}
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namespace {
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struct ForallToParallelLoop final
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: public impl::SCFForallToParallelLoopBase<ForallToParallelLoop> {
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void runOnOperation() override {
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Operation *parentOp = getOperation();
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IRRewriter rewriter(parentOp->getContext());
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parentOp->walk([&](scf::ForallOp forallOp) {
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if (failed(scf::forallToParallelLoop(rewriter, forallOp))) {
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return signalPassFailure();
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}
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});
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}
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};
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} // namespace
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std::unique_ptr<Pass> mlir::createForallToParallelLoopPass() {
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return std::make_unique<ForallToParallelLoop>();
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}
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