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77 lines
2.9 KiB
C++
77 lines
2.9 KiB
C++
//===- ParallelLoopSpecialization.cpp - loop.parallel specialization ------===//
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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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// Specializes parallel loops for easier unrolling and vectorization.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/Affine/IR/AffineOps.h"
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#include "mlir/Dialect/LoopOps/LoopOps.h"
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#include "mlir/Dialect/LoopOps/Passes.h"
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#include "mlir/Dialect/StandardOps/IR/Ops.h"
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#include "mlir/IR/AffineExpr.h"
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#include "mlir/IR/BlockAndValueMapping.h"
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#include "mlir/Pass/Pass.h"
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using namespace mlir;
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using loop::ParallelOp;
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/// Rewrite a loop with bounds defined by an affine.min with a constant into 2
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/// loops after checking if the bounds are equal to that constant. This is
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/// beneficial if the loop will almost always have the constant bound and that
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/// version can be fully unrolled and vectorized.
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static void specializeLoopForUnrolling(ParallelOp op) {
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SmallVector<int64_t, 2> constantIndices;
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constantIndices.reserve(op.upperBound().size());
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for (auto bound : op.upperBound()) {
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auto minOp = dyn_cast_or_null<AffineMinOp>(bound.getDefiningOp());
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if (!minOp)
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return;
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int64_t minConstant = std::numeric_limits<int64_t>::max();
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for (auto expr : minOp.map().getResults()) {
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if (auto constantIndex = expr.dyn_cast<AffineConstantExpr>())
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minConstant = std::min(minConstant, constantIndex.getValue());
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}
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if (minConstant == std::numeric_limits<int64_t>::max())
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return;
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constantIndices.push_back(minConstant);
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}
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OpBuilder b(op);
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BlockAndValueMapping map;
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Value cond;
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for (auto bound : llvm::zip(op.upperBound(), constantIndices)) {
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Value constant = b.create<ConstantIndexOp>(op.getLoc(), std::get<1>(bound));
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Value cmp = b.create<CmpIOp>(op.getLoc(), CmpIPredicate::eq,
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std::get<0>(bound), constant);
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cond = cond ? b.create<AndOp>(op.getLoc(), cond, cmp) : cmp;
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map.map(std::get<0>(bound), constant);
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}
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auto ifOp = b.create<loop::IfOp>(op.getLoc(), cond, /*withElseRegion=*/true);
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ifOp.getThenBodyBuilder().clone(*op.getOperation(), map);
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ifOp.getElseBodyBuilder().clone(*op.getOperation());
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op.erase();
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}
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namespace {
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struct ParallelLoopSpecialization
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: public FunctionPass<ParallelLoopSpecialization> {
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/// Include the generated pass utilities.
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#define GEN_PASS_LoopParallelLoopSpecialization
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#include "mlir/Dialect/LoopOps/Passes.h.inc"
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void runOnFunction() override {
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getFunction().walk([](ParallelOp op) { specializeLoopForUnrolling(op); });
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}
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};
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} // namespace
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std::unique_ptr<Pass> mlir::createParallelLoopSpecializationPass() {
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return std::make_unique<ParallelLoopSpecialization>();
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}
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