250 lines
9.7 KiB
C++
250 lines
9.7 KiB
C++
//===- Tiling.cpp - Implementation of tiling using TilingInterface -------===//
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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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// This file implements the tiling using TilingInterface.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/SCF/Transforms/TileUsingInterface.h"
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#include "mlir/Dialect/Affine/IR/AffineOps.h"
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#include "mlir/Dialect/Arithmetic/IR/Arithmetic.h"
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#include "mlir/Dialect/Func/IR/FuncOps.h"
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#include "mlir/Dialect/SCF/Utils/Utils.h"
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#include "mlir/Dialect/Tensor/IR/Tensor.h"
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#include "mlir/IR/Matchers.h"
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#include "mlir/IR/PatternMatch.h"
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#include "mlir/Interfaces/TilingInterface.h"
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#include "llvm/Support/Debug.h"
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#define DEBUG_TYPE "tile-using-interface"
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using namespace mlir;
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scf::SCFTilingOptions &
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scf::SCFTilingOptions::setTileSizes(ArrayRef<int64_t> ts) {
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assert(!tileSizeComputationFunction && "tile sizes already set");
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SmallVector<int64_t, 4> tileSizes(ts.begin(), ts.end());
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tileSizeComputationFunction = [tileSizes](OpBuilder &b, Operation *op) {
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OpBuilder::InsertionGuard guard(b);
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b.setInsertionPointToStart(
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&op->getParentOfType<func::FuncOp>().getBody().front());
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return llvm::to_vector<4>(map_range(tileSizes, [&](int64_t s) {
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Value v = b.create<arith::ConstantIndexOp>(op->getLoc(), s);
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return v;
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}));
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};
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return *this;
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}
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/// Generate an empty loop nest that represents the tiled loop nest shell.
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/// - `loopRanges` specifies the lb, ub and step of the untiled iteration space.
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/// - `tileSizeVals` is the tile sizes to use. Zero represent untiled loops.
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/// - In `offsets` and `sizes` return the multi-dimensional offset and size of
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/// the
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/// tile processed within the inner most loop.
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static SmallVector<scf::ForOp>
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generateTileLoopNest(OpBuilder &builder, Location loc,
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ArrayRef<Range> loopRanges, ArrayRef<Value> tileSizeVals,
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SmallVector<OpFoldResult> &offsets,
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SmallVector<OpFoldResult> &sizes) {
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assert(!loopRanges.empty() && "expected at least one loop range");
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assert(loopRanges.size() == tileSizeVals.size() &&
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"expected as many tile sizes as loop ranges");
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OpBuilder::InsertionGuard guard(builder);
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SmallVector<scf::ForOp> loops;
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offsets.resize(loopRanges.size());
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sizes.resize(loopRanges.size());
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// The tile size to use (to avoid out of bounds access) is minimum of
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// `tileSize` and `ub - iv`, where `iv` is the induction variable
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// of the tiled loop.
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AffineExpr s0, s1, d0;
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bindDims(builder.getContext(), d0);
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bindSymbols(builder.getContext(), s0, s1);
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AffineMap minMap = AffineMap::get(1, 2, {s0, s1 - d0}, builder.getContext());
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for (auto loopRange : llvm::enumerate(loopRanges)) {
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// No loops if tile size is zero. Set offset and size to the loop
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// offset and size.
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if (matchPattern(tileSizeVals[loopRange.index()], m_Zero())) {
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offsets[loopRange.index()] = loopRange.value().offset;
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sizes[loopRange.index()] = loopRange.value().size;
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continue;
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}
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auto loop = builder.create<scf::ForOp>(
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loc, loopRange.value().offset, loopRange.value().size,
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tileSizeVals[loopRange.index()], ValueRange{},
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[&](OpBuilder &bodyBuilder, Location bodyLoc, Value iv,
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ValueRange /*iterArgs*/) {
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Value boundedTileSize = builder.create<AffineMinOp>(
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bodyLoc, minMap,
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ValueRange{iv, tileSizeVals[loopRange.index()],
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loopRange.value().size});
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sizes[loopRange.index()] = boundedTileSize;
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builder.create<scf::YieldOp>(loc);
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});
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offsets[loopRange.index()] = loop.getInductionVar();
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loops.push_back(loop);
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builder.setInsertionPoint(loop.getBody()->getTerminator());
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}
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return loops;
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}
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scf::TileUsingSCFForOp::TileUsingSCFForOp(MLIRContext *context,
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scf::SCFTilingOptions options,
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PatternBenefit benefit)
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: OpInterfaceRewritePattern<TilingInterface>(context, benefit),
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options(std::move(options)) {}
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scf::TileUsingSCFForOp::TileUsingSCFForOp(StringRef opName,
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MLIRContext *context,
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scf::SCFTilingOptions options,
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PatternBenefit benefit)
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: OpInterfaceRewritePattern<TilingInterface>(context, benefit),
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options(std::move(options)) {}
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FailureOr<scf::SCFTilingResult>
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scf::TileUsingSCFForOp::returningMatchAndRewrite(
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TilingInterface op, PatternRewriter &rewriter) const {
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OpBuilder::InsertionGuard guard(rewriter);
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rewriter.setInsertionPointAfter(op);
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if (!options.tileSizeComputationFunction) {
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return rewriter.notifyMatchFailure(
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op, "missing tile size computation function");
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}
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// 1. Get the range of the loops that are represented by the operation.
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SmallVector<Range> iterationDomain = op.getIterationDomain(rewriter);
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size_t numLoops = iterationDomain.size();
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if (numLoops == 0) {
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return rewriter.notifyMatchFailure(
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op, "unable to tile op with no iteration domain");
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}
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// 2. Materialize the tile sizes. Enforce the convention that "tiling by zero"
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// skips tiling a particular dimension. This convention is significantly
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// simpler to handle instead of adjusting affine maps to account for missing
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// dimensions.
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SmallVector<Value, 4> tileSizeVector =
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options.tileSizeComputationFunction(rewriter, op);
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if (tileSizeVector.size() < iterationDomain.size()) {
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auto zero = rewriter.create<arith::ConstantIndexOp>(op.getLoc(), 0);
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tileSizeVector.append(numLoops - tileSizeVector.size(), zero);
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}
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scf::SCFTilingResult tilingResult;
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SmallVector<OpFoldResult> offsets, sizes;
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{
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// 3. Materialize an empty loop nest that iterates over the tiles. These
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// loops for now do not return any values even if the original operation has
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// results.
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tilingResult.loops = generateTileLoopNest(
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rewriter, op.getLoc(), iterationDomain, tileSizeVector, offsets, sizes);
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LLVM_DEBUG({
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if (!tilingResult.loops.empty()) {
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llvm::errs() << "LoopNest shell :\n";
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tilingResult.loops.front().dump();
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llvm::errs() << "\n";
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}
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});
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// 4. Generate the tiled implementation within the inner most loop.
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if (!tilingResult.loops.empty())
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rewriter.setInsertionPoint(
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tilingResult.loops.back().getBody()->getTerminator());
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SmallVector<Operation *> tiledImplementation = op.getTiledImplementation(
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rewriter, op.getDestinationOperands(rewriter), offsets, sizes, true);
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if (tiledImplementation.size() != 1) {
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return rewriter.notifyMatchFailure(
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op, "expected tiled implementation to return a single op");
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}
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tilingResult.tiledOp = tiledImplementation[0];
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LLVM_DEBUG({
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if (!tilingResult.loops.empty()) {
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llvm::errs() << "After tiled implementation :\n";
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tilingResult.loops.front().dump();
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llvm::errs() << "\n";
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}
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});
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}
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if (op->getNumResults() == 0) {
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rewriter.eraseOp(op);
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return tilingResult;
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}
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// 5. If the original operations has results, modify the loop nest to yield
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// the replacement values.
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SmallVector<Value> replacements;
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if (tilingResult.loops.empty()) {
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// 5a. If there were no loops, the tiled implementation results are the
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// replacements.
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rewriter.replaceOp(op, tilingResult.tiledOp->getResults());
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return tilingResult;
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}
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// 5b. `scf.for` with tensor semantics requires the loop nest to yield the
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// replacement values using destructive updates. Use the `TilingInterface`
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// to get the position of the result tiles and use that to generate the
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// destructive update pattern, i.e.,
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//
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// ```mlir
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// scf.for %iv0 = ... {
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// %0 = tiled_op
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// }
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// ```
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//
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// is transformed to
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//
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// ```mlir
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// %result = scf.for %iv0 = ... iter_args(%arg = %init) -> .. {
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// %0 = tiled_op
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// %1 = tensor.insert_slice %0 into %arg[..] [..] [..]
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// scf.yield %1
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// }
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// ```
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NewYieldValueFn yieldValueFn =
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[&](OpBuilder &b, Location loc,
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ArrayRef<BlockArgument> newBBArgs) -> SmallVector<Value> {
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SmallVector<Value> yieldedValues;
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Attribute one = b.getIndexAttr(1);
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for (auto resultNum : llvm::seq<unsigned>(0, op->getNumResults())) {
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SmallVector<OpFoldResult> resultTileOffsets, resultTileSizes;
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if (failed(op.getResultTilePosition(b, resultNum, offsets, sizes,
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resultTileOffsets,
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resultTileSizes))) {
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op.emitOpError("unable to get position of result ")
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<< resultNum << " of the tiled implementation";
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return {};
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}
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SmallVector<OpFoldResult> resultTileStrides(resultTileOffsets.size(),
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one);
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Value yieldedValue = b.create<tensor::InsertSliceOp>(
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op->getLoc(), tilingResult.tiledOp->getResult(resultNum),
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newBBArgs[resultNum], resultTileOffsets, resultTileSizes,
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resultTileStrides);
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yieldedValues.push_back(yieldedValue);
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}
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return yieldedValues;
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};
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SmallVector<scf::ForOp> newLoops = replaceLoopNestWithNewYields(
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rewriter, tilingResult.loops, op.getDestinationOperands(rewriter),
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yieldValueFn);
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for (auto loop : llvm::enumerate(tilingResult.loops)) {
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rewriter.eraseOp(loop.value());
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tilingResult.loops[loop.index()] = newLoops[loop.index()];
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}
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rewriter.replaceOp(op, tilingResult.loops.front().getResults());
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return tilingResult;
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}
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