226896c3a8
Do not hoist vector transfers that do not match exactly. In particular, do not hoist transfers with different vector types. This has lead to invalid IR (yielded vector type is different from iter_arg type) in downstream projects. Differential Revision: https://reviews.llvm.org/D155052
232 lines
9.5 KiB
C++
232 lines
9.5 KiB
C++
//===- Hoisting.cpp - Linalg hoisting transformations ---------------------===//
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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 functions concerned with hoisting invariant operations
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// in the context of Linalg transformations.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/Linalg/Transforms/Hoisting.h"
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#include "mlir/Analysis/SliceAnalysis.h"
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#include "mlir/Dialect/Affine/Analysis/AffineStructures.h"
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#include "mlir/Dialect/Affine/IR/AffineOps.h"
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#include "mlir/Dialect/Affine/IR/AffineValueMap.h"
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#include "mlir/Dialect/Affine/Utils.h"
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#include "mlir/Dialect/Arith/IR/Arith.h"
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#include "mlir/Dialect/Func/IR/FuncOps.h"
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#include "mlir/Dialect/Linalg/IR/Linalg.h"
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#include "mlir/Dialect/Linalg/Transforms/Transforms.h"
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#include "mlir/Dialect/SCF/IR/SCF.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/Dialect/Vector/IR/VectorOps.h"
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#include "mlir/Dialect/Vector/Utils/VectorUtils.h"
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#include "mlir/IR/BuiltinOps.h"
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#include "mlir/IR/Dominance.h"
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#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
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#include "mlir/Transforms/LoopInvariantCodeMotionUtils.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/TypeSwitch.h"
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#include "llvm/Support/Debug.h"
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using llvm::dbgs;
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#define DEBUG_TYPE "linalg-hoisting"
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#define DBGS() (dbgs() << '[' << DEBUG_TYPE << "] ")
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using namespace mlir;
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using namespace mlir::linalg;
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void mlir::linalg::hoistRedundantVectorTransfersOnTensor(func::FuncOp func) {
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IRRewriter rewriter(func->getContext());
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// TODO: walking in some reverse / inside-out order would be more efficient
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// and would capture more cases.
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func.walk([&](scf::ForOp forOp) {
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hoistRedundantSubsetExtractInsert(rewriter, forOp);
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});
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}
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static bool noAliasingUseInLoop(vector::TransferReadOp transferRead,
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LoopLikeOpInterface loop) {
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Value source = transferRead.getSource();
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while (auto subView = source.getDefiningOp<memref::SubViewOp>())
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source = subView.getSource();
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llvm::SmallVector<Operation *, 32> users(source.getUsers().begin(),
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source.getUsers().end());
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llvm::SmallDenseSet<Operation *, 32> processed;
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while (!users.empty()) {
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Operation *user = users.pop_back_val();
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// If the user has already been processed skip.
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if (!processed.insert(user).second)
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continue;
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if (auto subView = dyn_cast<memref::SubViewOp>(user)) {
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users.append(subView->getUsers().begin(), subView->getUsers().end());
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continue;
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}
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if (isMemoryEffectFree(user) || isa<vector::TransferReadOp>(user))
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continue;
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if (!loop->isAncestor(user))
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continue;
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return false;
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}
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return true;
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}
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void mlir::linalg::hoistRedundantVectorTransfers(func::FuncOp func) {
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bool changed = true;
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while (changed) {
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changed = false;
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// First move loop invariant ops outside of their loop. This needs to be
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// done before as we cannot move ops without interrupting the function walk.
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func.walk(
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[&](LoopLikeOpInterface loopLike) { moveLoopInvariantCode(loopLike); });
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func.walk([&](vector::TransferReadOp transferRead) {
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if (!isa<MemRefType>(transferRead.getShapedType()))
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return WalkResult::advance();
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LLVM_DEBUG(DBGS() << "Candidate for hoisting: "
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<< *transferRead.getOperation() << "\n");
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auto loop = dyn_cast<LoopLikeOpInterface>(transferRead->getParentOp());
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LLVM_DEBUG(DBGS() << "Parent op: " << *transferRead->getParentOp()
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<< "\n");
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if (!isa_and_nonnull<scf::ForOp, affine::AffineForOp>(loop))
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return WalkResult::advance();
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LLVM_DEBUG(DBGS() << "Candidate read: " << *transferRead.getOperation()
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<< "\n");
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SetVector<Operation *> forwardSlice;
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getForwardSlice(transferRead.getOperation(), &forwardSlice);
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// Look for the last TransferWriteOp in the forwardSlice of
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// `transferRead` that operates on the same memref.
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vector::TransferWriteOp transferWrite;
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for (auto *sliceOp : llvm::reverse(forwardSlice)) {
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auto candidateWrite = dyn_cast<vector::TransferWriteOp>(sliceOp);
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if (!candidateWrite ||
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candidateWrite.getSource() != transferRead.getSource())
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continue;
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transferWrite = candidateWrite;
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}
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// All operands of the TransferRead must be defined outside of the loop.
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for (auto operand : transferRead.getOperands())
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if (!loop.isDefinedOutsideOfLoop(operand))
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return WalkResult::advance();
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// Only hoist transfer_read / transfer_write pairs and singleton
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// transfer_reads for now.
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if (!transferWrite) {
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// Make sure there are no other accesses to the memref before
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// hoisting transfer_read.
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if (noAliasingUseInLoop(transferRead, loop))
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loop.moveOutOfLoop(transferRead);
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return WalkResult::advance();
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}
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LLVM_DEBUG(DBGS() << "Candidate: " << *transferWrite.getOperation()
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<< "\n");
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// Approximate aliasing by checking that:
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// 1. indices, vector type and permutation map are the same (i.e., the
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// transfer_read/transfer_write ops are matching),
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// 2. no other operations in the loop access the same memref except
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// for transfer_read/transfer_write accessing statically disjoint
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// slices.
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if (transferRead.getIndices() != transferWrite.getIndices() ||
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transferRead.getVectorType() != transferWrite.getVectorType() ||
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transferRead.getPermutationMap() != transferWrite.getPermutationMap())
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return WalkResult::advance();
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// TODO: may want to memoize this information for performance but it
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// likely gets invalidated often.
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DominanceInfo dom(loop);
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if (!dom.properlyDominates(transferRead.getOperation(), transferWrite))
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return WalkResult::advance();
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for (auto &use : transferRead.getSource().getUses()) {
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if (!loop->isAncestor(use.getOwner()))
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continue;
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if (use.getOwner() == transferRead.getOperation() ||
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use.getOwner() == transferWrite.getOperation())
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continue;
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if (auto transferWriteUse =
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dyn_cast<vector::TransferWriteOp>(use.getOwner())) {
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if (!vector::isDisjointTransferSet(
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cast<VectorTransferOpInterface>(transferWrite.getOperation()),
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cast<VectorTransferOpInterface>(
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transferWriteUse.getOperation())))
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return WalkResult::advance();
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} else if (auto transferReadUse =
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dyn_cast<vector::TransferReadOp>(use.getOwner())) {
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if (!vector::isDisjointTransferSet(
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cast<VectorTransferOpInterface>(transferWrite.getOperation()),
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cast<VectorTransferOpInterface>(
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transferReadUse.getOperation())))
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return WalkResult::advance();
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} else {
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// Unknown use, we cannot prove that it doesn't alias with the
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// transferRead/transferWrite operations.
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return WalkResult::advance();
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}
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}
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// Hoist read before.
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loop.moveOutOfLoop(transferRead);
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// Hoist write after.
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transferWrite->moveAfter(loop);
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// Rewrite `loop` with new yields by cloning and erase the original loop.
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OpBuilder b(transferRead);
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NewYieldValueFn yieldFn = [&](OpBuilder &b, Location loc,
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ArrayRef<BlockArgument> newBBArgs) {
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return SmallVector<Value>{transferWrite.getVector()};
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};
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// Transfer write has been hoisted, need to update the written vector by
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// the value yielded by the newForOp.
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return TypeSwitch<Operation *, WalkResult>(loop)
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.Case<scf::ForOp>([&](scf::ForOp scfForOp) {
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auto newForOp = replaceLoopWithNewYields(
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b, scfForOp, transferRead.getVector(), yieldFn);
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transferWrite.getVectorMutable().assign(
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newForOp.getResults().back());
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changed = true;
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loop.erase();
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// Need to interrupt and restart because erasing the loop messes up
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// the walk.
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return WalkResult::interrupt();
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})
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.Case<affine::AffineForOp>([&](affine::AffineForOp affineForOp) {
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auto newForOp = replaceForOpWithNewYields(
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b, affineForOp, transferRead.getVector(),
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SmallVector<Value>{transferWrite.getVector()},
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transferWrite.getVector());
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// Replace all uses of the `transferRead` with the corresponding
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// basic block argument.
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transferRead.getVector().replaceUsesWithIf(
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newForOp.getLoopBody().getArguments().back(),
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[&](OpOperand &use) {
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Operation *user = use.getOwner();
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return newForOp->isProperAncestor(user);
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});
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transferWrite.getVectorMutable().assign(
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newForOp.getResults().back());
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changed = true;
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loop.erase();
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// Need to interrupt and restart because erasing the loop messes up
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// the walk.
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return WalkResult::interrupt();
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})
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.Default([](Operation *) { return WalkResult::interrupt(); });
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});
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}
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}
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