9b5ef2bea8
This commit implements `LoopLikeOpInterface` on `scf.while`. This enables LICM (and potentially other transforms) on `scf.while`. `LoopLikeOpInterface::getLoopBody()` is renamed to `getLoopRegions` and can now return multiple regions. Also fix a bug in the default implementation of `LoopLikeOpInterface::isDefinedOutsideOfLoop()`, which returned "false" for some values that are defined outside of the loop (in a nested op, in such a way that the value does not dominate the loop). This interface is currently only used for LICM and there is no way to trigger this bug, so no test is added.
252 lines
9.4 KiB
C++
252 lines
9.4 KiB
C++
//===- AffineLoopInvariantCodeMotion.cpp - Code to perform loop fusion-----===//
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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 loop invariant code motion.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/Affine/Passes.h"
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#include "mlir/Analysis/SliceAnalysis.h"
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#include "mlir/Dialect/Affine/Analysis/AffineAnalysis.h"
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#include "mlir/Dialect/Affine/Analysis/AffineStructures.h"
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#include "mlir/Dialect/Affine/Analysis/LoopAnalysis.h"
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#include "mlir/Dialect/Affine/Analysis/Utils.h"
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#include "mlir/Dialect/Affine/IR/AffineOps.h"
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#include "mlir/Dialect/Affine/LoopUtils.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/IR/AffineExpr.h"
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#include "mlir/IR/AffineMap.h"
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#include "mlir/IR/Builders.h"
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#include "mlir/IR/Matchers.h"
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#include "mlir/Interfaces/SideEffectInterfaces.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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namespace mlir {
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namespace affine {
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#define GEN_PASS_DEF_AFFINELOOPINVARIANTCODEMOTION
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#include "mlir/Dialect/Affine/Passes.h.inc"
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} // namespace affine
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} // namespace mlir
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#define DEBUG_TYPE "licm"
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using namespace mlir;
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using namespace mlir::affine;
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namespace {
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/// Loop invariant code motion (LICM) pass.
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/// TODO: The pass is missing zero-trip tests.
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/// TODO: This code should be removed once the new LICM pass can handle its
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/// uses.
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struct LoopInvariantCodeMotion
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: public affine::impl::AffineLoopInvariantCodeMotionBase<
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LoopInvariantCodeMotion> {
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void runOnOperation() override;
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void runOnAffineForOp(AffineForOp forOp);
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};
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} // namespace
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static bool
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checkInvarianceOfNestedIfOps(AffineIfOp ifOp, Value indVar, ValueRange iterArgs,
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SmallPtrSetImpl<Operation *> &opsWithUsers,
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SmallPtrSetImpl<Operation *> &opsToHoist);
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static bool isOpLoopInvariant(Operation &op, Value indVar, ValueRange iterArgs,
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SmallPtrSetImpl<Operation *> &opsWithUsers,
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SmallPtrSetImpl<Operation *> &opsToHoist);
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static bool
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areAllOpsInTheBlockListInvariant(Region &blockList, Value indVar,
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ValueRange iterArgs,
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SmallPtrSetImpl<Operation *> &opsWithUsers,
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SmallPtrSetImpl<Operation *> &opsToHoist);
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// Returns true if the individual op is loop invariant.
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static bool isOpLoopInvariant(Operation &op, Value indVar, ValueRange iterArgs,
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SmallPtrSetImpl<Operation *> &opsWithUsers,
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SmallPtrSetImpl<Operation *> &opsToHoist) {
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LLVM_DEBUG(llvm::dbgs() << "iterating on op: " << op;);
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if (auto ifOp = dyn_cast<AffineIfOp>(op)) {
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if (!checkInvarianceOfNestedIfOps(ifOp, indVar, iterArgs, opsWithUsers,
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opsToHoist))
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return false;
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} else if (auto forOp = dyn_cast<AffineForOp>(op)) {
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if (!areAllOpsInTheBlockListInvariant(forOp.getRegion(), indVar, iterArgs,
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opsWithUsers, opsToHoist))
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return false;
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} else if (auto parOp = dyn_cast<AffineParallelOp>(op)) {
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if (!areAllOpsInTheBlockListInvariant(parOp.getRegion(), indVar, iterArgs,
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opsWithUsers, opsToHoist))
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return false;
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} else if (!isMemoryEffectFree(&op) &&
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!isa<AffineReadOpInterface, AffineWriteOpInterface,
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AffinePrefetchOp>(&op)) {
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// Check for side-effecting ops. Affine read/write ops are handled
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// separately below.
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return false;
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} else if (!matchPattern(&op, m_Constant())) {
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// Register op in the set of ops that have users.
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opsWithUsers.insert(&op);
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if (isa<AffineReadOpInterface, AffineWriteOpInterface>(op)) {
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auto read = dyn_cast<AffineReadOpInterface>(op);
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Value memref = read ? read.getMemRef()
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: cast<AffineWriteOpInterface>(op).getMemRef();
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for (auto *user : memref.getUsers()) {
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// If this memref has a user that is a DMA, give up because these
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// operations write to this memref.
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if (isa<AffineDmaStartOp, AffineDmaWaitOp>(user))
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return false;
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// If the memref used by the load/store is used in a store elsewhere in
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// the loop nest, we do not hoist. Similarly, if the memref used in a
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// load is also being stored too, we do not hoist the load.
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if (isa<AffineWriteOpInterface>(user) ||
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(isa<AffineReadOpInterface>(user) &&
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isa<AffineWriteOpInterface>(op))) {
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if (&op != user) {
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SmallVector<AffineForOp, 8> userIVs;
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getAffineForIVs(*user, &userIVs);
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// Check that userIVs don't contain the for loop around the op.
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if (llvm::is_contained(userIVs, getForInductionVarOwner(indVar)))
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return false;
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}
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}
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}
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}
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if (op.getNumOperands() == 0 && !isa<AffineYieldOp>(op)) {
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LLVM_DEBUG(llvm::dbgs() << "Non-constant op with 0 operands\n");
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return false;
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}
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}
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// Check operands.
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for (unsigned int i = 0; i < op.getNumOperands(); ++i) {
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auto *operandSrc = op.getOperand(i).getDefiningOp();
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LLVM_DEBUG(
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op.getOperand(i).print(llvm::dbgs() << "Iterating on operand\n"));
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// If the loop IV is the operand, this op isn't loop invariant.
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if (indVar == op.getOperand(i)) {
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LLVM_DEBUG(llvm::dbgs() << "Loop IV is the operand\n");
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return false;
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}
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// If the one of the iter_args is the operand, this op isn't loop invariant.
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if (llvm::is_contained(iterArgs, op.getOperand(i))) {
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LLVM_DEBUG(llvm::dbgs() << "One of the iter_args is the operand\n");
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return false;
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}
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if (operandSrc) {
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LLVM_DEBUG(llvm::dbgs() << *operandSrc << "Iterating on operand src\n");
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// If the value was defined in the loop (outside of the if/else region),
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// and that operation itself wasn't meant to be hoisted, then mark this
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// operation loop dependent.
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if (opsWithUsers.count(operandSrc) && opsToHoist.count(operandSrc) == 0)
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return false;
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}
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}
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// If no operand was loop variant, mark this op for motion.
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opsToHoist.insert(&op);
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return true;
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}
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// Checks if all ops in a region (i.e. list of blocks) are loop invariant.
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static bool
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areAllOpsInTheBlockListInvariant(Region &blockList, Value indVar,
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ValueRange iterArgs,
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SmallPtrSetImpl<Operation *> &opsWithUsers,
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SmallPtrSetImpl<Operation *> &opsToHoist) {
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for (auto &b : blockList) {
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for (auto &op : b) {
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if (!isOpLoopInvariant(op, indVar, iterArgs, opsWithUsers, opsToHoist))
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return false;
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}
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}
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return true;
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}
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// Returns true if the affine.if op can be hoisted.
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static bool
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checkInvarianceOfNestedIfOps(AffineIfOp ifOp, Value indVar, ValueRange iterArgs,
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SmallPtrSetImpl<Operation *> &opsWithUsers,
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SmallPtrSetImpl<Operation *> &opsToHoist) {
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if (!areAllOpsInTheBlockListInvariant(ifOp.getThenRegion(), indVar, iterArgs,
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opsWithUsers, opsToHoist))
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return false;
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if (!areAllOpsInTheBlockListInvariant(ifOp.getElseRegion(), indVar, iterArgs,
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opsWithUsers, opsToHoist))
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return false;
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return true;
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}
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void LoopInvariantCodeMotion::runOnAffineForOp(AffineForOp forOp) {
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auto *loopBody = forOp.getBody();
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auto indVar = forOp.getInductionVar();
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ValueRange iterArgs = forOp.getRegionIterArgs();
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// This is the place where hoisted instructions would reside.
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OpBuilder b(forOp.getOperation());
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SmallPtrSet<Operation *, 8> opsToHoist;
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SmallVector<Operation *, 8> opsToMove;
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SmallPtrSet<Operation *, 8> opsWithUsers;
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for (auto &op : *loopBody) {
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// Register op in the set of ops that have users. This set is used
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// to prevent hoisting ops that depend on these ops that are
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// not being hoisted.
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if (!op.use_empty())
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opsWithUsers.insert(&op);
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if (!isa<AffineYieldOp>(op)) {
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if (isOpLoopInvariant(op, indVar, iterArgs, opsWithUsers, opsToHoist)) {
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opsToMove.push_back(&op);
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}
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}
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}
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// For all instructions that we found to be invariant, place sequentially
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// right before the for loop.
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for (auto *op : opsToMove) {
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op->moveBefore(forOp);
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}
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LLVM_DEBUG(forOp->print(llvm::dbgs() << "Modified loop\n"));
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}
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void LoopInvariantCodeMotion::runOnOperation() {
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// Walk through all loops in a function in innermost-loop-first order. This
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// way, we first LICM from the inner loop, and place the ops in
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// the outer loop, which in turn can be further LICM'ed.
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getOperation().walk([&](AffineForOp op) {
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LLVM_DEBUG(op->print(llvm::dbgs() << "\nOriginal loop\n"));
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runOnAffineForOp(op);
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});
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}
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std::unique_ptr<OperationPass<func::FuncOp>>
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mlir::affine::createAffineLoopInvariantCodeMotionPass() {
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return std::make_unique<LoopInvariantCodeMotion>();
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}
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