251 lines
9.4 KiB
C++
251 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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/// Affine 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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