308571074c
This is an artifact from merging MLIR into LLVM, the file headers are now aligned with the rest of the project.
240 lines
8.2 KiB
C++
240 lines
8.2 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/Analysis/AffineAnalysis.h"
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#include "mlir/Analysis/AffineStructures.h"
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#include "mlir/Analysis/LoopAnalysis.h"
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#include "mlir/Analysis/SliceAnalysis.h"
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#include "mlir/Analysis/Utils.h"
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#include "mlir/Dialect/AffineOps/AffineOps.h"
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#include "mlir/Dialect/StandardOps/Ops.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/Pass/Pass.h"
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#include "mlir/Transforms/LoopUtils.h"
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#include "mlir/Transforms/Passes.h"
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#include "mlir/Transforms/Utils.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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#define DEBUG_TYPE "licm"
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using namespace mlir;
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namespace {
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/// Loop invariant code motion (LICM) pass.
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/// TODO(asabne) : The pass is missing zero-trip tests.
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/// TODO(asabne) : Check for the presence of side effects before hoisting.
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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 : public FunctionPass<LoopInvariantCodeMotion> {
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void runOnFunction() override;
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void runOnAffineForOp(AffineForOp forOp);
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};
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} // end anonymous namespace
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static bool
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checkInvarianceOfNestedIfOps(Operation *op, Value indVar,
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SmallPtrSetImpl<Operation *> &definedOps,
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SmallPtrSetImpl<Operation *> &opsToHoist);
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static bool isOpLoopInvariant(Operation &op, Value indVar,
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SmallPtrSetImpl<Operation *> &definedOps,
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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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SmallPtrSetImpl<Operation *> &definedOps,
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SmallPtrSetImpl<Operation *> &opsToHoist);
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static bool isMemRefDereferencingOp(Operation &op) {
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// TODO(asabne): Support DMA Ops.
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if (isa<AffineLoadOp>(op) || isa<AffineStoreOp>(op)) {
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return true;
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}
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return false;
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}
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// Returns true if the individual op is loop invariant.
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bool isOpLoopInvariant(Operation &op, Value indVar,
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SmallPtrSetImpl<Operation *> &definedOps,
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SmallPtrSetImpl<Operation *> &opsToHoist) {
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LLVM_DEBUG(llvm::dbgs() << "iterating on op: " << op;);
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if (isa<AffineIfOp>(op)) {
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if (!checkInvarianceOfNestedIfOps(&op, indVar, definedOps, opsToHoist)) {
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return false;
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}
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} else if (isa<AffineForOp>(op)) {
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// If the body of a predicated region has a for loop, we don't hoist the
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// 'affine.if'.
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return false;
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} else if (isa<AffineDmaStartOp>(op) || isa<AffineDmaWaitOp>(op)) {
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// TODO(asabne): Support DMA ops.
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return false;
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} else if (!isa<ConstantOp>(op)) {
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if (isMemRefDereferencingOp(op)) {
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Value memref = isa<AffineLoadOp>(op)
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? cast<AffineLoadOp>(op).getMemRef()
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: cast<AffineStoreOp>(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>(op) || isa<AffineDmaWaitOp>(op)) {
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return false;
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}
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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<AffineStoreOp>(user) ||
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(isa<AffineLoadOp>(user) && isa<AffineStoreOp>(op))) {
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if (&op != user) {
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SmallVector<AffineForOp, 8> userIVs;
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getLoopIVs(*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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}
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// Insert this op in the defined ops list.
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definedOps.insert(&op);
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if (op.getNumOperands() == 0 && !isa<AffineTerminatorOp>(op)) {
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LLVM_DEBUG(llvm::dbgs() << "\nNon-constant op with 0 operands\n");
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return false;
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}
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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() << "\nIterating 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() << "\nLoop IV is the operand\n");
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return false;
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}
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if (operandSrc != nullptr) {
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LLVM_DEBUG(llvm::dbgs()
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<< *operandSrc << "\nIterating on operand src\n");
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// If the value was defined in the loop (outside of the
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// if/else region), and that operation itself wasn't meant to
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// be hoisted, then mark this operation loop dependent.
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if (definedOps.count(operandSrc) && opsToHoist.count(operandSrc) == 0) {
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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 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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bool areAllOpsInTheBlockListInvariant(
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Region &blockList, Value indVar, SmallPtrSetImpl<Operation *> &definedOps,
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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, definedOps, opsToHoist)) {
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return false;
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}
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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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bool checkInvarianceOfNestedIfOps(Operation *op, Value indVar,
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SmallPtrSetImpl<Operation *> &definedOps,
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SmallPtrSetImpl<Operation *> &opsToHoist) {
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assert(isa<AffineIfOp>(op));
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auto ifOp = cast<AffineIfOp>(op);
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if (!areAllOpsInTheBlockListInvariant(ifOp.thenRegion(), indVar, definedOps,
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opsToHoist)) {
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return false;
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}
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if (!areAllOpsInTheBlockListInvariant(ifOp.elseRegion(), indVar, definedOps,
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opsToHoist)) {
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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 LoopInvariantCodeMotion::runOnAffineForOp(AffineForOp forOp) {
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auto *loopBody = forOp.getBody();
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auto indVar = forOp.getInductionVar();
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SmallPtrSet<Operation *, 8> definedOps;
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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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for (auto &op : *loopBody) {
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// We don't hoist for loops.
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if (!isa<AffineForOp>(op)) {
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if (!isa<AffineTerminatorOp>(op)) {
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if (isOpLoopInvariant(op, indVar, definedOps, 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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}
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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.getOperation()->print(llvm::dbgs() << "Modified loop\n"));
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}
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void LoopInvariantCodeMotion::runOnFunction() {
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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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getFunction().walk([&](AffineForOp op) {
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LLVM_DEBUG(op.getOperation()->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<OpPassBase<FuncOp>>
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mlir::createAffineLoopInvariantCodeMotionPass() {
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return std::make_unique<LoopInvariantCodeMotion>();
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}
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static PassRegistration<LoopInvariantCodeMotion>
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pass("affine-loop-invariant-code-motion",
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"Hoist loop invariant instructions outside of the loop");
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