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diff --git a/mlir/lib/Transforms/AffineLoopInvariantCodeMotion.cpp b/mlir/lib/Transforms/AffineLoopInvariantCodeMotion.cpp
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+//===- AffineLoopInvariantCodeMotion.cpp - Code to perform loop fusion-----===//
+//
+// Part of the MLIR Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements loop invariant code motion.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Analysis/AffineAnalysis.h"
+#include "mlir/Analysis/AffineStructures.h"
+#include "mlir/Analysis/LoopAnalysis.h"
+#include "mlir/Analysis/SliceAnalysis.h"
+#include "mlir/Analysis/Utils.h"
+#include "mlir/Dialect/AffineOps/AffineOps.h"
+#include "mlir/Dialect/StandardOps/Ops.h"
+#include "mlir/IR/AffineExpr.h"
+#include "mlir/IR/AffineMap.h"
+#include "mlir/IR/Builders.h"
+#include "mlir/Pass/Pass.h"
+#include "mlir/Transforms/LoopUtils.h"
+#include "mlir/Transforms/Passes.h"
+#include "mlir/Transforms/Utils.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+#define DEBUG_TYPE "licm"
+
+using namespace mlir;
+
+namespace {
+
+/// Loop invariant code motion (LICM) pass.
+/// TODO(asabne) : The pass is missing zero-trip tests.
+/// TODO(asabne) : Check for the presence of side effects before hoisting.
+/// TODO: This code should be removed once the new LICM pass can handle its
+/// uses.
+struct LoopInvariantCodeMotion : public FunctionPass<LoopInvariantCodeMotion> {
+ void runOnFunction() override;
+ void runOnAffineForOp(AffineForOp forOp);
+};
+} // end anonymous namespace
+
+static bool
+checkInvarianceOfNestedIfOps(Operation *op, Value indVar,
+ SmallPtrSetImpl<Operation *> &definedOps,
+ SmallPtrSetImpl<Operation *> &opsToHoist);
+static bool isOpLoopInvariant(Operation &op, Value indVar,
+ SmallPtrSetImpl<Operation *> &definedOps,
+ SmallPtrSetImpl<Operation *> &opsToHoist);
+
+static bool
+areAllOpsInTheBlockListInvariant(Region &blockList, Value indVar,
+ SmallPtrSetImpl<Operation *> &definedOps,
+ SmallPtrSetImpl<Operation *> &opsToHoist);
+
+static bool isMemRefDereferencingOp(Operation &op) {
+ // TODO(asabne): Support DMA Ops.
+ if (isa<AffineLoadOp>(op) || isa<AffineStoreOp>(op)) {
+ return true;
+ }
+ return false;
+}
+
+// Returns true if the individual op is loop invariant.
+bool isOpLoopInvariant(Operation &op, Value indVar,
+ SmallPtrSetImpl<Operation *> &definedOps,
+ SmallPtrSetImpl<Operation *> &opsToHoist) {
+ LLVM_DEBUG(llvm::dbgs() << "iterating on op: " << op;);
+
+ if (isa<AffineIfOp>(op)) {
+ if (!checkInvarianceOfNestedIfOps(&op, indVar, definedOps, opsToHoist)) {
+ return false;
+ }
+ } else if (isa<AffineForOp>(op)) {
+ // If the body of a predicated region has a for loop, we don't hoist the
+ // 'affine.if'.
+ return false;
+ } else if (isa<AffineDmaStartOp>(op) || isa<AffineDmaWaitOp>(op)) {
+ // TODO(asabne): Support DMA ops.
+ return false;
+ } else if (!isa<ConstantOp>(op)) {
+ if (isMemRefDereferencingOp(op)) {
+ Value memref = isa<AffineLoadOp>(op)
+ ? cast<AffineLoadOp>(op).getMemRef()
+ : cast<AffineStoreOp>(op).getMemRef();
+ for (auto *user : memref->getUsers()) {
+ // If this memref has a user that is a DMA, give up because these
+ // operations write to this memref.
+ if (isa<AffineDmaStartOp>(op) || isa<AffineDmaWaitOp>(op)) {
+ return false;
+ }
+ // If the memref used by the load/store is used in a store elsewhere in
+ // the loop nest, we do not hoist. Similarly, if the memref used in a
+ // load is also being stored too, we do not hoist the load.
+ if (isa<AffineStoreOp>(user) ||
+ (isa<AffineLoadOp>(user) && isa<AffineStoreOp>(op))) {
+ if (&op != user) {
+ SmallVector<AffineForOp, 8> userIVs;
+ getLoopIVs(*user, &userIVs);
+ // Check that userIVs don't contain the for loop around the op.
+ if (llvm::is_contained(userIVs, getForInductionVarOwner(indVar))) {
+ return false;
+ }
+ }
+ }
+ }
+ }
+
+ // Insert this op in the defined ops list.
+ definedOps.insert(&op);
+
+ if (op.getNumOperands() == 0 && !isa<AffineTerminatorOp>(op)) {
+ LLVM_DEBUG(llvm::dbgs() << "\nNon-constant op with 0 operands\n");
+ return false;
+ }
+ for (unsigned int i = 0; i < op.getNumOperands(); ++i) {
+ auto *operandSrc = op.getOperand(i)->getDefiningOp();
+
+ LLVM_DEBUG(
+ op.getOperand(i)->print(llvm::dbgs() << "\nIterating on operand\n"));
+
+ // If the loop IV is the operand, this op isn't loop invariant.
+ if (indVar == op.getOperand(i)) {
+ LLVM_DEBUG(llvm::dbgs() << "\nLoop IV is the operand\n");
+ return false;
+ }
+
+ if (operandSrc != nullptr) {
+ LLVM_DEBUG(llvm::dbgs()
+ << *operandSrc << "\nIterating on operand src\n");
+
+ // If the value was defined in the loop (outside of the
+ // if/else region), and that operation itself wasn't meant to
+ // be hoisted, then mark this operation loop dependent.
+ if (definedOps.count(operandSrc) && opsToHoist.count(operandSrc) == 0) {
+ return false;
+ }
+ }
+ }
+ }
+
+ // If no operand was loop variant, mark this op for motion.
+ opsToHoist.insert(&op);
+ return true;
+}
+
+// Checks if all ops in a region (i.e. list of blocks) are loop invariant.
+bool areAllOpsInTheBlockListInvariant(
+ Region &blockList, Value indVar, SmallPtrSetImpl<Operation *> &definedOps,
+ SmallPtrSetImpl<Operation *> &opsToHoist) {
+
+ for (auto &b : blockList) {
+ for (auto &op : b) {
+ if (!isOpLoopInvariant(op, indVar, definedOps, opsToHoist)) {
+ return false;
+ }
+ }
+ }
+
+ return true;
+}
+
+// Returns true if the affine.if op can be hoisted.
+bool checkInvarianceOfNestedIfOps(Operation *op, Value indVar,
+ SmallPtrSetImpl<Operation *> &definedOps,
+ SmallPtrSetImpl<Operation *> &opsToHoist) {
+ assert(isa<AffineIfOp>(op));
+ auto ifOp = cast<AffineIfOp>(op);
+
+ if (!areAllOpsInTheBlockListInvariant(ifOp.thenRegion(), indVar, definedOps,
+ opsToHoist)) {
+ return false;
+ }
+
+ if (!areAllOpsInTheBlockListInvariant(ifOp.elseRegion(), indVar, definedOps,
+ opsToHoist)) {
+ return false;
+ }
+
+ return true;
+}
+
+void LoopInvariantCodeMotion::runOnAffineForOp(AffineForOp forOp) {
+ auto *loopBody = forOp.getBody();
+ auto indVar = forOp.getInductionVar();
+
+ SmallPtrSet<Operation *, 8> definedOps;
+ // This is the place where hoisted instructions would reside.
+ OpBuilder b(forOp.getOperation());
+
+ SmallPtrSet<Operation *, 8> opsToHoist;
+ SmallVector<Operation *, 8> opsToMove;
+
+ for (auto &op : *loopBody) {
+ // We don't hoist for loops.
+ if (!isa<AffineForOp>(op)) {
+ if (!isa<AffineTerminatorOp>(op)) {
+ if (isOpLoopInvariant(op, indVar, definedOps, opsToHoist)) {
+ opsToMove.push_back(&op);
+ }
+ }
+ }
+ }
+
+ // For all instructions that we found to be invariant, place sequentially
+ // right before the for loop.
+ for (auto *op : opsToMove) {
+ op->moveBefore(forOp);
+ }
+
+ LLVM_DEBUG(forOp.getOperation()->print(llvm::dbgs() << "Modified loop\n"));
+}
+
+void LoopInvariantCodeMotion::runOnFunction() {
+ // Walk through all loops in a function in innermost-loop-first order. This
+ // way, we first LICM from the inner loop, and place the ops in
+ // the outer loop, which in turn can be further LICM'ed.
+ getFunction().walk([&](AffineForOp op) {
+ LLVM_DEBUG(op.getOperation()->print(llvm::dbgs() << "\nOriginal loop\n"));
+ runOnAffineForOp(op);
+ });
+}
+
+std::unique_ptr<OpPassBase<FuncOp>>
+mlir::createAffineLoopInvariantCodeMotionPass() {
+ return std::make_unique<LoopInvariantCodeMotion>();
+}
+
+static PassRegistration<LoopInvariantCodeMotion>
+ pass("affine-loop-invariant-code-motion",
+ "Hoist loop invariant instructions outside of the loop");
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