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//===- Promotion.cpp - Implementation of linalg Promotion -----------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the linalg dialect Promotion pass.
#include "PassDetail.h"
#include "mlir/Dialect/Arithmetic/IR/Arithmetic.h"
#include "mlir/Dialect/Complex/IR/Complex.h"
#include "mlir/Dialect/Linalg/IR/LinalgOps.h"
#include "mlir/Dialect/Linalg/IR/LinalgTypes.h"
#include "mlir/Dialect/Linalg/Passes.h"
#include "mlir/Dialect/Linalg/Transforms/Transforms.h"
#include "mlir/Dialect/Linalg/Utils/Utils.h"
#include "mlir/Dialect/SCF/SCF.h"
#include "mlir/IR/AffineExpr.h"
#include "mlir/IR/AffineExprVisitor.h"
#include "mlir/IR/AffineMap.h"
#include "mlir/IR/ImplicitLocOpBuilder.h"
#include "mlir/Support/LLVM.h"
#include "mlir/Transforms/FoldUtils.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/TypeSwitch.h"
#include "llvm/Support/CommandLine.h"
using namespace mlir;
using namespace mlir::linalg;
using namespace mlir::scf;
using llvm::MapVector;
#define DEBUG_TYPE "linalg-promotion"
/// Alloc a new buffer of `size` * `width` i8; where `width` is given by the
/// data `layout` for `elementType`.
/// Use AllocOp or AllocaOp depending on `options`.
/// Take an optional alignment.
static Value allocBuffer(ImplicitLocOpBuilder &b,
const LinalgPromotionOptions &options,
Type elementType, Value allocSize, DataLayout &layout,
Optional<unsigned> alignment = None) {
auto width = layout.getTypeSize(elementType);
IntegerAttr alignmentAttr;
if (alignment.hasValue())
alignmentAttr = b.getI64IntegerAttr(alignment.getValue());
// Static buffer.
if (auto cst = allocSize.getDefiningOp<arith::ConstantIndexOp>()) {
auto staticBufferType =
MemRefType::get(width * cst.value(), b.getIntegerType(8));
if (options.useAlloca) {
return b.createOrFold<memref::AllocaOp>(staticBufferType, ValueRange{},
return b.createOrFold<memref::AllocOp>(staticBufferType, ValueRange{},
// Fallback dynamic buffer.
auto dynamicBufferType = MemRefType::get(-1, b.getIntegerType(8));
Value mul = b.createOrFold<arith::MulIOp>(
b.create<arith::ConstantIndexOp>(width), allocSize);
if (options.useAlloca)
return b.create<memref::AllocaOp>(dynamicBufferType, mul, alignmentAttr);
return b.create<memref::AllocOp>(dynamicBufferType, mul, alignmentAttr);
/// Default allocation callback function. This allocates a promoted buffer when
/// no call back to do so is provided. The default is to allocate a
/// memref<..xi8> and return a view to get a memref type of shape
/// boundingSubViewSize.
static Optional<Value>
defaultAllocBufferCallBack(const LinalgPromotionOptions &options,
OpBuilder &builder, memref::SubViewOp subView,
ArrayRef<Value> boundingSubViewSize,
Optional<unsigned> alignment, DataLayout &layout) {
ShapedType viewType = subView.getType();
ImplicitLocOpBuilder b(subView.getLoc(), builder);
auto zero = b.createOrFold<arith::ConstantIndexOp>(0);
auto one = b.createOrFold<arith::ConstantIndexOp>(1);
Value allocSize = one;
for (auto size : llvm::enumerate(boundingSubViewSize))
allocSize = b.createOrFold<arith::MulIOp>(allocSize, size.value());
Value buffer = allocBuffer(b, options, viewType.getElementType(), allocSize,
layout, alignment);
SmallVector<int64_t, 4> dynSizes(boundingSubViewSize.size(),
Value view = b.createOrFold<memref::ViewOp>(
MemRefType::get(dynSizes, viewType.getElementType()), buffer, zero,
return view;
/// Default implementation of deallocation of the buffer use for promotion. It
/// expects to get the same value that the default allocation method returned,
/// i.e. result of a ViewOp.
static LogicalResult
defaultDeallocBufferCallBack(const LinalgPromotionOptions &options,
OpBuilder &b, Value fullLocalView) {
if (!options.useAlloca) {
auto viewOp = cast<memref::ViewOp>(fullLocalView.getDefiningOp());
b.create<memref::DeallocOp>(viewOp.source().getLoc(), viewOp.source());
return success();
namespace {
/// Helper struct that captures the information required to apply the
/// transformation on each op. This bridges the abstraction gap with the
/// user-facing API which exposes positional arguments to control which operands
/// are promoted.
struct LinalgOpInstancePromotionOptions {
LinalgOpInstancePromotionOptions(LinalgOp op,
const LinalgPromotionOptions &options);
/// SubViews to promote.
MapVector<int64_t, Value> subViews;
/// True if the full view should be used for the promoted buffer.
DenseMap<Value, bool> useFullTileBuffers;
/// Callback functions for allocation and deallocation of promoted buffers, as
/// well as to copy the data into and out of these buffers.
AllocBufferCallbackFn allocationFn;
DeallocBufferCallbackFn deallocationFn;
CopyCallbackFn copyInFn;
CopyCallbackFn copyOutFn;
/// Allow the use of dynamically-sized buffers.
bool dynamicBuffers;
/// Alignment of promoted buffer.
Optional<unsigned> alignment;
} // namespace
LinalgOp linalgOp, const LinalgPromotionOptions &options)
: subViews(), dynamicBuffers(options.dynamicBuffers),
alignment(options.alignment) {
assert(linalgOp.hasBufferSemantics() && "revisit usage of shaped operand");
auto vUseFullTileBuffers =
for (OpOperand *opOperand : linalgOp.getInputAndOutputOperands()) {
int64_t operandNumber = opOperand->getOperandNumber();
if (options.operandsToPromote &&
Operation *op = opOperand->get().getDefiningOp();
if (auto sv = dyn_cast_or_null<memref::SubViewOp>(op)) {
subViews[operandNumber] = sv;
useFullTileBuffers[sv] = vUseFullTileBuffers[operandNumber];
if (options.allocationFn) {
allocationFn = *options.allocationFn;
} else {
allocationFn = [&](OpBuilder &b, memref::SubViewOp subViewOp,
ArrayRef<Value> boundingSubViewSize,
DataLayout &layout) -> Optional<Value> {
return defaultAllocBufferCallBack(options, b, subViewOp,
boundingSubViewSize, alignment, layout);
if (options.deallocationFn) {
deallocationFn = *options.deallocationFn;
} else {
deallocationFn = [&](OpBuilder &b, Value buffer) {
return defaultDeallocBufferCallBack(options, b, buffer);
// Save the loc because `linalgOp` goes out of scope.
Location loc = linalgOp.getLoc();
auto defaultCopyCallBack = [loc](OpBuilder &b, Value src,
Value dst) -> LogicalResult {
b.create<linalg::CopyOp>(loc, src, dst);
return success();
copyInFn = (options.copyInFn ? *(options.copyInFn) : defaultCopyCallBack);
copyOutFn = (options.copyOutFn ? *(options.copyOutFn) : defaultCopyCallBack);
// Performs promotion of a `subView` into a local buffer of the size of the
// *ranges* of the `subView`. This produces a buffer whose size may be bigger
// than the actual size of the `subView` at the boundaries.
// This is related to the full/partial tile problem.
// Returns a PromotionInfo containing a `buffer`, `fullLocalView` and
// `partialLocalView` such that:
// * `buffer` is always the size of the full tile.
// * `fullLocalView` is a dense contiguous view into that buffer.
// * `partialLocalView` is a dense non-contiguous slice of `fullLocalView`
// that corresponds to the size of `subView` and accounting for boundary
// effects.
// The point of the full tile buffer is that constant static tile sizes are
// folded and result in a buffer type with statically known size and alignment
// properties.
// To account for general boundary effects, padding must be performed on the
// boundary tiles. For now this is done with an unconditional `fill` op followed
// by a partial `copy` op.
FailureOr<PromotionInfo> mlir::linalg::promoteSubviewAsNewBuffer(
OpBuilder &b, Location loc, memref::SubViewOp subView,
AllocBufferCallbackFn allocationFn, DataLayout &layout) {
auto viewType = subView.getType();
auto rank = viewType.getRank();
SmallVector<Value, 4> fullSizes;
SmallVector<OpFoldResult> partialSizes;
for (auto en : llvm::enumerate(subView.getOrCreateRanges(b, loc))) {
auto rangeValue = en.value();
// Try to extract a tight constant.
LLVM_DEBUG(llvm::dbgs() << "Extract tightest: " << rangeValue.size << "\n");
FailureOr<int64_t> upperBound =
Value size =
? rangeValue.size
: b.create<arith::ConstantIndexOp>(loc, upperBound.getValue());
LLVM_DEBUG(llvm::dbgs() << "Extracted tightest: " << size << "\n");
b.createOrFold<memref::DimOp>(loc, subView, en.index()));
SmallVector<int64_t, 4> dynSizes(fullSizes.size(), -1);
// If a callback is not specified, then use the default implementation for
// allocating the promoted buffer.
Optional<Value> fullLocalView = allocationFn(b, subView, fullSizes, layout);
if (!fullLocalView)
return failure();
SmallVector<OpFoldResult, 4> zeros(fullSizes.size(), b.getIndexAttr(0));
SmallVector<OpFoldResult, 4> ones(fullSizes.size(), b.getIndexAttr(1));
auto partialLocalView = b.createOrFold<memref::SubViewOp>(
loc, *fullLocalView, zeros, partialSizes, ones);
return PromotionInfo{*fullLocalView, partialLocalView};
static FailureOr<MapVector<int64_t, PromotionInfo>>
promoteSubViews(ImplicitLocOpBuilder &b,
LinalgOpInstancePromotionOptions options, DataLayout &layout) {
if (options.subViews.empty())
return failure();
MapVector<int64_t, PromotionInfo> promotionInfoMap;
for (auto v : options.subViews) {
memref::SubViewOp subView =
auto promotionInfo = promoteSubviewAsNewBuffer(
b, b.getLoc(), subView, options.allocationFn, layout);
if (failed(promotionInfo))
return failure();
promotionInfoMap[v.first] = *promotionInfo;
// Only fill the buffer if the full local view is used
if (!options.useFullTileBuffers[v.second])
Type subviewEltType = subView.getType().getElementType();
Value fillVal =
llvm::TypeSwitch<Type, Value>(subviewEltType)
.Case([&](FloatType t) {
return b.create<arith::ConstantOp>(FloatAttr::get(t, 0.0));
.Case([&](IntegerType t) {
return b.create<arith::ConstantOp>(IntegerAttr::get(t, 0));
.Case([&](ComplexType t) {
Value tmp;
if (auto et = t.getElementType().dyn_cast<FloatType>())
tmp = b.create<arith::ConstantOp>(FloatAttr::get(et, 0.0));
else if (auto et = t.getElementType().cast<IntegerType>())
tmp = b.create<arith::ConstantOp>(IntegerAttr::get(et, 0));
return b.create<complex::CreateOp>(t, tmp, tmp);
.Default([](auto) { return Value(); });
if (!fillVal)
return failure();
b.create<linalg::FillOp>(fillVal, promotionInfo->fullLocalView);
// Copy data into the promoted buffers. Use callback if provided.
for (auto v : options.subViews) {
auto info = promotionInfoMap.find(v.first);
if (info == promotionInfoMap.end())
if (failed(options.copyInFn(
b, cast<memref::SubViewOp>(v.second.getDefiningOp()),
return failure();
return promotionInfoMap;
static FailureOr<LinalgOp>
promoteSubViews(ImplicitLocOpBuilder &b, LinalgOp op,
LinalgOpInstancePromotionOptions options, DataLayout &layout) {
assert(op.hasBufferSemantics() && "expected linalg op with buffer semantics");
// 1. Promote the specified views and use them in the new op.
auto promotedBuffersAndViews = promoteSubViews(b, options, layout);
if (failed(promotedBuffersAndViews) ||
promotedBuffersAndViews->size() != options.subViews.size())
return failure();
// 2. Append all other operands as they appear, this enforces that such
// operands are not views. This is to support cases such as FillOp taking
// extra scalars etc. Keep a reference to output buffers;
SmallVector<Value, 8> opViews;
SmallVector<std::pair<Value, Value>, 8> writebackViews;
for (OpOperand *opOperand : op.getInputAndOutputOperands()) {
int64_t operandNumber = opOperand->getOperandNumber();
if (options.subViews.count(operandNumber) != 0) {
if (options.useFullTileBuffers[opOperand->get()])
if (operandNumber >= op.getNumInputs())
} else {
op->setOperands(0, opViews.size(), opViews);
OpBuilder::InsertionGuard guard(b);
// 3. Emit write-back for the promoted output views: copy the partial view.
for (auto viewAndPartialLocalView : writebackViews) {
if (failed(options.copyOutFn(b, viewAndPartialLocalView.second,
return failure();
// 4. Dealloc all local buffers.
for (const auto &pi : *promotedBuffersAndViews)
(void)options.deallocationFn(b, pi.second.fullLocalView);
return op;
mlir::linalg::promoteSubviewsPrecondition(Operation *op,
LinalgPromotionOptions options) {
LinalgOp linalgOp = dyn_cast<LinalgOp>(op);
// Transformation applies to buffers only.
if (!linalgOp || !linalgOp.hasBufferSemantics())
return failure();
// Check that at least one of the requested operands is indeed a subview.
for (OpOperand *opOperand : linalgOp.getInputAndOutputOperands()) {
auto sv =
if (sv) {
if (!options.operandsToPromote.hasValue() ||
return success();
// TODO: Check all subviews requested are bound by a static constant.
// TODO: Check that the total footprint fits within a given size.
return failure();
mlir::linalg::promoteSubViews(OpBuilder &builder, LinalgOp linalgOp,
LinalgPromotionOptions options) {
LinalgOpInstancePromotionOptions linalgOptions(linalgOp, options);
auto layout = DataLayout::closest(linalgOp);
ImplicitLocOpBuilder b(linalgOp.getLoc(), builder);
auto res = ::promoteSubViews(b, linalgOp, linalgOptions, layout);
if (failed(res))
return failure();
return res;
namespace {
struct LinalgPromotionPass : public LinalgPromotionBase<LinalgPromotionPass> {
LinalgPromotionPass() = default;
LinalgPromotionPass(bool dynamicBuffers, bool useAlloca) {
this->dynamicBuffers = dynamicBuffers;
this->useAlloca = useAlloca;
void runOnFunction() override {
getFunction().walk([&](LinalgOp op) {
auto options = LinalgPromotionOptions()
if (failed(promoteSubviewsPrecondition(op, options)))
LLVM_DEBUG(llvm::dbgs() << "Promote: " << *(op.getOperation()) << "\n");
ImplicitLocOpBuilder b(op.getLoc(), op);
// TODO: signalPassFailure() ?
(void)promoteSubViews(b, op, options);
} // namespace
// TODO: support more transformation options in the pass.
mlir::createLinalgPromotionPass(bool dynamicBuffers, bool useAlloca) {
return std::make_unique<LinalgPromotionPass>(dynamicBuffers, useAlloca);
std::unique_ptr<OperationPass<FuncOp>> mlir::createLinalgPromotionPass() {
return std::make_unique<LinalgPromotionPass>();