[Mlir-commits] [mlir] [mlir][tensor] Add a tensor.concat operation (PR #72779)

[Nicolas Vasilache]

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@@ -0,0 +1,86 @@
+//===- ConcatOpPatterns.cpp - Patterns related to tensor.concat lowering --===//
+//
+// Part of the LLVM 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
+//
+//===----------------------------------------------------------------------===//
+//
+#include "mlir/Dialect/Arith/IR/Arith.h"
+#include "mlir/Dialect/Arith/Utils/Utils.h"
+#include "mlir/Dialect/Tensor/IR/Tensor.h"
+#include "mlir/Dialect/Tensor/Transforms/Transforms.h"
+#include "mlir/IR/PatternMatch.h"
+
+using namespace mlir;
+using namespace mlir::tensor;
+
+namespace {
+
+/// Decompose `tensor.concat` into `tensor.empty` and a chain of slice inserts.
+///
+/// %concat = tensor.concat dim(1) %0, %1 :
+///         (tensor<2x3xf32>, tensor<2x4xf32>) -> tensor<2x7xf32>
+///
+/// Becomes
+///
+/// %empty = tensor.empty() : tensor<2x7xf32>
+/// %insert0 = tensor.insert_slice %0 into %empty[0, 0][2, 3][1, 1]
+/// %concat = tensor.insert_slice %1 into %insert0[0, 3][2, 4][1, 1]
+struct DecomposeTensorConcatOp : public OpRewritePattern<ConcatOp> {
+  using OpRewritePattern<ConcatOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(ConcatOp concatOp,
+                                PatternRewriter &rewriter) const override {
+
+    Location loc = concatOp.getLoc();
+    FailureOr<Value> dest =
+        tensor::getOrCreateDestination(rewriter, loc, concatOp->getResult(0));
+    if (failed(dest))
+      return failure();
+
+    auto empty = dest->getDefiningOp<tensor::EmptyOp>();
+    if (!empty)
+      return failure();
+
+    int64_t dim = concatOp.getDim();
+    Value dimValue = rewriter.createOrFold<arith::ConstantOp>(
+        loc, rewriter.getIndexAttr(dim));
+
+    int64_t rank = concatOp.getResultType().getRank();
+    SmallVector<OpFoldResult> strides(rank, rewriter.getIndexAttr(1));
+    SmallVector<OpFoldResult> offsets(rank, rewriter.getIndexAttr(0));
+    SmallVector<OpFoldResult> dimOffsets;
+    dimOffsets.push_back(rewriter.getIndexAttr(0));
+
+    for (auto input : concatOp.getInputs().drop_front()) {
+      Value size = rewriter.createOrFold<tensor::DimOp>(loc, input, dimValue);
+      Value currentOffset =
+          getValueOrCreateConstantIndexOp(rewriter, loc, dimOffsets.back());
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nicolasvasilache wrote:

We should already have better helpers that use `OpFoldResult` and `affine_apply` ops to make this more idiomatic and more concise IR.

https://github.com/llvm/llvm-project/pull/72779