From fdaa391e3df3c3a555d933122b0ef85eaf5eb63c Mon Sep 17 00:00:00 2001
From: Frederik Gossen <frgossen@google.com>
Date: Thu, 28 May 2020 14:04:39 +0000
Subject: [PATCH] [MLIR] Add `num_elements` to the shape dialect

The operation `num_elements` determines the number of elements for a given
shape.
That is the product of its dimensions.

Differential Revision: https://reviews.llvm.org/D80281
---
 mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td | 18 ++++++++++++++++++
 mlir/lib/Dialect/Shape/IR/Shape.cpp            | 26 ++++++++++++++++++++++++++
 mlir/test/Dialect/Shape/canonicalize.mlir      | 22 ++++++++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
index 57d1954a319..0d300d3c64c 100644
--- a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
+++ b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
@@ -278,6 +278,24 @@ def Shape_MulOp : Shape_Op<"mul", [SameOperandsAndResultType]> {
   let results = (outs Shape_SizeType:$result);
 }
 
+def Shape_NumElementsOp : Shape_Op<"num_elements", [
+    NoSideEffect,
+    DeclareOpInterfaceMethods<InferTypeOpInterface>]> {
+
+  let summary = "Returns the number of elements for a given shape";
+  let description = [{
+    Returns the number of elements for a given shape which is the product of its
+    dimensions.
+  }];
+
+  let arguments = (ins Shape_ShapeType:$shape);
+  let results = (outs Shape_SizeType:$result);
+
+  let assemblyFormat = "attr-dict $shape";
+
+  let hasFolder = 1;
+}
+
 def Shape_ReduceOp : Shape_Op<"reduce", []> {
   let summary = "Returns an expression reduced over a shape";
   let description = [{
diff --git a/mlir/lib/Dialect/Shape/IR/Shape.cpp b/mlir/lib/Dialect/Shape/IR/Shape.cpp
index a077948fdd3..b0103e15fa3 100644
--- a/mlir/lib/Dialect/Shape/IR/Shape.cpp
+++ b/mlir/lib/Dialect/Shape/IR/Shape.cpp
@@ -333,6 +333,32 @@ OpFoldResult GetExtentOp::fold(ArrayRef<Attribute> operands) {
 }
 
 //===----------------------------------------------------------------------===//
+// NumElementsOp
+//===----------------------------------------------------------------------===//
+
+OpFoldResult NumElementsOp::fold(ArrayRef<Attribute> operands) {
+
+  // Fold only when argument constant.
+  Attribute shape = operands[0];
+  if (!shape)
+    return {};
+
+  APInt product(64, 1);
+  for (auto value : shape.cast<DenseIntElementsAttr>())
+    product *= value;
+  Builder builder(getContext());
+  return builder.getIndexAttr(product.getLimitedValue());
+}
+
+LogicalResult NumElementsOp::inferReturnTypes(
+    MLIRContext *context, Optional<Location> location, ValueRange operands,
+    DictionaryAttr attributes, RegionRange regions,
+    SmallVectorImpl<Type> &inferredReturnTypes) {
+  inferredReturnTypes.push_back(SizeType::get(context));
+  return success();
+}
+
+//===----------------------------------------------------------------------===//
 // ShapeOfOp
 //===----------------------------------------------------------------------===//
 
diff --git a/mlir/test/Dialect/Shape/canonicalize.mlir b/mlir/test/Dialect/Shape/canonicalize.mlir
index 106171de608..69c312e6dad 100644
--- a/mlir/test/Dialect/Shape/canonicalize.mlir
+++ b/mlir/test/Dialect/Shape/canonicalize.mlir
@@ -161,6 +161,28 @@ func @nonfoldable_index_to_size(%ci : index) -> !shape.size {
 }
 
 // -----
+// Fold number of elements computation.
+// CHECK-LABEL: func @num_elements
+func @num_elements() -> !shape.size {
+  // CHECK-NOT: shape.const_shape
+  %shape = shape.const_shape [4, 5, 6]
+  // CHECK-NOT: shape.num_elements
+  %num_elements = shape.num_elements %shape
+  // CHECK: %[[NUM:.*]] = shape.const_size 120
+  // CHECK-NEXT: return %[[NUM]] : !shape.size
+  return %num_elements : !shape.size
+}
+
+// -----
+// No folding.
+// CHECK-LABEL: func @nonfoldable_num_elements
+func @nonfoldable_num_elements(%shape : !shape.shape) -> !shape.size {
+  // CHECK-NOT: shape.const_{{.*}}
+  %num_elements = shape.num_elements %shape
+  return %num_elements : !shape.size
+}
+
+// -----
 
 // Canonicalization of shape.get_extent
 
-- 
2.11.0