From 81469527ec99a3452c867d997d259ea70f81dda5 Mon Sep 17 00:00:00 2001
From: Frederik Gossen <frgossen@google.com>
Date: Thu, 25 Jun 2020 08:31:49 +0000
Subject: [PATCH] [MLIR][Shape] Add constant folding to `shape.rank`

Add constant folding for the `shape.rank` operation of the shape dialect.

Differential Revision: https://reviews.llvm.org/D82076
---
 mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td |  2 ++
 mlir/lib/Dialect/Shape/IR/Shape.cpp            | 13 +++++++++++++
 mlir/test/Dialect/Shape/canonicalize.mlir      | 24 ++++++++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
index 0785a40..379f861 100644
--- a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
+++ b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
@@ -179,6 +179,8 @@ def Shape_RankOp : Shape_Op<"rank", [NoSideEffect]> {
   let results = (outs Shape_SizeType:$rank);
 
   let assemblyFormat = "attr-dict $shape";
+
+  let hasFolder = 1;
 }
 
 def Shape_ToExtentTensorOp : Shape_Op<"to_extent_tensor", [NoSideEffect]> {
diff --git a/mlir/lib/Dialect/Shape/IR/Shape.cpp b/mlir/lib/Dialect/Shape/IR/Shape.cpp
index 664c0cb..cdbc892 100644
--- a/mlir/lib/Dialect/Shape/IR/Shape.cpp
+++ b/mlir/lib/Dialect/Shape/IR/Shape.cpp
@@ -438,6 +438,19 @@ void GetExtentOp::build(OpBuilder &builder, OperationState &result, Value shape,
 }
 
 //===----------------------------------------------------------------------===//
+// RankOp
+//===----------------------------------------------------------------------===//
+
+OpFoldResult RankOp::fold(ArrayRef<Attribute> operands) {
+  auto shape = operands[0].dyn_cast_or_null<DenseIntElementsAttr>();
+  if (!shape)
+    return {};
+  int64_t rank = shape.getNumElements();
+  Builder builder(getContext());
+  return builder.getIndexAttr(rank);
+}
+
+//===----------------------------------------------------------------------===//
 // NumElementsOp
 //===----------------------------------------------------------------------===//
 
diff --git a/mlir/test/Dialect/Shape/canonicalize.mlir b/mlir/test/Dialect/Shape/canonicalize.mlir
index a56a8f9..00f6b36 100644
--- a/mlir/test/Dialect/Shape/canonicalize.mlir
+++ b/mlir/test/Dialect/Shape/canonicalize.mlir
@@ -442,3 +442,27 @@ func @f(%arg0 : !shape.shape) {
   "consume.witness"(%0) : (!shape.witness) -> ()
   return
 }
+
+// -----
+
+// Fold `rank` based on constant shape.
+// CHECK-LABEL: @fold_rank
+func @fold_rank() -> !shape.size {
+  // CHECK-DAG: %[[RESULT:.*]] = shape.const_size 5
+  // CHECK-DAG: return %[[RESULT]] : !shape.size
+  %shape = shape.const_shape [3, 4, 5, 6, 7]
+  %rank = shape.rank %shape
+  return %rank : !shape.size
+}
+
+// -----
+
+// Do not fold `rank` if shape is dynamic.
+// CHECK-LABEL: @dont_fold_rank
+// CHECK-SAME: (%[[SHAPE:.*]]: !shape.shape) -> !shape.size
+func @dont_fold_rank(%shape : !shape.shape) -> !shape.size {
+  // CHECK-DAG: %[[RESULT:.*]] = shape.rank %[[SHAPE]]
+  // CHECK-DAG: return %[[RESULT]] : !shape.size
+  %rank = shape.rank %shape
+  return %rank : !shape.size
+}
-- 
2.7.4