[mlir] Convert ConstShapeOp to a static tensor type.

[akuegel]

Summary

ConstShapeOp knows its shape, so it should also have a static tensor type.

mlir/lib/Conversion/ShapeToStandard/ShapeToStandard.cpp

LogicalResult ConstShapeOpConverter::matchAndRewrite(
   SmallVector<Value, 4> extentOperands;
   for (auto extent : op.shape()) {
     extentOperands.push_back(
         rewriter.create<ConstantIndexOp>(loc, extent.getLimitedValue()));
   }
   Type indexTy = rewriter.getIndexType();
   Value tensor =
       rewriter.create<tensor::FromElementsOp>(loc, indexTy, extentOperands);
-  Type resultTy = RankedTensorType::get({ShapedType::kDynamicSize}, indexTy);
+  Type resultTy = RankedTensorType::get({op.shape().size()}, indexTy);
   rewriter.replaceOpWithNewOp<tensor::CastOp>(op, resultTy, tensor);
   return success();
 }
 
 namespace {
 class ConstSizeOpConversion : public OpConversionPattern<ConstSizeOp> {
 public:
   using OpConversionPattern<ConstSizeOp>::OpConversionPattern;

mlir/test/Conversion/ShapeToStandard/shape-to-standard.mlir

func @get_extent_from_extent_tensor(%extents : tensor<?xindex>, %idx : index)
   %result = shape.get_extent %extents, %idx : tensor<?xindex>, index -> index
   return %result : index
 }
 
 // -----
 
 // Lower `const_shape` to `tensor.from_elements`.
 // CHECK-LABEL: @const_shape
-// CHECK-SAME: () -> tensor<?xindex>
-func @const_shape() -> tensor<?xindex> {
+// CHECK-SAME: () -> tensor<3xindex>
+func @const_shape() -> tensor<3xindex> {
   // CHECK: %[[C1:.*]] = constant 1 : index
   // CHECK: %[[C2:.*]] = constant 2 : index
   // CHECK: %[[C3:.*]] = constant 3 : index
   // CHECK: %[[TENSOR3:.*]] = tensor.from_elements %[[C1]], %[[C2]], %[[C3]]
-  // CHECK: %[[RESULT:.*]] = tensor.cast %[[TENSOR3]] : tensor<3xindex> to tensor<?xindex>
-  // CHECK: return %[[RESULT]] : tensor<?xindex>
-  %shape = shape.const_shape [1, 2, 3] : tensor<?xindex>
-  return %shape : tensor<?xindex>
+  // CHECK: %[[RESULT:.*]] = tensor.cast %[[TENSOR3]] : tensor<3xindex> to tensor<3xindex>
+  // CHECK: return %[[RESULT]] : tensor<3xindex>
+  %shape = shape.const_shape [1, 2, 3] : tensor<3xindex>
+  return %shape : tensor<3xindex>
 }
 
 // -----
 
 // Lower `const_shape` in the case of rank 0.
 // CHECK-LABEL: func @const_shape_zero_elements
-// CHECK-SAME: () -> tensor<?xindex>
-func @const_shape_zero_elements() -> tensor<?xindex> {
+// CHECK-SAME: () -> tensor<0xindex>
+func @const_shape_zero_elements() -> tensor<0xindex> {
   // CHECK: %[[TENSOR:.*]] = tensor.from_elements : tensor<0xindex>
-  // CHECK: %[[RESULT:.*]] = tensor.cast %[[TENSOR]] : tensor<0xindex> to tensor<?xindex>
-  // CHECK: return %[[RESULT]] : tensor<?xindex>
-  %shape = shape.const_shape [] : tensor<?xindex>
-  return %shape : tensor<?xindex>
+  // CHECK: %[[RESULT:.*]] = tensor.cast %[[TENSOR]] : tensor<0xindex> to tensor<0xindex>
+  // CHECK: return %[[RESULT]] : tensor<0xindex>
+  %shape = shape.const_shape [] : tensor<0xindex>
+  return %shape : tensor<0xindex>
 }
 
 // -----
 
 // Lower `any` to its first operand.
 // CHECK-LABEL: @any_of_three
 // CHECK-SAME:  (%[[A:.*]]: tensor<?xindex>, %[[B:.*]]: tensor<?xindex>, %[[C:.*]]: tensor<?xindex>) -> tensor<?xindex>
 func @any_of_three(%a : tensor<?xindex>,