[mlir] Change DenseArrayAttr to TensorType

[Mogball]

Summary

Previously, DenseArrayAttr used VectorType for its shaped type.
VectorType is problematic for arrays because it doesn't support zero
dimensions, meaning that an empty array would have vector<i32> as its
type. ElementsAttr would think that an empty dense array is size 1, not
0. This patch switches over to TensorType, which does support zero
dimensions.

Fixes #56860

[Mogball]

rebase

[lattner]

Out of curiosity, why does DenseArrayAttr conform to ShapedType? That seems really specific to multidimensional things, why not just have an array-like getSize() interface like ArrayAttr?

[Mogball]

It's required by ElementsAttr interface. Whether DenseArrayAttr needs to conform to that interface is up for discussion, but it does provide a lot of the machinery for querying the underlying values.

[lattner]

It's required by ElementsAttr interface. Whether DenseArrayAttr needs to conform to that interface is up for discussion, but it does provide a lot of the machinery for querying the underlying values.

Got it, thanks!

mlir/lib/IR/AsmPrinter.cpp

case DenseArrayBaseAttr::EltType::I64:
       break;
     case DenseArrayBaseAttr::EltType::F32:
       os << "[:f32";
       break;
     case DenseArrayBaseAttr::EltType::F64:
       os << "[:f64";
       break;
     }
-    if (denseArrayAttr.getType().getRank())
+    if (denseArrayAttr.size())
       os << " ";
     denseArrayAttr.printWithoutBraces(os);
     os << "]";
   } else if (auto resourceAttr = attr.dyn_cast<DenseResourceElementsAttr>()) {
     os << "dense_resource<";
     printResourceHandle(resourceAttr.getRawHandle());
     os << ">";
   } else if (auto locAttr = attr.dyn_cast<LocationAttr>()) {

mlir/lib/IR/BuiltinAttributes.cpp

 /// Mapping from C++ element type to MLIR DenseArrayAttr internals.
 template <typename T>
 struct denseArrayAttrEltTypeBuilder;
 template <>
 struct denseArrayAttrEltTypeBuilder<int8_t> {
   constexpr static auto eltType = DenseArrayBaseAttr::EltType::I8;
   static ShapedType getShapedType(MLIRContext *context,
                                   ArrayRef<int64_t> shape) {
-    return VectorType::get(shape, IntegerType::get(context, 8));
+    return RankedTensorType::get(shape, IntegerType::get(context, 8));
   }
 };
 template <>
 struct denseArrayAttrEltTypeBuilder<int16_t> {
   constexpr static auto eltType = DenseArrayBaseAttr::EltType::I16;
   static ShapedType getShapedType(MLIRContext *context,
                                   ArrayRef<int64_t> shape) {
-    return VectorType::get(shape, IntegerType::get(context, 16));
+    return RankedTensorType::get(shape, IntegerType::get(context, 16));
   }
 };
 template <>
 struct denseArrayAttrEltTypeBuilder<int32_t> {
   constexpr static auto eltType = DenseArrayBaseAttr::EltType::I32;
   static ShapedType getShapedType(MLIRContext *context,
                                   ArrayRef<int64_t> shape) {
-    return VectorType::get(shape, IntegerType::get(context, 32));
+    return RankedTensorType::get(shape, IntegerType::get(context, 32));
   }
 };
 template <>
 struct denseArrayAttrEltTypeBuilder<int64_t> {
   constexpr static auto eltType = DenseArrayBaseAttr::EltType::I64;
   static ShapedType getShapedType(MLIRContext *context,
                                   ArrayRef<int64_t> shape) {
-    return VectorType::get(shape, IntegerType::get(context, 64));
+    return RankedTensorType::get(shape, IntegerType::get(context, 64));
   }
 };
 template <>
 struct denseArrayAttrEltTypeBuilder<float> {
   constexpr static auto eltType = DenseArrayBaseAttr::EltType::F32;
   static ShapedType getShapedType(MLIRContext *context,
                                   ArrayRef<int64_t> shape) {
-    return VectorType::get(shape, Float32Type::get(context));
+    return RankedTensorType::get(shape, Float32Type::get(context));
   }
 };
 template <>
 struct denseArrayAttrEltTypeBuilder<double> {
   constexpr static auto eltType = DenseArrayBaseAttr::EltType::F64;
   static ShapedType getShapedType(MLIRContext *context,
                                   ArrayRef<int64_t> shape) {
-    return VectorType::get(shape, Float64Type::get(context));
+    return RankedTensorType::get(shape, Float64Type::get(context));
   }
 };
 } // namespace
 
 /// Builds a DenseArrayAttr<T> from an ArrayRef<T>.
 template <typename T>
 DenseArrayAttr<T> DenseArrayAttr<T>::get(MLIRContext *context,
                                          ArrayRef<T> content) {
   auto size = static_cast<int64_t>(content.size());
-  auto shapedType = denseArrayAttrEltTypeBuilder<T>::getShapedType(
-      context, size ? ArrayRef<int64_t>{size} : ArrayRef<int64_t>{});
+  auto shapedType =
+      denseArrayAttrEltTypeBuilder<T>::getShapedType(context, size);
   auto eltType = denseArrayAttrEltTypeBuilder<T>::eltType;
   auto rawArray = ArrayRef<char>(reinterpret_cast<const char *>(content.data()),
                                  content.size() * sizeof(T));
   return Base::get(context, shapedType, eltType, rawArray)
       .template cast<DenseArrayAttr<T>>();
 }
 
 template <typename T>