[mlir] Remove types from attributes

This patch removes the `type` field from `Attribute` along with the
`Attribute::getType` accessor.

Going forward, this means that attributes in MLIR will no longer have
types as a first-class concept. This patch lays the groundwork to
incrementally remove or refactor code that relies on generic attributes
being typed. The immediate impact will be on attributes that rely on
`Attribute` containing a type, such as `IntegerAttr`,
`DenseElementsAttr`, and `ml_program::ExternAttr`, which will now need
to define a type parameter on their storage classes. This will save
memory as all other attribute kinds will no longer contain a type.

Moreover, it will not be possible to generically query the type of an
attribute directly. This patch provides an attribute interface
`TypedAttr` that implements only one method, `getType`, which can be
used to generically query the types of attributes that implement the
interface. This interface can be used to retain the concept of a "typed
attribute". The ODS-generated accessor for a `type` parameter
automatically implements this method.

Next steps will be to refactor the assembly formats of certain operations
that rely on `parseAttribute(type)` and `printAttributeWithoutType` to
remove special handling of type elision until `type` can be removed from
the dialect parsing hook entirely; and incrementally remove uses of
`TypedAttr`.

Reviewed By: lattner, rriddle, jpienaar

Differential Revision: https://reviews.llvm.org/D130092

1 files changed, 3 insertions, 1 deletions

diff --git a/mlir/lib/Rewrite/ByteCode.cpp b/mlir/lib/Rewrite/ByteCode.cpp
index 7125dd3..d4ca8b2 100644
--- a/mlir/lib/Rewrite/ByteCode.cpp
+++ b/mlir/lib/Rewrite/ByteCode.cpp
@@ -1652,7 +1652,9 @@ void ByteCodeExecutor::executeGetAttributeType() {
   LLVM_DEBUG(llvm::dbgs() << "Executing GetAttributeType:\n");
   unsigned memIndex = read();
   Attribute attr = read<Attribute>();
-  Type type = attr ? attr.getType() : Type();
+  Type type;
+  if (auto typedAttr = attr.dyn_cast<TypedAttr>())
+    type = typedAttr.getType();
 
   LLVM_DEBUG(llvm::dbgs() << "  * Attribute: " << attr << "\n"
                           << "  * Result: " << type << "\n");