[MLIR] Add IndexAttr to primitive attributes kinds in tablegen.

Summary:
OpBase.td defined attributes kind for all integer types expect index. This
commit fixes that by adding an IndexAttr attribute kind.

Differential Revision: https://reviews.llvm.org/D78195

Author: ulysseB

Diff for: mlir/include/mlir/IR/OpBase.td

@@ -845,6 +845,16 @@ def BoolAttr : Attr<CPred<"$_self.isa<BoolAttr>()">, "bool attribute"> {
   let constBuilderCall = "$_builder.getBoolAttr($0)";
 }
 
+// Index attribute.
+def IndexAttr :
+    TypedAttrBase<
+      Index, "IntegerAttr",
+      And<[CPred<"$_self.isa<IntegerAttr>()">,
+           CPred<"$_self.cast<IntegerAttr>().getType().isa<IndexType>()">]>,
+      "index attribute"> {
+  let returnType = [{ APInt }];
+}
+
 // Base class for any integer (regardless of signedness semantics) attributes
 // of fixed width.
 class AnyIntegerAttrBase<AnyI attrValType, string descr> :

Diff for: mlir/test/IR/attribute.mlir

@@ -8,6 +8,8 @@ func @int_attrs_pass() {
   "test.int_attrs"() {
     // CHECK: any_i32_attr = 5 : ui32
     any_i32_attr = 5 : ui32,
+    // CHECK-SAME: index_attr = 8 : index
+    index_attr = 8 : index,
     // CHECK-SAME: si32_attr = 7 : si32
     si32_attr = 7 : si32,
     // CHECK-SAME: ui32_attr = 6 : ui32

Diff for: mlir/test/lib/Dialect/Test/TestOps.td

@@ -199,6 +199,7 @@ def I64EnumAttrOp : TEST_Op<"i64_enum_attr"> {
 def IntAttrOp : TEST_Op<"int_attrs"> {
   let arguments = (ins
     AnyI32Attr:$any_i32_attr,
+    IndexAttr:$index_attr,
     UI32Attr:$ui32_attr,
     SI32Attr:$si32_attr
   );