[mlir][ods] Add query for derived attribute

[jpienaar]

Summary

For ODS generated operations, enable querying whether there is a derived
attribute with a given name.

[rriddle]

What is a derived attribute? When would this be used?

[jpienaar]

In D75411#1899715, @rriddle wrote:

What is a derived attribute? When would this be used?

Derived attributes are attributes that are not stored in the Op but instead computed from properties of the op (https://mlir.llvm.org/docs/OpDefinitions/#operation-arguments). E.g., a derived attribute T corresponding to the result type results in a convenience accessor T() that returns the result type but is not additionally stored. This allows for convenience functions that query the op (and return the result in convenient user usable format) without needing to store redundant information.

[rriddle]

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

401

nit: Can we just use llvm::is_contained instead? That would avoid bringing in StringSwitch to OperationSupport, which is included in a lot of places.

[jpienaar]

Switch to using is_contained

[jpienaar]

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

401

It is probably less efficient compared to the StringSwitch. But I do agree it is a smaller dependency though, and we could optimize this if it is problematic.

mlir/include/mlir/IR/OperationSupport.h

 
 #include "mlir/IR/Attributes.h"
 #include "mlir/IR/Identifier.h"
 #include "mlir/IR/Location.h"
 #include "mlir/IR/Types.h"
 #include "mlir/IR/Value.h"
 #include "mlir/Support/LogicalResult.h"
 #include "llvm/ADT/PointerUnion.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/TrailingObjects.h"
 #include <memory>
 
 namespace mlir {
 class Block;
 class Dialect;
 class Operation;
 struct OperationState;

mlir/test/mlir-tblgen/op-attribute.td

 
 // DECL-LABEL: DOp declarations
 // DECL: static void build({{.*}}, APInt i32_attr, APFloat f64_attr, StringRef str_attr, bool bool_attr, ::SomeI32Enum enum_attr, APInt dv_i32_attr, APFloat dv_f64_attr, StringRef dv_str_attr = "abc", bool dv_bool_attr = true, ::SomeI32Enum dv_enum_attr = ::SomeI32Enum::case5)
 
 // DEF-LABEL: DOp definitions
 // DEF: odsState.addAttribute("str_attr", (*odsBuilder).getStringAttr(str_attr));
 // DEF: odsState.addAttribute("dv_str_attr", (*odsBuilder).getStringAttr(dv_str_attr));
 
+// Test derived type attr.
+// ---
+def DerivedTypeAttrOp : NS_Op<"derived_type_attr_op", []> {
+  let results = (outs AnyTensor:$output);
+  DerivedTypeAttr element_dtype = DerivedTypeAttr<"return output().getType();">;
+}
+
+// DECL: bool isDerivedAttribute
+// DEF: bool DerivedTypeAttrOp::isDerivedAttribute(StringRef name) {
+// DEF:  return llvm::StringSwitch<bool>(name)
+// DEF:  .Case("element_dtype", true)
+// DEF:  .Default(false);
+// DEF: }
 
 // Test that only default valued attributes at the end of the arguments
 // list get default values in the builder signature
 // ---
 
 def EOp : NS_Op<"e_op", []> {
   let arguments = (ins
     I32Attr:$i32_attr,

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

for (auto &namedAttr : op.getAttributes()) {
     const auto &attr = namedAttr.attr;
     if (attr.isDerivedAttr()) {
       emitDerivedAttr(name, attr);
     } else {
       emitAttrWithStorageType(name, attr);
       emitAttrWithReturnType(name, attr);
     }
   }
+
+  // Generate helper method to query whether a named attribute is a derived
+  // attribute. This enables, for example, avoiding adding an attribute that
+  // overlaps with a derived attribute.
+  auto &method =
+      opClass.newMethod("bool", "isDerivedAttribute", "StringRef name");
+  auto &body = method.body();
+  body << "  return llvm::StringSwitch<bool>(name)";
+  for (auto namedAttr : op.getAttributes())
+    if (namedAttr.attr.isDerivedAttr())
+      body << "\n    .Case(\"" << namedAttr.name << "\", true)";
+  body << "\n    .Default(false);";
 }
 
 void OpEmitter::genAttrSetters() {
   // Generate raw named setter type. This is a wrapper class that allows setting
   // to the attributes via setters instead of having to use the string interface
   // for better compile time verification.
   auto emitAttrWithStorageType = [&](StringRef name, Attribute attr) {
     auto &method = opClass.newMethod("void", (name + "Attr").str(),