[mlir] NFC: make Dialect::getRegisteredInterface const

[math-fehr]

Summary

Make Dialect::getRegisteredInterface const. This is just an API change.

[rriddle]

Where are you encountering a const Dialect?

[math-fehr]

In D104862#2838991, @rriddle wrote:

Where are you encountering a const Dialect?

I have this ExtensibleDialect class that extend Dialect (and that is used by multiple dialects). In order to cast a Dialect to an ExtensibleDialect, I retrieve an interface that is only implemented on ExtensibleDialect.
Since classof requires a const Dialect*, I cannot currently retrieve the interface in this function.

[rriddle]

In D104862#2839037, @math-fehr wrote:

In D104862#2838991, @rriddle wrote:

Where are you encountering a const Dialect?

I have this ExtensibleDialect class that extend Dialect (and that is used by multiple dialects). In order to cast a Dialect to an ExtensibleDialect, I retrieve an interface that is only implemented on ExtensibleDialect.
Since classof requires a const Dialect*, I cannot currently retrieve the interface in this function.

I would cast away the const wherever you are encountering it (if it is required there). Technically Dialect shouldn't have any const API(https://mlir.llvm.org/docs/Rationale/UsageOfConst/), but it looks like that is being broken in a few places.

[math-fehr]

In D104862#2839038, @rriddle wrote:

In D104862#2839037, @math-fehr wrote:

In D104862#2838991, @rriddle wrote:

Where are you encountering a const Dialect?

I have this ExtensibleDialect class that extend Dialect (and that is used by multiple dialects). In order to cast a Dialect to an ExtensibleDialect, I retrieve an interface that is only implemented on ExtensibleDialect.
Since classof requires a const Dialect*, I cannot currently retrieve the interface in this function.

I would cast away the const wherever you are encountering it (if it is required there). Technically Dialect shouldn't have any const API(https://mlir.llvm.org/docs/Rationale/UsageOfConst/), but it looks like that is being broken in a few places.

Okay, thanks for the link!
I'm removing this patch then.

mlir/include/mlir/IR/Dialect.h

public:
   }
 
   //===--------------------------------------------------------------------===//
   // Interfaces
   //===--------------------------------------------------------------------===//
 
   /// Lookup an interface for the given ID if one is registered, otherwise
   /// nullptr.
-  const DialectInterface *getRegisteredInterface(TypeID interfaceID) {
+  const DialectInterface *getRegisteredInterface(TypeID interfaceID) const {
     auto it = registeredInterfaces.find(interfaceID);
     return it != registeredInterfaces.end() ? it->getSecond().get() : nullptr;
   }
-  template <typename InterfaceT> const InterfaceT *getRegisteredInterface() {
+  template <typename InterfaceT>
+  const InterfaceT *getRegisteredInterface() const {
     return static_cast<const InterfaceT *>(
         getRegisteredInterface(InterfaceT::getInterfaceID()));
   }
 
   /// Lookup an op interface for the given ID if one is registered, otherwise
   /// nullptr.
   virtual void *getRegisteredInterfaceForOp(TypeID interfaceID,
                                             OperationName opName) {