[mlir][Linalg] Add couple of convenience methods to `LinalgInterface`.

[mravishankar]

Summary

Add methods to

• Get block argument that is tied with an opOperand
• Get the yield value that is tied with a output opOperand.

[mravishankar]

Push missing changes.

[gysit]

LGTM!

mlir/include/mlir/Dialect/Linalg/IR/LinalgInterfaces.td

InterfaceMethod<
       /*methodBody=*/"",
       /*defaultImplementation=*/[{
         assert(opOperand->getOwner() == this->getOperation());
         return !opOperand->get().getType().template isa<ShapedType>();
       }]
     >,
     InterfaceMethod<
       /*desc=*/[{
+        Return the block argument for an `opOperand`.
+      }],
+      /*retTy=*/"BlockArgument",
+      /*methodName=*/"getTiedBlockArgument",
+      /*args=*/(ins "OpOperand *":$opOperand),
+      /*methodBody=*/"",
+      /*defaultImplementation=*/[{
+        assert(opOperand->getOwner() == this->getOperation());
+        return getBlock()->getArgument(opOperand->getOperandNumber());
+      }]
+    >,
+    InterfaceMethod<
+      /*desc=*/[{
         Return the input or output indexing map for `opOperand`.
       }],
       /*retTy=*/"AffineMap",
       /*methodName=*/"getTiedIndexingMap",
       /*args=*/(ins "OpOperand*":$opOperand),
       /*methodBody=*/"",
       /*defaultImplementation=*/[{
         assert(opOperand->getOwner() == this->getOperation());
InterfaceMethod<
       /*defaultImplementation=*/[{
         assert(opOperand->getOwner() == this->getOperation());
         int64_t resultIndex = opOperand->getOperandNumber() - getNumInputs();
         assert(resultIndex >= 0 &&
                resultIndex < this->getOperation()->getNumResults() );
         return this->getOperation()->getResult(resultIndex);
       }]
     >,
+    InterfaceMethod<
+      /*desc=*/[{
+        Return the value yielded by the region corresponding to an output
+        `opOperand`.
+      }],
+      /*retTy=*/"OpOperand *",
+      /*methodName=*/"getTiedYieldValue",
+      /*args=*/(ins "OpOperand*":$opOperand),
+      /*methodBody=*/"",
+      /*defaultImplementation=*/[{
+        assert(opOperand->getOwner() == this->getOperation());
+        int64_t resultIndex = opOperand->getOperandNumber() - getNumInputs();
+        assert(resultIndex >= 0 &&
+               resultIndex < this->getOperation()->getNumResults());
+        Operation *yieldOp = getBlock()->getTerminator();
+        return &yieldOp->getOpOperand(resultIndex);
+      }]
+    >,
     //===------------------------------------------------------------------===//
     // Other interface methods.
     //===------------------------------------------------------------------===//
     InterfaceMethod<
       /*desc=*/[{
         Return the single block constituting the body of the operation by
         calling the getBody method on the concrete operation.
       }],