[MLIR][Python] Python binding support for AffineIfOp (#108323)

Fix the AffineIfOp's default builder such that it takes in an
IntegerSetAttr. AffineIfOp has skipDefaultBuilders=1 which effectively
skips the creation of the default AffineIfOp::builder on the C++ side.
(AffineIfOp has two custom OpBuilder defined in the
extraClassDeclaration.) However, on the python side, _affine_ops_gen.py
shows that the default builder is being created, but it does not accept
IntegerSet and thus is useless. This fix at line 411 makes the default
python AffineIfOp builder take in an IntegerSet input and does not
impact the C++ side of things.

Author: kaitingwang

mlir/python/mlir/dialects/affine.py

@@ -156,3 +156,61 @@ def for_(
             yield iv, iter_args[0]
         else:
             yield iv
+
+
+@_ods_cext.register_operation(_Dialect, replace=True)
+class AffineIfOp(AffineIfOp):
+    """Specialization for the Affine if op class."""
+
+    def __init__(
+        self,
+        cond: IntegerSet,
+        results_: Optional[Type] = None,
+        *,
+        cond_operands: Optional[_VariadicResultValueT] = None,
+        has_else: bool = False,
+        loc=None,
+        ip=None,
+    ):
+        """Creates an Affine `if` operation.
+
+        - `cond` is the integer set used to determine which regions of code
+          will be executed.
+        - `results` are the list of types to be yielded by the operand.
+        - `cond_operands` is the list of arguments to substitute the
+          dimensions, then symbols in the `cond` integer set expression to
+          determine whether they are in the set.
+        - `has_else` determines whether the affine if operation has the else
+          branch.
+        """
+        if results_ is None:
+            results_ = []
+        if cond_operands is None:
+            cond_operands = []
+
+        if cond.n_inputs != len(cond_operands):
+            raise ValueError(
+                f"expected {cond.n_inputs} condition operands, got {len(cond_operands)}"
+            )
+
+        operands = []
+        operands.extend(cond_operands)
+        results = []
+        results.extend(results_)
+
+        super().__init__(results, cond_operands, cond)
+        self.regions[0].blocks.append(*[])
+        if has_else:
+            self.regions[1].blocks.append(*[])
+
+    @property
+    def then_block(self) -> Block:
+        """Returns the then block of the if operation."""
+        return self.regions[0].blocks[0]
+
+    @property
+    def else_block(self) -> Optional[Block]:
+        """Returns the else block of the if operation."""
+        if len(self.regions[1].blocks) == 0:
+            return None
+        return self.regions[1].blocks[0]