[TVMScript][Bugfix] Check for StructInfoProxy in R.match_cast

Prior to this commit, bare `StructInfoProxy` annotations could be used
to annotate variables (e.g. `var: R.Tensor`).  However, they could
not be used as the argument of a match cast (e.g. `R.match_cast(obj,
R.Tensor)`).  This breaks round-trips, as the `R.match_cast` printing
generates base `StructInfoProxy` objects.

This commit updates TVMScript parsing to handle bare `StructInfoProxy`
annotations as an argument to `R.match_cast`.

python/tvm/script/parser/relax/entry.py

@@ -47,6 +47,7 @@
 
 ############################## R.function ##############################
 
+
 # this formulation allows us to support having @R.function
 # appear as a decorator by itself or to have optional arguments
 # like @R.function(pure=False)
@@ -488,8 +489,31 @@ def __init__(self, value: Expr, struct_info: StructInfo) -> None:
 
 
 def match_cast(value: Expr, struct_info: StructInfo):
+    struct_info = _normalize_struct_info(struct_info)
+
     if value is None:
         raise ValueError("value of match_cast cannot be None")
     if struct_info is None:
         raise ValueError("struct_info of match_cast cannot be None")
     return MatchCastPair(value, struct_info)
+
+
+def _normalize_struct_info_proxy(annotation) -> StructInfoProxy:
+    if annotation is None:
+        return TupleProxy([])
+    elif callable(annotation):
+        return annotation()
+    elif isinstance(annotation, StructInfoProxy):
+        return annotation
+    else:
+        raise TypeError(f"Expected StructInfoProxy but got {type(annotation)}.")
+
+
+def _normalize_struct_info(
+    struct_info, dict_globals: Optional[Dict[str, Any]] = None
+) -> StructInfo:
+    if isinstance(struct_info, StructInfo):
+        return struct_info
+    else:
+        proxy = _normalize_struct_info_proxy(struct_info)
+        return proxy.as_struct_info(dict_globals)

python/tvm/script/parser/relax/parser.py

@@ -30,7 +30,12 @@
 from ...ir_builder import relax as R
 from ...ir_builder.base import IRBuilder
 from .._core import Parser, dispatch, doc
-from .entry import MatchCastPair, StructInfoProxy, TupleProxy
+from .entry import (
+    MatchCastPair,
+    StructInfoProxy,
+    _normalize_struct_info_proxy,
+    _normalize_struct_info,
+)
 
 
 def bind_assign_value(
@@ -91,13 +96,7 @@ def bind_assign_value(
 def eval_struct_info_proxy(self: Parser, node: doc.expr) -> StructInfoProxy:
     try:
         annotation = self.eval_expr(node)
-        if annotation is None:
-            return TupleProxy([])
-        if callable(annotation):
-            annotation = annotation()
-        if isinstance(annotation, StructInfoProxy):
-            return annotation
-        raise TypeError(f"Expected StructInfoProxy but got {type(annotation)}.")
+        return _normalize_struct_info_proxy(annotation)
     except Exception as err:
         self.report_error(node, str(err))
         raise err
@@ -106,7 +105,8 @@ def eval_struct_info_proxy(self: Parser, node: doc.expr) -> StructInfoProxy:
 def eval_struct_info(self: Parser, node: doc.expr, eval_str: bool = False) -> StructInfo:
     var_table = self.var_table.get() if eval_str else None
     try:
-        return eval_struct_info_proxy(self, node).as_struct_info(var_table)
+        struct_info = self.eval_expr(node)
+        return _normalize_struct_info(struct_info, var_table)
     except Exception as err:
         self.report_error(node, str(err))
         raise err
@@ -367,7 +367,6 @@ def visit_if(self: Parser, node: doc.If) -> None:
 @dispatch.register(token="relax", type_name="enter_token")
 def enter_token(self: Parser) -> Dict[str, Any]:
     def relax_call(self, *args) -> Expr:
-
         args = [convert_to_expr(arg) if isinstance(arg, tuple) else arg for arg in args]
 
         if all(isinstance(x, Expr) for x in args):

tests/python/tvmscript/test_tvmscript_roundtrip.py

@@ -113,9 +113,7 @@ def mmult(A: T.handle, B: T.handle, C: T.handle) -> None:
                                 T.ramp((x_c * 32), 1, 32)
                             ] + (
                                 T.broadcast(
-                                    A_1[
-                                        (((x_outer * 32768) + (x_c * 1024)) + (k_outer * 4)),
-                                    ],
+                                    A_1[(((x_outer * 32768) + (x_c * 1024)) + (k_outer * 4))],
                                     32,
                                 )
                                 * packedB[T.ramp(((y_outer * 32768) + (k_outer * 128)), 1, 32)]
@@ -4023,6 +4021,47 @@ def func(A: R.Tensor([10, 20], "float32")):
     return func
 
 
+def relax_match_cast_struct_info_proxy():
+    """StructInfoProxy subclasses may be used as expressions
+
+    This is a regression test.  The TVMScript parser allows StructInfo
+    to be specified using a default-constructible class
+    (e.g. `R.Tensor` or `R.Shape`) rather than an instance of that
+    class (e.g. `R.Tensor()` or `R.Shape()`).  In previous
+    implementations, this was only handled when the `StructInfo` was
+    used in an annotation context.  However, a `StructInfo` may also
+    appear as an argument, which is passed to `R.match_cast`.  Use of
+    a default-constructible class must be handled in this context as
+    well.
+    """
+
+    def make_ir_generator(proxy_subclass):
+        def inner():
+            @R.function
+            def func(A: R.Object):
+                B = R.match_cast(A, proxy_subclass)
+                return B
+
+            return func
+
+        inner.__name__ = subclass.__name__
+        return inner
+
+    # Not all subclasses of StructInfoProxy are default-constructible.
+    # This list is a subset of `StructInfoProxy.__subclasses__()`,
+    # excluding `PrimProxy` and `DTensorProxy`.
+    subclasses = [
+        tvm.script.parser.relax.entry.ObjectProxy,
+        tvm.script.parser.relax.entry.TensorProxy,
+        tvm.script.parser.relax.entry.CallableProxy,
+        tvm.script.parser.relax.entry.TupleProxy,
+        tvm.script.parser.relax.entry.ShapeProxy,
+    ]
+
+    for subclass in subclasses:
+        yield make_ir_generator(subclass)
+
+
 ir_generator = tvm.testing.parameter(
     launch_env_thread,
     opt_gemm_normalize,
@@ -4106,6 +4145,7 @@ def func(A: R.Tensor([10, 20], "float32")):
     return_zero_private,
     return_zero_private_with_attr,
     *op_of_literal(),
+    *relax_match_cast_struct_info_proxy(),
 )
 
 relax_ir_generator = tvm.testing.parameter(