[TIR] Do not drop 4th argument to tir.max

The `tir.op.comm_reducer` utility provides two distinct APIs, either
reducing along a tensor axis or reducing along a list of arguments.

Prior to this commit, when reducing along a list of arguments, the 4th
argument was silently dropped.  For example,
`tvm.tir.max(1,2,3,4,3,2,1)` would return `3`.

python/tvm/tir/op.py

@@ -3150,10 +3150,16 @@ def reducer(expr, axis, where=None, init=None, *args):
         if isinstance(axis, (tvm.tir.IterVar, list, tuple)):
             assert not args
             return _make_reduce(expr, axis, where, init)
+
         if where is None:
             assert not args
+            assert init is None
             return _reduce_directly(expr, axis)
-        return _reduce_directly(expr, axis, where, *args)
+        elif init is None:
+            assert not args
+            return _reduce_directly(expr, axis, where)
+        else:
+            return _reduce_directly(expr, axis, where, init, *args)
 
     doc_str = """Create a {0} expression over axis.
 

tests/python/unittest/test_tir_ops.py

@@ -15,8 +15,11 @@
 # specific language governing permissions and limitations
 # under the License.
 import tvm
+import tvm.testing
 from tvm import te
 
+import pytest
+
 
 def check_throws(f):
     try:
@@ -213,10 +216,23 @@ def test_if_then_else():
             raise ValueError("Unknown combinations")
 
 
+@pytest.mark.parametrize("num_args", list(range(2, 10)))
+def test_comm_reducer(num_args):
+    """Handle all arguments in tir comm_reducer
+
+    The `tir.comm_reducer` API has two distinct usages.  It can reduce
+    a tensor along a specified axis, similar to numpy.max, or it can
+    reduce several arguments together, simililar to Python's built-in
+    max().  This choice is based on the type of the second argument.
+
+    If the `tir.comm_reducer` is reducing all arguments, then all
+    arguments should be used.  In the past, the introduction of new
+    arguments intended for use when reducing along a tensor axis has
+    failed to forward these arguments when reducing along a list of
+    items.
+    """
+    assert tvm.tir.max(*range(num_args)) == num_args - 1
+
+
 if __name__ == "__main__":
-    test_const_fold()
-    test_const_fold2()
-    test_const_fold3()
-    test_const_fold4()
-    test_binary_dtype_match()
-    test_if_then_else()
+    tvm.testing.main()