Rewrite reshapes that only expand or squeeze dims

pytensor/graph/rewriting/basic.py

@@ -2800,16 +2800,6 @@ def _check_chain(r, chain):
     return r is not None
 
 
-def check_chain(r, *chain):
-    """
-    WRITEME
-
-    """
-    if isinstance(r, Apply):
-        r = r.outputs[0]
-    return _check_chain(r, reduce(list.__iadd__, ([x, 0] for x in chain)))
-
-
 def pre_greedy_node_rewriter(
     fgraph: FunctionGraph, rewrites: Sequence[NodeRewriter], out: Variable
 ) -> Variable:

pytensor/tensor/elemwise.py

@@ -166,15 +166,20 @@ def __init__(self, *, input_ndim: int, new_order: Sequence[int | Literal["x"]]):
         self.transposition = self.shuffle + drop
         # List of dimensions of the output that are broadcastable and were not
         # in the original input
-        self.augment = sorted(i for i, x in enumerate(new_order) if x == "x")
+        self.augment = augment = sorted(i for i, x in enumerate(new_order) if x == "x")
         self.drop = drop
 
-        self.is_left_expand_dims = self.augment and (
+        dims_are_shuffled = sorted(self.shuffle) != self.shuffle
+
+        self.is_transpose = dims_are_shuffled and not augment and not drop
+        self.is_squeeze = drop and not dims_are_shuffled and not augment
+        self.is_expand_dims = augment and not dims_are_shuffled and not drop
+        self.is_left_expand_dims = self.is_expand_dims and (
             input_ndim == 0 or new_order[-input_ndim:] == list(range(input_ndim))
         )
-        self.is_right_expand_dims = self.augment and new_order[:input_ndim] == list(
-            range(input_ndim)
-        )
+        self.is_right_expand_dims = self.is_expand_dims and new_order[
+            :input_ndim
+        ] == list(range(input_ndim))
 
         if self.inplace:
             self.view_map = {0: [0]}
@@ -215,16 +220,15 @@ def make_node(self, inp):
         return Apply(self, [input], [output])
 
     def __str__(self):
-        shuffle = sorted(self.shuffle) != self.shuffle
-        if self.augment and not (shuffle or self.drop):
+        if self.is_expand_dims:
             if len(self.augment) == 1:
                 return f"ExpandDims{{axis={self.augment[0]}}}"
             return f"ExpandDims{{axes={self.augment}}}"
-        if self.drop and not (self.augment or shuffle):
+        if self.is_squeeze:
             if len(self.drop) == 1:
-                return f"DropDims{{axis={self.drop[0]}}}"
-            return f"DropDims{{axes={self.drop}}}"
-        if shuffle and not (self.augment or self.drop):
+                return f"Squeeze{{axis={self.drop[0]}}}"
+            return f"Squeeze{{axes={self.drop}}}"
+        if self.is_transpose:
             return f"Transpose{{axes={self.shuffle}}}"
         return f"DimShuffle{{order=[{','.join(map(str, self.new_order))}]}}"