Revert "CLN: short-circuit case in Block.replace (pandas-dev#27768)"

This reverts commit 01f90c1.

Author: simonjayhawkins

pandas/core/internals/blocks.py

@@ -684,26 +684,8 @@ def replace(
         # If we cannot replace with own dtype, convert to ObjectBlock and
         # retry
         if not self._can_hold_element(to_replace):
-            if not isinstance(to_replace, list):
-                if inplace:
-                    return [self]
-                return [self.copy()]
-
-            to_replace = [x for x in to_replace if self._can_hold_element(x)]
-            if not len(to_replace):
-                # GH#28084 avoid costly checks since we can infer
-                #  that there is nothing to replace in this block
-                if inplace:
-                    return [self]
-                return [self.copy()]
-
-            if len(to_replace) == 1:
-                # _can_hold_element checks have reduced this back to the
-                #  scalar case and we can avoid a costly object cast
-                return self.replace(
-                    to_replace[0], value, inplace=inplace, regex=regex, convert=convert,
-                )
-
+            # TODO: we should be able to infer at this point that there is
+            #  nothing to replace
             # GH 22083, TypeError or ValueError occurred within error handling
             # causes infinite loop. Cast and retry only if not objectblock.
             if is_object_dtype(self):
@@ -728,27 +710,14 @@ def replace(
 
         mask = missing.mask_missing(values, to_replace)
 
-        if not mask.any():
-            if inplace:
-                return [self]
-            return [self.copy()]
-
         try:
             blocks = self.putmask(mask, value, inplace=inplace)
-            # Note: it is _not_ the case that self._can_hold_element(value)
-            #  is always true at this point.  In particular, that can fail
-            #  for:
-            #   "2u" with bool-dtype, float-dtype
-            #   0.5 with int64-dtype
-            #   np.nan with int64-dtype
         except (TypeError, ValueError):
             # GH 22083, TypeError or ValueError occurred within error handling
             # causes infinite loop. Cast and retry only if not objectblock.
             if is_object_dtype(self):
                 raise
 
-            assert not self._can_hold_element(value), value
-
             # try again with a compatible block
             block = self.astype(object)
             return block.replace(
@@ -905,7 +874,6 @@ def putmask(
 
         # if we are passed a scalar None, convert it here
         if not is_list_like(new) and isna(new) and not self.is_object:
-            # FIXME: make sure we have compatible NA
             new = self.fill_value
 
         if self._can_hold_element(new):