HEAD is breaking back-compat wrt loopy==2024.1

[kaushikcfd]

Minimal reproducer:

import loopy as lp
from pytools import memoize_on_first_arg


@memoize_on_first_arg
def get_id(kernel, insn):
    return insn.id

t_unit = lp.make_kernel(
    "{ : }",
    """
    a = 3.14
    """)

knl = t_unit.default_entrypoint
get_id(knl, knl.instructions[0])

With the following error:

Traceback (most recent call last):
  File "/home/kgk2/temp/foo.py", line 16, in <module>
    get_id(knl, knl.instructions[0])
  File "/home/kgk2/projects/firedrake_gpu/lib/python3.11/site-packages/pytools/__init__.py", line 815, in wrapper
    object.__setattr__(obj, cache_dict_name, {key: result})
                                             ^^^^^^^^^^^^^
  File "/home/kgk2/projects/firedrake_gpu/lib/python3.11/site-packages/pytools/__init__.py", line 537, in __hash__
    self._cached_hash = hash((
                        ^^^^^^
TypeError: unhashable type: 'dict'

[kaushikcfd]

Looks like "InstructionBase.happens_after" must be a persistent dict or immutable.Map.