Fix lru_cache type-conflation in dace.symbolic.simplify

[Spielopoly]

Summary

dace.symbolic.simplify is memoized with functools.lru_cache. lru_cache
keys its entries by hash/==, and in Python booleans are integers:

>>> hash(True) == hash(1)
True
>>> True == sympy.Integer(1)
True

As a result the cache cannot tell simplify(True) apart from
simplify(sympy.Integer(1)) — they collapse onto a single entry. Whichever is
evaluated first wins, and the other caller gets the wrong-typed result:

>>> from dace.symbolic import simplify
>>> simplify(True)                 # caches sympy.true under a key equal to 1
True
>>> simplify(sympy.Integer(1))     # cache hit -> returns the *boolean*
True                               # expected: 1  (a sympy.Integer)
>>> type(simplify(sympy.Integer(1)))
<class 'sympy.logic.boolalg.BooleanTrue'>

The same conflation applies to False / Integer(0).

Impact

The corruption is process-global and order dependent: any code path that
feeds a plain Python bool to simplify (for example a comparison like
simplify(s == 1), which evaluates to True/False before reaching
simplify) poisons the cache for every later simplify(sympy.Integer(1)) /
simplify(sympy.Integer(0)).

Downstream, this surfaces as a hard crash in memlet-volume propagation. For a
single-iteration map the propagated volume is sympy.Integer(1), so
propagate_subset (dace/sdfg/propagation.py) calls simplify(Integer(1)),
gets back BooleanTrue, and the Memlet.volume setter rejects it:

TypeError: Property volume must be a literal or symbolic expression,
got: <class 'sympy.logic.boolalg.BooleanTrue'>

Because it depends on evaluation order across the whole process, the failure is
intermittent and hard to attribute — an unrelated SDFG breaks long after the
bool was simplified.

Fix

Construct the cache with typed=True so arguments of different types are cached
under distinct entries, even when they hash and compare equal:

-@lru_cache(maxsize=2048)
+@lru_cache(maxsize=2048, typed=True)
 def simplify(expr: SymbolicType) -> SymbolicType:
     return sympy.simplify(expr)

With typed=True, simplify(True) (a bool) and simplify(sympy.Integer(1))
(a sympy.Integer) occupy separate cache slots, so neither can return the
other's result.

Testing

New regression test: tests/simplify_cache_typed_test.py. It covers:

• simplify(True) then simplify(Integer(1)) (and the reverse) stay correctly
  typed — both directions, for True/1 and False/0.
• Normal symbolic expressions still simplify and are still served from the cache
  (cache_info().hits).
• End-to-end: after a bool is passed to simplify, memlet-volume propagation
  over a single-iteration map still succeeds (this reproduced the original
  TypeError verbatim before the fix).

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a regression test suite and fixes a long-standing functools.lru_cache key-collision issue in dace.symbolic.simplify by using typed caching, preventing bool/sympy.Integer cache poisoning.

Changes:

• Switch dace.symbolic.simplify to @lru_cache(..., typed=True) to separate cache entries by argument type.
• Add regression tests covering True/1 and False/0 cache collisions.
• Add an end-to-end repro test ensuring memlet volume propagation is not broken by prior boolean simplification.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
dace/symbolic.py	Enables typed LRU caching for simplify to prevent bool/sympy.Integer conflation.
tests/simplify_cache_typed_test.py	Adds focused regression + end-to-end tests to prevent cache poisoning regressions.

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