Avoid applying Nat recursor to bvToNat. #2757
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sauclovian-g
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RyanGlScott
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Some SAWCore constants (e.g. `equalNat`) are implemented as primitives in the SAW backends, and also have definitions using e.g. Nat#rec that are used for Coq export. We now avoid unfolding such constants with `goal_normalize` because it typically results in goals that are unprovable by external solvers.
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The SAWCore simulator backend cannot evaluate the recursor
Nat#recon an argument derived from a symbolic bitvector expression withbvToNat. This situation leads to a panic message.Previously
goal_normalizewould happily unfold functions likeequalNatoraddNatto their low-level definitions usingNat#rec. Such functions are implemented as primitives in the various SAW backends, and as primitives they can be reasoned about successfully with symbolicbvToNatarguments.As of this PR,
goal_normalizenow avoids unfolding any function that is implemented as a primitive in the SAWCore simulator backends. This ensures that the resulting goal will still be evaluated in the backend in the same way as the original goal.Fixes #2749.