Tweak the term model to avoid a panic situation #1368
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This would occur when concrete nat values were round-tripped via a bitvector type in the term model, and into a sequence indexing primitive. This tweak fixes a particular instance of this problem, but highlights the fact that we need much more robust handing of the sequencing primitives and natural numbers.
Also, add a switch that controls if the evalutor will be have in a "symbolic" way. Adding a new `PrimExcept` constructor that allows primitives to cause fallback behavior after examining all their arguments. As with the existing `PrimFilterFun`, this causes term reconstruction in the term model evaluator, and raises an error in the other evaluators. We use this new type of primitive to remove cases that would otherwise panic. In addition, we add a flag to the `BasePrims` record that controls if we do symbolic muxing for sequence operations and `ite`. For the term model, we disable this behavior and fall back earlier on term reconstruction. This avoids constructing large mux trees in some cases.
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The term model is now more robust against panic situations, and fixes #1367 |
atomb
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Jul 6, 2021
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This looks pretty reasonable to me. I appreciate the improvements to error handling. And I agree: I'd be entirely in favor of a thorough audit of how all of our symbolic backends handle each of the primitives. In particular, it would be nice to have open issues for any primitive that could be handled by a specific backend but currently isn't. That would take some work to identify, though.
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This would occur when concrete nat values were round-tripped
via a bitvector type in the term model, and into a sequence
indexing primitive.
This tweak fixes a particular instance of this problem, but
highlights the fact that we need much more robust handing of the
sequencing primitives and natural numbers.