Bug: secret-forget-secrets does not work after yosys optimizer

[asraa]

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@j2kun - I thought it would be nice to check the Yosys optimizer pass for correctness by chaining yosys-optimizer with secret-forget-secrets and then lowering to LLVM to execute (this would have caught the bug)

The issue here seems to be that the secret.cast that transforms the multi-bit secrets to the tensor of single-bits has no conversion pattern. We already have code that extracts bits from plaintext multi-bits so we can use that here for an input conversion.

[j2kun]

I lost the train of thought on this bug. Is there a simple reproducer for the error?

[asraa]

Sure! Maybe the add_one example is the easiest. It hits this bug on anything with a multi-bit integer value.

bazel run -c dbg @heir//tools:heir-opt --  --yosys-optimizer --canonicalize --cse --secret-forget-secrets $(pwd)/tests/yosys_optimizer/arith_ops.mlir