Failure to split a computation consisting in iterating calls to sha256

[igarnier]

One can get the following error when running a long computation iterating calls to sha256:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Cannot expand, max po2 of 20 reached.', host/src/benches/iter_sha2.rs:82:89

This was observed on 0.17.0.

Steps to reproduce:

• Clone this branch: https://github.com/igarnier/zk-benchmarking/tree/iter-sha2-failure
• cd risczero
• cargo b -r
• target/release/host --out dummy.csv iter-sha2

The guest code is there: https://github.com/igarnier/zk-benchmarking/blob/iter-sha2-failure/risczero/methods/guest/src/bin/iter_sha2.rs

The error was triggered for num_iter = 10_000 (this is an upper bound, didn't try to bisect).

[SchmErik]

From reading the trace log, it doesn't look like this is setting the is_halted to true at the cycle count for the split. I expect to see this message: log::info!("SPLIT[{cycle}]> pc: 0x{pc:08x}");