Investigate caching Cairo Runner between runs

[JulianGCalderon]

When we want to run a CASM program, there are a couple of steps that need to be done always, regardless of how the program will be executed. For example:

• Loading instructions.
• Decoding instructions.
• Compiling hints.

This steps take time. Currently, there is no way of caching these values between runs. That is, they have to be computed every time I want to run the same program.

1. The first step is to find which values can be cached between runs. There may be some other values not mentioned here.

2. The next step is to measure/estimate how much would caching this value improve performance. We should note how much keeping this value cached costs.

3. Finally, we need to propose a new API that allows the user for retrieving/specifying this precomputed values.

[JulianGCalderon]

I profiled block range 30000-30010, and found that:

• 7% of the execution is spent loading the program onto the runner. This is done inside of initialize_entrypoint, but the program is loaded always regardless of the entrypoint to execute.
• 10% of the execution is spent compiling hints, inside of get_hint_data. All the hints are compiled, regardless of what is being executed.
• 3% of the execution is spent decoding instructions. When executing a program, not all instructions are decoded, only the ones executed.

I did not found anything else that is worth caching.

[JulianGCalderon]

I've been investigating if the loaded program could be cached, and how to do it.

• After Optimize Cairo 0 execution #2206, the actual load of the program takes only 1.5% of the execution.
• Samply is unable to tell me what actually is taking time, but there is nothing actually being computed (probably allocations are what takes most time), so I don't think caching those values would yield performance improvements.
• Adding support caching memory implies some refactoring the Cairo Runner, which is not easy to do. Also, doing so implies making the memory cells public.

TLDR: I don't think its worth to add support for caching the loaded program, at least not right know.

[JulianGCalderon]

Some experimental PRs:

• Add support for caching program segment #2221
• Add support for Hint Data caching #2220