Execute any Brillig opcodes which have constant inputs at compile time

[TomAFrench]

Problem

The brillig_integer_binary_operations integration test has zero arguments so should be able to be compiled down to an empty circuit. However, because of our usage of brillig opcodes we have 43 gates which need to be handled by the backend.

This is low-hanging fruit for compiler optimisation.

Happy Case

When performing ACIR gen on brillig opcodes we should check to see if all of the inputs are known constants. If so then we should execute the brillig opcode within the compiler and return constant AcirVars for the opcode outputs. This will allow us to use these values to perform later optimisations.

Alternatives Considered

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

Yes

Support Needs

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[kevaundray]

Changing to P-LOW since we have an issue open to optimize brillig functions which may supercede this

[TomAFrench]

@sirasistant @kevaundray Do you think it's worth merging #2190 as a stop-gap measure while #2066 is being worked on?

[sirasistant]

Looks like a good stop-gap to me yes!