This is only needed for RISCV, but witgen is more general than RISCV and
should allow memory accesses anywhere, especially since we have the std
memory machine.
The RISCV executor also checks this so it won't go unchecked.
Fixes#844
This PR adds a new machine to the STD: `WriteOnceMemory`. This can be
used in our RISC-V machine for bootloader inputs (#1203).
Most of the issues mentioned in the issue were fixed in the meantime or
had a simple workaround (like defining `let LATCH = 1`). The only
remaining issues were in the machine detection, which I fixed here.
I also re-factor two existing tests.
With this PR, we remember the mapping from Lookup / Permutation Identity
to Machine. This is cleaner, lets us save some work when calling a
machine and allows us to fail earlier if no machine can answer the call
(at machine extraction time, rather than runtime.
Changes:
- `Machine::process_plookup()`: Instead of passing in `right` and
`kind`, machines now only receive an `IdentityId`. If the machine needs
to access any of the expressions, references to it have to be stored
with the machine.
- `Machine::identities()`: New function that lets us ask the machine for
which identities it feels respondible.
- The `Machines` struct now stores the mapping from `IdentityId` to
machine index, allowing us to replace the loop of trying all machines
with a simple call to `Machines::call()`.
- The identity kind is now also stored in `Identity::id`. Previously,
this only stored a `usize` which is not necessarily unique. As mentioned
above, this change could be merged as part of a separate PR.
#### Benchmark Results:
```
executor-benchmark/keccak
time: [8.7242 s 8.9755 s 9.3876 s]
change: [-4.7814% +0.8652% +7.4252%] (p = 0.79 > 0.05)
No change in performance detected.
executor-benchmark/many_chunks_chunk_0
time: [38.731 s 39.313 s 40.081 s]
change: [-5.6906% -3.9986% -1.8421%] (p = 0.00 < 0.05)
Performance has improved.
```
This PR changes that `Identity` IDs are now globally unique, by doing to
things:
1. When dispensing IDs, we now have only one ID counter, instead of one
per type.
2. Fixed a bug in the condenser, where it would previously assign the
same ID when evaluating a `|| -> constr[]`.
- change AffineExpression to an enum of Constant|OneVar|ManyVars
- remove "cleaning" logic and keep coefficients ordered and clean
- rewrite of ExpressionEvaluator::evaluate_binary_operation to shortcut on Err when possible
