Split COMP rewards distribution

[TylerEther]

This pull request is for RFP 16: Dynamic COMP reward distribution, authored by me and Arr00.

Changes:

• Split comp distribution speeds (compSpeeds) into borrow-side speeds (compBorrowSpeeds) and supply-side speeds (compSupplySpeeds)
• Replace Comptroller#_setCompSpeed(CToken, unit) with _setCompSpeeds(CToken[], unit[], unit[]) to: 1. allow setting multiple reward speeds in a single call, and 2. allow setting differing supply/borrow speeds
• Update tests and frameworks to work with the new method above
• Add tests for split COMP rewards distribution: ensuring rates are set correctly and ensuring rewards are distributed correctly
• Add upgrade hook in Comptroller#_become to silently set borrow and supply rates to existing rates
• Update gas costs (slightly lower)

I've run all of the tests to ensure none fail; the changes work as expected.

The upgrade hook has yet to be tested... after these changes pass reviews, I'll deploy the contract and write an upgrade simulation.

[TylerEther]

Nice work, feeling a lot better about this now. Still hard to remember how this code works though

If I'm understanding it correctly, index is a cumulative sum of the COMP per CToken, so updateComp[Borrow/Supply]Index accrues COMP for the whole market on liquidity changes and speed changes, and distribute[Supplier/Borrower]Comp calculates an account's index delta and multiplies that by the amount of cTokens they are moving and distributes this amount of COMP..

:nerd_face:

[jflatow]

Nice work, feeling a lot better about this now. Still hard to remember how this code works though

If I'm understanding it correctly, index is a cumulative sum of the COMP per CToken, so updateComp[Borrow/Supply]Index accrues COMP for the whole market on liquidity changes and speed changes, and distribute[Supplier/Borrower]Comp calculates an account's index delta and multiplies that by the amount of cTokens they are moving and distributes this amount of COMP..

🤓

Yeah the math is the easy part :) The initialization logic scares me since that's where we had the 'quirk' and all I remember is it was so complicated we couldn't even explain it to OZ

[TylerEther]

Nice work, feeling a lot better about this now. Still hard to remember how this code works though

If I'm understanding it correctly, index is a cumulative sum of the COMP per CToken, so updateComp[Borrow/Supply]Index accrues COMP for the whole market on liquidity changes and speed changes, and distribute[Supplier/Borrower]Comp calculates an account's index delta and multiplies that by the amount of cTokens they are moving and distributes this amount of COMP.. nerd_face

Yeah the math is the easy part :) The initialization logic scares me since that's where we had the 'quirk' and all I remember is it was so complicated we couldn't even explain it to OZ

Ah yes. The problem was that state.block is updated every liquidity event whereas state.index is only updated when a distribution speed is set. So the prior initialization code was never called as it expected state.block to be 0 which is not the case when a market has activity. :slightly_smiling_face:

[ghswFTUSD]

it seems the implementation is still not actived?

[hayesgm]

This was merged in a separate PR as it's on main-net.