[Bug]: Solidity 0.4.24 allocates more memory than needed

[shoham-certora]

Summary

Certora identified a bug in the Solidity 0.4.24 compiler that affects the gas consumption of the Lido contract, with the help of the Certora prover. When creating a memory bytes array new bytes(48) in contracts/0.4.24/lib/SigningKeys.sol, the compiler actually allocates 32 * 48 = 1536 bytes, which is a waste of gas.

core/contracts/0.4.24/lib/SigningKeys.sol

Line 52 in 22cab0f

bytes memory tmpKey = new bytes(48);

We believe this affects also other constant size array allocations. We've also confirmed this issue exists in the currently deployed version.

Expected Behavior

Allocate on 48 bytes.

Potential Impact

Waste of gas.

Steps to Reproduce

Any call to SigningKeys.saveKeysSigs will allocate too much memory.

Possible Solutions

No response

Guidelines

• I agree to follow Code of Conduct.
• I have read Lido Contribution Guide.