[TASK] Investigate gas optimization: instantiate `Attestation` with `{}` notation

[alainncls]

Summary

It has been suggested that instantiating an Attestation struct using {} notation could save gas. This ticket aims to validate this claim and, if confirmed, apply the optimization across the codebase.

Objectives

1. Research & benchmark

   • Compare gas costs of instantiating an Attestation using {} notation vs. standard assignment.
   • Provide concrete gas measurements to determine if the optimization is significant.

2. Apply optimization (if confirmed)

   • Update all instances where Attestation is instantiated to use {} notation if it proves beneficial.
   • Ensure no unintended side effects in contract behaviour.

Impact

• Potential gas savings across Verax contracts.
• Improved efficiency for attestation-related transactions.

[evgeniytar]

Conducted some benchmarks on this and seems like { } annotation is indeed slightly more gas efficient.

As a comparison base I took this method that initiates Attestation.

linea-attestation-registry/contracts/src/stdlib/IndexerModuleV2.sol

Lines 187 to 207 in e2e7f11

	function _buildAttestation(
	AttestationPayload calldata attestationPayload,
	address attester,
	address portal
	) internal view returns (Attestation memory) {
	return
	Attestation(
	attestationRegistry.getNextAttestationId(),
	attestationPayload.schemaId,
	bytes32(0),
	attester,
	portal,
	uint64(block.timestamp),
	attestationPayload.expirationDate,
	0,
	attestationRegistry.getVersionNumber(),
	false,
	attestationPayload.subject,
	attestationPayload.attestationData
	);
	}

Here is a contract that I built for measuring gas usage

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract AttestationGasTest {
    struct Attestation {
        bytes32 uid;
        bytes32 schema;
        uint64 time;
        uint64 expirationTime;
        uint64 revocationTime;
        bytes32 refUID;
        address recipient;
        address attester;
        bool revocable;
        bytes data;
    }

    function _buildAttestationPositional(
        bytes32 uid,
        bytes32 schema,
        uint64 time,
        uint64 expirationTime,
        uint64 revocationTime,
        bytes32 refUID,
        address recipient,
        address attester,
        bool revocable,
        bytes memory data
    ) public pure returns (Attestation memory) {
        return Attestation(
            uid,
            schema,
            time,
            expirationTime,
            revocationTime,
            refUID,
            recipient,
            attester,
            revocable,
            data
        );
    }

    function _buildAttestationNamed(
        bytes32 uid,
        bytes32 schema,
        uint64 time,
        uint64 expirationTime,
        uint64 revocationTime,
        bytes32 refUID,
        address recipient,
        address attester,
        bool revocable,
        bytes memory data
    ) public pure returns (Attestation memory) {
        return Attestation({
            uid: uid,
            schema: schema,
            time: time,
            expirationTime: expirationTime,
            revocationTime: revocationTime,
            refUID: refUID,
            recipient: recipient,
            attester: attester,
            revocable: revocable,
            data: data
        });
    }

    uint256 constant N = 100;

    function testGas_Positional() public pure {
        bytes memory emptyData = "";
        bytes32 dummyBytes = keccak256("test");
        address dummyAddr = address(0x123);

        for (uint256 i = 0; i < N; i++) {
            _buildAttestationPositional(dummyBytes, dummyBytes, 1, 2, 3, dummyBytes, dummyAddr, dummyAddr, true, emptyData);
        }
    }

    function testGas_Named() public pure {
        bytes memory emptyData = "";
        bytes32 dummyBytes = keccak256("test");
        address dummyAddr = address(0x123);

        for (uint256 i = 0; i < N; i++) {
            _buildAttestationNamed(dummyBytes, dummyBytes, 1, 2, 3, dummyBytes, dummyAddr, dummyAddr, true, emptyData);
        }
    }
}

As result positional argument approach took 71449 gas per 100 initiations,

meantime {} annotation used 71383.

@alainncls does this research make sense for you?