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Gas Optimization Guide

Overview

This document describes the gas optimization techniques applied to AgenticPay EVM smart contracts. All optimizations are designed to maintain functional equivalence while reducing gas costs.

Techniques Applied

1. Yul Assembly for Critical Paths

Assembly is used in performance-critical operations where Solidity generates suboptimal EVM bytecode:

  • SLOAD/SSTORE optimizations: Direct storage slot access via sload/sstore avoids Solidity's bounds checking and automatic retry logic
  • Self-balance: selfbalance() replaces address(this).balance (saves ~20 gas per call)
  • Mappings: Direct slot computation for mapping reads avoids redundant keccak256 calculations

Example - SplitterV1:

uint256 len;
assembly {
    len := sload(recipients.slot)
}

2. Unchecked Arithmetic

Safe arithmetic (Solidity 0.8+ default) is bypassed where overflow is provably impossible:

  • Loop counters (++i)
  • Timestamp calculations (block.timestamp + delay)
  • Balance subtractions (checked earlier via if guards)
  • Fee calculations bounded by basis-point constraints

3. Custom Errors (Replace require)

All string-based require statements replaced with custom errors:

  • Before: require(ok, "Transfer failed");
  • After: revert TransferFailed(to, amount);
  • Savings: ~50 gas per occurrence (shorter deploy bytecode + cheaper reverts)

4. Storage Packing

State variables arranged to minimize slot usage:

  • uint16 for basis points (never exceeds 10,000)
  • bool for flags (packed with adjacent variables)
  • uint256 for timestamps (avoids unnecessary casting)

5. Storage Pointer (Reference) Usage

Using storage pointers instead of memory copies to avoid copying entire structs:

  • Before: Recipient memory r = recipients[i];
  • After: Recipient storage r = recipients[i];

6. Redundant SLOAD Elimination

Storage reads are cached in local variables when the value doesn't change:

uint16 _platformFeeBps;
assembly {
    _platformFeeBps := sload(platformFeeBps.slot)
}

7. Loop Optimizations

  • Pre-compute array lengths
  • Use unchecked { ++i; } pattern for iteration
  • Use storage references to avoid copying

Contract-Specific Optimizations

Contract Key Optimizations Estimated Savings
SplitterV1 Assembly SLOAD, storage pointers, unchecked math ~15-20%
TokenizedFiat Custom errors, unchecked math, storage caching ~10-15%
TimelockController Assembly mapping, unchecked math, require→custom errors ~10-15%
EmergencyPause Assembly mapping, storage optimizations ~10-15%
BridgeHTLC Custom errors, storage pointers, unchecked math ~10-15%
RelayPaymaster Custom errors, unchecked math ~10-15%
GasPriceOracle Assembly mapping reads, unchecked math ~15-20%

Running Gas Benchmarks

cd contracts/evm
REPORT_GAS=true npm run test:gas

To run specific gas benchmark tests:

npx hardhat test test/gas/GasBenchmark.test.ts

CI Gas Regression Gate

The CI pipeline includes a gas regression check that fails if gas increases beyond a threshold. See .github/workflows/contracts-evm.yml for configuration.