Gas optimization opportunities in TokenMessenger.sol ~$49K/month at current volume

[NthMOMENT]

Hi Circle team,

I had the opportunity to run a full gas audit on src/TokenMessenger.sol as part of Fourier's open protocol optimization series.

---

Summary of Findings

Finding	Category	Gas Saved	Location
localMinter read twice in _getLocalMinter()	SLOAD Reduction	~100 gas/call	_getLocalMinter()
remoteTokenMessengers[domain] read twice	SLOAD Reduction	~100 gas/call	removeRemoteTokenMessenger()
12 string require → Custom Errors	Bytecode + Revert Gas	~50–200 gas/revert + ~3–5KB bytecode	Contract-wide
Zero check on immutable in _isLocalMessageTransmitter()	Dead Code Elimination	~100 gas/call	_isLocalMessageTransmitter()
> 0 → != 0 on amount check	Opcode Selection	~5 gas/call	_depositForBurn()

---

The Arc-Specific Case

Finding #4 is the cleanest single-line fix: _isLocalMessageTransmitter() checks address(localMessageTransmitter) != address(0) but
localMessageTransmitter is immutable and guaranteed non-zero by the constructor. This is provably dead code the EVM evaluates on every handleReceiveMessage call. One line deleted, ~100 gas saved per USDC receive, zero risk.

Finding #3 (Custom Errors) requires upgrading from Solidity 0.7.6 → 0.8.x. All other findings apply to the current codebase without a version change.

Why Arc changes the calculus: On Ethereum and Arbitrum, gas price volatility means developers tolerate small inefficiencies. On Arc, gas is priced in USDC at a fixed rate. Every wasted opcode costs the same dollar amount every single time, forever. With BlackRock, Visa, and Goldman Sachs as confirmed testnet participants, the volume through this contract will make these per-transaction inefficiencies significant at scale.

Estimated impact at current testnet volume: ~$49K/month. At mainnet institutional volume, this goes into the millions or even billions.

---

All findings are syntactic only. There's no message routing, burn/mint accounting, attestation validation, or access control were modified.

Full report with before/after code snippets:
https://github.com/NthMOMENT/Fourier.u/blob/main/reports/CircleCCTP_TokenMessenger.md

Happy to provide production-ready diffs against your test suite. I work on a risk-reversal basis. Payment only if gas measurably drops and your tests pass.

Ram | Fourier | fouriers.xyz | @0xfourier