Gas Optimization: What Actually Matters

What you'll learn

• The Optimization Mindset
• Storage: The 80% of Optimization
• Calldata, Memory, and Arrays
• Custom Errors, External over Public, Modifier vs Internal
• The Solc Optimizer and via_ir
• Anti-patterns: Optimizations That Don't Help (or Hurt)

Key terms

Storage Packing

Declaring consecutive small state variables (uint128, uint64, address, bool, etc.) so they share a single 256-bit storage slot. The single biggest gas-optimization lever in most contracts.

Cold vs Warm SLOAD

First read of a storage slot in a transaction costs 2,100 gas (cold). Subsequent reads cost 100 gas (warm). Caching repeated reads in a local variable saves ~2,000 gas per redundant read.

SSTORE Refund

Writing zero to a previously non-zero slot refunds up to 4,800 gas (capped at 20% of total transaction gas after EIP-3529). Useful for cleanup operations like closing positions.

optimizer_runs

Solc setting that tunes the bytecode-size vs. per-call-gas trade-off. Higher values produce more inlining and cheaper calls but larger bytecode. 200 is balanced; AMMs use 1,000,000+; one-shot deployers use 1.

via_ir

Solc's newer optimization pipeline (Yul-based intermediate representation). Generally produces cheaper bytecode at the cost of much slower compilation. Used in production builds, often disabled during development.

Custom Error (re: gas)

Defined with the `error` keyword (0.8.4+). Saves ~50 gas per revert vs. `require` with a string, plus reduces bytecode size. Strict win.

unchecked { }

Solidity block that disables overflow / underflow checks for the contained arithmetic. Saves ~20-30 gas per operation. Use only in code paths where you can prove overflow is impossible (e.g. for-loop counters with known bounds).