Inefficient keccak256 call

Severity: Gas ID: asm-keccak256

Flags calls to the high-level keccak256(...) builtin that can be cheaply rewritten with inline assembly.

What it does

Reports keccak256(arg) calls and (when possible) emits a fix suggestion that uses inline assembly to compute the hash directly, avoiding the overhead of the high-level call.

Why is this bad?

The high-level keccak256 call performs additional memory management and ABI encoding compared to a direct keccak256(ptr, len) opcode invocation. In hot paths the difference is visible in gas reports.

Example

Bad

bytes32 h = keccak256(abi.encodePacked(a, b));

Good

bytes32 h;
assembly ("memory-safe") {
    let m := mload(0x40)
    mstore(m, a)
    mstore(add(m, 0x20), b)
    h := keccak256(m, 0x40)
}

Notes

This is a Gas-severity lint and is not applied to test or script files.