Method Token Optimization (CALLT)

Back to Native Contracts

By default, native contract calls are emitted as System.Contract.Call syscalls with the target contract hash and method name pushed onto the stack. The --callt compiler flag enables an optimization that replaces these with CALLT instructions referencing a method token table embedded in the NEF binary.

neo-solc contract.sol --callt -O3 -o build/contract

How It Works

Without --callt:

PUSHDATA1 <20-byte contract hash>
PUSHDATA1 <method name string>
PUSHINT8 <call flags>
SYSCALL System.Contract.Call

With --callt:

CALLT <2-byte token index>

The NEF header contains a method token table that maps each token index to a (contractHash, method, parametersCount, hasReturnValue, callFlags) tuple. The Neo VM resolves the token at load time.

Benefits

• Smaller bytecode — eliminates inline contract hash and method name strings per call site
• Lower GAS cost — fewer opcodes executed per native call
• Explicit manifest permissions — each method token generates a precise permission entry

INFO

CALLT is a pure optimization. It does not change contract behavior. Contracts compiled with and without --callt are functionally identical. Use --callt in production builds for best efficiency.

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