Cleaning Up Variables

In Ethereum Solidity, variables occupying fewer than 256 bits in memory or storage must be carefully "cleaned" (masked) because the EVM stack operates strictly on 256-bit words. When a uint8 is loaded, the compiler must guarantee the upper 248 bits are zeroed out before performing operations like JUMPI or comparisons.

Cleanup on NeoVM

💡 NeoVM Difference

NeoVM uses strictly typed StackItems, not a flat 256-bit word stack. Variable cleanup operations are largely unnecessary and omitted by the compiler.

On Neo, an integer is an arbitrary-precision BigInteger. There is no concept of "upper bits" containing garbage data from a previous operation.

uint8 a = 255;
uint256 b = a;

In EVM, this requires careful masking to ensure b does not inherit trailing bytes. In NeoVM, a is simply the BigInteger 255. Assigning it to b carries over the exact numeric value with zero structural masking required.

Struct and Array Cleanup

Similarly, when deleting data from storage, Ethereum must issue SSTORE 0 to zero out the data slot.

On NeoVM, delete operations compile directly to the System.Storage.Delete syscall, which entirely removes the Key-Value pair from the node's database, freeing up the state footprint efficiently.