Why does removing a SLOAD in constructor save so much gas? - solidity

Question

I changed the state variable in the constructor to a numeric value and printed the difference in gas consumed. Here's my code. The results showed that constructing the BeforeDemo consumed 93915 gas, constructing the AfterDemo consumed 76288 gas and the difference was 17627. I thought the difference came from one SLOAD but one SLOAD can't cost so much gas. Why is there so much difference between the two？
contract BeforeDemo {
uint256 public constant INITIAL_SUPPLY = 10000 * (10 ** 18);
constructor() {
check(INITIAL_SUPPLY);
}
function check(uint256 supply) public {
}
}
contract AfterDemo {
constructor() {
check(10000 * (10 ** 18));
}
function check(uint256 supply) public {
}
}

Answer 1

There is no SLOAD because constants are stored in the bytecode, not in storage. The difference in gas cos you see is due to the contract bytecode size.
When using uint256 public constant INITIAL_SUPPLY the compiler generates a public getter function for it:
function INITIAL_SUPPLY() public pure returns(uint256) { return 10000 * (10 ** 18) }
This means that more OPCODEs are run on contract deployment, resulting in a larger contract bytecode.
Contract deployment costs 32k gas + 200 per byte. On remix, I checked that BeforeDemo is 373 bytes long and AfterDemo is 284 bytes long.
(373 - 284) * 200 = 17800
So you get approx. 17800 gas difference on deployment because of the contract bytecode size.