Loading an array into memory, does it call `SLOAD` many times?

Question

Let's say I have an array in storage:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

contract Test  {
    uint256[] s_array = [1,2,3,4,5,6,7,7,8,8,8,8,8,8,8,8,8,8,8];

    function doStuff() public{
        uint256[] memory array = s_array;
    }
}

In my doStuff function, are we calling SLOAD multiple times to put each element into the array in memory? Or just once?

Answer 1

Yes, every element in an array is loaded with the sload opcode.

An example of loading element at position 0 from an array from the huff low-level language:

#define constant ARRAY_STARTING_SLOT = FREE_STORAGE_POINTER()

/* Macros */
#define macro READ_ELEMENT_ZERO_FROM_ARRAY() = takes (0) returns (0) {
    0x04 calldataload          // [array index to read from] array index should be 0
    iszero                        // [index == 0]
    success jumpi                 // [iszero_result]    

    0x00 0x00 revert

    success:
        [ARRAY_STARTING_SLOT]      // [ARRAY_STARTING_SLOT, iszero_result]
        0x00 mstore                // [iszero_result] // Memory now has the starting slot 
        0x20 0x00                  // [offset, size, iszero_result]
        sha3                       // [HashedStorageSlot, iszero_result] // sha3 reads from memory based on the offset & size given
        sload                      // [value_in_array, iszero_result]

        0x00 mstore                // [iszero_result] // Memory now has the starting slot
        0x20 0x00 return
} 

Every element you load into memory has to be pulled from an sload.