Unnecessary SLOADs and MLOADs in for-each loops

[code423n4]

Handle

pants

Vulnerability details

There are many for loops that follows this for-each pattern:

for (uint256 i = 0; i < array.length; i++) {
	// do something with `array[i]`
}

In such for loops, the array.length is read on every iteration, instead of caching it once in a local variable and read it from there.

Impact

Storage reads are much more expensive than reading local variables. Memory reads are a bit more expensive than reading local variables.

Tool Used

Manual code review.

Recommended Mitigation Steps

Read these values from storage / memory once, cache them in local variables and then read them again from the local variables. For example:

uint256 length = array.length;
for (uint256 i = 0; i < length; i++) {
	// do something with `array[i]`
}

[GalloDaSballo]

Agree that caching the length would save gas, this is because .length is set at an offset and accessing it costs gas
Additionally, when dealing with storage, it's always best to work from a memory cache to save gas