Reserve space for LocalVector if size is known

[YYF233333]

As stated in 99936(comment), use LocalVector::reserve() if we can.

This covers the core directory. All these cases are trival and should be riskless.

Some length are wrapped with MAX(length, 0) to avoid negative value. Please tell me if these check can be removed.

[AThousandShips]

This is not a codestyle change, just to be clear, this is performance improvements theoretically

[YYF233333]

This is not a codestyle change, just to be clear, this is performance improvements theoretically

IMO this should be considered a codestyle improvement before being regarded as a performance optimization. It's a best practice stuff. Not every reserve result in considerable performance gain, but by enforcing this style, we can avoid accidentally writing poorly performing code.

Should probably mention this in code standard, remind everyone to do this.

[AThousandShips]

We call things that are mostly or only style changes codestyle, otherwise it's very misleading as "this is only surface level"

[kiroxas]

This whole f variable should be removed, as it is only used for the pushback, which will make a copy anyway.

[YYF233333]

Should be addressed in another PR, will try impl this ASAP.

[Ivorforce]

IMO this should be considered a codestyle improvement before being regarded as a performance optimization.

If this was a codestyle change instead of an optimization, it would be a bad one because it increases the complexity of the code :)

It's a best practice stuff. Not every reserve result in considerable performance gain, but by enforcing this style, we can avoid accidentally writing poorly performing code.

I agree it's good practice to call reserve when the expected size is known.
And it's good practice because of performance considerations. If it was always of negligible benefit to call reserve, we wouldn't do it.