[Perf] use SmallVec?

[hsqStephenZhang]

Hi, should we use Smallvec in places like BasicBlock::args for better performance? Or is it not a concern for now?

[vaivaswatha]

Hi, should we use Smallvec in places like BasicBlock::args for better performance? Or is it not a concern for now?

Maybe not for block arguments, but it may make sense for operation results (typically a size of 1) and operands (typically size of 1-2).

I don't know how crucial this is right now though. It should likely be experiment driven, to see whether SmallVec helps and what the right size should be.