Personally, I only use alloca() if:

1. I know that the function will never be called recursively and

2. the total amount of stack allocation is limited to a few kilobytes at most.

alloca() is more problematic on embedded platforms because default stack sizes tend to be tiny. Either document your stack usage requirements or provide an option to disable all calls to alloca(). For example, Opus has the OPUS_NONTHREADSAFE_PSEUDOSTACK option.