C99 Features

[Nico Williams]

On Thu, Jun 18, 2015 at 12:24:04AM -0400, Nathaniel McCallum wrote:
> On Thu, 2015-06-18 at 01:13 +0000, Danilo Almeida wrote:
> >                                [...].  Nathaniel, do you have any 
> > performance numbers would help the case for the extra effort (and 
> > potential risk)?
> 
> Well, take common inner-function heap allocations and turn them into
> stack allocations. That is a significant performance gain.

Probably.  A decent heap allocator with per-thread magazines ought to be
good enough in most cases.

> VLAs make perfect sense for operations like fx_cf2 where you need to
> mix two keys together using intermediary buffers. If you validate that
> the input keys are valid types then you know that the buffer for that
> type will be a sensible size to put on the stack. This eliminates two
> unnecessary heap allocations.

Yes, but then, those keys are small.  So VLAs/alloca() here are fine.
alloca() has been around for a long time, no?  You don't need C99 to use
alloca().