Implement stack arrays even for unknown sizes

[Paul Richard Thomas]

Dear Richard and Dominique,

> VLAs and malloc based arrays may behave differently with respect to alias
> analysis (I'd have to look at some examples).  All effects other than malloc

- hmmm, yes.  I was forgetting what might happen with inlining.  It's
not evident, is it?

> overhead I would attribute to that.  That said, the general idea of the patch
> is sound and I see nothing wrong with it.  Both performance improvements
> and regressions are worth looking at - they hint at possible improvements
> in the middle-end parts of the compiler.

I absolutely agree.  I realise my input to this thread is possibly a
bit negative but this is far from my reaction to the general idea and
what is evidently within our reach.

Cheers

Paul