On Jan 17, 2012, at 11:21 AM, Comeau At9Fans <comeauat9fans@gmail.com> wrote:
On Mon, Jan 16, 2012 at 2:03 PM, Bakul Shah <bakul@bitblocks.com> wrote:

How do you deal with longjmp?

I don't have it in front of me, but I do seem to recall the Standard allows that the VLA might still be around though, believe it has an example with said, for better or worse...

Do you have a reference?

Ok, so, gunna make me look, let's see, ok: 7.13.2.1p5, note the may's and might's. There should be narrative backing those up.

On Jan 16, 2012, at 10:51 AM, Comeau At9Fans <comeauat9fans@gmail.com> wrote:

On Mon, Jan 16, 2012 at 10:41 AM, Bakul Shah <bakul@bitblocks.com> wrote:

A frame pointer is needed for C99's variable length arrays but not otherwise. Only an issue if ever plan9 C is extended to handle C99 or C1x. gcc has to do the right thing even with -fno-frame-pointer.

What we do in problematic cases with Comeau is to generate code to arrange for the allocation of the VLA on the heap. I'm not saying this is perfect, but at least it gets the feature implementable and up and running as "a portable implementation" versus perhaps not being able to implement it at all on some platforms.

Seems to me if you can port C, you can use a FP to implement VLAs without alloca games and more efficiently. You can always store the FP in stack local memory if out of registers.