Proposed doc update for Explicit Reg Vars 3/3

[Jeff Law]

On 10/12/2015 05:09 PM, David Wohlferd wrote:
> Patch 3/3 is the update for the Local Register Variables page (attached).
>
> This patch starts with a question.  Looking at bug
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64951 (register variable
> with template function) is this a bug that will be fixed? Or a
> limitation that should be doc'ed?  Both the current docs and the patch
> ignore this bug.
>
> As with patch #2, this is primarily about reformatting/reorganizing.
> Although it also adds the limitation from asm labels re statics.
>
> I was hoping to modify the text to say that local register variables can
> "only" be used to call Extended asm.  This would greatly simplify this
> section.  But there has been pushback on this (despite the fact that no
> one has really suggested any other reasonable use).  So I have softened
> this, and listed things from the existing docs that are explicitly not
> supported.
>
> For people who find the HTML easier to review:
>
> Here's the current text:
> https://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html
> And here's the new:
> http://limegreensocks.com/gcc/Local-Register-Variables.html
>
> dw
>
>
Like with the global register variables, please consider going processor 
agnostic here and using r<N> for some value of N rather than using 
severely dated m68k examples.

WRT your hope to limit this to only uses in extended asms.  That'd be 
nice, but that's never been an explicit limitation.  I would strongly 
hesitate to add that limitation at this point in time.

Jeff