Re: subreg rtl documentation

[Jeff Law <law at redhat dot com>]

Kenneth Zadeck wrote:

> I was just kidding.   i understand why you were being vague.   i knew it 
> was not to hide anything.
No worries.



> It sounds like you (plural) are tentatively saying that if we made the 
> same statements about subregs of mem after reload, we would be on ground 
> that the community would be willing to support.  That does not mean that 
> anyone plans to submit patches to break this, but it gives us a basis to 
> review things going forward. 
> So the vagueness simply needs to have a sense of purpose.    It is ok to 
> say this is an old edge of the compiler that no one understands and we 
> would like to see go away.   So if you want to exploit some feature of 
> this, good luck.
I'd lean more towards the crisper definition we're hammering out with 
some checks to ensure things don't go haywire.  If you chose to go with 
the squishy version, then I'd probably go with two main ideas.

  1. Current semantics we're pretty sure we've nailed down.

  2. Current semantics which are squishy
     2a. Explicit note that squishy semantics are likely to change
     2b. Where we hope the squishy semantics will go in the future
         (and at which point they turn into hard semantics).


And just to be absolutely clear, I'm jumping for joy to see this stuff 
being hammered out and documented.

Jeff