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Re: inline asm and multi-alternative constraints


On Fri, Nov 06, 2015 at 03:29:43PM -0700, Jeff Law wrote:
> It's never easy to predict whether or not something like this will be 
> contentious.  Worst case is you post, it's contentious, we iterate a bit 
> and reach some kind of resolution (ok, worst case is no resolution is 
> reached, but that doesn't happen to often).
> 
> In this case I simply don't see a way to sensibly document those 
> modifiers without bringing in the implementation details of register 
> class preferencing, reload, IRA & LRA.  And once those details are 
> brought into the picture, everyone loses.
> 
> I'm sure there's someone out there using '?' and '!' in a 
> multi-alternative asm constraint.  They may even read the docs and 
> complain and we can try to educate them why those modifiers are no 
> longer documented.

Another reason why we shouldn't document such things is that it makes
it harder to change (anything about) those things later, although they
really are implementation details.  The same goes for some constraints
and almost all output modifiers.


Segher


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