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Re: subreg against register allocation?


Ian Lance Taylor wrote:

>>> Well, as you know, subregs have two meanings which look similar but
>>> are in fact entirely different.  It's valid to set subregs of the same
>>> pseudo in parallel if the subregs represent different hard registers.

>> Are you aware of any examples of this in the compiler?  The explanation
>> is of course plausible, but do we know that we handle this correctly
>> everywhere?
> 
> Hmmm, you could be right.  

Of course, if we think this *should* work in principle (i.e., that it
makes sense for this to be meaningful RTL), and we don't know that it
doesn't work, it's reasonable to put this into GCC, changing the
documentation to specify the semantics of this form of RTL, and then
fixing any bugs as they occur.

Thanks,

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713


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