[Bug rtl-optimization/19210] [4.0 Regression] not using do-loop for some loops

[rakdver at atrey dot karlin dot mff dot cuni dot cz]

------- Additional Comments From rakdver at atrey dot karlin dot mff dot cuni dot cz  2004-12-31 00:56 -------
Subject: Re:  [4.0 Regression] not using do-loop for some loops

> Zdenek, I have troubles understanding how such a loop can ever be infinite:
> 
> - if wrapv, sooner or later K will reach any N (and thus, surely it will become 
> less or equal to any given N).
>
> - if nowrapv, my understanding is that all bets are off: if f() is called with 
> N<=3 the loop will terminate, otherwise it's undefined behaviour. In such a 
> situation, we can still perform doloop because it's not going to screw the 
> program any more than it is already.
> 
> What am I missing?

I am afraid your interpretation of the code does not make much sense to
me.  The loop always terminates except for the case when n == MAX_INT
and -fwrapv.  In case n == MAX_INT and -fno-wrapv the behavior is
undefined.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19210