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Re: Unstable build/host qsorts causing differing generated target code
Hi,
On Fri, 12 Jan 2018, Joseph Myers wrote:
> On Fri, 12 Jan 2018, Alexander Monakov wrote:
>
> > No. The qsort_chk effort was limited to catching instances where comparators
> > are invalid, i.e. lack anti-commutativity (may indicate A < B < A) or
> > transitivity property (may indicate A < B < C < A). Fixing them doesn't
> > imply making corresponding qsort invocations stable.
>
> Incidentally, does it detect being invalid because of comparing A != A?
> (I don't know if qsort implementations ever do compare an element to
> itself, but I did once notice in a patch review that a comparator could
> have compared an element unequal to itself).
Many years ago I ran into a qsort implementation (some Sun one? too long
ago) where indeed qsort was calling cmp(a,a). I ran into this case only
because one of the cmp() implementations didn't return 0 then, and qsort
was Very Surprised by that :)
Ciao,
Michael.