[csmith-dev] Alignment of struct members cause target dependent checksum

[John Regehr]

> would you have a quantifiation/estimate of "quite rare" ?

I'd say we've seen this may 10-15 times out of ~450 total compiler bugs 
we've reported.

The thing that's sort of interesting about the "wrong in the same way at 
all optimization level" bugs is that they're different.  Instead of 
being logic errors in optimization passes (this is what most wrong-code 
bugs are) they tend to be misinterpretations of the specification by the 
compiler team.  I'd argue that this kind of bug is probably best found 
by a standards conformance test suite (several are commercially 
available).  This kind of thing isn't really Csmith's strength.

> Would it make sense to have a two step process to minimize false positives
> something like:
>   1) same compiler -O -O2 -Os (or similar)
>   2) those that did not trigger in 1) rerun agains compiler A/B/C ?

Are you assuming that in step 2 the compiler might have different 
implementation-defined characteristics?  If so, then things are a bit 
tricky since manual work will be needed to sift through the outputs, and 
that gets old fast.

John