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Re: [RFC] UBSan unsafely uses VRP

On Wed, Nov 12, 2014 at 11:42:39AM +0300, Yury Gribov wrote:
> On 11/11/2014 05:15 PM, Jakub Jelinek wrote:
> >>There are also some unsafe code in functions
> >>ubsan_expand_si_overflow_addsub_check, ubsan_expand_si_overflow_mul_check
> >>which uses get_range_info to reduce checks number. As seen before vrp usage
> >>for sanitizers may decrease quality of error detection.
> >
> >Using VRP is completely intentional there, we don't want to generate too
> >slow code if you decide you want to optimize your code (for -O0 VRP isn't
> >performed of course).
> On the other hand detection quality is probably more important than
> important regardless of optimization level. When I use a checker, I don't
> want it to miss bugs due to overly aggressive optimization.
Yes, but as said above, VRP is only run with >-O2 and -Os.

> I wish we had some test to check that sanitizer optimizations are indeed
> conservative.

I think most of the tests we have are tested with various optimization


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