[RFC] UBSan unsafely uses VRP

[Yury Gribov]

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.

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

-Y