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Re: [RFC] UBSan unsafely uses VRP


On 11/12/2014 04:26 PM, Jakub Jelinek wrote:
But, if -O0 isn't too slow for them, having unnecessary bloat even at -O2
is bad the same.  But not using VRP at all, you are giving up all the cases
where you know something won't overflow because you e.g. sign extend
or zero extend from some smaller type, sum op such values, and something
with constant, or you can use a cheaper code to multiply etc.

Sure, I was not suggesting anything like that - just pointing out that we must be careful about potential loss of precision and do all we can to avoid it. Faster code should not justify lower quality (as used to be in 1960-s).

Turning off -faggressive-loop-optimizations is certainly the right thing for
-fsanitize=undefined (any undefined I'd say), so are perhaps selected other
optimizations.

Totally agree.

-Y


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