Re: basic VRP min/max range overflow question

[Robert Dewar <dewar@adacore.com>]

Paul Schlie wrote:

> The root of the concern being expressed is with respect to the compilers use
> of statically identified undefined behaviors as opportunities to invoke
> alternative semantics which are easily identified as being inconsistent with
> the target's native semantics, thus altering the logical behavior of the
> program than would otherwise have resulted. (without any halting solutions
> required)

You are still not understanding, these are NOT cases of "statically
identified undefined behavior". Those are the trivial cases that are
uninterestig.
> 
> As candidly, regardless of this being technically allowed, it should obvious
> that any optimization which may likely alter the behavior of a program
> should never be invoked without explicit request and ideally diagnosis of
> the resulting alternative possibly undesired and/or fatal behavior.

If the behavior is undefined, then it is undefined, and you cannot
talk about a change in behavior. This is what non-deterministic semantics
is about.
> 
> To be more clear, specifically as examples:
> 
> - As VRP relies on the static analysis of value ranges, primarily based
> on embedded implicit and/or explicit constant values which enables the

It most certainly is NOT possible to statically identify situations that
cause overflow. I cannot believe this is not clear to you.