Friendly-C

[deadalnix via Digitalmars-d]

On Friday, 29 August 2014 at 05:55:18 UTC, Ola Fosheim Gr wrote:
> On Friday, 29 August 2014 at 05:31:02 UTC, deadalnix wrote:
>> If the value in unspecified, rather than the behavior 
>> undefined, it means that no load or store can be optimized 
>> away or reordered, unless the compiler can prove that is won't 
>> fault.
>>
>> I'm talking about doubtful optimization to gain 0.5% here, but 
>> that everything single variable except locals must be 
>> considered volatile in the C sense.
>
> Why is that? If the value is unspecified then you can assume a 
> random value, so no single store is needed unless explicitly 
> volatile?
>
> Wrapping semantics is also bad for optimization, though. You 
> cannot reduce length < length+N to true in generic code, so you 
> need to establish bounds on x or create multiple execution 
> paths. This is usually silly when using a 64 bit int...

Because, if you don't have undefined BEHAVIOR, you can't change 
the BEHAVIOR. So you have to prove that store/loads won't fault 
before doing anything with them. As per spec. Or you'll change 
the BEHAVIOR.