Integer overflow checking

[deadalnix via Digitalmars-d]

On Wednesday, 13 April 2016 at 22:13:27 UTC, Walter Bright wrote:
> On 4/12/2016 5:06 AM, Andrei Alexandrescu wrote:
>> Interesting: http://blog.regehr.org/archives/1384 -- Andrei
>
> Curiously never mentioned is the following optimization:
>
>     return a+b*2+27;
>
> becomes:
>
>     LEA EAX,27[ESI][EDI*2]
>
> To overflow check:
>
>     ADD EDI,EDI
>     JO overflow
>     ADD EDI,27
>     JO overflow
>     MOV EAX,ESI
>     ADD EAX,EDI
>     JO overflow
>
> I don't see efficiency there, even with the JO's being free.

It is clearly not as optimal, but still pretty good. The article 
doesn't pretend it all come for free, just that it comes for much 
cheaper than before.