* * * * *
                                        
          A bit of background on compilers exploiting signed overflow
                                        
> Why do compilers even bother with exploiting undefinedness signed overflow?
> And what are those mysterious cases where it helps?
> 
> A lot of people (myself included) are against transforms that aggressively
> exploit undefined behavior, but I think it's useful to know what compiler
> writers are accomplishing by this.
> 
> TL;DR (Too Long; Didn't Read): C doesn't work very well if int!=register
> width, but (for backwards compat) int is 32-bit on all major 64-bit
> targets, and this causes quite hairy problems for code generation and
> optimization in some fairly common cases. The signed overflow UB (Undefined
> Behavior) exploitation is an attempt to work around this.
> 

Via Comment on ”Bug in my code from compiler optimization [video] | Hacker
News” [1], “A bit of background on compilers exploiting signed overflow [2]”

A cautionary tale about compiler writers exploiting undefined behavior. I
don't have much to add here, other than to spread a bit of awareness of why
this happens.

[1] https://news.ycombinator.com/item?id=38662881
[2] https://gist.github.com/rygorous/e0f055bfb74e3d5f0af20690759de5a7

Email Sean Conner at sean@conman.org

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