alt Hacker News> it is legal to optimize out any code paths that rely on this, even if they occur earlier in program order.
I don't think this is true. The compiler cannot remove or reorder instructions that have a visible effect.
if (p == 0)
printf("Ready?\n");
*p++;
Replies
saagarjha • today at 8:18 AM
No, this is explicitly legal. Most compilers will shy away from it these days since it made a lot of people upset, but it's definitely allowed.
> The compiler cannot remove or reorder instructions that have a visible effect.
You might be surprised! When it comes to UB compilers can and do reorder/eliminate instructions with side effects, resulting in "time travel" [0].
IIRC the upcoming version of the C standard bans this behavior, but the C++ standard still allows it (for now, at least).
[0]: https://devblogs.microsoft.com/oldnewthing/20140627-00/?p=63...