3 ms·

Very well put! I'll just add that the third option is usually not considered viable because the main point of using C/C++ is for performance, thus people writi

by pif 2y ago

Very well put! I'll just add that the third option is usually not considered viable because the main point of using C/C++ is for performance, thus people writing code want their compiler to optimize it as much as possible.

int_19h 2y ago
In practice, the people pushing the most for UB being a "license to kill" tend to be compiler implementors though, not their users.
- GrantMoyer 2y ago
  I don't think compilers consider undefined behavior a license to kill; I think the problem is genuinely hard. The priciple of explosion[1] tells us that any wrong assumption, even the most innocuous looking, can lead to an unboundedly wrong conclusion. The more complex your graph of logical deductions, the worse the problem gets (and good optimizations require a lot of complex logic). It may be possible to limit the bad effects of faulty assumptions by being very careful about how deductions propogate from unreliable assumptions. However it's certainly not easy, especially without throwing out all optimizations that interact with a potentially undefined operation. It is possible to design a languge such that a compiler doesn't need to make assumptions to perform optimizations, if programs are required to give enough information to compilers that they can statically prove properties they need to perform optimizations. But C and C++ are not designed that way, and it can't easily be retrofitted on top of them. [1]: https://en.wikipedia.org/wiki/Principle_of_explosion https://en.wikipedia.org/wiki/Principle_of_explosion
- gavinhoward 2y ago
  OT, but did you get the "license to kill" phrase from me (https://gavinhoward.com/2023/08/the-scourge-of-00ub/ https://gavinhoward.com/2023/08/the-scourge-of-00ub/) or someone else? I ask because when I wrote that post, I couldn't remember if I had heard the term before. In other words, I am not sure if I copied someone else or not, and if I did, I want to add attribution.
  - int_19h 2y ago
    I'm pretty sure I posted that comment after reading your post.

by pif 2y ago

int_19h 2y ago

In practice, the people pushing the most for UB being a "license to kill" tend to be compiler implementors though, not their users.

GrantMoyer 2y ago
I don't think compilers consider undefined behavior a license to kill; I think the problem is genuinely hard. The priciple of explosion[1] tells us that any wrong assumption, even the most innocuous looking, can lead to an unboundedly wrong conclusion. The more complex your graph of logical deductions, the worse the problem gets (and good optimizations require a lot of complex logic). It may be possible to limit the bad effects of faulty assumptions by being very careful about how deductions propogate from unreliable assumptions. However it's certainly not easy, especially without throwing out all optimizations that interact with a potentially undefined operation. It is possible to design a languge such that a compiler doesn't need to make assumptions to perform optimizations, if programs are required to give enough information to compilers that they can statically prove properties they need to perform optimizations. But C and C++ are not designed that way, and it can't easily be retrofitted on top of them. [1]: https://en.wikipedia.org/wiki/Principle_of_explosion https://en.wikipedia.org/wiki/Principle_of_explosion
gavinhoward 2y ago
OT, but did you get the "license to kill" phrase from me (https://gavinhoward.com/2023/08/the-scourge-of-00ub/ https://gavinhoward.com/2023/08/the-scourge-of-00ub/) or someone else? I ask because when I wrote that post, I couldn't remember if I had heard the term before. In other words, I am not sure if I copied someone else or not, and if I did, I want to add attribution.
- int_19h 2y ago
  I'm pretty sure I posted that comment after reading your post.