[OT] OT: Null checks.

[Derek Fawcus]

On Sunday, 4 May 2025 at 04:49:48 UTC, Timon Gehr wrote:
>
> My understanding is that null pointer dereference being UB is a 
> widespread assumption in the LLVM and GCC optimizers. Simply 
> "disabling the behavior" is not practical.


I recently read somewhere, (not sure if it was in these forums, 
Hacker News, or Lobsters), that recent versions of LLVM have now 
gained the ability to express that some forms of pointer will not 
experience that behaviour.

i.e. something in the syntax (text form, and presumably bitcode) 
allows one to indicate that dereference of a NULL pointer is not 
to be viewed as undefined behaviour, and so it most not optimise 
on the assumption that it is.

I assume that means a attempt to deref a NULL reference will then 
end up being passed to the actual CPU in terms of code generated.

I suspect this may only be the most recent version, possibly the 
pre-release development HEAD.  I have no idea about any 
equivalent in the GCC middle and back ends.