dip1000 and preview in combine to cause extra safety errors

[deadalnix]

On Wednesday, 8 June 2022 at 16:32:25 UTC, John Colvin wrote:
>> There is no frame of reference in which this result is in any 
>> way reasonable.
>
> My guess is that technically `foo` has undefined behaviour.

Sure, but that also mean it could format your hard drive, and 
it'd be hard to argue this is reasonable.

If the compiler understands of what's going on to decide it can 
recycle the memory, it understands enough to tell you you are 
using it after freeing and if it cannot, then it shouldn't do it.

In this case specifically, assuming the compiler see the memory 
doesn't escape and promoting [c] on stack, it should still do the 
right thing. That means the compiler is somehow getting out of 
its way to break the code.

That doesn't sound reasonable, no matter how you slice it.