Escape Analysis & Owner Escape Analysis

[Richard (Rikki) Andrew Cattermole]

On 05/09/2024 2:28 AM, IchorDev wrote:
> On Tuesday, 3 September 2024 at 03:00:20 UTC, Richard (Rikki) Andrew 
> Cattermole wrote:
>> An example of this is with a global, in the case of a variable thread 
>> local storage, it is possible in fully ``@safe`` code with DIP1000 
>> turned on to cause a segfault.
>>
>> ```d
>> import std;
>>
>> int* tlsGlobal;
>>
>> @safe:
>>
>> void main() {
>>     tlsGlobal = new int(2);
>>     assert(*tlsGlobal == 2);
>>
>>     toCall();
>>     assert(*tlsGlobal == 2); // Segfault
>> }
>>
>> void toCall() {
>>     tlsGlobal = null;
>> }
>> ```
> 
> But aren’t segfault always meant to be @safe anyway?
> ```d
> int* x;
> void main() @safe{
>    auto y = *x;
> }
> ```

In theory yes it's perfectly safe. However this example isn't meant to 
show that a solution to nullability is needed, but instead to show that 
you cannot make assumptions based upon what code is locally analyzed for 
things outside of it.

To assume that a non-function local variable will have a value that is 
known to the analysis over the course of a function body isn't correct 
and that pokes a massive hole in the analysis capabilities.