Hi d community,

I got a strange behavior since dmd 2.090 (dmd 2.089 is the last working version).

See this reduced code: https://run.dlang.io/is/yoyHXC

I would expect that foo() returns 2.
My guess in foo is: The return value of val is saved locally as a ref int and then the destructor of S is called (set the local cache to 0). Now the ref value is dereferenced and returned.

Now I am unsure if this is a bug or an undefined behavior that I don't know.
If this is a bug, then I don't know how to call it for the bug tracker.

I hope you can help me with this problem.

PS: This is only tested on my Linux system and on run.dlang.io.

- foerdi

On Friday, 8 May 2020 at 14:16:10 UTC, foerdi wrote:
> Now I am unsure if this is a bug or an undefined behavior that I don't know.

This is a regression, and a potentially pretty bad one, so thx for tracking it down!

> If this is a bug, then I don't know how to call it for the bug tracker.

Maybe something like 'return statement might access memory from destructed temporary'.

On Friday, 8 May 2020 at 14:32:33 UTC, kinke wrote:
> On Friday, 8 May 2020 at 14:16:10 UTC, foerdi wrote:
>> Now I am unsure if this is a bug or an undefined behavior that I don't know.
>
> This is a regression, and a potentially pretty bad one, so thx for tracking it down!
>
>> If this is a bug, then I don't know how to call it for the bug tracker.
>
> Maybe something like 'return statement might access memory from destructed temporary'.

Thanks, I filed a regression: https://issues.dlang.org/show_bug.cgi?id=20809

On Friday, 8 May 2020 at 14:16:10 UTC, foerdi wrote:
> Hi d community,
>
> I got a strange behavior since dmd 2.090 (dmd 2.089 is the last working version).
>
> See this reduced code: https://run.dlang.io/is/yoyHXC
>
> I would expect that foo() returns 2.
> My guess in foo is: The return value of val is saved locally as a ref int and then the destructor of S is called (set the local cache to 0). Now the ref value is dereferenced and returned.
>
> Now I am unsure if this is a bug or an undefined behavior that I don't know.
> If this is a bug, then I don't know how to call it for the bug tracker.
>
> I hope you can help me with this problem.
>
> PS: This is only tested on my Linux system and on run.dlang.io.
>
> - foerdi

Gets even weirder because this fixes it LOL???

int foo()
    out { }
do
{
    return bar.val;
}

What the??