• Heikuw (39/39) Aug 21 2021 What causes this example of safeD code to be compiled in dmd and
• jfondren (15/17) Aug 21 2021 The default behavior varies, but the dip1000 behavior is the same:
• Mathias LANG (3/5) Aug 22 2021 Most likely frontend differences. Check `pragma(msg,

Heikuw <foss.nexus gmail.com> writes:

What causes this example of safeD code to be compiled in dmd and 
ldc but not compiled in gcc?

code :

     immutable(int)* f(int* p)  trusted
     {
         version (none) p[2] = 13;
         // Invalid. p[2] is out of bounds. This line would 
exhibit undefined
         // behavior.

         version (none) p[1] = 13;
         // Invalid. In this program, p[1] happens to be 
in-bounds, so the
         // line would not exhibit undefined behavior, but a 
trusted function
         // is not allowed to rely on this.

         version (none) return cast(immutable) p;
         // Invalid.  safe code still has mutable access and could 
trigger
         // undefined behavior by overwriting the value later on.

         int* p2 = new int;
         *p2 = 42;
         return cast(immutable) p2;
         // Valid. After f returns, no mutable aliases of p2 can 
exist.
     }

     void main()  safe
     {
         int[2] a = [10, 20];
         int* mp = &a[0];
         immutable(int)* ip = f(mp);
         assert(a[1] == 20); // Guaranteed. f cannot access a[1].
         assert(ip !is mp); // Guaranteed. f cannot introduce 
unsafe aliasing.
     }


     result code in gdc compiler :
     main.d:25:15: error: cannot take address of local a in  safe 
function main
        25 |     int* mp = &a[0];
           |               ^

jfondren <julian.fondren gmail.com> writes:

On Saturday, 21 August 2021 at 07:16:46 UTC, Heikuw wrote:
 What causes this example of safeD code to be compiled in dmd 
 and ldc but not compiled in gcc?

The default behavior varies, but the dip1000 behavior is the same:

```
$ gdc -ftransition=dip1000 bug.d
bug.d:26:28: error: scope variable mp assigned to non-scope 
parameter p calling bug.f
    26 |     immutable(int)* ip = f(mp);
       |                            ^
$ dmd -preview=dip1000 bug.d
bug.d(26): Error: scope variable `mp` assigned to non-scope 
parameter `p` calling bug.f
$ ldc2 -preview=dip1000 bug.d
bug.d(26): Error: scope variable `mp` assigned to non-scope 
parameter `p` calling bug.f
```

Mathias LANG <geod24 gmail.com> writes:

On Saturday, 21 August 2021 at 07:16:46 UTC, Heikuw wrote:
 What causes this example of safeD code to be compiled in dmd 
 and ldc but not compiled in gcc?

Most likely frontend differences. Check `pragma(msg, 
__VERSION__);`.