null pointer dereference detection in DMD

[Richard (Rikki) Andrew Cattermole]

On 11/01/2025 2:43 PM, Walter Bright wrote:
> Curiously, compiling it with `gcc -O3` does not detect it. ImportC 
> doesn't detect it, either, a choice made because some C code uses such a 
> construct as a way to drop into the debugger.

Yeah you didn't turn the warning on.

```c
int main() {
     int* ptr;
     *ptr = 3;
     return 0;
}
```

flags: ``-Wnull-dereference -O``

```
<source>: In function 'main':
<source>:5:10: warning: null pointer dereference [-Wnull-dereference]
     5 |     *ptr = 3;
       |     ~~~~~^~~
ASM generation compiler returned: 0
<source>: In function 'main':
<source>:5:10: warning: null pointer dereference [-Wnull-dereference]
     5 |     *ptr = 3;
       |     ~~~~~^~~
Execution build compiler returned: 0
Program returned: 139
Program terminated with signal: SIGSEGV
```

https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

"Warn if the compiler detects paths that trigger erroneous or undefined 
behavior due to dereferencing a null pointer. This option is only active 
when -fdelete-null-pointer-checks is active, which is enabled by 
optimizations in most targets. The precision of the warnings depends on 
the optimization options used."