[fpc-pascal] alloca

[Marco van de Voort]

On 14-5-2022 10:49, Hairy Pixels via fpc-pascal wrote:
> Apparently what it does is advance the stack pointer x bytes and return a pointer to the new location so you could probably do that with some assembly. Of course this is dangerous because you can request more memory than exists in the current frame.

But optimizations sometimes eliminate the frame pointer and use the 
stackpointer directly to index e.g. local vars and params. Also when an 
exception happens, the stack pointer is not as expected in exception 
frames (don't know if that really is an issue, but I can image).  It 
would be interesting how C handles this (e.g. exceptions while alloca 
called in a loop?)

So the only non hacky way is to implement support in the compiler I think.