[LLVMdev] Kinda noob questions

[John McCall]

On Mar 14, 2011, at 6:44 PM, Judison wrote:
> Thank you John and John :P
> 
> these optimizations (mem2reg and the "few additional" ones) I have to enable then or something like this?? (I compile the .ll to .o with the sequence llvm-as, llc, as)

Look into 'opt'.

> Yet about dynamic stack allocation, what is (generally) better? to pre alloc everything at start, or let it be?
> 
> Imagine this pseudo-code
> 
> while (x) {
>   int b = 0;
>   ...
> }
> 
> using alloca where b is declared, it will grow the stack dynamically, but it will shrink it at } or in llvm's words in the end of a block where b is not accessible anymore? Can I force its deallocation??

Unless you're actually reliant on dynamic allocation — e.g. you don't know the size statically, or you're intending to repeatedly allocate memory — you should always allocate in the entry block.  LLVM is reasonably good at re-using stack slots when it can.

John.