[LLVMdev] Integer factorizations in clang

[Jean-Daniel Dupas]

Le 5 janv. 2012 à 15:59, Ivan Llopard a écrit :

> Hello,
> 
> I have a small test case :
> 
> a = b * c + b * d
> 
> and clang is fatorizing b to get only one multiplication (-O3) which is 
> normally good for most architectures. But in my case, that pattern takes 
> just one instruction and I would like to recover it as is.
> Where can I find this particular optimization in clang ?
> Is there a way of setting multiplications as being cheaper than 
> additions/subtracions in clang ?

Wouldn't it be simpler to detect factorize pattern in you code and generate the appropriate instruction as it if was a decomposed form.
It would have the benefit to properly optimize the code if the developer choose to use the factorized form directly.


-- Jean-Daniel