Integer factorizations in clang

Hi,

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 ?

Thanks in advance,

Ivan

As mentioned on llvmdev, the right way to handle this is to write a pattern that matches (a+b)*c -> yourinstruction(a,c,b,c)

-Chris