Integer factorizations in clang

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 ?

Thanks in advance,

Ivan

The best thing to do, I think, would be to teach your backend to select
this pattern as your better instruction.

John.