[cfe-dev] Integer factorizations in clang

John McCall rjmccall at apple.com
Thu Jan 5 11:06:21 PST 2012

On Jan 5, 2012, at 7:18 AM, Ivan Llopard wrote:
> 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 ?

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


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